U.S. patent application number 14/280540 was filed with the patent office on 2014-09-11 for methods of treating metal surfaces and devices formed thereby.
This patent application is currently assigned to Atotech Deutschland GmbH. The applicant listed for this patent is Atotech Deutschland GmbH. Invention is credited to Werner G. Kuhr, Zhiming Liu, Steven Z. Shi, Jen-Chieh Wei.
Application Number | 20140251502 14/280540 |
Document ID | / |
Family ID | 51486355 |
Filed Date | 2014-09-11 |
United States Patent
Application |
20140251502 |
Kind Code |
A1 |
Wei; Jen-Chieh ; et
al. |
September 11, 2014 |
Methods of Treating Metal Surfaces and Devices Formed Thereby
Abstract
Embodiments of the present invention relate generally to methods
of treating metal surfaces to enhance adhesion or binding to
substrates, and devices formed thereby. In some embodiments of the
present invention, methods of achieving improved bonding strength
without roughening the topography of a metal surface are provided.
The metal surface obtained by this method provides strong bonding
to resin layers. The bonding interface between the treated metal
and the resin layer exhibits resistance to heat, moisture, and
chemicals involved in post-lamination process steps, and therefore
can suitably be used in the production of PCB's. Methods according
to some embodiments of the present invention are especially useful
in the fabrication of high density multilayer PCB's, in particular
for PCB's having circuits with line/spacing of equal to and less
than 10 microns. Methods according to other embodiments of the
present invention are particularly useful in the coating of metal
surfaces in a wide variety of applications.
Inventors: |
Wei; Jen-Chieh; (Highlands
Ranch, CO) ; Liu; Zhiming; (Englewood, CO) ;
Shi; Steven Z.; (Santa Clara, CA) ; Kuhr; Werner
G.; (Denver, CO) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Atotech Deutschland GmbH |
Berlin |
|
DE |
|
|
Assignee: |
Atotech Deutschland GmbH
Berlin
DE
|
Family ID: |
51486355 |
Appl. No.: |
14/280540 |
Filed: |
May 16, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
14009517 |
May 19, 2014 |
|
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PCT/US10/41061 |
Jul 6, 2010 |
|
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14280540 |
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Current U.S.
Class: |
148/243 ;
148/284 |
Current CPC
Class: |
H05K 3/385 20130101;
H05K 2203/0315 20130101; C23C 8/80 20130101; C23C 8/02 20130101;
C23C 22/63 20130101; C23C 22/83 20130101; C23C 8/42 20130101 |
Class at
Publication: |
148/243 ;
148/284 |
International
Class: |
C23C 8/42 20060101
C23C008/42 |
Claims
1-14. (canceled)
15. A method of treating a metal surface to promote adhesion
between the metal surface and an organic material, comprising the
steps of: oxidizing the metal surface to form a metal oxide layer
on the metal surface; and terminating growth of the metal oxide
layer by a self limiting reaction between the metal oxide layer and
a surface modifier compound.
16. The method of claim 15 wherein the surface modifier compound is
selected from compounds that react with metal oxide surfaces to
control the reaction rate as the metal oxide is forming.
17. (canceled)
18. The method of claim 15 wherein the metal oxide layer has a
thickness of about 200 nanometers and less.
19-21. (canceled)
22. The method of claim 15 wherein the metal oxide layer is
comprised of copper oxide.
23. (canceled)
24. The method of claim 15 wherein the metal layer is oxidized with
an oxidant selected from any one of more of: sodium chlorite,
hydrogen peroxide, permaganate, perchlorate, persulphate, ozone, or
mixtures thereof.
25. The method of claim 15 wherein the method is carried out at a
temperature in the range of room temperature to about 80.degree.
C.
26. The method of claim 15 wherein the self limiting reaction
becomes stable after about 2 to 15 minutes.
27. The method of claim 15 wherein the steps of oxidizing and
terminating oxidation further comprises exposing the metal surface
to a solution comprising an oxidant and surface modifier
compound.
28. The method of claim 27 wherein the surface modifier compound is
in the oxidant solution.
29. The method of claim 15 further comprising the step of:
contacting the metal surface with one or more organic molecules
comprising a thermally stable base bearing one or more binding
groups configured to bind the metal surface and one or more
attachment groups configured to attach to the organic material.
30. The method of claim 29 wherein the one or more organic
molecules is a surface active moiety.
31. The method of claim 29 wherein the one or more organic
molecules is selected from the group of: a porphyrin, a porphyrinic
macrocycle, an expanded porphyrin, a contracted porphyrin, a linear
porphyrin polymer, a porphyrinic sandwich coordination complex, or
a porphyrin array.
32. (canceled)
33. The method of claim 30 wherein said surface active moiety is a
porphyrin.
34. The method of claim 29 wherein the one or more attachment group
is comprised of an aryl functional group and/or an alkyl attachment
group.
35. The method of claim 34 wherein the aryl functional group is
comprised of a functional group selected from any one or more of:
acetate, alkylamino, allyl, amine, amino, bromo, bromomethyl,
carbonyl, carboxylate, carboxylic acid, dihydroxyphosphoryl,
epoxide, ester, ether, ethynyl, formyl, hydroxy, hydroxymethyl,
iodo, mercapto, mercaptomethyl, Se-acetylseleno,
Se-acetylselenomethyl, S-acetylthio, S-acetylthiomethyl, selenyl,
4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl,
2-(trimethylsilyl)ethynyl, vinyl, and combinations thereof.
36. The method of claim 34 wherein the alkyl attachment group
comprises a functional group selected from any one or more of:
acetate, alkylamino, allyl, amine, amino, bromo, bromomethyl,
carbonyl, carboxylate, carboxylic acid, dihydroxyphosphoryl,
epoxide, ester, ether, ethynyl, formyl, hydroxy, hydroxymethyl,
iodo, mercapto, mercaptomethyl, Se-acetylseleno,
Se-acetylselenomethyl, S-acetylthio, S-acetylthiomethyl, selenyl,
4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl,
2-(trimethylsilyl)ethynyl, vinyl, and combinations thereof.
37-38. (canceled)
39. The method of claim 15 wherein the organic material is an
organic substrate comprised of any one of more of: electronic
substrates, PCB substrates, semiconductor substrates, photovoltaic
substrates, polymers, ceramics, carbon, epoxy, glass reinforced
epoxy, phenol, polyimide resines, glass reinforced polyimide,
cyanate, esters, Teflon, plastics and mixtures thereof.
40-100. (canceled)
Description
TECHNICAL FIELD
[0001] Embodiments of the present invention relate generally to
methods of treating metal surfaces to enhance adhesion or binding
to substrates and other materials, and devices formed thereby. In
some embodiments, the present invention relates to the manufacture
of printed circuit boards (PCB's) or printed wiring boards (PWB's),
and particularly to methods for treating metal surfaces, such as
but not limited to copper surfaces, to increase the adhesion
between a copper surface and an organic material, and devices
formed therefrom. In some embodiments of the present invention,
methods of achieving improved bonding strength without roughening
the topography of a metal surface are provided. The metal surface
obtained by this method provides strong bonding to resin
layers.
BACKGROUND OF THE INVENTION
[0002] Miniaturization, portability, and ever-increasing
functionalities of consumer electronics continually drive printed
circuit board manufacturing towards smaller and more densely packed
boards. Increased circuit layer count, decreased core and laminate
thicknesses, reduced copper line width and spacing, smaller
diameter through-holes and micro-vias are some of the key
attributes of high density interconnect (HDI) packages or
multilayer PCB's.
[0003] Copper circuitry forming the circuit layout of the PCB is
fabricated typically either by a subtractive process, or an
additive process, or their combination. In the subtractive process,
the desired circuit pattern is formed by etching downward from a
thin copper foil laminated to a dielectric substrate where the
copper foil is covered with a photoresist and a latent image of the
desired circuit is formed in the resist after light exposure, the
non-circuit area of the resist is washed away in a resist developer
and the underlying copper is etched away by an etchant. In the
additive process, the copper pattern is built upward from a bare
dielectric substrate in the channels of a circuit pattern formed by
photoresist. Further copper circuit layers are bonded together by
partially-cured dielectric resin, often called "prepreg," to form a
multilayer assembly of alternating copper circuitry conductive
layers and dielectric resin insulation layers. The assembly is then
subjected to heat and pressure to cure the partially-cured resin.
Through-holes are drilled and plated with copper to electrically
connect all circuit layers and thus form a multilayer PCB.
Processes for the fabrication of multilayer PCB's are well known in
the art and described in numerous publications, for example,
"Printed Circuits Handbook," Sixth Edition, Edited by C. F. Coombs,
Jr., McGraw-Hill Professional, 2007 and "Printed Circuit Board
Materials Handbook," Edited by M. W. Jawitz, McGraw-Hill, 1997.
Regardless of the PCB structures and fabricating methods, it is
essential to achieve good adhesion between the copper circuit layer
and resin insulation layer. Circuit boards of insufficient adhesion
cannot survive the high temperature of solder reflow and subsequent
soldering, resulting in delamination of the board and electrical
malfunctions.
[0004] The surface of the copper circuit as patterned is smooth;
however, this smooth surface does not adhere well to the resin
layer. It is theoretically known that increasing the contact area
between the two dissimilar materials would increase the adhesion
strength. To improve the bonding between the copper and the resin,
most conventional approaches rely on creating a highly roughened
copper surface to increase its surface area and introduce
micro-ravines and ridges into the surface that act as mechanical
bonding anchors to promote adhesion to the resin.
[0005] One of the most widely known and used approaches is the
so-called "black oxide process" in which a black colored oxide
layer having a rough surface is formed on top of the copper
surface. The black oxide consists of needle-shaped dendritic
crystals or whiskers of a mixture of cuprous oxide and cupric oxide
of up to 5 microns in length. This large crystalline structure
provides high surface area and mechanical anchoring effect and
hence good bondability. U.S. Pat. Nos. 2,364,993, 2,460,896, and
2,460,898 to Meyer first describe the oxidation of a copper surface
to a black oxide layer using an alkaline chlorite solution. Some
exemplary disclosures of earlier efforts in applying this method to
copper-resin bonding in PCB's include U.S. Pat. Nos. 2,955,974,
3,177,103, 3,198,672, 3,240,662, 3,374,129, and 3,481,777.
[0006] Although such needle-shaped oxide layer greatly increases
the surface area and bondability, the dendritic crystals are
fragile and easily damaged during the lamination process resulting
in bonding failure within the oxide layer. Subsequent modifications
to the oxide process have focused on optimizing the reagent
concentrations and other process parameters in order to reduce the
crystal size and therefore the thickness of the oxide layer to
improve mechanical stability. Some notable improvements in this
regard are represented by U.S. Pat. Nos. 4,409,037 and 4,844,981,
where there are described formulations of an alkaline chlorite
solution at specific concentration levels and hydroxide to chlorite
ratios. U.S. Pat. No. 4,512,818 describes the addition of water
soluble or dispersible polymer additives in an alkaline chlorite
solution to cause a black oxide coating of reduced thickness and
greater homogeneity. U.S. Pat. No. 4,702,793 describes a method of
pre-treating the copper surface with sulfuroxy acid reducing agent
to promote the rapid formation of a copper oxide. Other methods for
forming black oxide layers include oxidation of the copper surface
with hydrogen peroxide as described in U.S. Pat. No. 3,434,889,
alkaline permanganate as described in U.S. Pat. No. 3,544,389,
thermal oxidation as described in U.S. Pat. No. 3,677,828, and
phosphoric acid-dichromate solution as described in U.S. Pat. No.
3,833,433.
[0007] One problem associated with this oxide roughening approach
is that copper oxides are soluble in acid; and serious delamination
of the bonding interface occurs during later process steps which
involve the use of acid. For example, as noted earlier
through-holes are drilled through the multilayer board and plated
with copper to provide interconnection of the circuit layers. Resin
smear is often formed on the surface of the holes from drilling and
must be removed by a desmear process which involves permanganate
etch followed by acid neutralization. The acid can dissolve the
copper oxide up to several millimeters inward from the surface of
the hole, which is evidenced by the formation of a pink-ring around
the through-hole owing to the pink color of the underlying copper.
The formation of pink-rings corresponds to localized delamination
and represents serious defects in the PCB's. These defects have
become a significant bottleneck in the production of multilayer
PCB's and extensive efforts have been extended in seeking further
improvement in the oxide layer so that it is not susceptible to
acid attack and such localized delamination.
[0008] Approaches to solving the pink-ring problem have largely
involved post-treatment of the copper oxide. For example, U.S. Pat.
No. 3,677,828 describes a method of first oxidizing the copper
surface to form an oxide layer and then treating the oxide layer
with phosphoric acid to form a glass like film of copper phosphate
resulting in high bonding strength and acid resistance. U.S. Pat.
No. 4,717,439 describes a process for improving the acid resistance
of copper oxide by contacting the copper oxide with a solution
containing an amphoteric element which forms an acidic oxide such
as selenium dioxide. U.S. Pat. No. 4,775,444 describes a process of
first forming a copper oxide layer and then treating with chromic
acid to stabilize and/or protect the copper oxide from dissolution
in an acid.
[0009] A number of studies have shown that acid resistance is
improved by first forming cupric oxide on the surface of the copper
and subsequently reducing the cupric oxide to cuprous oxide or
copper-rich surface. U.S. Pat. No. 4,642,161 describes a method of
reducing the cupric oxide using a borane reducing agent represented
by the general formula BH.sub.3NHRR', wherein R and R' are each
selected from the group consisting of H, CH.sub.3 and
CH.sub.2CH.sub.3. U.S. Pat. No. 5,006,200 describes reducing agents
selected from the group consisting of diamine (N.sub.2H.sub.4),
formaldehyde (HCHO), sodium thiosulfate (Na.sub.2S.sub.2O.sub.3)
and sodium borohydride (NaBH.sub.4). U.S. Pat. Nos. 5,721,014,
5,750,087, 5,753,309, and WO 99/02452 describe reducing agents
consisting of cyclic borane compounds, such as morpholine borane,
pyridine borane, piperidine borane, etc. The most commonly
practiced method of reducing cupric oxide to form cuprous oxide is
by use of the reducing agent dimethylamine borane (DMAB). This
approach has reduced the radius of the pink-ring to certain degree,
but is still limited and has not solved the problem completely
since cuprous oxide is not completely insoluble in an acid.
[0010] Attempts to address the problem mentioned above have been
made, for example as shown in U.S. Pat. Nos. 5,492,595 and
5,736,065 which describe methods of reducing the copper oxide to
metallic copper while maintaining the needle-like structure of the
oxide. However, such needle-like structure is mechanically unstable
and suffers from crush-down during the lamination process.
Alternative oxide coating processes have been developed
subsequently. Some exemplary processes are described in U.S. Pat.
Nos. 5,532,094, 6,946,027B2, 5,807,493, 6,746,621B2, 5,869,130,
6,554,948, and 5,800,859. These alternative processes produce
highly roughed copper surface by combining the traditional
oxidation process with a controlled etch that roughens the
underlying copper surface while oxidizing it at the same time. In
many cases, an organic layer is coated simultaneously to act as
corrosion inhibitor or adhesion promoter. In U.S. Pat. No.
5,800,859, there is described a micro-roughening process using an
etching agent comprising hydrogen peroxide, an inorganic acid, and
a corrosion inhibitor such as triazole. U.S. Pat. Nos. 6,716,281B2,
6,946,027B2, 7,108,795 B2, 7,211,204 B2, and 7,351,353 B1 describe
similar approaches for providing roughened copper surfaces using a
composition comprising an oxidizer, a pH adjuster, a topography
modifier, a uniformity enhancer, and an azole inhibitor. For the
same purpose, U.S. Pat. Nos. 5,532,094, 5,700,389, 5,807,493,
5,885,476, 5,965,036, 6,426,020B1, and 6,746,621B2 describe a
micro-etching composition consisting of an oxidizer like hydrogen
peroxide, a cupric ion source, an organic acid, a halide ion
source, and an azole type inhibitor. These approaches have
increased the acid resistance; however, the interface bonding is
achieved mainly by mechanical anchors and the adhesion strength
diminishes rapidly as the surface roughness of the treated copper
surface decreases. Thus, improvements are still needed.
[0011] Moreover, producing repeatable oxide layers is difficult. A
significant problem with the formation of oxides is that their
growth is difficult to control. Traditional techniques for
controlling growth of an oxide layer are to use time or temperature
as the vehicle to promote or stop growth of the oxide. Such prior
art methods suffer from poor reliability and repeatability.
[0012] As is readily seen, while numerous approaches have been
developed for improving the adhesion between the copper surface and
dielectric resin, the approaches have relied on creating a highly
roughened surface to promote adhesion. It is universally thought in
the prior art that the copper surface must be roughened to increase
the surface area for bonding or adhering to the epoxy or dielectric
resins. This approach however suffers from serve limitations since
the width and/or spacing of the copper lines is limited thus
preventing further miniaturization of the circuitry. Moreover,
oxide layers formed by prior art methods suffer from poor
repeatability and reliability. The current trend toward higher
density and finer line circuitry with increased layer counts has
generated the need for higher bonding strength of copper to
dielectric resins while retaining the smooth surface. Clearly,
there is a present need for further advances and developments in
the art.
[0013] Moreover, protective coatings are used in almost every
industry where metal surfaces are exposed to atmosphere, corrosive
environments or complex interfaces. In prior art techniques, the
coating is typically applied after extensive cleaning and
pre-treatment of the metal surface, which is performed to create a
surface that will bond to the coating. These pretreatment steps can
be as simple as acid or base-washing, solvent washing, and
oxidation and/or reductive treatments to increase the surface area
and/or roughness of the surface. Additionally, many conventional
treatments involve the deposition of other metals, e.g., chromium
or titanium, that serve as better anchors for subsequent deposition
of additional organic layers. Finally, there has been a tremendous
effort to utilize organic (molecular) reagents to derivatize the
surface of these metals to provide additional adhesion to the
coatings. All of these prior art processes are time consuming and
expensive, and a significant advantage would be provided by a
process that minimize the number of steps and the chemical
concentration and complexity in the preparation of the metals for
coating.
SUMMARY OF THE INVENTION
[0014] Accordingly, some embodiments of the present invention
provide methods for treating a smooth metal surface to increase the
adhesion between the metal surface and an organic layer. A metal
surface treatment process that increases the bonding strength and
yet does not significantly roughen the metal surface as provided by
embodiments of the present invention is a complete departure from,
and is contrary to, the conventional prior art techniques.
[0015] In some embodiments of the present invention methods provide
for achieving improved bonding strength between materials without
roughening the metal surface.
[0016] In some embodiments, a method of treating a metal surface to
promote adhesion or binding between the metal surface and an
organic layer is provided, characterized in that the metal surface
is stabilized by forming a metal oxide layer thereon, and then the
metal oxide layer is conditioned with a molecular reagent and/or
reducing agent to achieve selective oxide thickness and
morphology.
[0017] In some embodiments, a method of treating a metal surface to
promote adhesion or binding between the metal surface and an
organic material is provided characterized in that: a metal oxide
layer or a stabilization layer is formed on the metal surface, and
formation of the metal oxide layer is controlled by a self-limiting
reaction between the metal oxide and a molecular reagent or a
surface modifier compound, also sometimes called an inhibitor
compound.
[0018] In some embodiments, the stabilization layer has a surface
roughness of up to about 140 nm Ra and exhibits morphology
comprising grains of an average size in the range of 200 nanometers
or less, and has a thickness in the range of about 100 to 200
nanometers. In some embodiments the stabilization layer is
comprised substantially of copper oxide. In some embodiments a
molecular layer is formed atop the stabilization layer.
[0019] In another aspect, embodiments of the present invention
provide a printed circuit board, comprising: at least one metal
layer; at least one epoxy layer; and a stabilization layer formed
between the metal layer and epoxy layer.
[0020] In further embodiments of the present invention methods of
bonding a smooth metal surface and a resin are provided in which
the bonding interface has desired resistance to heat, moisture, and
chemicals involved in post-lamination process steps, and therefore
is particularly suitable for multilayer PCB lamination, among other
applications.
[0021] In some embodiments of the present invention methods are
provided that enable fabrication of high density multilayer PCB's
with line and/or space widths of equal to and less than 10
microns.
[0022] In another aspect, the present invention can be utilized in
a significant number of applications. In one such example,
embodiments of the present invention can by used to form protective
coatings.
[0023] In another aspect, embodiments of the present invention
provide methods of fabricating a printed circuit board, comprising
the steps of: pre-cleaning a copper surface with an alkaline and/or
peroxide solution; stabilizing the copper surface by forming a
copper oxide layer thereon; terminating formation of the copper
oxide layer by a self limiting reaction between the copper oxide
and one or more surface modifier or inhibitor compounds; and
bonding the treated copper surface with a resin. In some
embodiments, one or more molecules may be coupled to the copper
oxide layer, the one or more organic molecules comprising a
thermally stable base bearing one or more binding groups configured
to bind the copper oxide surface and/or one or more attachment
groups configured to attach to the resin.
[0024] In yet another aspect, embodiments of the present invention
provide a method of controlling the growth of an oxide layer on the
surface of a metal comprising: terminating growth of the oxide
layer by a self limiting reaction between the oxide layer and one
or more surface modifier compounds.
[0025] Additionally, other embodiments of the present invention
provide a reduction composition, comprising: one or more
reductants; and one or more molecular reagent compounds.
[0026] Additionally, other embodiments of the present invention
provide an oxidant composition, comprising: one or more oxidants;
and one or more surface modifier or inhibitor compounds.
BRIEF DESCRIPTION OF THE FIGURES
[0027] The foregoing and other aspects of embodiments of the
present invention will be apparent upon consideration of the
following detailed description, taken in conjunction with the
accompanying drawings, in which like reference characters refer to
like parts throughout, and in which:
[0028] FIGS. 1A and 1B schematically illustrate one embodiment of
the metal-resin bonding process according to embodiments of the
present invention as compared to the conventional roughening
process;
[0029] FIG. 2 illustrates experimental process flow diagrams
illustrating one embodiment of the method of the present
invention;
[0030] FIGS. 3A and 3B show a simplified exemplary reaction scheme
for two embodiments of the present invention;
[0031] FIGS. 4A to 4D show SEM photographs of: (A) a smooth copper
surface prior to any treatment (i.e. the control); (B) a copper
surface treated according to one embodiment of the present
invention which shows the smoothness of the stabilization layer of
the treated surface; and compared to (C) a conventional rough black
oxide surface as described in the prior art; and (D) a micro-etch
roughened copper surface as described in the prior art;
[0032] FIG. 5 is a table which compares the surface roughness
expressed in both Ra and Rz of the copper surfaces shown in FIGS.
4A to 4D;
[0033] FIG. 6 graphically shows the Auger depth profile
demonstrating that the stabilization layer has a thickness of about
150 nm as prepared according to embodiments of the present
invention, compared to a conventional copper black oxide layer that
is typically greater than 1 micron in depth;
[0034] FIG. 7 is an example of a test sample layout used to conduct
peel strength tests on copper test strips on an epoxy
substrate;
[0035] FIGS. 8A and 8D are simplified cross sectional views showing
the preparation of test samples and illustrating the lamination
process used according to some embodiments;
[0036] FIGS. 9A and 9B illustrate peel strength and surface
roughness for epoxy laminated smooth copper surfaces treated
according to embodiments the present invention (referred to as
"treated smooth"), as compared to control smooth copper substrates
and conventional roughened copper surfaces;
[0037] FIG. 10 graphically illustrates the reproducibility of peel
strength and HAST stability for five batches of samples of epoxy
laminated smooth copper surfaces treated according to embodiments
the present invention;
[0038] FIGS. 11A and 11B show SEM cross-sectional views of a
laminated treated smooth copper surfaces according to embodiments
of the present invention (bottom surface) before and after HAST,
and compared to a standard rough surface (top surface); and
demonstrating that the methods of the present invention do not
significantly roughen the surface and that there is no delamination
at that interface after HAST;
[0039] FIG. 12A shows two SEM photographs (full and topographical
mode) of a peeled copper surface after HAST demonstrating that the
copper-resin interface breaks right at an untreated, smooth copper
surface control. FIG. 12B shows two SEM photographs (full and
topographical mode) of a peeled, treated smooth copper surface
according to embodiments of the present invention after HAST and
showing that most areas are covered by resin suggesting that
failure occurs within the resin, not at the copper-resin
interface;
[0040] FIG. 13 is a SEM photograph showing a cross-section of a
laser via formed on laminated treated smooth copper surface
according to embodiments of the present invention demonstrating
that no undercutting occurs after the desmear and plating
processes;
[0041] FIGS. 14A and 14B graphically illustrate peel strength and
surface roughness for solder resist laminated smooth copper surface
treated according to embodiments of the present invention, as
compared to control substrates and conventional roughened copper
surfaces;
[0042] FIGS. 15A and 15B show photos of SR pattern of copper lines
and via arrays (16A) and BGA pattern (16B); and
[0043] FIG. 16 is a SEM photograph of a cross-section of a SR via
formed on a laminated treated copper surface formed according to
embodiments of the present invention, which demonstrates that no
delamination occurs post desmear processing and plating.
DETAILED DESCRIPTION OF THE INVENTION
[0044] It is to be understood that both the foregoing general
description and the following description are exemplary and
explanatory only and are not restrictive of the methods and devices
described herein. In this application, the use of the singular
includes the plural unless specifically state otherwise. Also, the
use of "or" means "and/or" unless state otherwise. Similarly,
"comprise," "comprises," "comprising," "include," "includes,"
"including," "has," "have," and "having" are not intended to be
limiting.
[0045] Embodiments of the present invention provide significant
advances over the prior art in the manufacture of coatings and
electronics and in particular printed circuit boards by, among
other aspects, forming a stabilization layer on the surface of
metal substrates that adhere strongly to organic materials (such
as, without limitation, epoxy or resin substrates). The
stabilization layers have relatively smooth morphology, and as such
their strong adhesion to organic materials is surprising and
unexpected. In fact, the central teaching and approach of the prior
art methods is that the metal oxide surface must be roughened in
order for sufficient adhesion to occur.
[0046] Unique methods have been developed to form a stabilization
layer having desired thickness and morphology as well as an ability
to adhere to subsequent layers of organic materials deposited
thereon. That is, in some embodiments a modified metal oxide is
formed through selective control or alteration of the oxidation
step, the reduction step, or both with a molecular reagent that
modifies the growth and stability of that oxide layer. Typically,
oxide growth is very difficult to control. Prior art techniques
typically require post oxidation steps in order to reduce the
thickness of the oxide, to further condition the oxide morphology,
and the like. Embodiments of the present invention provide a
significant innovation by employing a surface modifier or inhibitor
compound that reacts with the oxide to control or limit the extent
of oxide growth. This can be accomplished by adding the surface
modifier to the oxidation solution as it is forming to slow down
the oxide growth and then block further oxidation. Alternatively, a
standard oxidation reaction can be utilized, followed with a
reduction step that has been modified by addition of the surface
modifier to provide stabilization. Embodiments of the present
invention utilize this reaction to control the growth rate,
thickness, and morphology of the oxide, and all of these aspects
can be accomplished in a single step. The resulting metal oxide
film, as formed, exhibits desirable thickness and morphological
properties without the need for post processing steps. Elimination
of post processing steps significantly reduces the complexity of
the process and provides significant cost savings.
[0047] Moreover, embodiments of the present invention provide
methods of controlling the growth of an oxide layer on the surface
of a metal. Specifically, in some embodiments growth of an oxide
layer is terminated by a self limiting reaction between the oxide
layer and one or more surface modifier or inhibitor compounds. In
some embodiments, examples of surface modifiers or inhibitor
compounds include surface active molecules (SAMs) as described in
detail below. Of significant advantage embodiments of the present
invention provide a stable, controllable process window. Such a
stable process window provides a robust, repeatable process. This
is a significant advance, particularly because with the prior art
methods there is continuous oxide growth of the metal oxide layer
which is one of the primary failure mechanisms of conventional PCB
boards.
[0048] The metal surface is stabilized by exposing the metal
surface to an oxidant. In an exemplary embodiment the oxidant is
selected from any one or more of: sodium chloride, hydrogen
peroxide, permanganate, perchlorate, persulphate, ozone or mixtures
thereof. The step of stabilizing the metal surface may be carried
out at a temperature in the range of room temperature to about
80.degree. C.
[0049] After oxidation, the metal oxide layer may be conditioned
with a reducing agent. In some embodiments the reducing agent is
selected from any one or more of formaldehyde, sodium thiosulfate,
sodium borohydride, a borane reducing agent represented by the
general formula BH.sub.3NHRR', wherein R and R' are each selected
from the group consisting of H, CH.sub.3 and CH.sub.2CH.sub.3, such
as dimethylamine borane (DMAB), a cyclic borane, such as morpholine
borane, pyridium borane, piperidine borane. Conditioning of the
metal oxide layer may be carried out at a temperature in the range
of room temperature to about 50.degree. C. In some embodiments the
entire method is carried out for a time in the range of about 2 to
20 minutes.
[0050] Additionally, some embodiments of the present invention
provide for, after conditioning, contacting the oxidized surface
with one or more organic molecules comprising a thermally stable
base bearing one or more binding groups configured to bind the
metal surface and one or more attachment groups configured to
attach to the organic material. In an exemplary embodiment the one
or more organic molecules is the surface modifier or inhibitor
compound.
[0051] In some embodiments, a method of treating a metal surface to
promote adhesion or binding between the metal surface and an
organic material is provided characterized in that: a stabilization
layer is formed on the metal surface, and formation of the
stabilization layer is controlled by a self-limiting reaction
between the metal oxide and a surface modifier or inhibitor
compound. Of significant advance, according to embodiments of the
present invention both formation of the oxide layer and control of
its growth (including termination) are achieved in one step.
[0052] Of particular advantage, the metal oxide layer, also
sometimes referred to as a stabilization layer, exhibits unique and
desirable features. In some embodiments the formed stabilization
layer has a thickness of about 200 nanometers and less. In some
embodiments the stabilization layer has morphology comprised of a
substantially amorphous structure.
[0053] In an exemplary embodiment the formed stabilization layer
has grains of a size in the range of 200 nanometers and less. In
other embodiments the formed stabilization layer has grains of a
size in the range of 150 nanometers and less. In some embodiments
the formed stabilization layer has grains that are substantially
randomly oriented. Typically, but not exclusively, the
stabilization layer is comprised of copper oxide and molecular
reagents.
[0054] To begin formation of the stabilization layer, oxidation
initiation is carried out by exposing the metal surface to an
oxidant. In some embodiments the oxidant solution is comprised of:
one or more oxidants, and one or more surface modifiers can be
added. In an exemplary embodiment one or more oxidants are
comprised of: sodium chlorite, hydrogen peroxide, permaganate,
perchlorate, persulphate, ozone, or mixtures thereof.
[0055] Any suitable concentration of oxidant solution may be used.
In some embodiments the oxidant solution is comprised substantially
of one or more oxidants in solution. In general, the surface
modifier is selected from compounds that react with the
stabilization layer in a self-limiting reaction. In some
embodiments, the surface active molecule (SAM) is selected such
that it reacts with the metal oxide surface to control the reaction
rate as the metal oxide is forming, and then eventually slows and
terminates the oxidation reaction. Optionally, functional groups
can be added to the surface modifier compound to provide additional
bonding with organic materials, such as but not limited to epoxies
and the like.
[0056] Once oxidation is initiated, oxide starts to grow on top of
the metal surface. As this stabilization layer is formed, the
surface modifier compound starts to react with oxygen containing
moieties on the surface of the metal. This will slow down and block
further oxidation and thus achieve self-limiting reaction of the
oxide formation.
[0057] Additionally, some embodiments of the present invention
provide for contacting the metal surface with one or more organic
or inorganic molecules which are surface active molecules (SAMs)
comprising a thermally stable base bearing one or more binding
groups configured to bind the metal surface and one or more
attachment groups configured to attach to the organic material. In
an exemplary embodiment the one or more surface modifier molecules
is a surface active moiety.
[0058] In some embodiments a method of treating a metal surface to
promote adhesion or binding between the metal surface and an
organic material is provided characterized in that: the metal
surface is stabilized by forming a stabilization layer thereon, and
then the stabilization layer is conditioned with a reducing agent
to achieve selective oxide thickness and morphology.
[0059] Of particular advantage, the metal oxide layer, also
sometimes referred to as a stabilization layer, exhibits unique
features. In some embodiments the stabilization layer after
conditioning has a thickness of about 200 nanometers and less. In
some embodiments the metal oxide has morphology comprised of a
substantially amorphous structure.
[0060] In an exemplary embodiment the stabilization layer has a
highly distributed grain structure, and after conditioning the
grains have a size in the range of 200 nanometers and less. In
other embodiments the stabilization layer has grains, and after
conditioning the grains have a size in the range of 100 nanometers
and less. In some embodiments the metal oxide has grains, and after
conditioning the grains are substantially randomly oriented.
Typically, but not exclusively, the stabilization layer is
comprised of copper oxide.
[0061] The metal surface is stabilized by exposing the metal
surface to an oxidant. In an exemplary embodiment the oxidant is
selected from any one or more of: sodium chlorite, hydrogen
peroxide, permanganate, perchlorate, persulphate, ozone, or
mixtures thereof. The step of stabilizing the metal surface may be
carried out at a temperature in the range of room temperature to
about 80.degree. C. Alternatively, the metal surface can be
stabilized by thermal oxidation and electrochemical anodic
oxidation.
[0062] After stabilization, the stabilization layer can be
conditioned with a reducing agent. In some embodiments the reducing
agent is selected from any one or more of: formaldehyde, sodium
thiosulfate, sodium borohydride, a borane reducing agent
represented by the general formula BH.sub.3NHRR', wherein R and R'
are each selected from the group consisting of H, CH.sub.3 and
CH.sub.2CH.sub.3, such as dimethylamine borane (DMAB), a cyclic
borane, such as morpholine borane, pyridium borane, piperidine
borane.
[0063] Conditioning of the stabilization layer may be carried out
at a temperature in the range of room temperature to about
50.degree. C. In some embodiments the entire method is carried out
for a time in the range of about 2 to 20 minutes.
[0064] Additionally, some embodiments of the present invention
provide for, after conditioning, contacting the metal surface with
one or more surface active molecules comprising a thermally stable
base bearing one or more binding groups configured to bind the
metal surface and one or more attachment groups configured to
attach to an organic material such as PCB epoxies and the like. In
an exemplary embodiment the one or more organic molecules is a
surface active moiety.
[0065] Any suitable surface active moiety may be employed. In some
embodiments the surface modifier moiety is selected from the group
consisting of a macrocyclic proligand, a macrocyclic complex, a
sandwich coordination complex and polymers thereof. Alternatively
the surface modifier moiety may be comprised of a porphyrin.
[0066] The one or more surface active molecules may be selected
from the group of: a porphyrin, a porphyrinic macrocycle, an
expanded porphyrin, a contracted porphyrin, a linear porphyrin
polymer, a porphyrinic sandwich coordination complex, a porphyrin
array, a silane, a tetraorgano-silane,
aminoethyl-aminopropyl-trimethoxysilane,
(3-Aminopropyl)trimethoxysilane,
(1-[3-(Trimethoxysilyl)propyl]urea), (3-Aminopropyl)
triethoxysilane, ((3-Glycidyloxypropyl)trimethoxysilane),
(3-Chloropropyl) trimethoxysilane,
(3-Glycidyloxypropyl)trimethoxysilane, Dimethyldichlorosilane,
3-(Trimethoxysilyl)propyl methacrylate, Ethyltriacetoxysilane,
Triethoxy(isobutyl)silane, Triethoxy(octyl)silane,
Tris(2-methoxyethoxy)(vinyl)silane, Chlorotrimethylsilane,
Methyltrichlorosilane, Silicon tetrachloride, Tetraethoxysilane,
Phenyltrimethoxysilane, Chlorotriethoxysilane,
ethylene-trimethoxysilane, an amine, a sugar or any combination of
the above. Alternatively, inorganic molecules from the group
consisting of molybdates, tungstates, tantalates, niobates,
vanadates, isopoly or heteropoly acids of molybdenum, tungsten,
tantalum, niobium, vanadium, and combinations of any of the
foregoing can be used for the same purpose.
[0067] In some embodiments the one or more attachment group is
comprised of an aryl functional group and/or an alkyl attachment
group. When the attachment group is an aryl, the aryl functional
group may be comprised of a functional group selected from any one
or more of: acetate, alkylamino, allyl, amine, amino, bromo,
bromomethyl, carbonyl, carboxylate, carboxylic acid,
dihydroxyphosphoryl, epoxide, ester, ether, ethynyl, formyl,
hydroxy, hydroxymethyl, iodo, mercapto, mercaptomethyl,
Se-acetylseleno, Se-acetylselenomethyl, S-acetylthio,
S-acetylthiomethyl, selenyl,
4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl,
2-(trimethylsilyl)ethynyl, vinyl, and combinations thereof.
[0068] When the attachment group is comprised of an alkyl, the
alkyl attachment group comprises a functional group selected from
any one or more of: acetate, alkylamino, allyl, amine, amino,
bromo, bromomethyl, carbonyl, carboxylate, carboxylic acid,
dihydroxyphosphoryl, epoxide, ester, ether, ethynyl, formyl,
hydroxy, hydroxymethyl, iodo, mercapto, mercaptomethyl,
Se-acetylseleno Se-acetylselenomethyl. S-acetylthio,
S-acetylthiomethyl, selenyl,
4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl,
2-(trimethylsilyl)ethynyl, vinyl, and combinations thereof.
[0069] In an alternative embodiment the at least one attachment
group is comprised of an alcohol or a phosphonate. In further
embodiments, the at least one attachment group may be comprised of
any one of more of: amines, alcohols, ethers, other nucleophile,
phenyl ethynes, phenyl allylic groups, phosphonates and
combinations thereof.
[0070] In general, in some embodiments the organic molecule is
comprised of a thermally stable unit or base with one more binding
groups X and one or more attachment groups Y. In certain
embodiments, the organic molecule is heat-resistant metal-binding
molecule, and may be comprised of one or more "surface active
moieties," also referred to in associated applications as "redox
active moieties" or "ReAMs". One embodiment of the invention
encompasses the use of compositions of molecular components using
surface active moieties generally described in U.S. Pat. Nos.
6,208,553, 6,381,169, 6,657,884, 6,324,091, 6,272,038, 6,212,093,
6,451,942, 6,777,516, 6,674,121, 6,642,376, 6,728,129, US
Publication Nos: 20070108438, 20060092687, 20050243597,
20060209587, 20060195296, 20060092687, 20060081950, 20050270820,
20050243597, 20050207208, 20050185447, 20050162895, 20050062097,
20050041494, 20030169618, 20030111670, 20030081463, 20020180446,
20020154535, 20020076714, 2002/0180446, 2003/0082444, 2003/0081463,
2004/0115524, 2004/0150465, 2004/0120180, 2002/010589, U.S. Ser.
Nos. 10/766,304, 10/834,630, 10/628,868, 10/456,321, 10/723,315,
10/800,147, 10/795,904, 10/754,257, 60/687,464, all of which are
expressly incorporated in their entirety. Note that while in the
associated applications listed immediately above, the
heat-resistant molecule is sometime referred to as "redox active
moieties" or "ReAMs," in the instant application term surface
active moiety is more appropriate. In general, in some embodiments
there are several types of surface active moieties useful in the
present invention, all based on polydentate proligands, including
macrocyclic and non-macrocyclic moieties. A number of suitable
proligands and complexes, as well as suitable substituents, are
outlined in the references cited above. In addition, many
polydentate proligands can include substitution groups (often
referred to as "R" groups herein and within the cited references,
and include moieties and definitions outlined in U.S. Pub. No.
2007/0108438, incorporated by reference herein specifically for the
definition of the substituent groups.
[0071] Suitable proligands fall into two categories: ligands which
use nitrogen, oxygen, sulfur, carbon or phosphorus atoms (depending
on the metal ion) as the coordination atoms (generally referred to
in the literature as sigma (a) donors) and organometallic ligands
such as metallocene ligands (generally referred to in the
literature as pi donors, and depicted in U.S. Pub. No. 2007/0108438
as Lm).
[0072] In addition, a single surface active moiety may have two or
more redox active subunits, for example, as shown in FIG. 13A of
U.S. Pub. No. 2007/0108438, which utilizes porphyrins and
ferrocenes.
[0073] In some embodiments, the surface active moiety is a
macrocyclic ligand, which includes both macrocyclic proligands and
macrocyclic complexes. By "macrocyclic proligand" herein is meant a
cyclic compound which contains donor atoms (sometimes referred to
herein as "coordination atoms") oriented so that they can bind to a
metal ion and which are large enough to encircle the metal atom. In
general, the donor atoms are heteroatoms including, but not limited
to, nitrogen, oxygen and sulfur, with the former being especially
preferred. However, as will be appreciated by those in the art,
different metal ions bind preferentially to different heteroatoms,
and thus the heteroatoms used can depend on the desired metal ion.
In addition, in some embodiments, a single macrocycle can contain
heteroatoms of different types.
[0074] A "macrocyclic complex" is a macrocyclic proligand with at
least one metal ion; in some embodiments the macrocyclic complex
comprises a single metal ion, although as described below,
polynucleate complexes, including polynucleate macrocyclic
complexes, are also contemplated.
[0075] A wide variety of macrocyclic ligands find use in the
present invention, including those that are electronically
conjugated and those that may not be. A broad schematic of a
suitable macrocyclic ligand is shown and described in FIG. 15 of
U.S. Pub. No. 2007/0108438. In some embodiments, the rings, bonds
and substitutents are chosen to result in the compound being
electronically conjugated, and at a minimum to have at least two
oxidation states.
[0076] In some embodiments, the macrocyclic ligands of the
invention are selected from the group consisting of porphyrins
(particularly porphyrin derivatives as defined below), and cyclen
derivatives. A particularly preferred subset of macrocycles
suitable in the invention include porphyrins, including porphyrin
derivatives. Such derivatives include porphyrins with extra rings
ortho-fused, or ortho-perifused, to the porphyrin nucleus,
porphyrins having a replacement of one or more carbon atoms of the
porphyrin ring by an atom of another element (skeletal
replacement), derivatives having a replacement of a nitrogen atom
of the porphyrin ring by an atom of another element (skeletal
replacement of nitrogen), derivatives having substituents other
than hydrogen located at the peripheral meso-, 3- or core atoms of
the porphyrin, derivatives with saturation of one or more bonds of
the porphyrin (hydroporphyrins, e.g., chlorins, bacteriochlorins,
isobacteriochlorins, decahydroporphyrins, corphins, pyrrocorphins,
etc.), derivatives having one or more atoms, including pyrrolic and
pyrromethenyl units, inserted in the porphyrin ring (expanded
porphyrins), derivatives having one or more groups removed from the
porphyrin ring (contracted porphyrins, e.g., corrin, corrole) and
combinations of the foregoing derivatives (e.g. phthalocyanines,
sub-phthalocyanines, and porphyrin isomers). Additional suitable
porphyrin derivatives include, but are not limited to the
chlorophyll group, including etiophyllin, pyrroporphyrin,
rhodoporphyrin, phylloporphyrin, phylloerythrin, chlorophyll a and
b, as well as thehemoglobin group, including deuteroporphyrin,
deuterohemin, hemin, hematin, protoporphyrin, mesohemin,
hematoporphyrin mesoporphyrin, coproporphyrin, uruporphyrin and
turacin, and the series of tetraarylazadipyrromethines.
[0077] As will be appreciated by those in the art, each unsaturated
position, whether carbon or heteroatom, can include one or more
substitution groups as defined herein, depending on the desired
valency of the system.
[0078] In addition, included within the definition of "porphyrin"
are porphyrin complexes, which comprise the porphyrin proligand and
at least one metal ion. Suitable metals for the porphyrin compounds
will depend on the heteroatoms used as coordination atoms, but in
general are selected from transition metal ions. The term
"transition metals" as used herein typically refers to the 38
elements in groups 3 through 12 of the periodic table. Typically
transition metals are characterized by the fact that their valence
electrons, or the electrons they use to combine with other
elements, are present in more than one shell and consequently often
exhibit several common oxidation states. In certain embodiments,
the transition metals of this invention include, but are not
limited to one or more of scandium, titanium, vanadium, chromium,
manganese, iron, cobalt, nickel, copper, zinc, yttrium, zirconium,
niobium, molybdenum, technetium, ruthenium, rhodium, palladium,
silver, cadmium, hafnium, tantalum, tungsten, rhenium, osmium,
iridium, platinum, palladium, gold, mercury, rutherfordium, and/or
oxides, and/or nitrides, and/or alloys, and/or mixtures
thereof.
[0079] There are also a number of macrocycles based on cyclen
derivatives. FIGS. 17 and 13C of U.S. Pub. No. 2007/0108438,
depicts a number of macrocyclic proligands loosely based on
cyclen/cyclam derivatives, which can include skeletal expansion by
the inclusion of independently selected carbons or heteroatoms. In
some embodiments, at least one R group is a surface active subunit,
preferably electronically conjugated to the metal. In some
embodiments, including when at least one R group is a surface
active subunit, two or more neighboring R2 groups form cyclo or an
aryl group. In the present invention, the at least one R group is a
surface active subunit or moiety.
[0080] Furthermore, in some embodiments, macrocyclic complexes
relying organometallic ligands are used. In addition to purely
organic compounds for use as surface active moieties, and various
transition metal coordination complexes with 8-bonded organic
ligand with donor atoms as heterocyclic or exocyclic substituents,
there is available a wide variety of transition metal
organometallic compounds with pi-bonded organic ligands (see
Advanced Inorganic Chemistry, 5th Ed., Cotton & Wilkinson, John
Wiley & Sons, 1988, chapter 26; Organometallics, A Concise
Introduction, Elschenbroich et al., 2nd Ed., 1992, 30 VCH; and
Comprehensive Organometallic Chemistry II, A Review of the
Literature 1982-1994, Abel et al. Ed., Vol. 7, chapters 7, 8, 1.0
& 11, Pergamon Press, hereby expressly incorporated by
reference). Such organometallic ligands include cyclic aromatic
compounds such as the cyclopentadienide ion [C.sub.5H.sub.5(-1)]
and various ring substituted and ring fused derivatives, such as
the indenylide (-1) ion, that yield a class of
bis(cyclopentadieyl)metal compounds, (i.e. the metallocenes); see
for example Robins et al., J. Am. Chem. Soc. 104:1882-1893 (1982);
and Gassman et al., J. Am. Chem. Soc. 108:4228-4229 (1986),
incorporated by reference. Of these, ferrocene
[(C.sub.5H.sub.5).sub.2Fe] and its derivatives are prototypical
examples which have been used in a wide variety of chemical
(Connelly et al., Chem. Rev. 96:877-910 (1996), incorporated by
reference) and electrochemical (Geiger et al., Advances in
Organometallic Chemistry 23:1-93; and Geiger et al., Advances in
Organometallic Chemistry 24:87, incorporated by reference)
reactions. Other potentially suitable organometallic ligands
include cyclic arenes such as benzene, to yield bis(arene)metal
compounds and their ring substituted and ring fused derivatives, of
which bis(benzene)chromium is a prototypical example, Other acyclic
n-bonded ligands such as the allyl(-1) ion, or butadiene yield
potentially suitable organometallic compounds, and all such
ligands, in conjunction with other 7c-bonded and 8-bonded ligands
constitute the general class of organometallic compounds in which
there is a metal to carbon bond. Electrochemical studies of various
dimers and oligomers of such compounds with bridging organic
ligands, and additional non-bridging ligands, as well as with and
without metal-metal bonds are all useful.
[0081] In some embodiments, the surface active moieties are
sandwich coordination complexes. The terms "sandwich coordination
compound" or "sandwich coordination complex" refer to a compound of
the formula L-Mn-L, where each L is a heterocyclic ligand (as
described below), each M is a metal, n is 2 or more, most
preferably 2 or 3, and each metal is positioned between a pair of
ligands and bonded to one or more hetero atom (and typically a
plurality of hetero atoms, e.g., 2, 3, 4, 5) in each ligand
(depending upon the oxidation state of the metal). Thus sandwich
coordination compounds are not organometallic compounds such as
ferrocene, in which the metal is bonded to carbon atoms. The
ligands in the sandwich coordination compound are generally
arranged in a stacked orientation (i.e., are generally cofacially
oriented and axially aligned with one another, although they may or
may not be rotated about that axis with respect to one another)
(see, e.g., Ng and Jiang (1997) Chemical Society Reviews 26:
433-442) incorporated by reference. Sandwich coordination complexes
include, but are not limited to "double-decker sandwich
coordination compound" and "triple-decker sandwich coordination
compounds". The synthesis and use of sandwich coordination
compounds is described in detail in U.S. Pat. Nos. 6,212,093;
6,451,942; 6,777,516; and polymerization of these molecules is
described in WO 2005/086826, all of which are included herein,
particularly the individual substitutent groups that find use in
both sandwich complexes and the "single macrocycle" complexes.
[0082] In addition, polymers of these sandwich compounds are also
of use; this includes "dyads" and "triads" as described in U.S.
Ser. Nos. 6,212,093; 6,451,942; 6,777,516; and polymerization of
these molecules as described in WO 2005/086826, all of which are
incorporated by reference and included herein.
[0083] Surface active moieties comprising non-macrocyclic chelators
are bound to metal ions to form non-macrocyclic chelate compounds,
since the presence of the metal allows for multiple proligands to
bind together to give multiple oxidation states.
[0084] In some embodiments, nitrogen donating proligands are used.
Suitable nitrogen donating proligands are well known in the art and
include, but are not limited to, NH2; NFIR; NRR'; pyridine;
pyrazine; isonicotinamide; imidazole; bipyridine and substituted
derivatives of bipyridine; terpyridine and substituted derivatives;
phenanthrolines, particularly 1,10-phenanthroline (abbreviated
phen) and substituted derivatives of phenanthrolines such as
4,7-dimethylphenanthroline and dipyridol[3,2-a:2',3'-c]phenazine
(abbreviated dppz); dipyridophenazine;
1,4,5,8,9,12-hexaazatriphenylene (abbreviated hat);
9,10-phenanthrenequinone diimine (abbreviated phi);
1,4,5,8-tetraazaphenanthrene (abbreviated tap);
1,4,8,11-tetra-azacyclotetradecane (abbreviated cyclam) and
isocyanide. Substituted derivatives, including fused derivatives,
may also be used. It should be noted that macrocylic ligands that
do not coordinatively saturate the metal ion, and which require the
addition of another proligand, are considered non-macrocyclic for
this purpose. As will be appreciated by those in the art, it is
possible to covalent attach a number of "non-macrocyclic" ligands
to form a coordinatively saturated compound, but that is lacking a
cyclic skeleton.
[0085] Suitable sigma donating ligands using carbon, oxygen, sulfur
and phosphorus are known in the art. For example, suitable sigma
carbon donors are found in Cotton and Wilkenson, Advanced Organic
Chemistry, 5th Edition, John Wiley & Sons, 1988, hereby
incorporated by reference; see page 38, for example. Similarly,
suitable oxygen ligands include crown ethers, water and others
known in the art. Phosphines and substituted phosphines are also
suitable; see page 38 of Cotton and Wilkenson.
[0086] The oxygen, sulfur, phosphorus and nitrogen-donating ligands
are attached in such a manner as to allow the heteroatoms to serve
as coordination atoms.
[0087] In addition, some embodiments utilize polydentate ligands
that are polynucleating ligands, e.g. they are capable of binding
more than one metal ion. These may be macrocyclic or
non-macrocyclic. The molecular elements herein may also comprise
polymers of the surface active moieties as outlined above; for
example, porphyrin polymers (including polymers of porphyrin
complexes), macrocycle complex polymers, surface active moieties
comprising two surface active subunits, etc. can be utilized. The
polymers can be homopolymers or heteropolymers, and can include any
number of different mixtures (admixtures) of monomeric surface
active moiety, wherein "monomer" can also include surface active
moieties comprising two or more subunits (e.g. a sandwich
coordination compound, a porphyrin derivative substituted with one
or more ferrocenes, etc.). Surface active moiety polymers are
described in WO 2005/086826, which is expressly incorporated by
reference in its entirety.
[0088] In certain embodiments, the attachment group Y comprises an
aryl functional group and/or an alkyl attachment group. In certain
embodiments, the aryl functional group comprises a functional group
selected from the group consisting of amino, alkylamino, bromo,
iodo, hydroxy, hydroxymethyl, formyl, bromomethyl, vinyl, allyl,
S-acetylthiomethyl, Se-acetylselenomethyl, ethynyl,
2-(trimethylsilyl)ethynyl, mercapto, mercaptomethyl,
4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl, and
dihydroxyphosphoryl. In certain embodiments, the alkyl attachment
group comprises a functional group selected from the group
consisting of bromo, iodo, hydroxy, formyl, vinyl, mercapto,
selenyl, S-acetylthio, Se-acetylseleno, ethynyl,
2-(trimethylsilyl)ethynyl,
4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl, and
dihydroxyphosphoryl. In certain embodiments, the attachment group
comprises an alcohol or a phosphonate.
[0089] In some embodiments, the surface active moieties are
silanes, characterized by the formula, A.sub.(4-x)SiB.sub.xY,
wherein each A is independently a hydrolysable group, e.g. a
hydroxyl or alkoxy group, where x=1 to 3, and B is independently an
alkyl or aryl group, that may or may not contain attachment groups.
Y, as described above.
[0090] Embodiments of the present invention are suitable for use
with many organic substrates. In an exemplary embodiment, the
organic substrate may be comprised of any one or more of:
electronic substrates, PCB substrates, semiconductor substrates,
photovoltaic substrates, polymers, ceramics, carbon, epoxy, glass
reinforced epoxy, phenol, polyimide resines, glass reinforced
polyimide, cyanate, esters, Teflon, plastics, paints and mixtures
thereof.
[0091] In another aspect, embodiments of the present invention
provide a printed circuit board, comprising: at least one metal
layer; at least one epoxy layer; and a stabilization layer formed
between the metal layer and epoxy layer.
[0092] In some embodiments the stabilization layer is comprised of
a metal oxide having a thickness of about 200 nanometers and less.
In other embodiments the stabilization layer is comprised of a
metal oxide exhibiting a substantially amorphous structure. In yet
additional embodiments, the stabilization layer is comprised of a
metal oxide having a thickness of about 150 nanometers and less and
exhibiting a substantially amorphous structure.
[0093] Generally, the stabilization layer is comprised of a
stabilization layer having grains, wherein the grains have a grain
size in the range of 200 nanometers and less. In another embodiment
the grains have a grain size in the range of 100 nanometers and
less. Typically, but not exclusively, the metal oxide is comprised
of copper oxide.
[0094] Of particular advantage, embodiments of the present
invention provide an approach for treating a "smooth" metal
substrate. In some embodiments the invention enables the use of a
smooth metal substrate, meaning a metal substrate that has not been
previously roughened. In the instance of a copper substrate, such a
substrate can be from a variety of sources. For example, copper
substrates suitable for use in methods of the present invention
include, but are not limited to, electrolytic or electroplated
copper, electroless copper, and rolled copper, and not restricted
by the method of preparing the same.
[0095] In some embodiments the metal layer has a roughness of about
0.13 .mu.m Ra. In some embodiments the formed copper oxide, or also
referred to as "treated smooth copper surface" or the stabilization
layer of the present invention, has a roughness of about 0.14 .mu.m
Ra thus demonstrating the method of the present invention does not
significantly roughen the surface.
[0096] In further aspects, a printed circuit board is provided
comprising a polymer material, such as an epoxy, which may contain
a substantial amount of a filler material, such as glass, silica,
or other materials, modified on its surface with a chemical
adhesive material, such as a porphyrin, that substantially alters
its chemical affinity for a metal, such as but not limited to
copper, in order to facilitate strong adhesion between the polymer
composite and the metal layer. A second layer of the chemical
adhesive layer may be applied to the metal surface, to promote
adhesion between it and subsequent polymer (epoxy/glass) layers. In
some embodiments, the PCB is a multilayer conductive structure.
[0097] For example in one aspect, a printed circuit board is
provided, comprising: at least one metal layer; a layer of organic
molecules attached to the at least one metal layer; and an epoxy
layer atop said layer of organic molecules. In some embodiments the
at least one metal layer exhibits a peel strength of greater than
1.0 kg/cm and a surface roughness of less than 150 nm. In some
embodiments, the at least one metal layer further comprises
patterned metal lines formed thereon, wherein the patterned metals
lines have a width of equal to and less than 25 microns.
Additionally, patterned metal lines may have a width of equal to
and less than 15 microns, 10 microns or 5 microns.
[0098] In another aspect of the present invention, a printed
circuit board is provided having one or more metal layers and one
or more epoxy layers formed thereon, characterized in that: at
least one of said one or more metal layers exhibits a peel strength
of greater than 1.0 kg/cm and a surface roughness of less than 150
nm. Embodiments of the present invention enable the formation of
very small line widths. In some embodiments the metal layer is
comprised of patterned metal lines formed thereon, said patterned
metals lines having a width of equal to and less than 25 microns.
In other embodiments the metal layer comprises patterned metal
lines formed thereon, where the patterned metals lines have a width
of equal to and less than 15 microns, and further less than 10
microns. In even further embodiments, patterned metal lines may be
formed thereon wherein the patterned metals lines have a width of
equal to and less than 5 microns.
[0099] In another aspect, the present invention provides methods of
fabricating a printed circuit board, comprising the steps of:
pre-cleaning a copper surface with an alkaline and/or peroxide
solution; stabilizing the copper surface by forming a copper oxide
layer thereon; terminating formation of the copper oxide by a self
limiting reaction between the copper oxide and one or more surface
modifier or inhibitor compounds; and bonding the treated copper
surface with a resin. Is some embodiments, one or more molecules
may be coupled to the copper oxide layer, the one or more organic
molecules comprising a thermally stable base bearing one or more
binding groups configured to bind the copper oxide surface and one
or more attachment groups configured to attach to the resin.
[0100] Referring to FIG. 1A, there is illustrated one exemplary
embodiment of a simplified schematic of a smooth metal-resin
bonding interface 100A comprising a smooth metal substrate 102
bonded to a resin substrate 104. A stabilization layer 106 of
either a dense oxide layer combined with or without an organic
layer 108 is formed on top of the metal to prevent the metal
surface from corrosion or chemical attack. In some embodiments it
may be desirable, but not necessary, to facilitate chemical bonding
by further conditioning or priming the stabilization layer with an
organic molecular layer 108 to form active bonding sites X which
will react with functional groups Y in the resin, forming covalent
bonds. In the exemplary embodiment, the smooth metal-resin
interface 100A possesses superior adhesion strength and resistance
to heat, moisture, and chemical attacks; as compared to roughened
copper-resin interface 100B shown in FIG. 1B which is known in the
previous arts as having the interface bonding achieved mainly by
mechanical anchors.
[0101] Referring to FIG. 2, in order to further illustrate the
features of the present invention, an exemplary experimental
process flow is schematically illustrated therein and comprises
four major steps: (1) surface pre-treatment 200, (2) surface
stabilization and conditioning and optional functionalization 210,
(3) optional surface reduction (if necessary) 220, (4) vacuum
lamination 240, and, (5) heat treatment (if necessary) 260. The
specific sub-steps and experimental data are shown for illustrative
purposes only and are not intended to limit the scope of the
invention in any way. FIG. 2 also shows where in the process the
peel strength tests are carried out, however this is shown only to
illustrate the testing procedures. The broad method steps of the
present invention do not include the peeling test steps.
[0102] In an exemplary method shown in FIG. 2, surface
pre-treatment 200 is carried out by alkaline clean, rinsing, soft
etching and acid clean, and rinsing and drying the substrate. Next
the surface is stabilized at step 210. In this embodiment the
surface is stabilized by surface oxidation. The step of surface
oxidation comprises exposing the metal surface to an oxidant
solution comprising one or more oxidants and one or more surface
active moieties. This one step produces a stabilization layer of
desired thickness and morphology. Optional functionalization may
then occur, followed by rinsing and drying the substrate.
[0103] If necessary, optional reduction may occur at step 220. In
one example, the sample is treated in a reducing bath of 40 g/L
dimethylamine borane (DMAB) with pH adjusted to 12.6 at 35.degree.
C. for 2 minutes. This allows densification of the oxide layer and
removes extra oxide. At this time, a molecular reagent can be used
to functionalize the stabilization layer. The sample was then
rinsed and dried by hot air.
[0104] After the stabilization step 210 and optional reduction step
220, vacuum lamination is carried out by assembling the laminate
film over the stabilized substrate, applying vacuum lamination, and
optional vacuum press is applied at step 240.
[0105] Next optional heat treatment 260 is performed to cure or
anneal the laminated assembly. Peel strength testing may then be
performed if desired.
[0106] Referring to FIGS. 3A and 3B, two separate embodiments of
the present invention are schematically illustrated. For example in
FIG. 3A a metal 300 is treated with a standard surface oxidation to
form an oxide layer 310. Oxide layer growth occurs by conventional
means such as by chemical or thermal oxidation. After formation of
the oxide layer 310 the oxide layer 310 is reduced to form
stabilization layer 320 of the present invention. A molecular
reagent is optionally added to the reductant treatment solution to
form the stabilization layer 320. FIG. 3B shows an alternative
embodiment where a metal 350 is treated with a molecular reagent
optionally added to an oxidant during an oxidation step to limit
the growth of the oxide layer and thereby form a stabilization
layer 360. In both cases, adhesion of subsequent layers is enhanced
by the presence of the stabilization layer 320, 360 without causing
significant roughening of the metal surface.
[0107] In another aspect, the present invention can be utilized in
a significant number of applications. In one such example,
embodiments of the present invention can be used to form protective
coatings. In some embodiments, methods of the present invention
wherein a molecular component that modifies the surface, is added
to one of the treatments solutions (e.g., oxidation bath or
reduction bath), are provided which greatly simplify the
preparation of the metal surface. Since the MI chemistry works in
the presence of other reagents (e.g., oxidants or reductants), the
process is shorter and provides more uniform coverage and
stability. It can dramatically reduce the cost of the surface
preparation process and provide additional features (such as
greater smoothness and/or enhanced reliability of adhesion of
subsequent layers) for the modified metal surface. The modified
surfaces can be used as is, or can be modified with other,
established chemistries to provide additional functionality.
Embodiments of the present invention are also useful with other
materials that form stable oxides, including silica, alumina, or
zirconia. A short list of applications according to some
embodiments of the present invention include, but are not limited
to, the following:
[0108] Alkali- and scratch-resistant hard coating-bonded
substrates, coating solutions for them, and manufacture of polymer
coupler-coated metal oxide particles for them;
[0109] Organic/inorganic hybrid polyimide compositions resistant to
atomic oxygen;
[0110] Coatings for automobile power cables, and process for making
the compositions;
[0111] Sealing compositions containing surface-treated inorganic
materials for liquid crystal display panels;
[0112] Adhesives for metal plates. The adhesive should have high
shear strength and high peeling strength. The metal composite plate
using the adhesive has high damping coefficient and can be used for
of damping/sound-muffling sheets;
[0113] Water-repellent coatings on glass plates for vehicle or
architectural window. A water-repellent glass plate for vehicle or
paned windows is fabricated by covering the glass surface with a
repellent coating covalently bonded to the surface;
[0114] Preparation of compatible gelatin-epoxy alumina composite
membrane for protein separation. The coating should have has good
hydrophilicity and biocompatibility, and can be widely used in many
kinds of chemical separations;
[0115] Manufacture of resin-coated substrates, prepregs, and
resin-coated metal foils;
[0116] Aggregation-free, surface-treated inorganic powders. The
inorganic powders are surface-treated with organic compounds which
have polar parts and nonpolar parts and are liquid at ambient temp.
The powders may also be surface-treated with coupling agents. The
surface-treated inorganic powders are dispersed in resin
compositions for use as EMC (epoxy molding compd.), liquid
sealants, substrate materials, adhesives for electronic parts,
resin compounds, or coatings;
[0117] Multifunctional Polymers for Persistent Surface
Derivatization and Their Antimicrobial Properties. These require
covalent surface anchoring and polymer crosslinking that is capable
of forming long-lasting coatings on reactive and nonreactive
surfaces. Polymers containing reactive groups form strong links to
oxide surfaces, thereby anchoring the polymer chains at multiple
points;
[0118] Transparent gas-barrier films with good adhesion between
plastic substrates and inorganic layers for packaging
materials;
[0119] Aluminum electrode foil surface that must be resistant to
negative substances and react with molecular coupling agents that
can used as electrodes for batteries and/or capacitors;
[0120] Functional microparticles-modified melt-blown nonwoven
fabric. The production method requires surface-modified functional
microparticles combined with melting and extruding the resin slices
by conventional processes;
[0121] Nanostructured fumed metal oxides for thermal interface
pastes, which are effective as thermally insulating solid
components in thermal pastes.
[0122] A chrome-free composition useful for the surface treatment
of a steel sheet, which imparts excellent anti-corrosive property,
processability, workability, powder coating property and
lubrication property to a steel sheet coated with the same. The
composition for surface treatment solution having excellent powder
coating property, which comprises acrylic urethane resin, colloidal
composite oxide, molecular coupling agent, silica and isocyanate
crosslinking agent, and method for producing plated steel sheet
coated with the same;
[0123] Semiconductor device fabrication comprises a void-type
receiving layer on a substrate and a Si film formed on the
receiving layer by using a porous film containing silica, alumina,
and/or alumina hydrate coated with a metal;
[0124] Surface modification of nano/micro particle hybrid
composites for scratch and abrasion resistant polyacrylate coatings
using SAMs to promote dispersion;
[0125] Fluoropolymer-coated galvanized steel plates with good
lubricating properties and their manufacture;
[0126] Scratch resistant coating materials containing
surface-modified aluminum oxide nanoparticles. Coating materials
with improved scratch resistance contain an organic binder, such as
aq. acrylic, two component polyurethane or UV-curable binder,
additives and surface-modified aluminum oxide nanoparticles;
[0127] Improved electroless plating of copper with high adhesion to
nickel plating. The electroless plating method is carried out by
the following steps: (1) treating a substrate to be plated with a
SAM coupling agent, (2) immersing the treated substrate in a Ni
plating bath for electroless plating of Ni on the treated surface
of the substrate, and (3) immersing the Ni-plated substrate in a Cu
plating bath with pH.ltoreq.10 for electroless plating of Cu on the
Ni plating. The Ni plating has high adhesion to the substrate, and
the Cu plating has high adhesion to the Ni plating;
[0128] Improved stability of surface modifiers on alumina
nanoporous membranes. Stability of SAMs covalently bound to the
surface of nanoporous alumina membranes. may dramatically improve
the stability of immobilized molecules;
[0129] Improved resin bond strength to silica-coated Ti
substrate;
[0130] Application to nylon composite containing copper oxide
particles to obtain high friction coefficient materials. The
existing process method comprises (1) treating copper oxide
particles and aluminum oxide particles with surface coupling agent
in acetone, drying, and grinding; (2) treating carbon fiber in air
for oxidation; (3) mixing treated copper oxide particles, aluminum
oxide particles, carbon fiber, and nylon in a ball mill for 6-8 h;
and following the standard procedure; and
[0131] Improved coating for lamps comprising a network obtainable
by conversion of a SAM-modified surface by means of a sol-gel
process, is described where silica particles obtainable from an
acid-stabilized colloidal silica dispersion are substantially
incorporated in the network.
Experimental
[0132] A number of experiments were conducted as described below.
These examples are shown for illustration purposes only and are not
intended to limit the invention in any way.
EXAMPLES
Example 1
Treatment of a Smooth Copper Substrate
[0133] This example illustrates one exemplary approach for treating
a smooth copper substrate according to some embodiments of the
present invention. As discussed above, methods of the invention
enable the use of a treated smooth metal substrate, meaning a metal
substrate that has not been previously roughened. In one example,
the metal surface is copper, and in particular a smooth copper
surface, meaning a copper substrate that has not been previously
roughened. Such a copper substrate can be from a variety of
sources. For example, copper substrates suitable for use in methods
of the present invention include, but are not limited to,
electrolytic or electroplated copper, electroless copper, and
rolled copper, and not restricted by the method of preparing the
same In this Example 1, an electrolytic copper substrate was first
cleaned with 20-40 g/L sodium hydroxide solution at 40-60.degree.
C. for 2-5 minutes, and then rinsed with water. The copper
substrate was further cleaned in 1-3 wt % hydrogen peroxide
solution plus 2-5 wt % sulfuric acid at RT for 1-5 minute, and 5-20
wt % sulfuric acid solution at RT for 1 minute, and then followed
by water rinse. The substrate was then stabilized by oxidation in a
140-200 g/L chlorite solution with 10-50 g/L sodium hydroxide
containing less than 1% of a SAM at 50-80.degree. C. for 2-8
minutes followed by water rinse. The sample can then be treated in
a reducing bath of 10-40 g/L dimethylamine borane (DMAB) with pH
adjusted to 10.5-12.5 at RT-40.degree. C. for 2-5 minutes. The
sample was then rinsed and dried by hot air. The surface morphology
and the thickness of the stabilization layer can be adjusted by
varying the concentrations of the treatment solutions, the
temperature, and duration, and characterized by SEM, XRD, and Auger
depth profile.
[0134] FIG. 4A is an exemplary SEM micrograph at a magnification of
50,000 showing the morphology of a conventional electrolytic copper
surface (i.e. a smooth copper surface, or in other words a copper
surface that has not been roughened) with nodular grains and
directional grain growth reflecting the long range order of the
crystalline structure. In comparison, the morphology of an
electrolytic copper surface treated according to the methods of the
present invention forming the stabilization layer thereon is shown
in FIG. 4B. As is very apparent, the stabilization layer on the
treated copper surface shown in FIG. 4B exhibits a morphology of
finer grains, unidirectional grain growth, and greater uniformity.
By contrast, FIG. 4C shows a conventional black oxide surface which
exhibits a much thicker and fragile fibrous structure. FIG. 4D is
an exemplary SEM micrograph of a conventional micro-etched copper
surface which shows morphology of highly un-uniform micro-ravines
and ridges.
[0135] The tabular data of FIG. 5 compares the surface roughness
expressed in both Ra and Rz, and demonstrates that the treatment of
the present invention does not roughen the copper surface, unlike
conventional oxidation and reduction processes, which roughen the
surface considerably.
[0136] The stabilization layer of the treated smooth copper surface
prepared according to Example 1 was further characterized by Auger
Electron Spectroscopy (AES) to determine the surface composition
and thickness distribution of the layer. Referring to FIG. 6, the
AES depth profile for the treated smooth copper surface shows that
the stabilization layer contains mixed copper and copper oxide,
presumably cuprous oxide, and its thickness is about 100 nm. In
contrast, the conventional black oxide layer extends to a distance
above 1000 nm. The thickness of the stabilization layer is desired
to be within a range of about 100 to 200 nm for securing good
bonding strength.
Example 2
Demonstration of the Enhancement of Resin Bonding on a Smooth
Copper Substrate
[0137] This example illustrates one exemplary approach to enhance
the adhesion of epoxy on a smooth copper substrate. The
above-mentioned treated Cu test strips were laid out on a temporary
backing as illustrated in FIG. 7. A commercial build-up (BU) epoxy
(or dielectric) laminate film of 35 .mu.m thickness, which had been
stabilized at ambient condition for at least 3 hours, was laid on
top of the Cu strips as illustrated by the schematic steps shown in
FIGS. 8A to 8D. The assembly was then vacuum laminated at
100.degree. C., 30 s vacuum, and 30 s press at 3 Kg/cm.sup.2. The
lamination step was repeated twice to form a total of 3 plies of BU
films.
[0138] It is worthy to note that the copper surface changed from
reddish into a light brown or green after surface treatment, and
then became black after the lamination suggesting that a chemical
bonding reaction had taken place. The resin surface contains
chemically reactive groups, such as hydroxyls, amines, epoxies, and
others, which can react with the oxygen rich copper surface by
forming bonds.
[0139] To quantify the adhesion strength, a rigid backing substrate
(stiffener) was laminated on top of the BU film as illustrated by
FIG. 8B. The assembly was then heat treated or cured in a
convection oven at 180.degree. C. for 90 min.
[0140] Next the assembly was diced to remove the temporary backing
substrate and separate into individual test coupons for peel
strength testing and testing using the highly accelerated stress
test (HAST). The adhesion strength of the resulting laminate was
quantified by a force gauge of a peel tester on a peel strip of 10
mm width at a 90 degree peel angle and peel speed of 50 mm/min.
Specifically, peel strength was tested on the substrates as
initially formed, and then after preconditioning and reflow.
Preconditioning was carried out at 125.degree. C. for 25 hours,
followed by 30.degree. C. and 60% relative humidity (RH) for 192
hours. Reflow was carried out three times at 260.degree. C.
Thereafter HAST testing was conducted at 130.degree. C. and 85% RH
for 96 hours. FIGS. 9A and 9B illustrate the impact of the
treatment on the peel strength retention post HAST testing. The
smooth control without (i.e. without a stabilization layer
according the invention) dropped 88% in peel strength post HAST,
and the conventional roughened control showed a 40% loss. In
significant contrast the treated smooth copper substrate (i.e. with
the stabilization layer formed according to the invention) showed
not only higher initial peel strength but also a higher retention
of only 26% loss. The tabular data of FIG. 9B also demonstrate that
the enhancement in peel strength stability was achieved without a
significant change in the surface roughness. This result is
superior, and would not have been predicted, according to the
teaching of the prior art.
[0141] Of significant advantage embodiments of the present
invention provide a stable, controllable process window. Such a
stable process window provides a robust, repeatable process. FIG.
10 illustrates the reproducibility or robustness of peel strength
and HAST stability for five batches of samples of epoxy laminated
smooth copper surfaces treated according to embodiments the present
invention. FIGS. 11A and 11B show SEM cross-sectional views of
laminated treated smooth copper surface with stabilization layer
according to embodiments of the present invention before and after
HAST as compared to a standard roughened surface, further
demonstrating that methods of the present invention do not
significantly roughen the copper surface and that no delamination
occurs after reflow and HAST reliability tests.
[0142] FIGS. 12A and 12B are exemplary SEM micrographs of peeled
copper surfaces showing that the copper-resin interface breaks
right at the copper surface for a smooth copper control (FIG. 12A),
whereas the interface breaks within the resin for a treated smooth
copper with stabilization layer (FIG. 12B) formed according to
methods of the present invention. The surprising result
demonstrates that the bonding strength between the resin and the
treated copper surface of the present invention is stronger than
the bonding strength of the bulk resin materials themselves.
Example 3
Demonstration of Fine Line Patterning and Electrical Isolation
Reliability
[0143] Devices were formed to demonstrate that patterning of fine
lines is enabled by embodiments of the present invention.
Specifically, comb patterns of lines and spaces with equal
dimensions (50/50, 30/30, 20/20, 10/10, and 8/8 .mu.m) were treated
and laminated following the same procedures as described in Example
1 and Example 2. SEM cross-sectional views confirmed again that the
methods of the invention did not roughen the copper lines and there
was no delamination after reflow and HAST tests. The electrical
isolation resistance remained at above 10.sup.12.OMEGA. at 2 V
after reflow and HAST, which is five orders of magnitude higher
than that of PCB manufacturing specifications. Table 1 below
summarizes the results. Good results were obtained on all of these
structures, indicating that treatment of the present invention
significantly improves the ability to pattern copper lines at fine
line spacing, a significant advance in the art.
TABLE-US-00001 TABLE 1 Fine line patterning and electrical
isolation reliability Line/Space No Isolation Resistance Dimension
Delamination post HAST .times. 10.sup.12 .OMEGA. (um) post HAST at
2 V 50/50 micron Pass 1.27 30/30 micron Pass 1.30 20/20 micron Pass
1.43 10/10 micron Pass 1.29 8/8 micron Pass 1.10
Example 4
Demonstration of Laser Drilling and Via Clean/Plating Compatibility
of Epoxy Laminated Cu Surface
[0144] Devices with laser vias were formed and then further
processed to demonstrate process compatibility. Specifically,
smooth copper substrates were treated and laminated following the
same procedures as described in Example 1 and Example 2. Via arrays
of 30, 40, 50, 75, 100, 150, and 200 .mu.m diameter were prepared
through CO.sub.2 and UV laser drilling. The via structures were
then subjected to a soft etch and acid clean or desmear process
followed by electroless copper plating and then electroplating.
FIG. 13 shows SEM cross-sections of laser vias formed on laminated
smooth treated copper surfaces formed according to embodiments of
the present invention demonstrating no undercutting and
delamination post desmear and plating processes.
Example 5
Demonstration of the Enhancement of Solder Resist Bonding on a
Smooth Copper Substrate
[0145] This example illustrates one exemplary approach to enhance
the adhesion of solder resist on smooth copper substrates. The
smooth copper test strips were treated following the same
procedures as described in Example 1 and laid out on a temporary
backing as illustrated in FIG. 7. A commercial solder resist (SR)
laminate film of 30 .mu.m thickness, which had been stabilized at
ambient condition for at least 3 hours, was laid on top of the
copper strips as illustrated by FIG. 8A. The assembly was then
vacuum laminated at 75.degree. C., 30 s vacuum, and 60 s press at 1
Kg/cm.sup.2. The assembly was then subjected to 400 mJ/cm.sup.2 UV
exposure followed by curing in a convection oven at 150.degree. C.
for 60 min and post UV curing at 1000 mJ/cm.sup.2.
[0146] To quantify the adhesion strength, a rigid backing substrate
(stiffener) was laminated on top of the SR film as illustrated by
step 2 of FIG. 8B. The assembly was then diced to remove the
temporary backing substrate and then separated into individual test
coupons for peel strength testing and highly accelerated stress
test (HAST) testing. Specifically, peel strength was tested on the
substrates as initially formed, and then after preconditioning,
reflow, and HAST. FIGS. 14A and 14B illustrate the impact of the
treatment methods of the present invention on the peel strength
retention post HAST testing. The smooth control without treatment
dropped 87% in peel strength post HAST, and the conventional
roughened control showed 69% loss. In significant contrast the
treated smooth copper surface formed according to embodiments of
the present invention showed not only higher initial peel strength
but also a higher retention of only 22% loss. The tabular data of
FIG. 14B also demonstrates that the enhancement in peel strength
stability was achieved without significant change in surface
roughness.
Example 6
Demonstration of UV Patterning and Via Clean/Plating Compatibility
of SR Laminated Cu Surface
[0147] Devices of via array and copper lines were formed and then
further processed to demonstrate the process compatibility.
Specifically, smooth copper substrates were treated and laminated
following the same procedures as described in Example 5. Via arrays
of bottom diameter ranging from 80 to 440 .mu.m and copper lines of
62 to 500 .mu.m width were formed through UV exposure and
development. FIG. 15A shows the copper line pattern and via arrays,
and FIG. 15B shows the ball grid array (BGA) pattern. The patterned
structures were then subjected to a soft etch and an acid clean or
desmear process followed by electroless Ni plating and then Au
emersion deposition. FIG. 16 shows SEM cross-sections of SR vias
formed on laminated smooth copper demonstrating no delamination
post desmear and plating processes. Good results were obtained on
all of these structures, suggesting that treatment methods of the
present invention significantly improved the ability to pattern SR
at fine line spacing, a significant advance in the art.
[0148] In summary, a number of inventive embodiments are provided
herein. In some embodiments, a method of treating a metal surface
to promote adhesion between the metal surface and an organic
material is provided characterized in that: a metal oxide layer is
formed on the metal surface, and formation of the metal oxide layer
is controlled by a self-limiting reaction between the metal oxide
and a surface modifier compound. Formation of the metal oxide layer
may be controlled such that the metal oxide layer has a thickness
of about 200 nanometers and less, or optionally a thickness in the
range of about 100 nanometers to 200 nanometers. Formation of the
metal oxide layer may be controlled such that the metal oxide layer
has morphology comprised of a substantially amorphous structure. In
some embodiments, the metal oxide layer has grains of a size in the
range of 250 nanometers and less, or optionally in the range of 200
nanometers and less. The grains may be substantially randomly
oriented after conditioning. The metal oxide layer may be comprised
of copper oxide.
[0149] In some embodiments the metal oxide layer is formed by
exposing the metal surface to an oxidant. The oxidant may be
selected from any one or more of: sodium chlorite, hydrogen
peroxide, permaganate, perchlorate, persulphate, ozone, or mixtures
thereof.
[0150] In some embodiments the surface modifier compound is
selected from compounds that react with metal oxide surfaces to
control the reaction rate as the metal oxide is forming. The
surface modifier compound may be selected to such that it
eventually slows and terminates the oxidation reaction. The method
may be carried out at a temperature in the range of room
temperature to about 80.degree. C. In some embodiments the self
limiting reaction becomes stable after about 2 to 15 minutes.
[0151] In another aspect, a method of treating a metal surface to
promote adhesion between the metal surface and an organic material
is provided comprising the steps of: oxidizing the metal surface to
form a metal oxide layer on the metal surface; and terminating
growth of the metal oxide layer by a self limiting reaction between
the metal oxide layer and a surface modifier compound. In some
embodiments, the steps of oxidizing and terminating oxidation
further comprises exposing the metal surface to a solution
comprising an oxidant and surface modifier compound. Optionally,
methods further include contacting the metal surface with one or
more organic molecules comprising a thermally stable base bearing
one or more binding groups configured to bind the metal surface and
one or more attachment groups configured to attach to the organic
material.
[0152] In some embodiments, the one or more organic molecules is a
surface active moiety or molecule. In some embodiments the one or
more surface organic molecules is selected from the group of: a
porphyrin, a porphyrinic macrocycle, an expanded porphyrin, a
contracted porphyrin, a linear porphyrin polymer, a porphyrinic
sandwich coordination complex, or a porphyrin array. The surface
active moiety may be selected from the group consisting of a
macrocyclic proligand, a macrocyclic complex, a sandwich
coordination complex and polymers thereof.
[0153] The attachment group may be comprised of an aryl functional
group and/or an alkyl attachment group. In some embodiments the
aryl functional group is comprised of a functional group selected
from any one or more of: acetate, alkylamino, allyl, amine, amino,
bromo, bromomethyl, carbonyl, carboxylate, carboxylic acid,
dihydroxyphosphoryl, epoxide, ester, ether, ethynyl, formyl,
hydroxy, hydroxymethyl, iodo, mercapto, mercaptomethyl,
Se-acetylseleno, Se-acetylselenomethyl, S-acetylthio,
S-acetylthiomethyl, selenyl,
4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl,
2-(trimethylsilyl)ethynyl, vinyl, and combinations thereof. In some
embodiments the alkyl attachment group comprises a functional group
selected from any one or more of: acetate, alkylamino, allyl,
amine, amino, bromo, bromomethyl, carbonyl, carboxylate, carboxylic
acid, dihydroxyphosphoryl, epoxide, ester, ether, ethynyl, formyl,
hydroxy, hydroxymethyl, iodo, mercapto, mercaptomethyl,
Se-acetylseleno, Se-acetylselenomethyl, S-acetylthio,
S-acetylthiomethyl, selenyl,
4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl,
2-(trimethylsilyl)ethynyl, vinyl, and combinations thereof. In one
example, the at least one attachment group is comprised of an
alcohol or a phosphonate. In another embodiment, the at least one
attachment group is comprised of any one of more of: amines,
alcohols, ethers, other nucleophile, phenyl ethynes, phenyl allylic
groups, phosphonates and combinations thereof.
[0154] In some embodiments methods of forming a coating on a metal
surface are provided characterized in that: a metal oxide layer is
formed on the metal surface, and formation of the metal oxide layer
is controlled by a self-limiting reaction between the metal oxide
and a surface modifier compound.
[0155] In other embodiments, methods of forming a coating on a
metal surface are provided, comprising the steps of: oxidizing the
metal surface to form a metal oxide layer on the metal surface; and
terminating growth of the metal oxide layer by a self limiting
reaction between the metal oxide layer and a surface modifier
compound.
[0156] Further, methods of forming a coating on a metal surface are
provided, comprising the steps of: stabilizing the metal surface;
and conditioning the stabilized metal surface.
[0157] In another aspect of the present invention, a printed
circuit board is provided, comprising: at least one metal layer; at
least one epoxy layer; and a stabilization layer formed between the
metal layer and epoxy layer. The stabilization layer may be
comprised of a metal oxide having a thickness of about 200
nanometers and less. In some embodiments the stabilization layer is
comprised of a metal oxide exhibiting a substantially amorphous
structure. In some embodiments the stabilization layer is comprised
of a metal oxide having a thickness of about 200 nanometers and
less and exhibiting a substantially amorphous structure. The
stabilization layer may further be comprised of a metal oxide layer
having grains, wherein the grains have a grain size in the range of
250 nanometers and less, or optionally have a grain size in the
range of 200 nanometers and less. In some embodiments the metal
oxide is comprised of copper oxide. The metal layer may have a
roughness of up to about 0.14 .mu.m Ra, and the metal oxide may
have a roughness of up to about 0.14 .mu.m Ra.
[0158] In some embodiments the metal layer further comprises
patterned metal lines formed thereon, said patterned metals lines
having a width of equal to and less than about 25 microns,
optionally the patterned metal lines have a width of equal to and
less than about 15 microns, and optionally the patterned metal
lines have a width of equal to and less than about 10 microns, and
further optionally the patterned metal lines have a width of equal
to and less than about 5 microns.
[0159] In another aspect, a method of fabricating a printed circuit
board is provided, comprising the steps of: pre-cleaning a copper
surface with an alkaline and/or peroxide solution; stabilizing the
copper surface by forming a copper oxide layer thereon; terminating
formation of the copper oxide by a self limiting reaction between
the copper oxide and one or more surface modifier compounds; and
bonding the treated copper surface with a resin.
[0160] In some embodiments a method of controlling the growth of an
oxide layer on the surface of a metal is provided comprising:
terminating growth of the oxide layer by a self limiting reaction
between the oxide layer and one or more surface modifier
compounds.
[0161] Embodiments of the present invention further provide an
oxidant composition, comprising one or more oxidants; and one or
more surface modifier compounds. In some embodiments the surface
modifier compound is selected from one or more surface active
molecules (SAMs) as described above.
[0162] Further, methods of treating a metal surface to promote
adhesion or binding between the metal surface and an organic
material are provided characterized in that: the metal surface is
stabilized by forming a metal oxide layer thereon, and then the
metal oxide layer is conditioned with a reducing agent to achieve
selective oxide thickness and morphology. In some embodiments the
reducing agent is selected from any one or more of: formaldehyde,
sodium thiosulfate, sodium borohydride a borane reducing agent
comprised of the general formula: BH.sub.3NHRR', wherein R and R'
are each selected from the group consisting of: H, CH3 and CH2CH3,
such as a cyclic borane, morpholine borane, pyridium borane,
piperidine borane, or dimethylamine borane (DMAB).
[0163] In some embodiments stabilizing the metal surface is carried
out at a temperature in the range of room temperature to about
80.degree. C., or optionally at a temperature in the range of room
temperature to about 50.degree. C. In some embodiments the method
is carried out for a time in the range of about 2 to 20
minutes.
[0164] In another aspect, methods of treating a metal surface to
promote adhesion between the metal surface and an organic material
are provided, comprising the steps of: stabilizing the metal
surface; and conditioning the stabilized metal surface. In one
example, stabilizing the metal surface comprises forming a metal
oxide layer on the metal surface. In one example, the step of
conditioning the metal surface comprises reducing the metal oxide
layer with a reducing agent. In some embodiments, the metal oxide
layer after conditioning has a thickness of about 200 nanometers
and less. In some embodiments, the metal oxide layer after
conditioning is comprised of a substantially amorphous structure.
The metal oxide layer may have grains, and after conditioning the
grains have a size in the range of 250 nanometers and less, or
optionally in the range of 200 nanometers and less. In some
embodiments the grains become substantially randomly oriented after
conditioning. In one example, the metal oxide layer is comprised of
copper oxide.
[0165] In one aspect, after conditioning the metal surface is
contacted with one or more organic molecules comprising a thermally
stable base bearing the one or more binding groups configured to
bind the metal surface and the one or more attachment groups
configured to attach to the organic material. In some embodiments
the organic material is comprised of any one of more of: electronic
substrates. PCB substrates, semiconductor substrates, photovoltaic
substrates, polymers, ceramics, carbon, epoxy, glass reinforced
epoxy, phenol, polyimide resines, glass reinforced polyimide,
cyanate, esters, Teflon, plastics and mixtures thereof.
[0166] In yet a further aspect, methods of fabricating a printed
circuit board are provided, comprising the steps of: pre-cleaning a
copper surface with an alkaline and/or peroxide solution;
stabilizing the copper surface by forming a copper oxide layer
thereon; conditioning the copper oxide layer with a reducing agent;
and bonding the treated copper surface with a resin. Additionally,
a further step of coupling one or more molecules to the copper
oxide layer is provided, the one or more organic molecules
comprising a thermally stable base bearing one or more binding
groups configured to bind the copper oxide surface and one or more
attachment groups configured to attach to the resin.
[0167] The foregoing methods, devices and description are intended
to be illustrative. In view of the teachings provided herein, other
approaches will be evident to those of skill in the relevant art,
and such approaches are intended to fall within the scope of the
present invention.
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