U.S. patent application number 11/386901 was filed with the patent office on 2007-09-27 for precoat composition for organic solderability preservative.
Invention is credited to Brian Larson, Witold Paw.
Application Number | 20070221503 11/386901 |
Document ID | / |
Family ID | 38532195 |
Filed Date | 2007-09-27 |
United States Patent
Application |
20070221503 |
Kind Code |
A1 |
Larson; Brian ; et
al. |
September 27, 2007 |
Precoat composition for organic solderability preservative
Abstract
An improved method of enhancing the solderability of a copper
surface comprising the steps of contacting one or more copper
surfaces with a pretreatment composition comprising a dilute
solution of an aliphatic carboxylic acid and an additive selected
from the group consisting of amines and ammonia and thereafter
contacting the one or more surfaces with an organic solderability
preservative composition. The improved organic solderability
preservative process of the invention forms a more uniform coating
that has a better appearance and color.
Inventors: |
Larson; Brian; (Cheshire,
CT) ; Paw; Witold; (New Fairfield, CT) |
Correspondence
Address: |
John L. Cordani;Carmody & Torrance LLP
50 Leavenworth Street
P.O. Box 1110
Waterbury
CT
06721-1110
US
|
Family ID: |
38532195 |
Appl. No.: |
11/386901 |
Filed: |
March 22, 2006 |
Current U.S.
Class: |
205/85 |
Current CPC
Class: |
H05K 3/282 20130101;
C23F 11/149 20130101; C23F 11/126 20130101; H05K 2203/0392
20130101; H05K 2203/124 20130101; C23F 11/10 20130101 |
Class at
Publication: |
205/085 |
International
Class: |
C25D 5/54 20060101
C25D005/54 |
Claims
1. A method of enhancing the solderability of a copper surface
comprising the steps of: a) contacting the copper surface with a
pretreatment composition comprising a solution of an aliphatic
carboxylic acid and optionally, but preferably, an additive
selected from the group consisting of amines and ammonia; and
thereafter b) contacting the one or more surfaces with an organic
solderability preservative composition.
2. A method according to claim 1 wherein the organic solderability
preservative composition comprises an aqueous solution of one or
more materials selected from the group consisting of substituted or
unsubstituted triazoles, substituted or unsubstituted imidazoles,
substituted or unsubstituted benzimidazoles, substituted or
unsubstituted benzotriazoles, and substituted or unsubstituted
azoles.
3. The method according to claim 2, wherein the aliphatic
carboxylic acid is selected from the group consisting of carboxylic
acids with from 5 to 9 carbons.
4. The method according to claim 3, wherein the aliphatic
carboxylic acid comprises heptanoic acid.
5. The method according to claim 2, wherein the additive is used
and comprises an amine which is selected from the group consisting
of triethanolamine, dimethylamine, dipropylamine, diethanolamine,
ammonia, and ethanolamine.
6. The method according to claim 5, wherein the amine is
triethanolamine.
7. The method according to claim 5, wherein the aliphatic
carboxylic acid and the amine are each present in the pretreatment
composition at a concentration between about 1 to about 10 g/l.
8. The method according to claim 2, wherein the pH of the
pretreatment solution is between about 4.5 and about 9.5.
9. The method according to claim 8, wherein the pH of the
pretreatment solution is about 6.0.
10. The method according to claim 2, wherein the pretreatment
composition comprises the additive.
11. The method according to claim 2, wherein a rinsing step is
performed between the pretreatment step and the organic
solderability preservative step.
12. The method according to claim 2, wherein said step of
contacting the electronic component with the pretreatment
composition comprises immersing the electronic component in the
pretreatment composition.
13. The method according to claim 12, wherein the electronic
component is immersed in the pretreatment composition for about 1
to about 5 minutes.
14. The method according to claim 1, wherein the organic
solderability preservative composition comprises at least one
azole.
15. The method according to claim 14, wherein the at least one
azole is an imidazole.
Description
FIELD OF THE INVENTION
[0001] The present invention is directed to an organic
solderability preservative process for coating copper circuitry
during printed wiring board manufacture. The improved process of
the invention comprises the use of a pre-coat coating prior to the
main organic solderability preservative bath to enhance
solderability of the copper surfaces.
BACKGROUND OF THE INVENTION
[0002] In the manufacture of printed wiring boards (PWB) having
metal containing components which are to be soldered, it is
necessary to protect the metal from oxidation to enhance its
solderability. Typically, many such electronic components have
copper circuitry thereon and may also have gold leads or other
electrical connections which are generally used to connect the
electronic component to other electronic components.
[0003] Processes currently used to protect copper prior to
soldering typically employ a protective coating deposited on the
copper. Prior art processes include hot air solder leveling (HASL),
organic solderability preservatives (OSP) and other metallic
printed circuit board surface finishes. The protective coating
provides protection against copper solderability degradation caused
by various process steps in the fabrication process.
[0004] Copper protective coating systems utilize a number of steps
including cleaning, microetching and acid rinsing followed by the
formation of a protective coating on the copper using a solution
containing a protective forming agent.
[0005] In general, the surface of the copper or copper alloy is
first cleaned by immersion of the board in a cleaner and then
preferably etched to increase the adhesion of the copper. The
copper is then immersed in a solution containing an organic
solderability preservative material such as triazole, imidazole,
benzimidazole or derivatives thereof. Spraying or other forms of
coating may also be used.
[0006] Cleaning of the PWB may be performed using any number of
cleaners including alkaline, acid or neutral cleaners and is
preferably an acidic cleaner comprising sulfuric acid, hydrochloric
acid or citric acid. The PWB is typically contacted with the
cleaner for up to about 5 minutes at a temperature of 80.degree. to
120.degree. F.
[0007] An etchant is preferably used to microetch the surface of
the copper. Etchants such as an acidified persulfate salt such as
sodium persulfate or sulfuric/peroxide type material at
70.degree.-100.degree. F. for about 1 min. are typically
employed.
[0008] All the steps in the conventional OSP process are followed
by rinsing the substrate typically with deionized water. Rinsing is
usually performed at an ambient temperature.
[0009] Organic solderability protective coatings typically comprise
a material such as a triazole, an imidazole or benzimidazole, or a
derivative thereof. The substrate is treated with the OSP solution
to form a protective layer on the copper metallurgy. This is
usually performed at a temperature of 95.degree. to 115.degree. F.,
preferably about 105.degree. to 110.degree. F. for about 15 seconds
to 1 minute.
[0010] A number of patents have been issued for OSP coatings with
an objective of providing protective coatings that are more uniform
and have a better appearance, and with the goal of also improving
solderability.
[0011] U.S. Pat. No. 5,658,611 to Ishiko et al., the subject matter
of which is herein incorporated by reference in its entirety,
provides an aqueous surface protection composition for PWB's
containing a benzimidazole derivative that is adjusted to a pH of
1-5 with a salt forming acid of a heavy metal such as copper,
manganese and zinc in an amount of less than 50 ppm.
[0012] U.S. Pat. No. 5,173,130 to Kinoshita et al., the subject
matter of which is herein incorporated by reference in its
entirety, describes a process for the surface treatment of copper
which comprises immersing the surface of the copper in an aqueous
solution containing a benzimidazole compound having an alkyl group
of at least three carbon atoms at the 2-position and an organic
acid. Similarly, in U.S. Pat. Nos. 5,498,301 and 5,560,785 to Hirao
et al., the subject matter of each of which is herein incorporated
by reference in its entirety, describe a water-based surface
treatment agent used to protect copper on a printed wiring board
with excellent heat-resistance and moisture-resistance which uses a
2-arylimidazole compound as an active ingredient.
[0013] U.S. Pat. No. 5,362,334 to Adams et al., the subject matter
of which is herein incorporated by reference in its entirety,
describes a composition and process for the surface treatment of
metallic surfaces such as copper circuitry on printed circuit
boards which comprises treating the surface with an aqueous
solution comprising a benzimidazole compound having either a
halogenated phenyl group, a halogenated benzyl group or a
halogenated ethyl phenyl group in the 2-position.
[0014] U.S. Pat. No. 5,376,189 to Kukanskis, the subject matter of
which is herein incorporated by reference in its entirety,
describes a composition and process for the treatment of metallic
surfaces such as copper on printed circuit boards which comprises
treating the surface with an aqueous solution comprising a
benzimidazole compound which has at least one carboxylic or
sulfonic acid group directly or indirectly attached to the
benzimidazole compound. The carboxylic acid or sulfonic acid group
was believed to increase the solubility of the benzimidazole which
provides for longer bath life and ease of operation.
[0015] U.S. Pat. No. 6,635,123 to Cavallotti et al., the subject
matter of which is herein incorporated by reference in its
entirety, provides for the addition of zinc salts in the OSP
solution to improve copper surface characteristics. The addition of
the zinc salts causes surface oxidation to decrease, both during
soldering and during exposure to the atmosphere, and improves the
wettability of the copper surface, even after extended periods at
elevated temperatures. In addition, the addition of the zinc salts
improves the adhesion of the tin solder alloy to the surface.
[0016] Other prior art processes have suggested forming a
precoating layer on the copper surface prior to applying the final
protective coating. For example, U.S. Pat. No. 4,373,656 to Parker,
Jr. et al., the subject matter of which is herein incorporated by
reference in its entirety, describes a method for treating bare
copper printed circuit boards comprising first subjecting the
copper surfaces to a mild etch solution, stabilizing the surfaces
by treatment with an aqueous solution of phosphoric acid in
combination with a glycol and subsequently treating the surface
with an azole (e.g., imidazole).
[0017] U.S. Pat. No. 6,524,644 to Wengenroth, the subject matter of
which is herein incorporated by reference in its entirety, provides
a pre-treatment step before the OSP coating to provide an enhanced
final protective coating, comprising a benzimidazole compound and
an alkanolamine. The pretreatment coating described by Wengenroth
is believed to preserve the solderability of the copper surface
while substantially excluding gold surfaces from attracting the OSP
coating, which could case cosmetic defects in the form of staining
and possibly reduce the conductivity of the gold contact
surface.
[0018] The inventors of the present invention have determined that
additional improvements to the OSP coating process can be made that
produce a more uniform coating having a better appearance and
color. To that end, the inventors of the present invention have
developed a novel pretreatment composition comprising an aliphatic
carboxylic acid and preferably an amine. Once a substrate has been
coated with the novel precoat composition of the invention, the
substrate can be processed in the normal manner (i.e., coated with
an OSP comprising an azole compound).
SUMMARY OF THE INVENTION
[0019] It is an object of the present invention to provide an
improved OSP coating process that uses a pretreatment composition
prior to the OSP coating.
[0020] It is another object of the present invention to use the
improved OSP coating process of the invention to prepare electronic
components such as printed wiring boards.
[0021] To that end, the present invention is directed to a method
of enhancing the solderability of a copper surface comprising the
steps of:
[0022] a) contacting one or more copper surfaces with a
pretreatment composition comprising a solution of an aliphatic
carboxylic acid and preferably an additive selected from the group
consisting of amines and ammonia; and thereafter
[0023] b) contacting the one or more surfaces with an organic
solderability preservative composition.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0024] The present invention is directed to an improved protective
coating system for coating copper metallurgy on printed wiring
boards (PWB's) including copper pads and through holes.
[0025] In the present invention, a conventional azole-based OSP
coating is improved by using a pre-treatment step, wherein the
copper surfaces are contacted with a pre-treatment solution
comprising an aliphatic carboxylic acid and preferably an amine
before the OSP treatment. The inventors of the present invention
have found that the use of the pretreatment composition of the
invention enhances the final protective coating on the copper
surfaces and provides a more uniform coating that also has a better
appearance and color.
[0026] More particularly, the present invention is directed to a
method of enhancing the solderability of a copper surface
comprising the steps of:
[0027] a) contacting one or more copper surfaces with a
pretreatment composition comprising a dilute solution of an
aliphatic carboxylic acid and preferably an additive selected from
the group consisting of amines and ammonia; and thereafter
[0028] b) contacting the one or more surfaces with an organic
solderability preservative composition.
[0029] The improved pretreatment layer of the invention is
preferably a dilute mixture of an aliphatic carboxylic acid and an
additive selected from amines and ammonia, although amines are
generally most preferred. The aliphatic carboxylic acid is
preferably of the C5-C9 chain length, including pentanoic acid,
hexanoic acid, heptanoic acid, octanoic acid, and nonanoic acid. In
a preferred embodiment, the aliphatic carboxylic acid is heptanoic
acid. If used, the amine is typically selected from the group
consisting of triethanolamine, dimethylamine, dipropylamine,
diethanolamine, ammonia, and ethanolamine. In a preferred
embodiment, the amine is triethanolamine or a similar compound.
[0030] One example of a solution that is usable in the practice of
the invention is a dilute solution of heptanoic acid and
triethanolamine at approximately 1 g/l each. Such solution is
preferably approximately equimolar, i.e., contains about the same
number of molecules of each component, and can be viewed as a
solution of a salt between the triethanolamine and the heptanoic
acid, with a pH of approximately 6. Preferably the concentration of
the aliphatic carboxylic acid and the amine in the solution can be
varied between about 1 g/l to about 10 g/l for each ingredient,
preferably from about 1 g/l to about 5 g/l for each ingredient.
Varying the ratio of acid and amine, and thus modifying the pH
between about 4.5 and 9.5 is practical in the practice of this
invention. A copper surface of a PCB leaving the precoat is
hydrophobic, indicating the formation of a film. This film may be
thinned, modified or desorbed during rinsing as evidenced by loss
of hydrophobicity of the copper surface.
[0031] The pretreatment composition of the invention can be used at
room temperature or higher. Preferably, the step of contacting the
electronic component with the pretreatment composition comprises
immersing the electronic component in the pretreatment composition.
In this case, the dwell time of the electronic component in the
solution can be between 1 and 5 minutes, preferably about 1 to 2
minutes.
[0032] A rinsing step may also be performed between the
pretreatment step and the organic solderability preservative step
to remove excess pretreatment solution.
[0033] A number of OSP solutions have been developed which may be
used to form the OSP coating, examples of several of which have
been cited herein. However, any suitable OSP solution described in
the prior art may be used to provide the final coating on the
substrate metallurgy. Preferably, the organic solderability
preservative comprises at least one azole, and more preferably, the
azole is an imidazole.
[0034] The pretreatment composition and step of this invention is
followed, preferably after rinsing, with the application of an
organic solderability preservative. The organic solderability
preservative is preferably an aqueous solution of a substituted or
unsubstituted triazole, substituted or unsubstituted imidazole,
substituted or unsubstituted benzimidozole, substituted or
unsubstituted benzotriazole and/or substituted or unsubstituted
azole. The inventors have found that imidazoles or benzimidazoles
substituted with an alkyl group in the 2-position or the 5-position
are most beneficial. 5-methyl Benzimidazole is particularly
preferred. The concentration of the foregoing azoles in the aqueous
OSP solution is preferably from 0.5 to 50 g/l and the pH is
preferably from about 3 to 11. The copper surface is contacted with
the OSP solution by immersion, spray or flood at from room
temperature to about 180.degree. F.
[0035] The benefit of using the precoat of the invention is a
better organic solderability preservative coating, which provides a
more uniform coating and that also has a better appearance. As a
result, solderability is also better.
[0036] After the OSP treatment, the substrate is rinsed and
typically dried by dry forced air. The substrate may then be
soldered and is protected against oxidation until the soldering
step is performed.
[0037] It can thus be seen that the present invention provides an
improved solderable copper surface by using a novel precoat
composition prior to an organic solderability preservative.
* * * * *