U.S. patent application number 10/653582 was filed with the patent office on 2005-03-03 for chromium-free antitarnish adhesion promoting treatment composition.
This patent application is currently assigned to Olin Corporation. Invention is credited to Chen, Szuchain F., Howell, Leonard R..
Application Number | 20050048298 10/653582 |
Document ID | / |
Family ID | 34104766 |
Filed Date | 2005-03-03 |
United States Patent
Application |
20050048298 |
Kind Code |
A1 |
Howell, Leonard R. ; et
al. |
March 3, 2005 |
CHROMIUM-FREE ANTITARNISH ADHESION PROMOTING TREATMENT
COMPOSITION
Abstract
The present invention is directed to an aqueous, antitarnish and
adhesion promoting treatment composition, comprising: zinc ions;
metal ions selected from the group consisting of tungsten ions,
molybdenum ions, cobalt ions, nickel ions, zirconium ions, titanium
ions, manganese ions, vanadium ions, iron ions, tin ions, indium
ions, silver ions, and combinations thereof; and optionally, an
electrolyte that does not contain potassium or sodium ions; wherein
the treatment composition is substantially free of chromium, and
wherein the treatment composition forms a coating on a substrate or
material that enhances adhesion of a polymer to the material. The
present invention is also directed to materials coated with the
above treatment composition, and methods of coating materials using
the above composition.
Inventors: |
Howell, Leonard R.; (Vernon,
CT) ; Chen, Szuchain F.; (Hamden, CT) |
Correspondence
Address: |
WIGGIN AND DANA LLP
ATTENTION: PATENT DOCKETING
ONE CENTURY TOWER, P.O. BOX 1832
NEW HAVEN
CT
06508-1832
US
|
Assignee: |
Olin Corporation
|
Family ID: |
34104766 |
Appl. No.: |
10/653582 |
Filed: |
September 2, 2003 |
Current U.S.
Class: |
428/469 ;
428/457; 428/472 |
Current CPC
Class: |
C25D 3/565 20130101;
H05K 2203/135 20130101; C23C 22/40 20130101; Y10S 428/901 20130101;
Y10T 428/1291 20150115; Y10T 428/12472 20150115; H05K 3/282
20130101; Y10T 428/31678 20150401; Y10T 428/12993 20150115; Y10S
428/935 20130101; Y10T 428/12438 20150115; H05K 3/385 20130101;
Y10T 428/12792 20150115 |
Class at
Publication: |
428/469 ;
428/472; 428/457 |
International
Class: |
B32B 015/04 |
Claims
1.-17. (Cancelled).
18. A material coated with an antitarnish and adhesion treatment
coating, said antitarnish and adhesion treatment coating comprising
zinc or zinc oxide atoms; and metal or metal oxide atoms selected
from the group consisting of tungsten, molybdenum, cobalt, nickel,
zirconium, titanium, manganese, vanadium, iron, tin, indium,
silver, and combinations thereof; wherein said coating is
substantially free of chromium, and wherein said coating provides a
tarnish resistance at least for 30 min at 250.degree. C., and
wherein said coating contains nodular structures that enhance
adhesion of a polymer to said material.
19. The coated material of claim 18, wherein said material
comprises a material selected from the group consisting of copper,
copper alloy, nickel, iron, aluminum, steel, stainless steel, zinc,
tin, silver, palladium, gold, titanium, carbon, metallized
non-conductors, and combinations thereof.
20. The coated material of claim 18, wherein the thickness of said
coating on said substrate ranges from about 15 to about 500
Angstroms.
21. The coated material of claim 18, wherein said coating contains
from about 25 to about 1000 of said nodular structures per 16
square microns.
22. The coated material of claim 18, wherein said nodular
structures each have an average length in the range of from about
0.01 micron to about 1 micron, and an aspect ratio (length to
diameter) of from about 1:1 to about 8:1.
23. The coated material of claim 18, comprising a coated
substrate.
24. The substrate of claim 23, comprising an electronic device.
25. The substrate of claim 23, comprising a device/leadframe
assembly.
26. The coated material of claim 18, wherein said enhanced adhesion
comprises greater than 1000 psi following exposure of said coated
substrate to 85% RH/80-85.degree. C. for 168 hr, followed by a
thermal shock in approximately 260.degree. C. solder for 120
sec.
27.-43. (cancel).
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention is directed to tarnish-resistant and
adhesion promoting treatment compositions, and more particularly to
tarnish-resistant and adhesion promoting treatment compositions
that are substantially free of chromium.
[0003] 2. Brief Description of the Art
[0004] Tarnish resistance of metal and tenacious adhesion between
metals and polymer has been long sought for various applications
such as printed circuits, electronic packaging, automotive body
trim (aluminum to PVC or ABS plastics, for example), steel belted
tires, and paint or other polymeric coatings. For example, the
tarnish resistance of Cu foil for printed circuit application is
required for shelf life and to withstand the heat exposure during
lamination and soldering in printed circuit processing. The
antitarnish coatings also prevent the oxidation of Cu and reaction
with the polymeric substrate upon humidity and temperature
exposures during the service life of the parts. This function is
critical to maintain a good bond between Cu and polymer. In terms
of electronic packaging applications, good adhesion is required in
an electrical connector between a metallic jack and the molded
plastic insulating sheath that surrounds it. As a second example,
the inner leads of a metallic leadframe may be encapsulated in a
polymer molding resin in the assembly of an electronic package to
house an integrated circuit.
[0005] The adhesion between a polymer resin and a metallic
substrate is improved by coating the metallic substrate with a
second metal that forms a more tenacious bond to the polymer resin.
Suitable coatings include refractory oxide-forming metals such as
nickel and nickel alloys, or intermetallic-forming coatings such as
tin on a copper substrate. These coatings, as well as others, are
disclosed in U.S. Pat. No. 4,888,449 to Crane et al., which is
incorporated by reference in its entirety herein.
[0006] Currently, zinc/chromium (ZnCr)-containing coatings are
widely used on copper foils and lead frames in electronic
applications to improve the tarnish resistance and bond strength of
metal to polymeric substrates. These coatings are typically
electrodeposited in an alkaline solution containing NaOH, Zn and
Cr(VI) ions to form a mixture of Zn/Cr oxides, which provide
tarnish resistance.
[0007] U.S. Pat. No. 4,387,006 discloses a method of treating the
surface of a copper foil used in printed wire boards. The copper
foil is electrolytically treated in an aqueous solution of zinc
chromate containing zinc ions and chromium (VI) ions and immersed
in an aqueous solution containing aminosilane, sodium silicate,
and/or potassium silicate.
[0008] U.S. Pat. Nos. 5,230,932; 5,098,796; and 5,022,968 disclose
a technique and compositions for improving the tarnish and
oxidation resistance of copper and copper-based alloy materials.
The material is electrolytically coated by immersion in an aqueous
electrolyte containing NaOH, zinc ions and chromium (VI) ions. The
coating provides tarnish resistance at temperatures in excess of
190.degree. C.
[0009] U.S. Pat. No. 5,250,363 to Chen discloses a technique for
improving the tarnish and oxidation resistance of a metallic
substrate. The substrate is immersed in an aqueous solution
containing NaOH, zinc ions, and chromium (VI) ions, and a
chromium-zinc coating is electrolytically applied to the substrate.
The coating provides tarnish resistance at temperatures in excess
of 230.degree. C., and is easily removable by immersion in sulfuric
acid.
[0010] It is also claimed that under certain conditions, several of
these coatings could reduce moisture penetration between lead frame
and molding compound. This effect could greatly reduce the "pop
corn effect," which is believed to be caused by formation of water
vapor from accumulated moisture trapped under the die attach paddle
when the device is subjected to a soldering temperature (e.g.,
temperatures of approximately 230.degree. C.). This generation of
water vapor is believed to be the cause of device failure due to
cracks and delamination. Moreover, as industry moves away from
solder containing lead and other toxic elements due largely to
environmental concerns and tightening regulations, alternative
solders are likely to have even higher soldering temperatures, and
the attributes of metal/polymer adhesion will likely become more
important.
[0011] Many compositions are known that provide for adhesion
between a metal and a polymeric substance. U.S. Pat. No. 5,573,845
to Parthasarathi et al. discloses a composite material having a
metallic core with a desired surface finish. An acicular (nodular)
superficial coating layer having an apparent thickness of less than
275 angstroms is adjacent to at least a portion of the metallic
core. The superficial coating layer is removable from the metallic
core without appreciable change to the metallic core surface
finish.
[0012] U.S. Pat. No. 5,449,951 to Parthasarathi et al. discloses a
lead frame with enhanced adhesion to a polymer resin. The lead
frame is coated with a thin layer containing chromium, zinc, or a
mixture of chromium and zinc. The coated leadframe exhibits
improved adhesion to a polymeric resin.
[0013] In International Publication Number WO 00/74131 A 1 to Lee
et al. a method of assembling a semiconductor device package is
disclosed wherein a device/leadframe assembly is formed and then an
adhesion enhancing coating is deposited on the exposed surfaces of
the device/leadframe assembly, followed by encapsulation. The
coating is a metallic coating which could be an inorganic Zn--Cr
coating. This publication is specifically incorporated by reference
herein in its entirety.
[0014] U.S. Pat. No. 5,252,855 to Ogawa et al discloses improving
the adhesion between a copper base metallic substrate and a polymer
resin by anodically oxidizing the substrate to form an aggregate of
acicular crystals. Anodization of aluminum alloy substrates
enhances the strength of a polymer bond as disclosed in U.S. Pat.
No. 4,939,316 to Mahulikar et al. Other satisfactory coatings
include oxidation resistant materials having a thickness of
300-5,000 angstroms as disclosed in U.S. Pat. No. 5,192,995 to
Yamazaki et al.
[0015] As disclosed in the above art, sodium (Na) and/or potassium
(K) ions are frequently used in immersion baths. However, sodium
and potassium ions suffer a disadvantage in that these ions could
potentially diffuse into the silicon die and cause failures in the
produced devices. Such failures have been well documented (See, for
example "Metallization Contamination," Microelectronic Defects
Database, CALCE Electronic Products and Systems Center, University
of Maryland, Apr. 12, 2000, identifying chloride and sodium
contamination from molding compounds, die coatings, and die attach
coatings; and Barnes and Robinson, "The Impact of Ionic Impurities
in Die Attach Adhesives on Device Performance", Proceedings of 34th
Electronics Components Conf., May, 1984, p. 68, identifying die
attach adhesives as a particular source of ionic
contamination).
[0016] In addition, the presence of Cr(VI) ions in a plating
solution invokes environmental concerns in handling and disposal.
Although Cr(VI)-containing plating baths have been used throughout
the world for decades, the use of Cr (VI) is coming under
increasing scrutiny due to growing concerns with health and
environmental effects. Thus, it would be desirable to either
replace a Cr(VI) plating bath with a less toxic Cr(III) bath, or
eliminate the Cr entirely.
[0017] Thus there is a need in the art to provide aqueous adhesion
promoting and tarnish resistance treatment compositions that are
substantially free of chromium (VI) and that utilize optional
electrolytes that do not contain potassium or sodium ions. The
present invention is believed to be an answer to that need.
SUMMARY OF THE INVENTION
[0018] In one aspect, the present invention is directed to an
aqueous, antitarnish and adhesion promoting treatment composition,
comprising: zinc ions; metal ions selected from the group
consisting of tungsten ions, molybdenum ions, cobalt ions, nickel
ions, zirconium ions, titanium ions, manganese ions, vanadium ions,
iron ions, tin ions, indium ions, silver ions, and combinations
thereof; and optionally, an electrolyte that does not contain
potassium or sodium ions; wherein the treatment composition is
substantially free of chromium, and wherein the treatment
composition is capable of forming a coating on a material, wherein
the coating enhances adhesion of a polymer to the material.
[0019] In another aspect, the present invention is directed to a
material coated with an antitarnish and adhesion treatment coating,
comprising: zinc or zinc oxide atoms; and metal or metal oxide
atoms selected from the group consisting of tungsten, molybdenum,
cobalt, nickel, zirconium, titanium, manganese, vanadium, iron,
tin, indium, silver, and combinations thereof; wherein the coating
is substantially free of chromium, and wherein the coating provides
a tarnish resistance at least for 30 min at 250.degree. C., and
wherein the coating contains nodular structures that enhance
adhesion of a polymer to the material.
[0020] In yet another aspect, the present invention is directed to
a method of forming a material coated with an antitarnish and
adhesion promoting coating, comprising the steps of: contacting the
material with an aqueous, antitarnish and adhesion promoting
treatment composition, comprising: zinc ions; metal ions selected
from the group consisting of tungsten ions, molybdenum ions, cobalt
ions, nickel ions, zirconium ions, titanium ions, manganese ions,
vanadium ions, iron ions, tin ions, indium ions, silver ions, and
combinations thereof; and optionally, an electrolyte that does not
contain potassium or sodium ions; wherein the treatment composition
is substantially free of chromium; and passing an electric current
through the treatment composition under conditions which deposit
the antitarnish and adhesion promoting coating on the material to
form the material coated with the antitarnish and adhesion
promoting coating, wherein the coating enhances adhesion of a
polymer to the material.
[0021] These and other aspects will be described in more detail in
the following detailed description of the invention.
BRIEF DESCRIPTION OF THE FIGURES
[0022] The invention will be more fully understood from the
following detailed description taken in conjunction with the
accompanying drawings in which:
[0023] FIGS. 1(a), 1(b), and 1(c) show scanning electron
micrographs (SEM) of surfaces treated in accordance with the
compositions and methods of the present invention following 2, 5,
and 10 second plating times, respectively; and
[0024] FIG. 2 shows bar graphs depicting various surface treatments
and their effect on bond strength between mold compound and the
treated surfaces.
DETAILED DESCRIPTION OF THE INVENTION
[0025] The present inventors have surprisingly found that it is
possible to produce an aqueous, antitarnish and adhesion promoting
treatment composition that permits formation of a tenacious bond
between metals and polymers and addresses environmental and health
effects regarding handling and disposal of such compositions. In
accordance with the invention, the present inventors have now
discovered an aqueous, antitarnish and adhesion promoting treatment
composition that possesses improved bond adhesion between polymeric
materials and metal, uses a Na/K-free plating solution to prevent
contamination of a silicon die with such elements, and is
substantially free of chromium (VI) to eliminate environmental and
health implications in handling such solutions.
[0026] As indicated above, the present invention is directed to an
aqueous, antitarnish and adhesion promoting treatment composition,
comprising: (1) zinc ions; (2) metal ions selected from the group
consisting of tungsten ions, molybdenum ions, cobalt ions, nickel
ions, zirconium ions titanium ions, manganese ions, vanadium ions,
iron ions, tin ions, indium ions, silver ions, and combinations
thereof; and (3) optionally, an electrolyte that does not contain
potassium or sodium ions; wherein said treatment composition is
substantially free of chromium, and wherein said treatment
composition forms a coating on a material or substrate that
enhances adhesion of a polymer to the material or substrate. Each
of these components is discussed in more detail below.
[0027] The zinc ion component of the treatment composition of the
present invention can be derived from any zinc salt that allows
formation of substantial amounts of zinc ions in aqueous solution.
Examples of useful zinc salts include, but are not limited to, zinc
sulfate, zinc oxide, zinc chloride, zinc fluoborate, zinc acetate,
and combinations thereof. It is also understood that hydrates of
the above zinc salts may also be employed in the composition of the
present invention, either singly, or in combination. In one
preferred embodiment, for example, the zinc salt is zinc sulfate
heptahydrate (ZnSO.sub.4.7H.sub.2O).
[0028] Preferably, the zinc ions are present in the composition of
the invention from about 0.1 to about 100 g/L, and more preferably
from about 0.5 to about 50 g/L, and most preferably from about 0.5
to about 20 g/L, all based on the total volume of the composition.
In one preferred embodiment, the zinc salt is zinc sulfate
heptahydrate (ZnSO.sub.4.7H.sub.2O), and ranges from about 2 to
about 80 g/L in the present composition.
[0029] The aqueous, antitarnish and adhesion promoting treatment
composition of the present invention further includes metal ions
which can form codeposits with zinc and result in an overall
nodular structure being deposited on the surface of a material or
substrate. Useful metal ions include tungsten ions, molybdenum
ions, cobalt ions, nickel ions, zirconium ions, titanium ions,
manganese ions, vanadium ions, iron ions, tin ions, indium ions,
and silver ions. The metal ions may be employed singly, or in any
combination, in the treatment composition of the present
invention.
[0030] The metal ions may be derived from a corresponding metal
salt, or a hydrate thereof, or a metal acid. Examples of metal
salts or metal salt hydrates useful in the composition of the
present invention include nickel sulfate or nickel sulfate hydrate,
ammonium molybdate, molybdenum oxide, potassium permanganate,
manganese sulfate, and combinations thereof. Examples of metal
acids include molybdic acid, tungstic acid, tungstosilicic acid,
and combinations thereof. In one preferred exemplary embodiment,
the metal ions are molybdenum ions, tungsten ions, or a combination
thereof. The invention is not limited to these examples and other
metal salts, or hydrates there of, or metal acids, could be
employed.
[0031] Preferably, the metal ions are present in the composition of
the invention from about 5 to about 20,000 ppm, and more preferably
from about 15 to about 2,000 ppm, and most preferably from about 25
to about 300 ppm, all based on the total parts of the
composition.
[0032] In many instances, the zinc salt provides sufficient
conductivity to the composition of the invention to permit
deposition of zinc and metal ions onto a material or substrate.
However, if the concentration of zinc salt is low, sufficient
electrical conductivity may not exist for proper electrolytic
deposition of the composition. In such cases, it is preferable to
add an additional electrolyte to the treatment composition so that
proper deposition can take place. Any water-soluble salt may be
used as an electrolyte; however, it is desirable that such
electrolyte does not contain sodium or potassium. As described in
WO 00/74131, the presence of sodium or potassium ions in the
aqueous plating composition results in diffusion of these ions into
silicon dies treated in accordance with the teachings of WO
00/74131 and subsequent failures in the electronic devices.
Therefore, electrolytes that are free of sodium or potassium are
preferred.
[0033] Nonlimiting examples of useful electrolytes include ammonium
sulfate, boric acid, citric acid, gluconic acid, rubidium
hydroxide, ammonium chloride, and combinations thereof. In general,
the electrolyte component comprises from about 1 g/L to about 500
g/L, and more preferably from about 5 g/L to about 200 g/L, and
most preferably from about 10 g/L to about 50 g/L.
[0034] As indicated above, the aqueous, antitarnish and adhesion
promoting treatment composition of the invention is substantially
free of chromium. The presence of chromium only results from
unavoidable contamination from the source chemicals or the
environment. As defined herein, "substantially free of chromium"
generally refers to levels of chromium lower than about 0.001% by
weight, based on the total weight of the composition. Chromium (VI)
has been shown to be toxic and suffers from environmental, health,
and safety disadvantages. Thus, it is believed that the composition
of the present invention, being substantially chromium free, does
not suffer these disadvantages.
[0035] The treatment composition of the present invention can be
made by mixing the proper amount of zinc and metal compounds, and
optional electrolyte in water to establish the desired
concentrations of each component. The pH of the solution is
established by addition of an acid (e.g., boric acid, sulfuric
acid, hydrochloric acid, citric acid, gluconic acid, and the like)
or a base that does not contain sodium or potassium (e.g., calcium
hydroxide, magnesium hydroxide, rubidium hydroxide, ammonium
hydroxide, and the like). The preferred pH range for the treatment
composition of the present invention is from about 0.5 to about
14.0; a more preferred pH range is from about 1.5 to about 13.5; a
most preferred pH range is from about 2.5 to about 13.0.
Additionally, if the composition of the invention has a pH in the
neutral range (e.g., pH 5-9), a complexing agent such as the salts
of citric acid or gluconic acid may be needed to maintain the metal
ions in a soluble state in the plating solution.
[0036] In general, the chromium-free antitarnish adhesion promoting
treatment composition of the invention may be implemented by known
processes for applying a coating. For example, prior to coating a
material or substrate, the material or substrate may be
electrocleaned in a commercial alkaline cleaner or NaOH to remove
any residual lubricant, oil, dirt, or surface oxides. An exemplary
concentration of the cleaner is typically 30 g/l with a bath
temperature of 130.degree. F. and a current density of 30 asf
(ampere per square foot) for 20 sec. However, any desired cleaning
parameters could be employed as are known in the art. After the
cleaning, the samples are dipped into a 5% sulfuric acid solution
to activate the surface.
[0037] During deposition, the following conditions are desirable.
The temperature of the plating bath during deposition preferably
may range from about 100 to about 150.degree. F., more preferably
from about 110 to about 140.degree. F., and most preferably from
about 120 to about 140.degree. F. The current density used during
deposition may preferably range from about 2 to about 200 asf, more
preferably from about 5 to about 100 asf, and most preferably from
about 5 to about 30 asf. The deposition times preferably may range
from about 1 to about 200 seconds, more preferably from about 2 to
about 50 seconds, and most preferably from about 2 to about 20
seconds.
[0038] When deposited onto a material or substrate, the composition
of the present invention forms a coating containing nodular
structures as shown in FIGS. 1(a), 1(b), and 1(c). The thickness of
the coating preferably ranges from about 15 to about 500 Angstroms,
depending on the conditions of the deposition (discussed in more
detail below). There are, on average, preferably from about 25 to
about 1000 of the nodular structures per 16 square microns and most
preferably the average density is from about 50 to about 500
nodular structures per square micron. The average length of each
nodular structure is preferably from about 0.01 micron to about 1
micron, and more preferably the average length is from about 0.05
to about 0.5 microns. The preferred aspect ratio (length to
diameter) is preferably from about 1:1 to about 8:1 and more
preferably from about 2:1 to about 6:1.
[0039] It is believed that most of the nodular structures do not
extend perpendicularly from the surface, but rather extend from the
surface at a variety of angles, forming an interwoven mesh. A
polymer flowing onto the voids between individual nodular
structures follows a tortuous path between the interstices, and on
solidification, the polymer appears to be mechanically locked in
place. The coating layer also enhances adhesion of the material or
substrate to a polymer. The presence of nodular structures on the
substrate surface enhances mechanical locking of a polymer adhesive
relative to a surface without the nodular structures. For example,
a bond strength in the range of preferably greater than 1000 psi,
and more preferably preferably 1100-2400 psi, depending on the type
of polymer adhesive, can be obtained after the exposure of the
samples to 85% RH/80-85.degree. C. for 168 hr, followed by a
thermal shock in approximately 260.degree. C. solder for 120 sec.
The coating layer is firmly bonded to the metallic substrate and
not prone to separation at either the interface between the
metallic substrate and the coating layer or within the coating
layer itself as is typical with copper oxide coatings. Without the
nodular antitarnish coating as described in this invention, the
bond strength between the metal and polymer is typically less than
one half of that described above.
[0040] The coating layer imparts oxidation resistance at
temperatures at which the composite material may be exposed during
storage, processing or use. These temperatures are typically up to
about 250.degree. C. While the coating layer has discontinuous
voids and interstices, none extend completely through the coating
layer or an oxidation site results. In addition to oxidation
resistance, the coating layer provides corrosion resistance to
dilute concentrations of chlorides, sulfides and other contaminants
found in an industrial environment or on the fingers of an
operator.
[0041] The antitarnish adhesion promotion coatings and methods of
application described in this invention can be applied to any
conductor and in any step of the process based on electrochemical
principles. For examples, copper and copper alloys as well as
nickel, iron, aluminum, steel, stainless steel, zinc, tin, silver,
palladium, gold, titanium, carbon, and any other material or
substrate that is conductive enough to pass the electrical current
can be electroplated. In addition, even a nonconductor that has
been metallized could also render itself to be electroplated. In
another example, it is convenient to apply this antitarnish coating
after the silver plating in a leadframe manufacturing process. If
needed, this coating can be removed at the locations where wire
bonding is required using a mask in the subsequent silver stripping
process, which is typically applied to remove the back plating or
spill-over plating of silver. Alternatively, this antitarnish
coating can be applied after the IC chip attachment and wire
bonding. This way, removal of this coating in the wire bond areas
is not needed.
[0042] The present invention is further described in detail by
means of the following Examples. All parts and percentages are by
weight, and all temperatures are degrees Celsius unless explicitly
stated otherwise.
EXAMPLES
Example 1
[0043] A C110 copper foil (>99.9% Cu and <0.05% O) was
electrocleaned in a commercial alkaline cleaner to remove residual
lubricant, contaminants, and oxides from the surface. The cleaned
copper foil was then dipped in a solution containing 10 g/L
ZnSO.sub.4.7H.sub.20, 10 g/L (NH.sub.4).sub.2SO.sub.4 and 25 ppm W
(tungsten, as tungstosilicic acid). A plating current of 10 amperes
per square foot (ASF) was applied to an area of 0.035 ft.sup.2 for
2, 5 and 10 second intervals. The sample was then rinsed and dried.
FIGS. 1(a), 1(b), and 1(c) show scanning electron micrographs
(SEMs) of the treated surfaces at the three time intervals. In each
case, the nodular morphology is visible.
[0044] The copper foil sample was subjected to a tape test using a
Scotch 600 tape. The tape was first pressed onto the plated surface
and then pulled away from the surface. The glue was visibly left
behind on the plated sample, indicating that a nodular structure
was deposited onto the copper foil.
[0045] The sample was further subjected to a 250.degree. C. bake
for 30 minutes. The sample showed no oxidation after the bake,
while an untreated portion was heavily oxidized. This result
indicated that the deposited coating provided a good tarnish
resistance. The baked sample was further subjected to the tape test
using the Scotch 600 tape described above. The glue was visibly
left behind on the plated sample, again indicating the presence of
nodular structures on the surface of the copper foil.
Example 2
[0046] A C110 copper foil sample having pure copper dendrites on
one side and bare on the other was dipped in 5 wt % H.sub.2SO.sub.4
for 30 seconds to remove any existing surface oxides. The sample
was placed in a fixture that exposes only one surface to an aqueous
plating composition containing 10 g/l ZnSO.sub.4.7H.sub.2O, 20 g/l
(NH.sub.4).sub.2SO.sub.4 and 25 ppm W, and a plating current of 10
ASF was applied to an area of 0.104 ft.sup.2 for 5 sec. The sample
was then rinsed and dried. The procedure was repeated on a second
sample exposing the opposite surface to the same solution and
plating current. The samples were further subjected to a 95.degree.
C./55% RH test for 60-min to simulate a long-term storage in a hot
and humid condition. The sample was subsequently baked for 30 min
at 190.degree. C. and showed no oxidation. The untreated portion
was heavily oxidized. This indicated that the coating provided a
good tarnish resistance.
Example 3
[0047] A C110 copper foil was electrocleaned in a commercial
alkaline cleaner to remove the residual lubricant, contaminants,
and oxides from the surface. A plating current of 5 ASF was applied
to an area of 0.035 ft.sup.2 for 5 sec in a solution containing 5
g/l ZnSO.sub.4.7H.sub.2O, 3 g/l NiSO.sub.4.6H.sub.2O, 50 ml
KMnO.sub.4 N/10 and 2.5 ml/l MITIQUE (inorganic acid composition
that contains 1-3% ammonium molybdate; Hubbard Hall, Waterbury,
Conn.). The sample was then rinsed and dried, and subjected to a
tape test using a Scotch 600 tape. The tape was first pressed onto
the plated surface and then pulled away from the surface. The glue
was visibly left behind on the plated sample. This result indicates
that a nodular structure was deposited.
[0048] The sample was further subjected to a 250.degree.
C..times.10-min bake test and the sample showed no oxidation after
the bake. The untreated portion was heavily oxidized. This result
indicated that the coating provided a good tarnish resistance.
Example 4
[0049] A C7025 copper foil (foil (96.2% Cu, 3.0% Ni, 0.65% Si, and
0.15% Mg) having 0.03 inch thickness was electrocleaned in a
commercial alkaline cleaner to remove the residual lubricant,
contaminants, and oxides from the surface. A plating current of 10
ASF was applied to an area of 0.035 ft.sup.2 for 10 sec in a
solution containing 10 g/l ZnSO.sub.4.7H.sub.2O and 1.5 ml/l
MITIQUE. The sample was then rinsed and dried. Tape testing using
Scotch 600 tape resulted in glue transfer to the treated surface,
and indicated a nodular or roughened surface was obtained.
Additional samples were plated, encapsulated using Sumicon 6300
molding compound and subjected to 168 hr 85% RH/85.degree. C.
moisture testing as described in Testing Standard IPC/JEDEC
J-STD-020A. After exposure the samples were solder floated for 120
sec at approximately 260.degree. C. and adhesion strength measured
in a pull test, where the encapsulated metal sample was pull apart
from the mold compound and the separation force was registered
using an Instron tensile tester. Little loss of bond strength was
found to occur when compared to samples not exposed to the
temperature/humidity. In comparison, the samples without the
nodular treatment typically lost more than 50% of its original bond
strength.
Example 5
[0050] A C110 copper foil was electrocleaned in a commercial
alkaline cleaner to remove the residual lubricant, contaminants,
and oxides from the surface. A plating current of 10 ASF was
applied to an area of 0.035 ft.sup.2 for 10 sec in a solution
containing 10 g/l ZnSO.sub.4.7H.sub.2O and 45 ppm MoO.sub.3. The
sample was then rinsed and dried, and subjected to a tape test
using a Scotch 600 tape. The tape was first pressed onto the plated
surface and then pulled away from the surface. The glue was visibly
left behind on the plated sample. This result indicates that a
nodular structure was deposited.
[0051] The sample was further subjected to a 250.degree.
C..times.10-min bake test and the sample showed no oxidation after
the bake. The untreated portion was heavily oxidized. This result
indicated that the coating provided a good tarnish resistance.
Example 6
[0052] A C7025 copper foil having 0.03 inch thickness was
electrocleaned in a commercial alkaline cleaner to remove the
residual lubricant, contaminants, and oxides from the surface. A
plating current of 10 ASF was applied to an area of 0.035 ft.sup.2
for 10 sec in a solution containing 10 g/l ZnSO.sub.4.7H.sub.2O and
30 ppm Mo (as molybdic acid). The sample was then rinsed and dried,
and subjected to a tape test using Scotch 600 tape. The tape
testing resulted in glue transfer to the treated surface, and
indicated a nodular or roughened surface was obtained. Additional
samples were plated, encapsulated using Sumicon 6300 and Shinetsu
KMC-289-3ECS molding compounds subjected to 168 hr 85%
RH/85.degree. C. moisture testing as described in IPC/JEDEC
J-STD-020A. After exposure the samples were solder floated for 120
sec at approximately 260.degree. C., and adhesion strength
measured. As shown in FIG. 2, little loss of bond strength was
found to occur when compared to non-exposed samples.
Example 7
[0053] A C7025 copper foil having 0.03 inch thickness was
electrocleaned in a commercial alkaline cleaner to remove the
residual lubricant, contaminants, and oxides from the surface. A
plating current of 10 ASF was applied to an area of 0.035 ft2 for 5
sec in a solution containing 15 g/l ZnSO.sub.4.7H.sub.2O, 15 g/l
(NH.sub.4).sub.2SO.sub.4 and 25 ppm W (as tungstosilicic acid). The
sample was then rinsed and dried, and subjected to a tape test
using a Scotch 600 tape. The tape was first pressed onto the plated
surface and then pulled away from the surface. The glue was visibly
left behind on the plated sample. This result indicates that a
nodular structure was deposited.
[0054] The sample was further subjected to a 250.degree.
C..times.10-min bake test and the sample showed no oxidation after
the bake. The untreated portion was heavily oxidized. This result
indicated that the coating provided a good tarnish resistance.
[0055] Additional samples were plated, encapsulated using Sumicon
6300 and Shineto KMC-289-3ECS molding compounds subjected to 168 hr
85% RH/85.degree. C. moisture testing as described in IPC/JEDEC
J-STD-020A. After exposure, the samples were solder floated for 120
sec at approximately 260.degree. C., and adhesion strength
measured. As shown in FIG. 2, no loss of bond strength was found to
occur when compared to non exposed samples.
Example 8
[0056] C7025 copper foil having 0.03 inch thickness was
electrocleaned in a commercial alkaline cleaner to remove the
residual lubricant, contaminants, and oxides from the surface. A
plating current of 5 ASF was applied to an area of 0.035.sup.2 ft
for 4 sec in a solution containing 12.5 g/l NaOH, 2.25 g/l zinc and
0.65 g/l W. The sample was then rinsed and dried. The sample was
subjected to a tape test using Scotch 600 tape. The tape was first
pressed onto the plated surface and then pulled away from the
surface. The glue was visibly left behind on the plated sample.
This result indicates that a nodular structure was deposited.
[0057] The sample was further subjected to a 250.degree.
C..times.30-min bake test and the sample showed no oxidation after
the bake. The untreated portion was heavily oxidized. This result
indicated that the coating provided a good tarnish resistance.
[0058] While the invention has been described in combination with
embodiments thereof, it is evident that many alternatives,
modifications and variations will be apparent to those skilled in
the art in light of the foregoing description. Accordingly, it is
intended to embrace all such alternatives, modifications and
variations as fall within the spirit and broad scope of the
appended claims. All patent applications, patents, and other
publications cited herein are incorporated by reference in their
entireties.
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