U.S. patent number RE30,180 [Application Number 05/729,879] was granted by the patent office on 1979-12-25 for plural copper-layer treatment of copper foil and article made thereby.
This patent grant is currently assigned to Yates Industries, Inc.. Invention is credited to Adam M. Wolski, Charles B. Yates.
United States Patent |
RE30,180 |
Wolski , et al. |
December 25, 1979 |
Plural copper-layer treatment of copper foil and article made
thereby
Abstract
Copper foil is subjected to a two-step electrochemical copper
treatment to improve its bond strength, the first step of said
treatment involving the use of a copper and arsenic-containing
electrolyte. A treatment involving the use of the aforementioned
two-step electrochemical copper pretreatment prior to the
application of an electrochemical copper treatment. Treated copper
foil and printed circuit boards resulting therefrom.
Inventors: |
Wolski; Adam M. (Edgewater
Park, NJ), Yates; Charles B. (Edgewater Park, NJ) |
Assignee: |
Yates Industries, Inc.
(Bordentown, NJ)
|
Family
ID: |
26883547 |
Appl.
No.: |
05/729,879 |
Filed: |
October 5, 1976 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
Reissue of: |
187923 |
Oct 8, 1971 |
03918926 |
Nov 11, 1975 |
|
|
Current U.S.
Class: |
428/601; 156/151;
205/111; 205/152; 205/176; 205/182; 428/612; 428/642; 428/675;
428/936 |
Current CPC
Class: |
C25D
3/58 (20130101); C25D 5/10 (20130101); C25D
5/16 (20130101); H05K 3/384 (20130101); H05K
2201/0355 (20130101); Y10T 428/12472 (20150115); H05K
2203/0723 (20130101); Y10T 428/12681 (20150115); Y10T
428/1291 (20150115); Y10T 428/12396 (20150115); H05K
2203/0307 (20130101) |
Current International
Class: |
C25D
5/16 (20060101); C25D 3/56 (20060101); C25D
5/00 (20060101); C25D 3/58 (20060101); C25D
5/10 (20060101); H05K 3/38 (20060101); C25D
005/10 (); C25D 003/58 (); B23P 003/00 () |
Field of
Search: |
;29/199,195E,195P,195T,195G,183.5 ;204/40,44 ;156/151
;428/601,612,642,675,936 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Kaplan; G. L.
Attorney, Agent or Firm: Finnegan, Henderson, Farabow &
Garrett
Claims
We claim:
1. A process for improving the bond strength of copper foil through
the electrochemical treatment of a surface thereof comprising said
surface to a two-step electrochemical pretreatment prior to the
application of said electrochemical treatment, the first step of
said pretreatment comprising subjecting said surface to an arsenic
and copper-containing electrolyte under conditions such as to
electrolytically deposit thereon a first copper layer which
increases the bond strength of the raw foil; the second step of
said pretreatment comprising subjecting said surface to a
copper-containing electrolyte under conditions such as to
electrolytically deposit thereon a second copper layer which
substantially conforms to the configuration of the first layer and
reduces the powder transfer characteristics of said first layer;
and then giving said pretreated foil an electrochemical treatment
in which said surface is subjeced to a copper-containing
electrolyte under conditions such as to electrolytically deposit
thereon a third, copper-containing, microcrystalline layer which
further increases the bond strength of said foil.
2. A process as defined in claim 1 wherein said electrochemical
treatment involves the use of an arsenic and copper-containing
electrolyte.
3. A process as defined in claim 2 wherein the copper and arsenic
content in the electrolyte in said first step and in said
electrochemical treatment are approximately as follows:
4. A process as defined in claim 2 wherein the copper and arsenic
content in the electrolyte in said first step and in said
electrochemical treatment are approximately as follows:
5. A process as defined in claim 2 wherein a sufficient amount of
arsenic is present in the electrolyte in said first step of said
pretreatment to increase the bond strength resulting from said
electrochemical treatment over what it would have been had said
electrochemical treatment been applied to foil which had not been
pretreated.
6. A process as defined in claim 1 wherein approximately 1-4 grams
of electrodeposit per square meter of foil surface is deposited
during said electrochemical treatment.
7. A process for improving the bond strength of copper foil
comprising subjecting a surface of said foil to three
electrochemical treatments such as to electrode-posit thereon three
copper layers, said three treatments being carried out
approximately under the following conditions:
8. A process as defined in claim 7 wherein the conditions for said
three treatments are approximately as follows:
9. A process as defined in claim 7 wherein the conditions for said
three treatments are approximately as follows:
10. A process for improving the bond strength of copper foil
through the electrochemical treatment of a surface thereof
comprising subjecting said surface to a two-step electrochemical
treatment, the first step of said treatment comprising subjecting
said surface to an arsenic and copper-containing electrolyte under
conditions such as to electrolytically deposit thereon a first
copper layer which increases the bond strength of the raw foil; the
second step of said treatment comprising subjecting said surface to
a copper-containing electrolyte under conditions such as to
electrolytically deposit thereon a second copper layer which
substantially conforms to the configuration of the first layer and
reduces the powder transfer characteristics of said first
layer.
11. The product of the process of claim 1.
12. The product of the process of claim 6.
13. The product of the process of claim 2.
14. The product of the process of claim 3.
15. The product of the process of claim 4.
16. The product of the process of claim 5.
17. The product of the process of claim 7.
18. The product of the process of claim 8.
19. The product of the process of claim 9.
20. The product of the process of claim 10.
21. Copper foil having on a face thereof three electrodeposited
superposed layers, the layer closest to said face containing
arsenic and copper, the intermediate layer being a copper
electrodeposit which substantially conforms to the configuration of
said closest layer and serves to reduce the powder transfer
characteristics of said closest layer; the third outermost layer
being copper-containing and microcrystalline, said third layer
increasing the bond strength of said foil over and above the bond
strength provided by said closest and intermediate layers.
22. Copper foil as defined in claim 21 wherein said third outermost
layer is copper-arsenic.
23. A printed circuit board comprised of a dielectric substrate
bonded to which is the copper foil of claim 21, the portion of said
foil being closest to said substrate being said third layer.
24. A printed circuit board comprised of a dielectric substrate
bonded to which is the copper foil of claim 22, the portion of said
foil being closest to said substrate being said third layer. .Iadd.
25. A process for improving the bond strength of copper foil
through the electrochemical treatment of a surface thereof
comprising subjecting said surface to a two-step electrochemical
pretreatment prior to the application of said electrochemical
treatment, the first step of said pretreatment comprising
subjecting said surface to an electrolyte containing (1) copper and
(2) arsenic, antimony, bismuth, selenium or tellurium under
conditions such as to electrolytically deposit thereon a first
copper layer which increases the bond strength of the raw foil; the
second step of said pretreatment comprising subjecting said surface
to a copper-containing electrolyte under conditions such as to
electrolytically deposit thereon a second copper layer which
substantially conforms to the configuration of the first layer and
reduces the powder transfer characteristics of said first layer;
and then giving said pretreated foil an electrochemical treatment
in which said surface is subjected to a copper-containing
electrolyte under conditions such as to electrolytically deposit
thereon a third, copper-containing microcrystalline layer which
further increases the bond strength of said foil. .Iaddend..Iadd.
26. A process as defined in claim 25 wherein approximately 1-4
grams of electrodeposit per square meter of foil surface is
deposited during said electrochemical treatment. .Iaddend..Iadd.
27. A process as defined in claim 25 wherein said electrochemical
treatment involves the use of an electrolyte containing (1) copper
and (2) arsenic, antimony, bismuth, selenium or tellurium.
.Iaddend..Iadd. 28. A process as defined in claim 27 wherein a
sufficient amount of arsenic, antimony, bismuth, selenium or
tellurium is present in the electrolyte in said first step of said
pretreatment to increase the bond strength resulting from said
electrochemical treatment over what it would have been had said
electrochemical treatment been applied to foil which had not been
pretreated. .Iaddend..Iadd. 29. A process for improving the bond
strength of copper foil through the electrochemical treatment of a
surface thereof comprising subjecting said surface to a two-step
electrochemical treatment, the first step of said treatment
comprising subjecting said surface to an electrolyte containing (1)
copper and (2) arsenic, antimony, bismuth, selenium or tellurium
under conditions such as to electrolytically deposit thereon a
first copper layer which increases the bond strength of the raw
foil; the second step of said treatment comprising subjecting said
surface to a copper-containing electrolyte under conditions such as
to electrolytically deposit thereon a second copper layer which
substantially conforms to the configuration of the first layer and
reduces the powder transfer characteristics of said first layer.
.Iaddend..Iadd. 30. The product of the process of claim 25.
.Iaddend..Iadd. 31. The product of the process of claim 26.
.Iaddend..Iadd. 32. The product of the process of claim 27.
.Iaddend..Iadd. 33. The product of the process of claim 28.
.Iaddend..Iadd. 34. The product of the process of claim 29.
.Iaddend..Iadd. 35. Copper foil having on a face thereof three
electrodeposited superposed layers, the layer closest to said face
containing (1) copper and (2) arsenic, antimony, bismuth, selenium
or tellurium, the intermediate layer being a copper electrodeposit
which substantially conforms to the configuration of said closest
layer and serves to reduce the powder transfer characteristics of
said closest layer; the third outermost layer being
copper-containing and microcrystalline, said third layer increasing
the bond strength of said foil over and above the bond strength
provided by said closest and intermediate layers. .Iaddend..Iadd.
36. Copper foil as defined in claim 35 wherein said third outermost
layer also contains arsenic, antimony, bismuth, selenium or
tellurium. .Iaddend..Iadd. 37. A printed circuit board comprised of
a dielectric substrate bonded to which is the copper foil of claim
35, the portion of said foil being closest to said substrate being
said third layer. .Iaddend..Iadd. 38. A printed circuit board
comprised of a dielectric substrate bonded to which is the copper
foil of claim 36, the portion of said foil being closest to said
substrate being said third layer. .Iaddend..Iadd. 39. Copper foil
having on a face thereof two electrodeposited superposed layers,
the layer closest to said face containing (1) copper and (2)
arsenic, antimony, bismuth, selenium or tellurium, the second layer
being a copper electrodeposit which substantially conforms to the
configuration of said closest layer and serves to reduce the powder
transfer characteristics of said closest layer. .Iaddend..Iadd. 40.
Copper foil as defined in claim 39 wherein said second layer
contains copper and arsenic. .Iaddend..Iadd. 41. A printed circuit
board comprised of a dielectric substrate bonded to which is the
copper foil of claim 39, the portion of said foil being closest to
said substrate being said second layer. .Iaddend. .Iadd. 42. A
printed circuit board comprised of a dielectric substrate bonded to
which is the copper foil of claim 40, the portion of said foil
being closest to said substrate being said second layer. .Iaddend.
.Iadd. 43. A process as defined in claim 25 wherein in said first
step of said pretreatment the surface is subjected to an
electrolyte containing (1) copper and (2) arsenic, antimony or
bismuth. .Iaddend..Iadd. 44. A process as defined in claim 27
wherein said electrochemical treatment involves the use of an
electrolyte containing (1) copper and (2) arsenic, antimony or
bismuth. .Iaddend.
Description
BACKGROUND OF THE INVENTION
The present invention relates to improved treatment operations for
the treatment of copper foil.
In the production of printed electronic circuits, it is a common
practice to bond metal foil to a substrate material, generally a
synthetic polymer, and to subject the composite structure to acid
etching to form the desired circuit. Since the adhesive foil often
serves as the mechanical support of the circuit elements as well as
serving as the conductor paths, considerable effort has been
directed in the past to treating the foil so as to increase its
bond strength with respect to the substrate to which it is to be
attached. As a result of such efforts, treatments have been
developed which serve to increase the surface area of the matte
surface on a side of the copper foil through the deposition of a
dendritic copper electrodeposit so that when adhesively bonded to a
plastic substrate material, a tenacious bond will result.
In order to obtain the maximum increase in bond strength from a
given treatment, it has been not uncommon to increase the amount of
copper deposited on the copper foil. While such increase permits
the achievement of enhanced bond strength, however, it has
simultaneously served to create significant powder and oxide
transfer problems. While these problems are avoided through a
decrease in the thickness of the copper electrodeposit on the foil,
the necessary consequence of such decrease has been an undesirable
loss in bond strength.
SUMMARY OF THE INVENTION
One embodiment of the present invention is directed to a treatment
process which provides copper foil which not only possesses
extraordinarily high bond strength but which is not characterized
by the powder and oxide transfer problems noted above. This process
involves subjecting copper foil to a two-step electrochemical
pretreatment prior to the application of an electrochemical
treatment, the first step of said pretreatment involving the use of
an arsenic and copper-containing electrolyte to form a first copper
layer which increases the bond strength of the raw foil, the second
step of the pretreatment involving the use of a copper-containing
electrolyte to electrodeposit a second, gilding copper layer which
substantially conforms to the configuration of the first layer so
as to reduce the powder transfer characteristics of the first
layer, the final electrochemical treatment involving the use of a
metallic ion-containing electrolyte under conditions such as to
electrolytically deposit a third, microcrystalline layer which
further increases the bond strength of said foil.
A second embodiment of the present invention is directed to a
two-step electrochemical copper treatment which involves subjecting
copper foil to the aforementioned two-steps as the total
treatment.
OBJECTS AND ADVANTAGES OF THE INVENTION
It is accordingly an object of the present invention to provide a
novel method and articles made therefrom for providing foil with
excellent bond strength making it particularly well adapted for use
in printed electronic circuit applications.
These and other objects and advantages of the present invention
will become more apparent in connection with the ensuing
description and appended claims.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
In accordance with one embodiment of the present invention, copper
foil is first subjected to a two-step pretreatment to prepare it
for and improve the effectiveness of the final electrochemical
treatment. In the first pretreatment step, conditions are selected
so as to provide the surface of the foil which is to be bonded to a
supporting substrate with a copper and arsenic-containing
electrodeposit which will increase the bond strength of the raw
foil from about 5-61/2 lbs./in. of width of laminate to about
91/2-10 lbs./in. of width of laminate..sup.1 The copper
electrodeposit resulting from this first pretreatment step roughens
the surface of the foil but is structurally less sound than would
be desirable in treated foil destined for printed circuit
applications. In order to improve the structural characteristics of
the foil, a second pretreatment step is employed to apply a
"locking" or "gilding" copper electrodeposit on the first
electrodeposit resulting from the first pretreatment step. This
second electrodeposit does not substantially interfere with the
bond strength resulting from the first pretreatment step (the
resulting bond strength is in the order of 9-10 lbs./in. of width)
while reducing or eliminating the disadvantageous powder transfer
characteristics which the foil otherwise would have as a result of
the first pretreatment step.
Following the foregoing pretreatment steps, the copper foil is
subjected to a third electrochemical treatment so as to deposit on
the second electrodeposited copper layer a third, microcrystalline,
copper and arsenic-containing electro-deposited layer.
The amount of copper deposited during this third treatment is
limited so as to avoid undesirable powder and oxide transfer
problems. Notwithstanding this fact, this last electrochemical
treatment results in an extraordinary and wholly unexpected
increase in bond strength over and above the amount of bond
enhancement otherwise attainable with the same step through
treatment on raw foil. Thus, the third electrochemical treatment
provides an increase of as much as 3-4 lbs./in. of width of
laminate up to about 14 lbs./in. of width of laminate. Such a 3-4
lbs./in. increase in bond strength would not be unusual in a
conventional treatment process. What is unusual is that such an
increase can be obtained without concomitant powder and oxide
transfer problems and from a limited thickness deposit which
normally would be expected to provide only half as much increase in
bond strength.
Table A below shows the approximate desirable ranges of conditions
for use in carrying out the process of the present invention
(preferred ranges are set forth parenthetically).
TABLE A ______________________________________ First Second Last
Pretreatment Pretreatment Electrochemical Condition Step Step
Treatment ______________________________________ Cathode 100-300
100-300 50-200 current (150-300) (150-250) (50-150) density (ASF)
Temperature 60-120 90-160 70-100 (.degree.F.) (70-100) (100-140)
(75-85) Copper concen- 10-40 40-120 40-10 tration (g/l, (20-30)
(60-80) (4.5-5.5) calc. as Cu) Acid concen- 30-100 30-100 30-100
tration (g/l, (50-100) (50-100) (50-65) calc as H.sub.2 SO.sub.4)
Arsenic concen- .03-5 -- 0-.5 tration (g/l, (.3-1.5) -- (.15-.3)
calc. as As) Circulation 0-1/10 0-1/10 0-1/10 (fraction of total
volume recirculated per minute) Time (secs.) 5-30 5-30 5-30 (10-14)
(8-12) (8-12) Cathode copper foil copper foil copper foil Anode
preferably preferably preferably insoluble insoluble insoluble lead
lead lead ______________________________________
As will be apparent to those skilled in the art, the particular
conditions employed within a given one of the aforelisted ranges
will be influenced by the condition employed within the others of
said ranges. By way of example, the higher the copper
concentration, the lower the temperature and the higher the cathode
current density.
The degree of electrolyte circulation employed is that which is
sufficient to maintain substantially homogeneous the electrolyte
composition and temperature.
The electrodeposits resulting from each of the two pretreatments
and the final treatment step will generally vary within the
following approximate thickness ranges:
TABLE B ______________________________________ Thickness (g/m.sup.2
of foil surface) ______________________________________ First
Pretreatment Step 4-12 (preferably 6) Second Pretreatment Step 4-12
(preferably 6) Third Treatment Step 1-4 (preferably 11/2)
______________________________________
While at least some of the advantages of the present invention will
be obtained even if limits such as those in the third treatment
step are exceeded, best results are obtained (viz., avoidance of
powder and oxide transfer problems while obtaining significant bond
enhancement) within the limits noted. Indeed, the greatest
significance of the present invention is that these limits needn't
be exceeded to achieve a major increase in bond strength.
Of critical importance in the practice of the present invention is
the use of arsenic in the first pretreatment step. If no arsenic is
employed in that step, the results of the first two pretreatment
steps will be a plurality of copper electrodeposits on the copper
foil which are sufficiently unreceptive to third electrochemical
treatment so that a significant powder or oxide transfer problem
will result. By including arsenic in the first pretreatment step,
the two-step pretreatment results in a pretreated foil which is
better suited (viz., is more receptive) to receipt of the final
electrochemical treatment.
It is of interest to note that while arsenic is included in the
first pretreatment electrodeposited copper layer, the amount
deposited is small compared to the amount of arsenic in solution.
This no doubt may be explained by the fact that arsenic has great
difficulty co-depositing when copper concentration is as high as it
is in the first pretreatment step.
Arsenic is included in a proportionately somewhat greater quantity
in the final treatment electrodeposit. It is to be noted, however,
that while best results are attained employing arsenic in the third
treatment, advantages of the present invention (though diminished
somewhat) are nevertheless attainable without its use.
The second pretreatment step is critical as well. If the final
treatment were applied directly to the first treatment without an
intermediate gilding layer, the resulting powder and oxide transfer
problems would be both significant and unacceptable. By interposing
a gilding layer between the two, this problem is avoided.
As previously noted, the increase in bond strength obtained from
the final electrochemical treatment is not only extraordinary but
is totally surprising. In order to obtain this type of increase in
bond strength without the pretreatment, one would have to operate
under electrolytic conditions such as to provide significant powder
and oxide transfer problems. Attempts to eliminate these powder and
oxide transfer problems without the pretreatment would result in
loss of the significant increase in bond otherwise obtainable with
it. What is truly astonishing is that the final electrochemical
treatment employed in the present process can be operated to
produce as small a copper deposit as was previously noted while
obtaining the astounding bond improvement noted above.
The process of the present invention is preferably carried out in
three separate treatment tanks as a series operation. In other
words, copper foil is passed through the first tank and thereafter
passed in sequence through second and third tanks. Alternatively
(though not preferred), all three treatments can be carried out in
a single tank with the draining of the tank between treatments,
though this would preclude continuous operation.
The particular apparatus employed to apply each of the
electrodeposited layers to the surface of the copper foil forms no
part of the present invention. Such layers can, however, be
conveniently applied by passing the copper foil through an
electrolyte adjacent plate anodes with the copper foil passed in
serpentine fashion in proximity to such anodes and, by appropriate
contact between the copper foil and conducting rollers, the copper
foil is made cathodic in the circuit. By passing the copper foil
through such a system so that the surface of the foil to be coated
faces the active face of the anodes, the metal to be coated on said
surface will be electrodeposited thereon from the electrolyte. As
will be appreciated, in order to carry out the preferred
arrangement, the apparatus used will employ three separate
treatment tanks.
As previously mentioned, it is within the contemplation of the
present invention not only to provide a novel method for producing
copper foil having good bond strength and copper foil produced
thereby but to provide laminates comprised of said copper foil
bonded to an appropriate substrate. As will be apparent, the
particular substrate used in this laminate will vary depending upon
the use for which the laminate is intended and the service
conditions under which such laminate will be used. Particularly
appropriate substrates which adapt the laminate for use in forming
printed circuits include epoxy resin-impregnated fiberglass
supports such as those previously noted, epoxy-impregnated paper,
phenolic resin-impregnated paper and the like. Both flexible and
non-flexible supports such as Teflon-impregnated fiberglass
("Teflon" is the trademark for polytetrafluoroethylene), Kel-F
impregnated fiberglass ("Kel-F" is a trademark for certain
fluorocarbon products including polymers of trifluorochloroethylene
and certain copolymers) and the like are also usable. Other
flexible substrates include polyimides such as those known under
the designations "Kapton" and "H-Film" (both are manufactured by
duPont and are polyimide resins produced by condensing a
pyromellitic anhydride with an aromatic diamine).
The adhesives used to bond the treated copper foil to the substrate
are those conventionally used for the specific application in
question, "FEP" (a fluorinated ethylene propylene resin in the form
of a copolymer of tetrafluoroethylene and hexafluoropropylene
having properties similar to Teflon) being particularly appropriate
for the Teflon and Kel-F and conventional epoxy resins being useful
for the other materials. The method of bonding the copper foil to
the substrate is conventional and forms no part of the present
invention, typical details of such bonding being set forth for
example in the U.S. Pat. No. 3,328,275 to Waterbury.
The following example further illustrates preferred operations
within the scope of the present invention.
Example 1
In this example, copper layers are applied to foil in an
electrolytic cell of the general type previously described. The
foil is passed in continuous sequence through each of three tanks
as noted.
A roll of 1 oz. copper foil is electrodeposited with a copper layer
in a first treatment tank containing an aqueous electrolyte and
utilizing the following conditions:
______________________________________ Cathode current density
(ASF) 160 Temperature (.degree.F.) 75 copper concentration (g/l, 30
calculated as Cu) Acid concentration (g/l, 60 calculated as H.sub.2
SO.sub.4) Arsenic concentration (obtained 1.25 from arsenic acid,
calculated as g/l of As) Circulation (fraction of 3/50 total volume
recirculated/ min.) Time (sec.) 12 Cathode copper foil Anode
insoluble lead ______________________________________
The copper foil so treated has on one of its surfaces a powdery
copper electrodeposit. As a result of this treatment step, the
treated foil has a bond strength of about 91/2-10 lbs./in.
This foil is then treated in a second treatment tank containing an
aqueous electrolyte to electrodeposit a gilding or locking copper
layer over the previously applied nodular copper layer. This
gilding or locking treatment is carried out utilizing the following
conditions:
______________________________________ Cathode current density
(ASF) 200 Temperature (.degree.F.) 120 Copper concentration (g/l,
70 calculated as Cu) Acid concentration (g/l, 60 calculated as
H.sub.2 SO.sub.4) Circulation (fraction of 3/50 total vol.
recirculated/min.) Time (sec.) 12 Cathode copper foil Anode
insoluble lead ______________________________________
The foil so treated has a bond strength of about 9-10 lbs./in.
The copper foil which has been subjected to the foregoing two
pretreatment steps is then passed into a third treatment tank
containing an aqueous electrolyte utilizing the following
conditions:
______________________________________ Cathode current density
(ASF) 60 Temperature (.degree.F.) 80 Copper concentration (g/l, 5
calculated as Cu) Acid concentration (g/l, 60 calculated as H.sub.2
SO.sub.4) Arsenic (obtained from arsenic .25 acid, calculated as
g/l of As) Circulation (fraction of total 3/50 vol.
recirculated/min.) Time (sec.) 12 Cathode copper foil Anode
insoluble lead ______________________________________
The foil so treated has a bond strength of about 14 lbs./in.
The copper foil used in the treatment process of the present
invention is preferably electrolytically formed but may be formed
by rolling techniques as well. The arsenic used in the first
pretreatment step and in the final electrochemical treatment step
is preferably used in its (+5) form as by adding arsenic acid or
arsenic oxide to the electrolyte, though any acid soluble compounds
of arsenic may be used for this purpose.
Best results are obtainable using arsenic as the additive in the
first pretreatment step and in the final electrochemical treatment
step. In lieu of arsenic, other additives may be employed.
Preferred among these substitute additives is antimony, with
bismuth, selenium and tellurium being less preferred.
In the preceding portion of the specification, a novel process has
been described for treating copper foil to improve its bond
strength. This process comprises two pretreatment steps and a third
electrochemical treatment, the latter preferably involving the use
of a copper and arsenic-containing electrolyte. While this
three-step process constitutes the preferred embodiment of the
present invention, advantages of the present invention are also
attainable with another embodiment involving only the first and
second pretreatment steps as the complete treatment applied to the
foil. Such a two-step treatment provides an electrodeposit which
not only enhances bond strength significantly but which is
extremely dense and strong.
The invention may be embodied in other specific forms without
departing from the spirit or essential characteristics thereof. The
present embodiments are therefore to be considered in all respects
as illustrative and not restrictive, the scope of the invention
being indicated by the appended claims rather than by the foregoing
description, all changes which come within the meaning and range of
equivalency of the claims are therefore intended to be embraced
therein.
* * * * *