U.S. patent application number 09/917701 was filed with the patent office on 2001-11-15 for process for reducing extraneous metal plating.
Invention is credited to Konrad, John Joseph, Papathomas, Konstantinos I., Wells, Timothy Leroy, Wilson, James Warren.
Application Number | 20010040047 09/917701 |
Document ID | / |
Family ID | 22456695 |
Filed Date | 2001-11-15 |
United States Patent
Application |
20010040047 |
Kind Code |
A1 |
Konrad, John Joseph ; et
al. |
November 15, 2001 |
Process for reducing extraneous metal plating
Abstract
Printed circuit boards, cards and chip carriers are fabricated
by treating an already circuitized substrate with a swelling agent,
then treating the circuitized substrate with a composition
containing an alkaline permanganate, a chromate and/or chlorite and
then applying a metal layer to coat the circuitized portion of the
substrate.
Inventors: |
Konrad, John Joseph;
(Endicott, NY) ; Papathomas, Konstantinos I.;
(Endicott, NY) ; Wells, Timothy Leroy; (Apalachin,
NY) ; Wilson, James Warren; (Vestal, NY) |
Correspondence
Address: |
Burton A. Amernick
Connolly Bove Lodge & Hutz LLP
Suite 800
1990 M Street, N.W.
Washington
DC
20036-3425
US
|
Family ID: |
22456695 |
Appl. No.: |
09/917701 |
Filed: |
July 31, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09917701 |
Jul 31, 2001 |
|
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09133029 |
Aug 12, 1998 |
|
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Current U.S.
Class: |
174/250 ;
427/97.3; 427/98.5; 427/98.7; 427/99.1; 427/99.5 |
Current CPC
Class: |
H05K 2201/0761 20130101;
H05K 3/26 20130101; H05K 3/244 20130101; Y10T 428/24917 20150115;
C23C 18/1844 20130101; H05K 3/184 20130101; C23C 18/1651 20130101;
H05K 2203/0796 20130101 |
Class at
Publication: |
174/250 ;
427/96 |
International
Class: |
H05K 001/00; B05D
005/12; H02B 001/24 |
Claims
What is claimed is:
1. A method for fabricating a printed circuit board, printed
circuit card or chip carrier which comprises: providing a
circuitized substrate; treating said circuitized substrate with a
swelling agent; treating said circuitized substrate with a
composition comprising at least one member selected from the group
consisting of alkaline permanganate, chromate, and chlorite; and
applying a metal layer on said treated circuitized substrate to
coat the circuitized portion of said substrate.
2. The method of claim 1 wherein the circuitized substrate
comprises metal lines spaced 75 microns or less apart.
3. The method of claim 1 wherein said circuitized substrate
contains metal lines spaced about 28 microns apart.
4. The method of claim 1 wherein said circuitized substrate
contains copper lines.
5. The method of claim 1 wherein said swelling agent is present in
a swelling composition that contains water and an alkaline reacting
material.
6. The method of claim 5 wherein said swelling agent is selected
from the group consisting of alcohols, ethers, cyclic ethers,
pyrrolidones and lactones.
7. The method of claim 6 wherein the amount of said swelling agent
in said composition is about 5% to about 50% by volume.
8. The method of claim 5 wherein said alkaline material is sodium
hydroxide.
9. The method of claim 1 wherein said composition comprises an
alkaline permanganate.
10. The method of claim 9 wherein said alkaline permanganate is
sodium permanganate.
11. The method of claim 9 wherein said alkaline permanganate is
potassium permanganate.
12. The method of claim 9 wherein said composition contains about
50 to about 70 g/l of said permanganate.
13. The method of claim 1 wherein said metal layer is provided by
electrolessly depositing a nickel layer followed by electrolessly
depositing a layer of a precious metal.
14. The method of claim 13 wherein said precious metal is selected
from the group consisting of gold, platinum, palladium and
rhodium.
15. The method of claim 13 wherein said precious metal is gold.
16. The method of claim 1 wherein said swelling agent is selected
from the group consisting of butyl carbitol, ethylene glycol,
N-methyl pyrrolidone and .gamma.-butyrolactone.
17. A fine-line circuitized substrate and chip carrier fabricated
according to the method of claim 1.
18. A multi-layered circuitized structure obtained by the method
according to claim 1 for use in highly dense cards, circuit boards
and chip carriers.
19. The method of claim 1 which further comprises treating said
circuitized substrate with a reducing agent to neutralize alkaline
material prior to said applying a metal layer.
20. The method of claim 4 which further comprises carrying out a
copper cleaning step prior to said applying a metal layer.
Description
TECHNICAL FIELD
[0001] The present invention relates to a method for fabricating
printed circuit boards, cards and chip carriers and is especially
directed to a method for plating a metal layer on the circuitized
portions of an already circuitized substrate. More particularly,
the method of the present invention reduces bridging that can occur
during the plating.
BACKGROUND OF THE INVENTION
[0002] In the manufacture of printed circuit cards and boards, a
dielectric sheet material is employed as the substrate. A
conductive circuit pattern is provided on one or both of the major
surfaces of the substrate. The conductive pattern can be formed on
the surface of the substrate using a variety of known techniques.
These known techniques include the subtractive technique, where a
layer of for example copper is etched to form the desired circuit
pattern, the EDB (electroless direct bond) technique, where copper
is electrolessly plated directly on the surface of the substrate in
the desired pattern, and the peel-apart technique, where the
desired circuit pattern is plated up from a thin layer of
peeled-apart copper. Since the substrate employed is a dielectric,
when it is desired to plate directly on the surface of the
substrate, various techniques for seeding or catalyzing the
substrate are used.
[0003] Furthermore, in various situations, it is desirable to
selectively plate on the metallic surfaces (usually copper) as
opposed to the dielectric surfaces of the substrate. This is
especially true for plating copper areas that are to be used for
electrical connection. For example, it is common practice to
overplate copper lines with a barrier layer, typically a metal such
as nickel followed by a second overplating with a precious metal
such as gold, palladium or rhodium. Examples of such processes are
disclosed in U.S. Pat. Nos. 4,940,181 and 5,235,139, disclosures of
which are incorporated herein by reference.
[0004] However, there is a tendency for the nickel and/or precious
metal to plate not only on the already present circuit lines, but
also to deposit on a portion of the dielectric substrate or
insulator located between lines. This problem is especially
pronounced when dealing with very fine lines that are only
separated by very small intervals. For example, circuit boards
having surface conductive paths whose spacing is 50 microns or
below have a tendency to suffer from bridging or short circuiting
due to the subsequent plating of the nickel and/or precious metal.
It would therefore be desirable to provide a process for plating
only already circuitized lines whereby the problem of bridging is
significantly reduced if not entirely eliminated.
SUMMARY OF THE INVENTION
[0005] The present invention is concerned with a method that
significantly reduces the problem of extraneous plating in areas
between circuitry on a circuitized substrate. More particularly, it
has been found according to the present invention that treating an
already circuitized substrate with a swelling agent and with a
composition of an alkaline permanganate, a chromate or chlorite
significantly reduces if not entirely eliminates the bridging
problem. Accordingly, the method of the present invention relates
to fabricating a printed circuit board which comprises providing a
circuitized substrate and treating the circuitized substrate with a
swelling agent. The substrate is then treated with a composition of
an alkaline permanganate, a chromate or chlorite followed by
applying a metal layer on the treated circuitized substrate to coat
the circuitized portion of the substrate.
[0006] Still other objects and advantages of the present invention
will become readily apparent by those skilled in the art from the
following detailed description, wherein it is shown and described
only the preferred embodiments of the invention, simply by way of
illustration of the best mode contemplated of carrying out the
invention. As will be realized the invention is capable of other
and different embodiments, and its several details are capable of
modifications in various obvious respects, without departing from
the invention. Accordingly, the description is to be regarded as
illustrative in nature and not as restrictive.
BEST AND VARIOUS MODES FOR CARRYING OUT INVENTION
[0007] The process of the present invention is applicable to
treating a variety of circuitized dielectric (non-conductor)
substrates. Dielectric substrates described in the prior art,
including thermoplastic and thermosetting resins, may be plated in
accordance with the present invention.
[0008] Typical thermosetting polymeric materials include epoxy,
phenolic base materials, and polyamides. Combinations of epoxies
with cyanates, BT (bismalemide) resins or polyimides are also quite
suitable. The dielectric materials may be molded articles of the
polymers containing fillers and/or reinforcing agents, such as
glass-filled epoxy or phenolic base materials. Examples of some
phenolic type materials include copolymers of phenol, resorcinol
and cresole. Examples of some suitable thermoplastic polymeric
materials include polyolefins such a polypropylene, polysulfones,
polycarbonates, nitrile rubbers, ABS polymers and fluorinated
polymeric materials such as polytetrafluoroethylene.
[0009] More typically, the dielectric substrates employed are FR-4
epoxy compositions. A typical FR-4 epoxy composition contains 70-90
parts of brominated polyglycidyl ether of bisphenol-A and 10-30
parts of tetrakis (hydroxypenyl) ethane tetraglycidyl ether cured
with 3 to 4 parts of dicyandiamide and 0.2 to 0.4 parts of a
tertiary amine, all parts being parts by weight per 100 parts of
resin solids.
[0010] Another typical FR-4 epoxy composition contains:
[0011] A) about 25 to about 30 parts by weight of a tetrabrominated
diglycidyl ether of bisphenol-A, having an epoxy equivalent weight
of about 350 to about 450;
[0012] B) about 10 to about 15 parts by weight of a tetrabrominated
diglycidyl ether of bisphenol-A having an epoxy equivalent weight
of about 600 to about 750; and
[0013] C) about 55 to about 65 parts by weight of at least
epoxidized non-linear novolak, having at least terminal epoxy
groups, along with suitable curing and/or hardening agents.
[0014] Another typical FR-4 epoxy composition contains about 70 to
about 90 parts of brominated polyglycidyl ether of bisphenol-A, and
10 to 30 parts of tetrakis (hydroxyphenyl) ethane tetraglycidyl
ether cured with 0.8 to 1 part of 2-methyl imidazole.
[0015] Still another FR-4 epoxy composition employs tetrabromo
bisphenol-A as curing agent, along with 2-methyl imidazole as the
catalyst.
[0016] The desired pattern of circuit line is provided on the
substrate employing any of the well known copper plating
techniques. A typical example is a subtractive copper plating
technique such as that disclosed in Principles of Electronic
Packaging by Seraphim, Laski & Li, McGraw-Hill, 1989,
disclosure of which is incorporated herein by reference. Other
metals include nickel and cobalt.
[0017] Since the present invention is especially concerned with
plated features that are relatively close to each other, the
spacing between adjacent lines is typically about 75 microns or
less, a particular example being about 28 microns.
[0018] According to the present invention, the now circuitized
substrate is treated with a swelling agent. The swelling agent is
typically an organic swelling agent and is usually present as a
composition in order along with an alkaline reacting substance.
Examples of suitable organic swelling material include monohydric
alcohols, di- and polyhydric alcohols, ethers, cyclic ethers,
lactones, and pyrrolidones. Suitable alcohols include methanol,
ethanol, isopropanol, alkanol amines, 1,2,3-propane triol,
1-hexanol, ethylene glycol, ethanol amine, 1,6-hexane diol,
triethylene glycol, 2,2-dimethyl-1,3-propane diol, 1,2-propane
diol, 1,5-pentane diol, 1,4-butane diol, 1,3-butane diol and
1,2-butane diol.
[0019] Suitable ethers include propylene glycol monomethyl ether,
propylene glycol monopropyl ether and diethylene glycol monobutyl
ether (butyl "carbitol"). A suitable pyrrolidone includes N-methyl
pyrrolidone and a suitable lactone includes
gamma-butyrolactone.
[0020] Preferred swelling agents are butyl carbitol, ethylene
glycol, N-methyl pyrrolidone, and .gamma.-butyrolactone.
[0021] The swelling agent is typically present in an aqueous
composition at a concentration of about 5% to about 50% by volume
and more typically about 10% to about 20% by volume. A typical
butyl carbitol composition contains about 10 to about 20% by volume
butyl carbitol.
[0022] In addition, according to preferred aspects of the present
invention the swelling solution also includes an alkaline reacting
material such as an alkali metal hydroxide such as sodium
hydroxide. When present, the alkaline material is typically present
in the composition in amounts of about 20 to about 80 grams/liter,
and more typically about 40 to about 60 grams/liter.
[0023] The temperature of the swelling agent composition is
typically at about 70 to about 80.degree. C. during the treatment.
The swelling composition according to the present invention can be
brought into contact with the circuitized substrate to be treated
in various ways. Normally, the circuitized substrate is dipped in
the solution. Alternatively, the swelling solution can also be
applied to the circuitized substrate by spraying, splashing or
injecting.
[0024] Typically, the substrate is maintained in contact with the
swelling solution for about 2 to about 15 minutes.
[0025] Next, the circuitized substrate is treated with a
composition containing alkaline permanganate, or a chromate or a
chlorite. In the case of permanganate composition, typically it is
an aqueous solution that contains from about 20 to about 90
grams/liter, and more typically about 50 to about 70 grams/liter of
the permanganate. The permanganate is typically potassium
permanganate or sodium permanganate. Also the permanganate
composition usually contains an alkali metal hydroxide such as
sodium hydroxide or potassium hydroxide. Typical permanganate
compositions contain about 50 to about 70 grams/liter of
NaMnO.sub.4 or KMn.sub.4; about 40 to about 60 grams/liter of NaOH
or KOH, with the remainder being water.
[0026] The treating composition according to the present invention
can be brought into contact with the circuitized substrate in
various ways. Normally, the circuitized substrate is dipped in the
permanganate solution. Alternatively, the treating solution can
also be applied to the circuitized substrate by spraying, splashing
or injecting. When the treating solution is an alkaline
permanganate, the solution is usually at a temperature of about 70
to about 80.degree. C. during the contact. The contact with the
treating composition is typically about 2 to about 20 minutes.
[0027] According to preferred aspects of the present invention, the
substrate is also contacted with a reducing agent in a sufficient
amount to neutralize any remaining alkaline material that has been
used. The amount can be readily determined by those skilled in the
art once aware of the present invention. Suitable reducing
compositions include sulfuric acid/hydrogen peroxide solutions and
other mild acids.
[0028] After the treatment, a metal layer is applied to the
circuitized substrate to coat the circuitized portion of the
substrate. It has been found according to the present invention
that a significant reduction in extraneous plating is achieved by
the above treatment according to the present invention.
[0029] Typically, the treated circuitized substrate is subjected to
an electroless nickel plating composition such as nickel-boron or a
nickel-phosphorous plating solution such as MacDermid Planar
electroless nickel XD-6263T or Atotech CNN electroless nickel.
After this, the treated circuitized substrate is subjected to a
precious metal plating solution such as an electroless gold,
palladium, platinum or rhodium plating solution.
[0030] In addition, clean water rinses can be employed between the
various steps discussed above. Moreover, according to preferred
aspects of the present invention, a copper cleaning operation such
as ENTEK is carried out on the treated circuitized substrate prior
to applying the metal coating.
[0031] The foregoing description of the invention illustrates and
describes the present invention. Additionally, the disclosure shows
and describes only the preferred embodiments of the invention but,
as mentioned above, it is to be understood that the invention is
capable of use in various other combinations, modifications, and
environments and is capable of changes or modifications within the
scope of the inventive concept as expressed herein, commensurate
with the above teachings and/or the skill or knowledge of the
relevant art. The embodiments described hereinabove are further
intended to explain best modes known of practicing the invention
and to enable others skilled in the art to utilize the invention in
such, or other, embodiments and with the various modifications
required by the particular applications or uses of the invention.
Accordingly, the description is not intended to limit the invention
to the form disclosed herein. Also, it is intended that the
appended claims be construed to include alternative
embodiments.
* * * * *