U.S. patent application number 15/095645 was filed with the patent office on 2016-08-04 for solution and process to treat surfaces of copper alloys in order to improve the adhesion between the metal surface and the bonded polymeric material.
The applicant listed for this patent is Atotech Deutschland GmbH. Invention is credited to Jurgen Barthelmes, Patrick Lam, Din-Ghee Neoh, Kiyoshi Watanabe, Christian Wunderlich.
Application Number | 20160222523 15/095645 |
Document ID | / |
Family ID | 36636657 |
Filed Date | 2016-08-04 |
United States Patent
Application |
20160222523 |
Kind Code |
A1 |
Wunderlich; Christian ; et
al. |
August 4, 2016 |
SOLUTION AND PROCESS TO TREAT SURFACES OF COPPER ALLOYS IN ORDER TO
IMPROVE THE ADHESION BETWEEN THE METAL SURFACE AND THE BONDED
POLYMERIC MATERIAL
Abstract
The invention concerns processes and solutions for the treatment
of copper alloy surfaces, which are subsequently to be firmly
bonded to polymeric material. The solution is used, in particular
for firmly bonding lead frames to encapsulating molding compounds
(polymeric material). The solution contains an oxidant, at least
one acid, at least one adhesion-enhancing compound characterized in
that the solution additionally contains fluoride ions in an amount
of at least 100 mg per litre and chloride ions in an amount of 5 to
40 mg per litre. The solution is particularly useful for treatment
of copper alloy surfaces, containing alloying elements selected
from the group consisting of Si, Ni, Fe, Zr, P, Sn and Zn.
Inventors: |
Wunderlich; Christian;
(Velten, DE) ; Barthelmes; Jurgen; (Berlin,
DE) ; Watanabe; Kiyoshi; (Kanagawa, JP) ;
Neoh; Din-Ghee; (Singapore, SG) ; Lam; Patrick;
(Hong Kong, HK) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Atotech Deutschland GmbH |
Berlin |
|
DE |
|
|
Family ID: |
36636657 |
Appl. No.: |
15/095645 |
Filed: |
April 11, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15041840 |
Feb 11, 2016 |
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15095645 |
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12224016 |
Sep 18, 2008 |
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PCT/EP2007/000826 |
Jan 31, 2007 |
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15041840 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L 2924/0002 20130101;
H05K 2203/124 20130101; H01L 2924/0002 20130101; H05K 3/383
20130101; C23F 1/44 20130101; H01L 2924/00 20130101; C23F 1/18
20130101 |
International
Class: |
C23F 1/18 20060101
C23F001/18 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 17, 2006 |
EP |
06003278.6 |
Claims
1. A solution for treating a surface of copper alloys to improve
adhesion of polymeric materials thereto, comprising a) an oxidant
b) at least one acid c) at least one adhesion-enhancing compound
characterized in that the solution additionally contains: d)
fluoride ions in an amount of at least 100 mg per litre, e)
chloride ions in an amount of 5 to 40 mg per litre.
2. The solution according to claim 1, characterized in that the
adhesion-enhancing compound is selected from the group consisting
of triazoles, benzotriazoles, imidazoles, tetrazoles and
purines.
3. The solution according to claim 2, characterized in that the
triazole has the following chemical formula E1: ##STR00007##
Wherein R.sub.17, R.sub.18 are selected from the group consisting
of hydrogen, alkyl, substituted alkyl, amino, phenyl, substituted
phynyl and carboxalkyl, where R.sub.17 and R.sub.18 can be the same
or different and can be a part of the homo- or heterocyclic ring
condensed onto the triazole ring.
4. The solution according to claim 2, characterized in that the
triazole is selected from the group consisting of benzotriazole,
methylbenzotriazole, ethyl benzotriazole and
dimethylbenzotriazole.
5. The solution according to claim 2, characterized in that the
tetrazole has the following chemical formula E2: ##STR00008##
wherein R.sub.19 is selected from the group consisting of hydrogen,
alkyl, substituted alkyl, halogenalkyl, amino, phenyl, substituted
phenyl, benzyl, carboxy, carboxyalkyl, alkoxycarbonyl,
aminocarbonyl and R.sub.20 --CONH wherein R.sub.20 is hydrogen,
alkyl, substituted alkyl, phenyl or substituted phenyl.
6. The solution according to claim 5, characterized in that the
tetrazole is selected from the group consisting of 5-aminotetrazole
and 5-phenyltetrazole.
7. The solution according to claim 1, characterized in that the
adhesion-enhancing compound is a mixture of at least one
nitrogen-containing, five-membered heterocyclic compound that does
not contain sulfur, selenium or tellurium atoms in the heterocycle
and at least one compound selected from the group consisting of
sulfinic acids, selenic acids, telluric acids, heterocyclic
compounds that contain at least one sulfur, selenium and/or
tellurium atom in the heterocycle, as well as sulfonium, selenonium
and telluronium salts, where the sulfonium, selenonium and
telluronium salts are compounds of general formula A: ##STR00009##
where A is S, Se or Te, R.sub.1, R.sub.2 and R.sub.3 are selected
from the group consisting of alkyl, substituted alkyl, alkenyl,
phenyl, substituted phenyl, benzyl, cycloalkyl and substituted
cycloalkyl, where R.sub.1, R.sub.2 and R.sub.3 can be the same or
different, and X'' is the anion of an inorganic or organic acid or
hydroxide, with the proviso that the acid according to component b)
is not a sulfinic, selenic or telluric acid according to component
c).
8. The solution according to claim 7, characterized in that it
contains sulfinic acids selected from the group consisting of
aromatic sulfinic acids and compounds of chemical formula B:
##STR00010## wherein R.sub.4, R.sub.5 and R.sub.6 are selected from
the group consisting of hydrogen, alkyl, substituted alkyl, phenyl,
substituted phenyl and R.sub.7 --(CO)-- wherein R.sub.7 is
hydrogen, alkyl, substituted alkyl, phenyl or substituted phenyl,
where R.sub.4, R.sub.5 and R.sub.6 can be the same or
different.
9. The solution according to claim 7 characterized in that it
contains formamidine sulfinic acid.
10. The solution according to claim 7, characterized in that it
contains aromatic sulfinic acids selected from the group consisting
of benzene sulfinic acid, toluene sulfinic acids, chlorobenzene
sulfinic acids, nitrobenzene sulfinic acids and carboxybenzene
sulfinic acids.
11. The solution according to claim 7, characterized in that it
contains at least one heterocyclic compound selected from the group
consisting of thiophenes, thiazoles, isothiazoles, thiadiazoles and
thiatriazoles.
12. The solution according to claim 11, characterized in that it
contains at least one thiophene selected from the group consisting
of compounds of chemical formula C: ##STR00011## wherein R.sub.8,
R.sub.9, R.sub.10, R.sub.11 are selected from the group consisting
of hydrogen, alkyl, substituted alkyl, phenyl, substituted phenyl,
halogen, amino, alkylamino, dialkylamino, hydroxy, alkoxy, carboxy,
carboxyalkyl, alkoxycarbonyl, aminocarbonyl and R.sub.12 --CONH--
wherein R.sub.12 is hydrogen, alkyl, substituted alkyl, phenyl or
substituted phenyl, where R.sub.8, R.sub.9, R.sub.10 and R.sub.11
can be the same or different and can be a part of the homo- or
heterocyclic ring condensed onto the thiophene ring.
13. The solution according to claim 11, characterized in that it
contains at least one thiophene selected from the group consisting
of aminothiophene carboxylic acids, their esters and amides.
14. The solution according to claim 11, characterized in that the
thiazole is selected from the group consisting of compounds of
chemical formula D: ##STR00012## wherein R.sub.13, R.sub.14,
R.sub.15 are selected from the group consisting of hydrogen, alkyl,
substituted alkyl, phenyl, substituted phenyl, halogen, amino,
alkylamino, dialkylamino, hydroxy, alkoxy, carboxy, carboxyalkyl,
alkoxycarbonyl, aminocarbonyl and R.sub.16 --CONH-- wherein
R.sub.16 is hydrogen, alkyl, substituted alkyl, phenyl or
substituted phenyl, where R.sub.13, R.sub.14 and R.sub.15 can be
the same or different and can be a part of the homo- or
heterocyclic ring condensed onto the thiazole ring.
15. The solution according to claim 11, characterized in that the
thiazole is selected from the group consisting of aminothiazoles
and substituted aminothiazoles.
16. The solution according to claim 11, characterized in that the
thiadiazole is selected from the group consisting of
aminothiadiazoles and substituted aminothiadiazoles.
17. The solution according to claim 7, characterized in that the
sulfonium salt is selected from the group consisting of
trimethylsulfonium salts, triphenylsulfonium salts, methionine
alkyl sulfonium salts and methionine benzyl sulfonium salts.
18. The solution according to claim 7, characterized in that the
nitrogen-containing, five-membered heterocyclic compound selected
from the group consisting of triazoles, tetrazoles, imidazoles,
pyrazoles and purines.
19. A solution according to claim 1, one of the preceding claims
wherein the amount of fluoride ions is at least 0.5 g/l, preferably
at least 2.0 g/l.
20. A solution according to claim 1, characterized in that the
fluoride ions are from a source selected from the group consisting
of sodium fluoride, potassium fluoride, ammonium fluoride and
tetrafluoro boric acid.
21. The solution according to claim 1, characterized in that
sulfuric acid is selected to be the acid for component b) in the
solution.
22. The solution according to claim 1, characterized in that the
amount of chloride ions is 15 to 25 mg per litre.
23. A process to pretreat copper alloy surfaces to allow a tight
bond to be subsequently formed between the copper alloy surfaces
and polymeric material in which the copper surfaces are brought
into contact with the solution according to claim 1.
24. A process to pretreat copper alloy surfaces according to claim
23 characterized in that the copper alloy contains at least one
alloying element selected from the group consisting of Si, Ni, Fe,
Zr, P, Sn and Zn.
25. A process according to claim 24 wherein the copper alloy
surface is on a lead frame and pretreated to create a tight bond
between the copper alloy layers and moulding compounds.
Description
[0001] The invention concerns a solution and a process to treat
copper alloy surfaces so that a tight bond can be subsequently
formed between the treated copper surfaces and polymeric material.
The solution preferably serves to treat surfaces of lead frames
made of copper alloys containing alloying elements selected from
the group of Si, Ni, Fe, Zr, P, Sn.
[0002] In manufacturing lead frames and printed circuit boards
alike, various steps are carried out in which copper surfaces must
be tightly bonded to an organic substrate. In some cases, the
required adhesion of the formed bonds must be ensured over a long
period. In other cases, a tight bond only has to exist for a short
period, e.g. when a polymeric material only remains on the copper
or copper alloy surfaces during manufacture of the workpiece.
[0003] The easiest way to increase the adhesion is to etch and
hence roughen the copper surfaces before forming the bond.
Microetching solutions have long been used in the production of
printed circuit boards and contain for example sulfuric acid
solutions of hydrogen peroxide or sodium peroxodisulfate.
[0004] Another procedure is described in U.S. Pat. No. 3,645,772. A
treatment solution is used for the copper surfaces that e.g.
contains 5-aminotetrazole.
[0005] Long-term stability is especially necessary when
encapsulating molding compounds (polymeric material) into lead
frames.
[0006] Various procedures for pretreating printed circuit boards
have been developed. Commonly, before lamination an oxide layer on
the copper surfaces is formed. In this process, known as the brown
or black oxide process, very aggressive reaction conditions are
used to form the oxide. A disadvantage of this procedure is that
the oxide layer used for enhancing adhesion to the polymeric
material is not very resistant to acid and especially to
hydrochloric treatment solutions. They are hence attacked in
subsequent processes for plating the through-holes in the boards.
The adhesive bond is eliminated, and delamination occurs at the
attacked sites (pink ring: An externally-visible attack on the
black oxide layer directly next to a hole in printed circuit boards
with the discoloration of the originally black oxide layer.
[0007] The above-cited problem is solved by reducing the oxide
layer surface before lamination. The reduced black oxide is more
stable than normal black oxide against chemicals used in plating
the through-holes. The additional reduction step costs a great
deal, however. In addition, the chemicals used for reduction are
not very resistant to oxidation from air, so that the useful life
of the baths and storage life of the supplementary chemicals are
limited. An attempt to eliminate this problem is made in JP A
08097559. The reduced copper oxide layers are provided with a
protective layer by treating them with an aqueous solution
containing an aminothiazole and/or aminobenzothiazole compound.
However, the problems of expensive reduction chemicals, their low
resistance to oxidation and the layer's sensitivity to acid are not
completely eliminated.
[0008] Another option for promoting adhesion is to treat the copper
surfaces with an aqueous or alcoholic solution of an azole
compound. Such a procedure is e.g. presented in WO 96/19097 A1. The
copper surfaces are treated with a solution that contains 0.1-20
weight percent hydrogen peroxide, an inorganic acid (e.g. sulfuric
acid), an organic corrosion inhibitor (e.g. benzotrizole), and a
wetting agent. The hydrogen peroxide etches the copper surface to
produce microrough surfaces.
[0009] U.S. Pat. No. 5,869,130 describes a process for treating
metal surfaces with a composition comprising an oxidizer, an acid,
a corrosion inhibitor, a source of halide ions and optionally a
water soluble polymer in order to increase the adhesion of
polymeric materials to the metal surface.
[0010] U.S. Pat. No. 6,562,149 B1 discloses processes and solutions
for the preliminary treatment of copper surfaces which are
subsequently to be firmly bonded to organic substrates. The
solution is used, in particular, for firmly bonding laminated
multilayered printed circuit boards and for firmly bonding resists
to the copper surfaces of printed circuit boards. The solutions
contain (a) hydrogen peroxide; (b) at least one acid; (c) at least
one nitrogen-containing, five-membered heterocyclic compound which
does not contain any sulphur, selenium or tellurium atom in the
heterocycle; and (d) at least one adhesive compound from the group
consisting of sulfinic acids, seleninic acids, tellurinic acids,
heterocyclic compounds containing at least one sulphur, selenium
and/or tellurium atom in the heterocycle, and sulfonium, selenonium
and telluronium salts.
[0011] However, as compared to the printed circuit board production
the common metallic substrates used for lead frames are copper
alloys with a certain, relatively low amount of alloying elements,
required to achieve the mechanical and electrical properties
sought.
[0012] Some alloys, however, are only partially attacked or with a
reduced reaction rate. This leads to unsatisfactory roughness or
insoluble residues or smut on the alloy surface. The result in both
cases in a non optimized adhesion improvement achieved by the
process.
[0013] The present invention is therefore based on the problem of
avoiding the disadvantages of the state of the art and finding a
treatment solution and a process that can create a tight bond
between the copper alloy surfaces and polymeric material surfaces
and is at the same time suitable to treat a wide range of different
copper alloy compositions. The process should be simple, easy to
use, and inexpensive. It is also important that treatment with the
solutions produce a material bond that is not problematic (no smut
formation, decomposition of the pre-treatment solution etc.). The
used treatment solutions should therefore be particularly suitable
for manufacturing lead frames.
[0014] This problem is solved by the solution cited in claim 1 and
the treatment process cited in claim 23.
[0015] The solution according to the invention is for treating
copper alloy surfaces to allow a tight bond to be formed with
plastic materials, and it comprises: [0016] a) an oxidant [0017] b)
at least one acid [0018] c) at least one adhesion-enhancing
compound [0019] d) fluoride ions in an amount of more than 100 mg
per litre [0020] e) chloride ions in an amount of 5 to 40 mg per
litre.
[0021] Adhesion-enhancing compounds are to be selected that are
sufficiently soluble in the acidic, preferably sulfuric acid
solution.
[0022] The process according to the invention is carried out by
bringing the copper alloy surfaces into contact with the
solution.
[0023] The solution is also suitable for treatment of copper alloy
surfaces, thereafter depositing a second metal layer on the such
treated copper alloy surface and finally bond a polymeric material
thereto. The second metal layer can for example be a deposit of
Ni--Pd--Au or Ag, forming a solderable layer.
[0024] By roughening the copper alloy surface with a treatment
solution according to claim 1, the adhesion properties of the
polymeric material to the second metal layer are also greatly
enhanced, which can be seen from the Example 4.
[0025] Preferred embodiments of the invention are the
subject-matter of dependent claims 2-22.
[0026] For example adhesion-enhancing compounds selected from the
group consisting of triazoles, benzotriazoles, imidazoles,
tetrazoles, purines and mixtures thereof may be used. These
compounds react with the copper alloy surfaces to form a protective
complex layer.
[0027] Preferred tetrazole compounds are 5-aminotetrazole and
5-phenyltetrazole. A preferred imidazole compound may be
benzimidazole. 5-aminotetrazole, 5-phenyltetrazole, benzotriazole,
methylbenzotriazole and ethylbenzotriazole are preferred compounds
given their favorable solubility in the treatment solution and
their availability. Preferred combinations are benzotriazole,
methylbenzotriazole, ethylbenzotriazole, 5-aminotetrazole and
5-phenyltetrazole as the nitrogen-containing, heterocyclic
compounds with aminothiophene carboxylic acids, their esters and
amides, aminothiazoles and substituted aminothiazoles as the
heterocyclic compounds.
[0028] In order to improve the long-term stability of the bond
between the metal surface and the polymeric material, a mixture of
at least one nitrogen-containing, five-membered heterocyclic
compound that does not contain sulfur, selenium or tellurium atoms
in the heterocycle and at least one adhesion-promoting compound
selected from the group consisting of sulfinic acids, selenic
acids, telluric acids, heterocyclic compounds that contain at least
one sulfur, selenium and/or tellurium atom in the heterocycle, as
well as sulfonium, selenonium and telluronium salts, where the
sulfonium, selenonium and telluronium salts are compounds of
general formula A:
##STR00001##
where A is S, Se or Te, R.sub.1, R.sub.2 and R.sub.3 is alkyl,
substituted alkyl, alkenyl, phenyl, substituted phenyl, benzyl,
cycloalkyl and substituted cycloalkyl, where R.sub.1, R.sub.2 and
R.sub.3 can be the same or different, and X.sup.- is the anion of
an inorganic or organic acid or hydroxide, with the proviso that
the acid according to component b) is not identical to a sulfinic,
selenic or telluric acid according to component d), is applied.
[0029] Preferred sulfinic acids are compounds of chemical formula
B:
##STR00002##
wherein R.sub.4, R.sub.5 and R.sub.6 are selected from the group
consisting of hydrogen, alkyl, substituted alkyl, phenyl,
substituted phenyl and R.sub.7 --(CO)-- wherein R.sub.7 is
hydrogen, alkyl, substituted alkyl, phenyl or substituted phenyl,
where R.sub.4, R.sub.5 and R.sub.6 can be the same or
different.
[0030] It is preferable for the solution to contain formamidine
sulfinic acid. Preferable aromatic sulfinic acids are benzene
sulfinic acid, toluene sulfinic acids, chlorobenzene sulfinic
acids, nitrobenzene sulfinic acids and carboxybenzene sulfinic
acids.
[0031] Other preferable adhesion-promoting heterocyclic compounds
are thiophene, thiazole, isothiazole, thiadiazole and
thiatriazole.
[0032] Suitable thiophenes are compounds of chemical formula C:
##STR00003##
wherein R.sub.8, R.sub.9, R.sub.10, R.sub.11 are selected from the
group consisting of hydrogen, alkyl, substituted alkyl, phenyl,
substituted phenyl, halogen, amino, alkylamino, dialkylamino,
hydroxy, alkoxy, carboxy, carboxyalkyl, alkoxycarbonyl,
aminocarbonyl and R.sub.12 --CONH-- wherein R.sub.12 is hydrogen,
alkyl, substituted alkyl, phenyl or substituted phenyl, where
R.sub.8, R.sub.9, R.sub.10 and R.sub.11 can be the same or
different and can be a part of the homo- or heterocyclic ring
condensed onto the thiophene ring.
[0033] Particularly preferred thiophenes are aminothiophene
carboxylic acids, their esters and amides. For example,
3-aminothiophene-2-carboxylic acid methyl ester can be
advantageously used.
[0034] Suitable thiazoles are compounds of chemical formula D:
##STR00004##
wherein R.sub.13, R.sub.14, R.sub.15 are selected from the group
consisting of hydrogen, alkyl, substituted alkyl, phenyl,
substituted phenyl, halogen, amino, alkylamino, dialkylamino,
hydroxy, alkoxy, carboxy, carboxyalkyl, alkoxycarbonyl,
aminocarbonyl and R.sub.16 --CONH-- wherein R.sub.16 is hydrogen,
alkyl, substituted alkyl, phenyl or substituted phenyl, where
R.sub.13, R.sub.14 and R.sub.15 can be the same or different and
can be a part of the homo- or heterocyclic ring condensed onto the
thiazole ring.
[0035] Particularly suitable thiazoles are aminothiazole and
substituted aminothiazole.
[0036] Other preferred thiadiazole adhesion-promoting compounds are
from the group consisting of aminothiadiazoles and substituted
aminothiadiazoles.
[0037] In addition, the preferred sulfonium salts are salts of
trimethylsulfonium, triphenylsulfonium, methionine alkylsulfonium
and methionine benzylsulfonium.
[0038] The nitrogen-containing, five-member heterocyclic compounds
that do not contain any sulfur, selenium or tellurium atom in the
heterocycle can be monocyclic and polycyclic condensed ring
systems. For example, the compounds can contain an anellated
benzene, naphthalene or pyrimidine ring provided that they are
sufficiently soluble in the acid solution. It is preferable for the
solution to contain triazoles, tetrazoles, imidazoles, pyrazoles
and purines or their derivatives.
[0039] In particular, the solution contains triazoles of chemical
formula E1:
##STR00005##
wherein R.sub.17, R.sub.18 are selected from the group consisting
of hydrogen, alkyl, substituted alkyl, amino, phenyl, substituted
phenyl and carboxyalkyl, where R.sub.17 and R.sub.18 can be the
same or different and can be a part of the homo- or heterocyclic
ring condensed onto the triazole ring.
[0040] Benzotriazole, methylbenzotriazole, ethylbenzotriazole and
dimethylbenzotriazole are particularly preferable.
[0041] In addition, the solution can contain tetrazoles of chemical
formula E2:
##STR00006##
wherein R.sub.19 is selected from the group consisting of hydrogen,
alkyl, substituted alkyl, halogenalkyl, amino, phenyl, substituted
phenyl, benzyl, carboxy, carboxyalkyl, alkoxycarbonyl,
aminocarbonyl and R.sub.20 --CONH wherein R.sub.20 is hydrogen,
alkyl, substituted alkyl, phenyl or substituted phenyl.
[0042] Preferred tetrazole compounds are 5-aminotetrazole and
5-phenyltetrazole. A preferred imidazole compound may be
benzimidazole. 5-aminotetrazole, 5-phenyltetrazole, benzotriazole,
methylbenzotriazole and ethylbenzotriazole are preferred compounds
given their favorable solubility in the treatment solution and
their availability.
[0043] Preferred combinations are benzotriazole,
methylbenzotriazole, ethylbenzotriazole, 5-aminotetrazole and
5-phenyltetrazole as the nitrogen-containing, heterocyclic
compounds with aminothiophene carboxylic acids, their esters and
amides, aminothiazoles and substituted aminothiazoles as the
heterocyclic compounds.
[0044] The process according to the invention is an extremely easy
way to treat copper alloy surfaces to allow them to tightly bond
with polymeric materials. Basically one step is necessary, i.e.,
treating the copper or copper alloy surface with the solution
according to the invention to allow them to bond with polymeric
materials. The adhesion does not decrease even after a long time.
Particularly preferred solutions are the subject-matter of claim
7.
[0045] The advantageous effect of the solution according to the
invention was surprising since it was found that relatively small
amounts of chloride and bromide of 50 mg/l and above already
strongly reduce the functionality of the etching solution. Applying
such solutions is disclosed in the prior art (U.S. Pat. No.
5,869,130) for treating copper surfaces but is not suitable to etch
copper alloy surfaces which is the subject of the present
invention.
[0046] In contrast, the addition of fluoride improves the complete
attack onto these alloys and leads to the desired roughness
properties of the copper alloy surface. Alloys containing Si in
particular, are most effectively treated, as the Si smut on the
surface as well as in the solution is removed within the etching
solution itself. Without the addition of fluoride, insoluble
residues are formed, which lead to low adhesion values and uneven
appearance, not acceptable in lead frame manufacturing. Furthermore
the alloying elements often result in a decrease of the stability
of the treatment solution. Dissolved iron for example catalyses the
decomposition of hydrogen peroxide. Surprisingly, addition of
fluoride prevents such decomposition while in contrast chloride and
bromide do not reduce the decomposition rate of the treatment
solution.
[0047] The properties of lead frame alloy surfaces become more and
more important as a result of the lead free soldering applications
for the electronic industry. Lead free soldering generates higher
temperatures to the electronic components. Because of higher
soldering temperatures the risk of the "popcorn effect" rises. This
effect arises, when humidity penetrates the device and the water
evaporates explosively upon heating during the post-treatment steps
and destroys the bond between the polymeric material and the metal
surface. This effect destroys electronic devices. A good adhesion
of the polymeric material to the metal substrate minimizes the risk
of the "popcorn effect" to occur.
[0048] As a result of the good adhesion gained by applying the
solution according to the present invention, no air moisture can
penetrate into the interface polymeric material/metal
substrate.
[0049] The fluoride ion amount additionally affects the etch rate
of the metal surface. In a certain range increase in the fluoride
ion concentration results in an increased etch rate. Applying the
solution according to Example 1 with a sodium fluoride
concentration of 2.5 g/l results in an etch rate of 1.0 .mu.m/min.
If the solution contains 5.0 g/l sodium fluoride the etch rate is
increased to 1.6 .mu.m/min. Thereafter, further increasing the
fluoride ion concentration does not affect the etch rate
significantly. It has to be pointed out that the optimum amount of
fluoride ions for a given metal depends on its composition and can
be determined individually by standard measurement methods.
[0050] As mentioned above, the solution according to the present
invention also comprises chloride ions in an amount of 5 to 40 mg
per litre. It was discovered that the chloride ions have a
beneficial effect on the roughness of the surface to which the
solution according to the present invention is applied.
Particularly good results are obtained when the concentration of
chloride ions is in the range of 15 to 25 mg per litre.
[0051] In the present invention the adhesion between the alloy
substrate and the polymeric material is measured quantitatively in
values N/mm.sup.2.
[0052] The peel strength was measured by pushing "Mold tablets"
after curing and hardening, with a contact area to the test surface
of 10 mm.sup.2 with a Dage 4000 equipment, using a shear speed of
0.2 mm/s. The test was performed at 20.degree. C.
[0053] In the production of lead frames, an important and widely
used Si-containing alloy is C7025. Besides Cu and Ni it contains up
to 1.2% of silicon.
[0054] Another alloy which is particularly preferred for use in the
present invention is C194. It contains 97% of Cu, 2.3% of Fe and
0.1% of Mn. Like the above mentioned C7025 alloy, C194 is used in
the production of lead frames.
[0055] The copper alloy surfaces should first be cleaned to ensure
that the treatment is effective. Any conventional cleaning solution
can be used. Normally, wetting agents and sometimes complexing
agents (such as triethanol-amine)-containing aqueous solutions are
used.
[0056] After the cleaned copper alloy surfaces are rinsed, they can
be brought into contact with a so-called predipping solution that
contains one of the five-membered heterocyclic compounds dissolved
in water, preferably at a concentration of 0.1-10 g/l, and
especially 0.5-2 g/l. This treatment helps the adhesion-promoting
layer to be formed in the subsequent treatment step. In particular,
any delays in the formation of the layer are avoided. The layer
starts forming directly when the surface contacts the solution of
the invention.
[0057] The surfaces are then treated with the solution according to
the invention without being rinsed beforehand.
[0058] The microetching by the oxidant, preferably hydrogen
peroxide in connection with the acid yields microrough copper alloy
surfaces. Since this increases the surface area, the subsequent
adhesion of the copper alloy surfaces to the polymeric material
also increases. The change in color of the surface during treatment
is caused by a thin copper oxide layer. It is preferable for the
acid in the solution according to the invention to be an inorganic
acid, and especially sulfuric acid. Other acids can of course be
used.
[0059] The treatment is preferably carried out at 20-60.degree. C.
The treatment time is preferably 10-600 sec. The higher the
temperature, the faster-acting the solution. The treatment times
can hence even be much shorter. From a practical standpoint, a
preferable average temperature would be 35-45.degree. C. to better
control the reaction. Average treatment times are 20-90 sec. In
addition, a top temperature limit may have to be set due to
possible incompatibilities between certain solution components at
high temperatures, e.g., wetting agents that have difficulty
dissolving at high temperatures.
[0060] The preferable concentration ranges in the solution are:
TABLE-US-00001 Sulfuric acid, conc. 10-250 g/l Hydrogen peroxide,
30 weight percent 1-100 g/l
[0061] Adhesion-enhancing compound:
TABLE-US-00002 triazoles, benzotriazoles, imidazoles, 0.5-50 g/l
tetrazoles and mixtures thereof purines 0.5-50 g/l
[0062] Further components:
TABLE-US-00003 Sulfinic, selenic and/or telluric acid 0.05-10 g/l
Adhesion-promoting heterocyclic 0.05-20 g/l compound Sulfonium,
selenonium 0.01-10 g/l and/or telluronium salts fluoride ions
0.2-25 g/l, more preferred 1-10 g/l, most preferred 2-5 g/l
Chloride ions 5-40 mg/l, preferably 15-25 mg/l
[0063] After they are treated with the solution according to the
invention, the copper surfaces are rinsed. Then they are dried,
e.g. with hot air.
[0064] The workpieces, for example lead frames, with the copper or
copper alloy surfaces can be treated in conventional dipping
systems.
[0065] The following examples serve further to clarify the
invention:
EXAMPLE 1
[0066] An aqueous solution was created by mixing the following
components:
TABLE-US-00004 Sulfuric acid, 96 weight percent 50 ml Hydrogen
peroxide, 40 ml 30 weight percent in water Benzotriazole 10 g
Formamidine sulfinic acid 0.5 g Sodium fluoride 5.0 g Sodium
chloride 33 mg Deionized water added to 1 l.
[0067] The solution was heated to 40.degree. C., and a copper alloy
surface (lead frame C7025) containing Cu, Ni (2.2-4.2%), Si
(0.25-1.2%) and small amounts of Mg and Zn was dipped in the
solution for 60 sec. After being treated, the alloy was rinsed with
deionized water and finally dried.
[0068] Thereafter as polymeric material a commercially available
mold (KMC-289, Shinetsu) was applied to such treated alloy surface,
dried and hardened at a temperature of 175.degree. C.
[0069] The peel strength of the lead frame was measured by a button
shear test. An adhesion value of 18.5 N/mm.sup.2 was found. The
measured roughness, expressed in RSAI (Relative Surface Area
Increase) was 44%.+-.3% (absolute).
COMPARATIVE EXAMPLE 2
[0070] Example 1 was repeated with a solution that did not contain
sodium fluoride.
[0071] The lead frame surface shows black smut which can easily be
taken away by finger wiping. On this sample a peel adhesion value
of only 9.1 N/mm.sup.2 was obtained. The measured roughness was
42%.+-.3% (absolute).
COMPARATIVE EXAMPLE 3
[0072] Example 1 was repeated with a solution that did not contain
sodium chloride.
[0073] The lead frame surface shows not black smut, but the
roughness was reduced to lower than 12% RSAI. The peel adhesion
value was always below 5 N/mm.sup.2.
EXAMPLE 4
[0074] An aqueous solution was created by mixing the following
components:
TABLE-US-00005 Sulfuric acid, 96 weight percent 50 ml Hydrogen
peroxide, 40 ml 30 weight percent in water Benzotriazole 10 g
Formamidine sulfinic acid 0.5 g Sodium fluoride 5.0 g Sodium
chloride 33 mg Deionized water added to 1 l.
[0075] The solution was heated to 40.degree. C., and a copper alloy
surface (lead frame C7025) containing Cu, Ni (2.2-4.2%), Si
(0.25-1.2%) and small amounts of Mg and Zn was dipped in the
solution for 60 sec. After being treated, the alloy was rinsed with
deionized water and finally dried.
[0076] Thereafter, a layer of Ni--Pd--Au was deposited on the
treated copper alloy surface utilizing a commercially available
metallization process (Atotech Deutschland GmbH).
TABLE-US-00006 Soak cleaner 50.degree. C. 3 min Rinsing Cath.
Degreaser 40.degree. C. 60 sec Rinsing 5% H2SO4 Nickel sulphamat HS
60.degree. C. 40 sec (thickness of deposited Rinsing Ni-layer ~0.7
.mu.m) Pallacor PPF 35.degree. C. 2 sec (thickness of deposited
Rinsing Pd-layer ~0.03 .mu.m) Aurocor PPF 35.degree. C. 1 sec
(thickness of deposited Rinsing, drying Au- layer ~0.005 .mu.m)
[0077] Finally, as polymeric material a commercially available mold
(KMC-289, Shinetsu) was applied to such treated alloy surface,
dried and hardened at a temperature of 150.degree. C.
[0078] An adhesion value was achieved which is slightly smaller
than that according to Example 1.
COMPARATIVE EXAMPLE 5
[0079] Example 4 was repeated but with a solution that did not
contain sodium fluoride.
[0080] The lead frame surfaces shows smut residues and had
therefore to be cleaned in an additional post treatment step
utilizing 50 ml/l H.sub.2SO.sub.4 96%, 20 g/l sodium
peroxodisulfate and 4 g/l sodium fluoride instead of 5%
H.sub.2SO.sub.4 prior to metallization with Ni--Pd--Au. As a result
only a poor peel adhesion value was obtained.
* * * * *