U.S. patent application number 11/757190 was filed with the patent office on 2007-11-29 for process for producing an article with a coating of electrically conductive polymer.
This patent application is currently assigned to ORMECON GMBH. Invention is credited to Bernhard Wessling.
Application Number | 20070275159 11/757190 |
Document ID | / |
Family ID | 34975185 |
Filed Date | 2007-11-29 |
United States Patent
Application |
20070275159 |
Kind Code |
A1 |
Wessling; Bernhard |
November 29, 2007 |
PROCESS FOR PRODUCING AN ARTICLE WITH A COATING OF ELECTRICALLY
CONDUCTIVE POLYMER
Abstract
A process for producing a coated article, which has (i) at least
one electrically non-conductive base layer, (ii) at least one layer
of copper and/or a copper alloy, and (iii) a layer which contains
at least one electrically conductive polymer. The article is
characterized in that the copper or copper alloy layer (ii) is
positioned between the base layer (i) and the layer (iii)
containing the conductive polymer.
Inventors: |
Wessling; Bernhard;
(Bargteheide, DE) |
Correspondence
Address: |
SWANSON & BRATSCHUN, L.L.C.
8210 SOUTHPARK TERRACE
LITTLETON
CO
80120
US
|
Assignee: |
ORMECON GMBH
Ferdinand-Harten-Str. 7
Ammersbek
DE
22949
|
Family ID: |
34975185 |
Appl. No.: |
11/757190 |
Filed: |
June 1, 2007 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
11165411 |
Jun 23, 2005 |
|
|
|
11757190 |
Jun 1, 2007 |
|
|
|
Current U.S.
Class: |
427/96.1 ;
427/299; 427/331; 427/97.7 |
Current CPC
Class: |
Y10T 428/26 20150115;
Y10T 428/12903 20150115; Y10T 428/265 20150115; Y10T 428/31678
20150401; Y10T 428/31681 20150401; H05K 2201/0329 20130101; C09D
5/24 20130101; Y10T 428/12882 20150115; H05K 3/282 20130101 |
Class at
Publication: |
427/096.1 ;
427/097.7; 427/299; 427/331 |
International
Class: |
B05D 5/12 20060101
B05D005/12; B28B 19/00 20060101 B28B019/00; C23C 30/00 20060101
C23C030/00; H01C 17/06 20060101 H01C017/06 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 23, 2004 |
DE |
102004030388.6 |
Claims
1. A process for the production of a coated article comprising: (1)
applying a layer of one of copper and a copper-containing alloy
onto the surface of an electrically non-conductive base layer; (2)
structuring the layer produced in step (1); and (3) applying a
layer which contains at least one intrinsically conductive polymer
onto the structured copper or copper alloy layer.
2. The process according to claim 1, further comprising cleaning
the copper or copper alloy layer following step (1).
3. The process according to claim 1, further comprising subjecting
the copper or copper alloy layer to an oxidative pretreatment after
at least one of step (1) of claim 1 or a cleaning of the copper or
copper alloy layer following step (1).
4. The process according to claim 1, wherein the layer applied in
step (3) has a layer thickness of 10 nm to 1 .mu.m.
5. The process according to claim 4, wherein the layer applied in
step (3) has a layer thickness of less than 500 nm.
6. The process according to claim 5, wherein the layer applied in
step (3) has a layer thickness of less than 200 nm.
7. The process according to claim 1, wherein the layer applied in
step (3) contains 5 wt. % to 98 wt. % of intrinsically conductive
polymer, based on the mass of the layer applied in step (3).
8. The process according to claim 1, wherein the layer applied in
step (3) further comprises an electrically non-conductive
polymer.
9. The process according to claim 8, wherein the layer applied in
step (3) contains at least one complexing agent capable of
complexing copper in addition to the at least one electrically
non-conductive polymer.
10. The process according to claim 9, wherein the complexing agent
is selected from the group consisting of benzimidazoles,
imidazoles, benzotriazoles, thiourea, imidazole-2-thiones and
mixtures thereof.
11. The process according to claim 1, wherein the intrinsically
conductive polymer is selected from the group consisting of
polyaniline (PAni), polythiophene (PTh), polypyrrole (PPy),
poly(3,4-ethylenedioxythiophenes) (PEDT), polythieno-thiophene
(PTT), derivatives thereof and mixtures thereof.
12. The process according to claim 1, wherein a polymer blend with
a content of at least one intrinsically conductive polymer is used
as the intrinsically conductive polymer.
13. The process according to claim 1, wherein the base layer
contains a material selected from the group consisting of epoxide,
epoxide composite, Teflon, cyanate ester, ceramic, cellulose,
cellulose composite, cardboard and polyimide.
14. The process according to claim 1, wherein the base layer has a
layer thickness of 0.1 to 3 mm.
15. The process according to claim 1, wherein the base layer has a
layer thickness of 5 to 210 .mu.m.
16. The process according to claim 1, further comprising: (4)
applying a metal or alloy layer, which is positioned between the
layer applied in step (1) and the layer applied in step (3).
17. The process according to claim 16, wherein the layer applied in
step (4) contains a material selected from the group consisting of
silver, tin, gold, palladium and platinum.
18. The process according to claim 16, wherein the layer applied in
step (4) has a layer thickness of 10 to 800 nm.
19. A method of preparing a printed circuit board comprising using
a dispersion which contains a dispersion medium which is liquid at
room temperature and contains an electrically conductive polymer,
to prevent one of the corrosion of the printed circuit board and
loss of the solderability of the printed circuit board.
20. The method according to claim 19, wherein the dispersion
contains at least one further component, which is selected from a
group consisting of electrically non-conductive components,
complexing agents, viscosity modifiers, flow aids, drying aids,
gloss improvers, and flatting agents.
21. The method according to claim 19, wherein the dispersion medium
contains at least one of water and an organic solvent miscible with
water.
Description
RELATED APPLICATION DATA
[0001] This application is a divisional of U.S. patent application
Ser. No. 11/165,411, filed Jun. 23, 2005, entitled ARTICLE WITH A
COATING OF ELECTRICALLY CONDUCTIVE POLYMER AND PROCESS FOR
PRODUCTION THEREOF, which application claims benefit of commonly
assigned and copending German Patent Application Serial Number 10
2004 030 388.6, filed Jun. 23, 2004, entitled ARTICLE WITH A
COATING OF ELECTRICALLY CONDUCTIVE POLYMER AND PROCESS FOR
PRODUCTION THEREOF, which applications are incorporated herein in
their entirety by reference.
TECHNICAL FIELD
[0002] The present invention concerns the production of coated
articles which contain a layer of copper or a copper alloy and a
layer of an electrically conductive polymer and which are
particularly suitable as printed circuit boards or for the
production of printed circuit boards.
BACKGROUND ART
[0003] Copper is one of the most widely used metallic materials of
our time. Although copper is a semiprecious metal, this material is
readily oxidizable, which often has an adverse effect on its use
properties. This manifests itself not only visually but also has in
particular practical technical disadvantages. Particular problems
arise in the coating of printed circuit boards, which are then
assembled in soldering processes, copper wires which are used as
electrical conductors, or copper pipes. Finely divided copper
powders are practically impossible to produce and use without
oxidation protection.
[0004] Copper is normally not provided with protective coatings
like iron and steel, which in the case of lacquers often have to be
applied in several layers. Instead, as protection against copper
corrosion, substances which form complexes with copper, such as for
example imidazoles, benzimidazoles, benzotriazoles, thiourea and
imidazole-2-thione, are predominantly used.
[0005] Such organic complexing agents are admittedly inexpensive
and easy to process, however they display a number of
disadvantages. Thus formulations with imidazoles or benzimidazoles
often contain formic acid and sometimes other organic acids which
smell unpleasant, are corrosive and have toxicological
disadvantages. In addition, the thermal stability is low.
[0006] Therefore, in the production of printed circuit boards, for
protection against corrosion copper is often coated with other
metals such as for example gold, silver or tin, in order to
preserve the solderability of the copper contacts and the
copper-plated drill holes, which is lost in a very short time
through oxidation.
[0007] An overview of common solderable final surfaces and their
technical, economic, ecological and toxicological advantages and
disadvantages are disclosed in "Alternative Technologies for
Surface Finishing--Cleaner Technology for Printed Wired Board
Manufacturers", EPA, Office of Pollution Prevention and Toxics,
June 2001, EPA 744-R-01-001.
[0008] Metallic coatings are in general very suitable for printed
circuit boards, however they also display a number of
disadvantages. Coatings with gold are expensive not only on account
of the high gold price, but in addition require special processes
for the application of the gold layer. For example, gold cannot
chemically be applied in so-called horizontal plants but only in
vertical plants, which results in additional high process
costs.
[0009] The application of silver is poorly reproducible, and the
necessary plants are difficult to regulate.
[0010] Tin is admittedly satisfactory from the technical and
economic point of view in particular when it is applied with the
aid of an organic metal, such as for example in the ORMECON
CSN-process of Ormecon GmbH, however its deposition as a rule
requires several minutes, which renders correspondingly large-sized
plants necessary in order to ensure a high throughput.
[0011] From EP 0 807 190 B1, a process for the production of
metallized materials is known, wherein the material to be
metallized is first coated with an intrinsically conductive
polymer, the intrinsically conductive polymer is then activated by
reduction and finally the metal is applied in a non-electrochemical
manner, in that the coated material is brought into contact with a
solution of ions of the metal. The process is particularly suitable
for the deposition of tin onto copper but also for the
metallization of plastic surfaces.
[0012] EP 0 407 492 B1 discloses a process for the coating of
substrates with thin layers of intrinsically conductive polymers,
wherein for example polyaniline is non-electro-chemically deposited
from a metastable dispersion onto a substrate. As substrates, inter
alia metals such as gold, platinum, iron, copper and aluminium are
mentioned. With metals that are less noble than silver, the layers
of conductive polymer lead to the formation of metal oxide layers
and should be suitable inter alia for corrosion protection.
[0013] EP 0 656 958 B1 concerns a process for the production of
corrosion-protected metallic materials such as iron, steel, copper
and aluminium, wherein a layer of an intrinsically conductive
polymer is applied onto a metallic material and then the coated
material is passivated with oxygen-containing water. It is pointed
out that the application of the conductive polymer alone does not
guarantee adequate corrosion protection, and the metallic material
is therefore preferably provided with a corrosion-protecting
coating after the passivation. The conductive polymer can be
removed again before the application of the corrosion-protecting
coating.
SUMMARY OF THE INVENTION
[0014] The object of the invention is to make available coated
articles which contain a layer of copper or a copper alloy, wherein
on the one hand the copper or the copper alloy is effectively
protected against oxidation and on the other hand a loss of the
solderability of the copper or the copper alloy during storage is
prevented.
[0015] This object is achieved through a process for producing a
coated article which has [0016] (i) at least one electrically
nonconductive base layer, [0017] (ii) at least one layer of copper
and/or a copper alloy, and [0018] (iii) a layer which contains at
least one electrically conductive polymer.
[0019] The article is characterized in that the copper or copper
alloy layer (ii) is positioned between the base layer (i) and the
layer (iii) containing the conductive polymer.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 is a simplified plan view of a printed circuit board
featuring a test design.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0021] The solution according to the invention is surprising in
that, as was not to be expected with regard to the state of the
art, the coating with an electrically conductive polymer alone
would allow an effective protection of copper against oxidation and
corrosion. Certainly no improvement as regards the preservation of
the solderability of copper and copper alloys was to be expected.
According to the state of the art, layers of conductive polymer
cause the formation of thin metal oxide layers on the surface of
metals which are less noble than silver. The formation of such
oxide layers is however substantially held responsible for the loss
of the solderability of copper.
[0022] The thickness of the layer (iii) is preferably less than 1
.mu.m, which contradicts the general expectation, according to
which a larger effect would be achieved with thicker layers. The
thickness of the layer (iii) is preferably at least about 10 nm.
Particularly preferred are layer thicknesses less than 500 nm,
particularly preferably less than 200 nm.
[0023] The layer contains at least one electrically conductive
polymer, which is preferably used in the form of an organic metal.
Combinations of different substances from this substance class can
be used. In the context of this invention, if not otherwise stated,
polymers are understood to mean organic polymers.
[0024] Electrically conductive polymers or conductive polymers,
which are also described as "intrinsically conductive polymers",
are understood to mean substances which are built up of small
molecule compounds (monomers), are at least oligomeric by
polymerization, and thus contain at least 3 monomer units which are
linked by chemical bonding, display a conjugated Tr-electron system
in the neutral (nonconductive) state and can be converted by
oxidation, reduction or protonation (which is often described as
"doping") into an ionic form which is conductive. The conductivity
is at least 10.sup.-7 S/cm and is normally less than 10.sup.5
S/cm.
[0025] As doping agents, for example iodine, peroxides, Lewis and
protic acids are used in the case of doping by oxidation, or for
example sodium, potassium, calcium in the case of doping by
reduction.
[0026] Conductive polymers can be chemically exceptionally diverse
in composition. As monomers, for example acetylene, benzene,
naphthalene, pyrrole, aniline, thiophene, phenylene sulphide,
peri-naphthalene and others, and derivatives thereof, such as
sulpho-aniline, ethylenedioxythiophene, thieno-thiophene and
others, and alkyl or alkoxy derivatives thereof or derivatives with
other side-groups, such as sulphonate, phenyl and other
side-groups, have proved useful. Combinations of the aforesaid
monomers can also be used as monomers. For this, for example
aniline and phenylene sulphide are linked, and these A-B dimers
then used as monomers. Depending on the objective, for example
pyrrole, thiophene or alkylthiophenes, ethylenedioxythiophene,
thieno-thiophene, aniline, phenylene sulphide and others can be
bound together into A-B structures and these then converted into
oligomers or polymers.
[0027] Most conductive polymers display a more or less strong rise
in conductivity with increasing temperature, which identifies them
as non-metallic conductors. Other conductive polymers display a
metallic behaviour at least in a temperature range close to room
temperature in that their conductivity decreases with increasing
temperature. A further method of recognizing metallic behaviour
consists in the plotting of the so-called "reduced activation
energy" of the conductivity against the temperature at low
temperatures (down to near 0 K). Conductors with a metallic
contribution to the conductivity display a positive gradient of the
curve at low temperature. Such substances are described as "organic
metals".
[0028] Organic metals are known per se. According to WeBling et
al., Eur. Phys. J. E 2, 2000, 207-210, the transition from the
state of a nonmetallic to an at least partially metallic conductor
can be effected by a single-step frictional or dispersion procedure
after completion of the synthesis of the intrinsically conductive
polymer, the process technology basis whereof is described in EP 0
700 573 A. In this way, through the dispersion procedure the
conductivity is also increased, without the chemical composition of
the conductive polymer used being significantly altered.
[0029] Preferred intrinsically conductive polymers are those
mentioned above. In particular, the following can be mentioned as
examples: polyaniline (PAni), polythiophene (PTh),
poly(3,4-ethylenedioxy-thiophens) (PEDT), polydiacetylene,
polyacetylene (PAc), poly-pyrrole (PPy), polyisothianaphthene
(PITN), polyheteroarylene-vinylene (PArV), wherein the
heteroarylene group can for example be thiophene, furan or pyrrole,
poly-p-phenylene (PpP), polyphenylene sulphide (PPS),
polyperinaphthalene (PPN), polyphthalocyanine (PPc) and others, and
derivatives thereof (which are for example formed with monomers
substituted with side-chains or -groups), copolymers thereof and
physical mixtures thereof. Particularly preferred are polyaniline
(PAni), polythiophene (PTh), polypyrrole (PPy),
poly(3,4-ethylenedioxythiophenes) (PEDT), polythieno-thiophene
(PTT) and derivatives thereof and mixtures thereof. Most preferred
is polyaniline.
[0030] The layer (iii) can consist exclusively of one or several
conductive polymers and/or organic metals or contain mixtures of
one or more conductive polymers with other substances such as
electrically non-conductive components. According to a preferred
version, the layer (iii) contains polymer blends, that is mixtures
of conductive polymer/organic metal (or a combination of several)
with electrically non-conductive polymers. Particularly suitable as
non-conductive polymers are water-soluble or water-dispersible
polymers, in particular polystyrene-sulphonic acid, polyacrylates,
polyvinyl butyrates, polyvinyl-pyrrolidones, polyvinyl alcohols and
mixtures thereof. Conductive and non-conductive polymers are
preferably used in the ratio of 1:1.5 to 1:20.
[0031] The layer (iii) can also contain further additives, in
particular viscosity modifiers, flow aids, drying aids, gloss
improvers, flatting agents and mixtures thereof, preferably in a
concentration of 0.10 to 5 wt. % additive based on the mass of the
layer (iii). The layer (iii) preferably contains 5 to 98 wt. %, in
particular 15 to 40 wt. % of conductive polymer, based on the mass
of the layer (iii).
[0032] It has been found that a combination of the conductive
polymer(s)/organic metal(s) with complexing agents such as are
capable of complexing copper can be advantageous. Preferred
complexing agents are imidazoles, benzimidazoles or comparable
complexing agents, such as benzotriazoles, thiourea,
imidazole-2-thione and mixtures thereof, which are characterized by
relatively good thermal stability.
[0033] As base layer (i), all materials used in printed circuit
board technology are suitable, in particular epoxides and epoxide
composites, Teflon, cyanate esters, ceramics, cellulose and
cellulose composites, such as for example cardboard, materials
based on these substances and flexible base layers, for example
based on polyimide. The base layer preferably has a layer thickness
of 0.1 to 3 mm.
[0034] The copper layer or copper alloy layer (ii) preferably has a
thickness of 5 to 210 .mu.m, in particular 15 to 35 .mu.m.
[0035] Between the layer (ii) and the layer (iii), a further metal
or alloy layer (iv) can be positioned. The layer (iv) preferably
contains silver, tin, gold, palladium or platinum. According to a
preferred version, the layer (iv) contains mainly, i.e. more than
50 wt. % based on the mass of the layer (iv), one or several of the
said metals. The said metals can in particular be present as an
alloy with copper. According to another preferred version, the
layer (iv) consists exclusively of the said metals, either in pure
form or in the form of an alloy. The layer (iv) preferably has a
layer thickness of 10 to 800 nm. As well as the metal or the alloy,
the layer (iv) can contain organic components, in a concentration
of preferably 1 to 80 wt. % based on the total mass of the layer
(iv) (metal content 20 to 99 wt. %). Preferred organic components
are conductive polymers or organic metals, or organic copper
complexing agents such as thiourea or benzotriazoles.
[0036] The articles according to the invention are particularly
suitable for the production of printed circuit boards, and the
articles are preferably printed circuit boards which are also
described as boards. These are thin plates used for the assembly of
electrical components, which can have holes. The holes serve for
example for the connection of the upper and underside of the
plates, for the supply of solder or for accommodating the leads of
components for further soldering.
[0037] For the production of the coated articles according to the
invention and in particular of printed circuit boards [0038] (1) a
layer of copper or a copper-containing alloy is applied onto the
surface of a base layer; [0039] (2) the layer produced in step (1)
is structured; and [0040] (3) a layer which contains at least one
electrically conductive polymer is applied onto the structured
copper or copper alloy layer.
[0041] According to a preferred version of the process, the copper
or copper alloy layer (ii) is degreased and cleaned following step
(1). For this the articles are preferably treated with normal
commercial acidic or basic cleaners. Cleaners based on sulphuric
acid and citric acid, such as for example the cleaner ACL 7001 from
Ormecon GmbH, are preferred. The articles are preferably left in
the cleaning bath for about 2 minutes at 45.degree. C. and then
washed with water.
[0042] In addition, it is preferable to pretreat the copper or
copper alloy layer (ii) oxidatively following step (1) or after the
cleaning, for example by etching the surface with H.sub.2O.sub.2 or
inorganic peroxides. Suitable etching solutions are commercially
available, for example the hydrogen peroxide-containing solution
Etch 7000 from Ormecon GmbH. The articles are preferably left in
the etching solution for about 2 minutes at 30.degree. C.
[0043] The layer produced in step (1) is preferably structured by
lithographic or etching processes, whereby the land pattern is
created. The steps (1) and (2) can nowadays also be replaced by the
direct application of a structured Cu conductor track or similar
processes.
[0044] Following step (2), drill holes ("holes") are optionally
created, which are then copper-plated.
[0045] The implementation of the individual steps of the above
process is known per se to the skilled person. Preferably the layer
(iii) is applied to the article by treating this, after rinsing
with water, with a dispersion of the conductive polymer(s) or
organic metal(s) in a dispersion agent which is liquid at room
temperature, for example by immersion of the article in the
dispersion or by application thereof onto the article. The
electrically conductive polymer or polymers are preferably
contained in the dispersion medium in colloidal form. Preferably
the article is contacted with the dispersion for about 1 minute at
room temperature. Additional components, such as electrically
non-conductive polymers and additives can be dissolved in the
dispersion medium or also be present therein in colloidal form. As
dispersion media, organic solvents, preferably organic solvents
miscible with water, water and mixtures thereof are suitable.
Preferred solvents miscible with water are alcohols, in particular
alcohols with a boiling point of more than 100.degree. C. and
preferably below 250.degree. C. After the application of the
dispersion onto the article, this is gently dried and if necessary
further dispersion is applied, until the desired layer thickness is
attained. The production and use of dispersions suitable for
coating is known from the state of the art, see for example EP 0
407 492 B1.
[0046] Water and aqueous solvents are preferred as the dispersion
medium. These are advantageous not only with regard to emissions
and the non-wetting of the solder stop lacquer; it has also been
found that water and aqueous solvents yield better results. This
was surprising in that oxidation processes on copper proceed
particularly rapidly in an aqueous environment. Solder stop lacquer
is used to mask the areas of the printed circuit board which must
not be wetted by the solder during the assembly process. The solder
stop lacquer should not be wetted by the conductive polymer, since
otherwise this would cause short circuits between the contact
points.
[0047] Preferably dispersions which contain no formic acid are
used, however, other acids and/or buffers can be contained in the
dispersions.
[0048] Particularly suitable dispersions are commercially
obtainable, for example dispersions based on polyaniline, such as
dispersions of polyaniline-polystyrenesulphonic acid blends in
water, e.g. the product D 1012 from Ormecon GmbH, and dispersions
of polyaniline-polyvinylpyrrolidone in water, e.g. the product D
1021 from Ormecon GmbH.
[0049] It is also possible for polymer blends with a content of
preferably 0.1 to 45 wt. % and particularly preferably 5 to 35 wt.
% of intrinsically conductive polymer to be used instead of the
pure intrinsically conductive polymer. As well as intrinsically
conductive polymer, these polymer blends contain other polymers,
copolymers or polymer mixtures, such as for example polyamides,
polyesters, polyethers, such as polyethylene oxides, water-based
copolymer latices, such as for example vinyl acetate butyl
acrylate, or other copolymer latices and/or polyvinyl alcohols.
Particularly preferred other polymers are polyamides.
[0050] The coated articles according to the invention are
characterized in particular in that they not only can be soldered
well after prolonged storage, but also are solderable several
times, i.e. can be used in multistage soldering processes,
so-called reflow processes. In this respect, by means of the coated
articles according to the invention a significant approximation of
the soldering and ageing properties to printed circuit boards with
metallic final surfaces could be achieved, which can be stored for
up to 12 months, without impairing their solderability, and which
can be soldered several times after storage. In contrast to this,
conventional printed circuit boards, which are treated with
copper-complexing agents alone, so-called "OSP" (Organic
Solderability Preservative), to maintain their solderability are as
a rule already no longer solderable after storage for only 3 to 6
months, let alone suitable for multiple reflow processes. The
printed circuit boards are regarded as particularly suitable for
reflow processes if the soldering angle is less than 90.degree.,
preferably 60.degree. or less. As OSP's, acidic, aqueous
formulations based for example on benzotriazoles, which contain
formic acid and/or acetic acid, are mostly used.
[0051] Below, the invention is further explained by means of a
diagram and by non-limiting embodiments, wherein FIG. 1 shows a
printed circuit board 10 with a test design 12.
Embodiments
EXAMPLES 1 TO 2
Production of Coated Printed Circuit Boards
[0052] Epoxy resin composite printed circuit boards 10 were cleaned
and degreased using a normal commercial cleaner based on sulphuric
acid and citric acid (ACL 7001, Ormecon GmbH) in a cleaning bath
for 2 minutes at 45.degree. C. The printed circuit boards had a
test design 12 (see FIG. 1), which has been agreed with test
institutes and printed circuit board manufacturers and is modelled
on real printed circuit board structures. These boards enable the
solderability to be measured and assessed. Next, the printed
circuit boards 10 were rinsed with tap-water at room temperature
and then treated with an H2O2-containing etching solution (Etch
7000, Ormecon GmbH) for 2 minutes at 30.degree. C. After etching,
the boards were again rinsed with tap-water at room temperature and
then coated with the conductive organic polymers listed in Table 1.
For this, the boards were immersed in an aqueous dispersion of the
polymer in question at room temperature for 1 minute. After this,
the printed circuit boards were dried at 45 to 75.degree. C.
TABLE-US-00001 TABLE 1 Polymers Used for Coating the Boards Example
Conductive Polymer 1 polyaniline-polypyrrolidone blend.sup.1) 2
polyaniline-polypyrrolidone blend.sup.1) with addition of a copper
complexing agent.sup.2) .sup.1)D 1021, Ormecon GmbH
.sup.2)Benzotriazole (2 MZA, Shikoku Co.)
[0053] Dispersion 1 contained 1.25 wt. % of solids and dispersion 2
1.25 wt. %, and in dispersion 2 the solids fraction contained 6 wt.
% of the copper complexing agent, based on the mass of the solids
fraction.
EXAMPLES 3 AND 4
Production of Coated Printed Circuit Boards (Comparison)
[0054] Analogously to Examples 1 to 2, printed circuit boards were
coated with normal commercial agents based on benzotriazole in
accordance with the respective use instructions (Glicoat Tough Ace
F2 (LX); Shikoku Co., Japan, Example 3 and Entek Plus Cu 106 A,
Enthone OMI Co., Netherlands, Example 4).
EXAMPLE 5
Soldering Angle Measurement
[0055] Some of the printed circuit boards 10 produced in Examples 1
to 4 were subjected to an accelerated ageing process, in that some
boards were stored for 1 hour at 100.degree. C. and others for 4
hours at 144.degree. C. The soldering angle (wetting angle:
according to the Standard NF A 89 400 P or ANSI-J-STD 003 I.E.C.
68-2-69) of the freshly prepared boards and those aged at
100.degree. C. or 144.degree. C. were determined with a normal
commercial meniscograph (Type ST 60, Metronelec Co.). The device
measures the wetting force against time and converts this to
soldering angles by normal procedures (see manual). In each case,
the soldering angle was measured with no reflow cycle, and after 2
and after 3 reflow cycles. The reflow cycles serve for the
simulation of repeated soldering operations and were effected in an
HA 06 Hot-Air/Quartz Reflow Oven (C.I.F./Athelec Co., France),
which by means of temperature profiles simulates multiple
soldering.
[0056] The results of the soldering angle measurements are shown in
Table 2. TABLE-US-00002 TABLE 2 Results of Soldering Angle
Measurement.sup.1) Freshly Produced Boards 1 Hr Aging at
100.degree. C. 4 Hrs Aging at 155.degree. C. Ex. 1.sup.st SO
2.sup.nd SO 3.sup.rd SO 1.sup.st SO 2.sup.nd SO 3.sup.rd SO
1.sup.st SO 2.sup.nd SO 3.sup.rd SO 1 10 61 61 22 68 76 49 74 77 2
20 65 82 24 50 73 33 70 76 3* 29 68 99 30 39 91 70 102 93 4* 21 51
84 21 50 75 52 83 96 .sup.1)Soldering angle in .degree. after 2
seconds, measured with lead-containing solder (Sn/Pb = 60/40) SO
Soldering operation *Comparison Experiment
[0057] The results in Table 2 show that the soldering angles
increase with increasing ageing and in particular with repeated
soldering. While the soldering angles in the first soldering
operation for the printed circuit boards 10 according to the
invention and the printed circuit boards according to the state of
the art still lie at a comparable order of magnitude even after the
second ageing step, a marked increase in the soldering angle, which
sometimes already lies above the critical value of 90.degree.
(Example 3), is already observed with the comparison boards in the
second soldering operation. In the third soldering operation, the
soldering angles of both comparison boards are over 90.degree., at
93.degree. and 96.degree., which indicates poor wetting of the
surfaces and inadequate solderability. In contrast to this, with
the boards according to the invention, after four hours' storage at
155.degree. C. no increase in the soldering angle is detectable on
transition from the second to the third soldering operation, so
that even in the aged state these boards are without reservation
suitable for repeated soldering operations.
EXAMPLE 6
Production of Coated Printed Circuit Boards
[0058] Epoxy resin composite Cu printed circuit boards with a test
design 12 (see FIG. 1) were cleaned and degreased in accordance
with Example 1 in a cleaning bath for 2 minutes at 45.degree. C.
using a normal commercial cleaner based on sulphuric acid and
citric acid (ACL 7001, Ormecon GmbH). Next, the printed circuit
boards 10 were rinsed three times (<1 min) at room temperature
with tap-water and then treated with an H2O2-containing etching
solution (Micro Etch MET 7000, concentration: 2 vol. %, Ormecon
GmbH) for 2 minutes at 35.degree. C. After etching, the boards 10
were again rinsed 3 times (<1 min) at room temperature with
tap-water and then coated with an aqueous dispersion of
electrically conductive polyaniline (PA, concentration: 0.5%
organic metal). For this, the boards 10 were immersed in the
dispersion for about 3 minutes at 35.degree. C. After this, the
printed circuit boards were rinsed three times (<0.5 min) with
deionized water (50.degree. C.) and then thoroughly dried. After
the treatment, the printed circuit boards 10 had a thin, uniform
and planar, transparent coating with a thickness of 100 to 200 nm.
Next the soldering angle was determined in the manner described in
Example 5. The results are shown in Table 3. Printed circuit boards
which had been coated with tin (Sn) in the conventional way served
as a comparison.
[0059] The results show that the solderability of the coated boards
according to the invention is comparable with that of tin-coated
boards. TABLE-US-00003 TABLE 3 Results of Soldering Angle
Measurement.sup.1) 1 Hr Aging at 4 Hrs Aging at Coating 2 .times.
Reflow 3 .times. Reflow 100.degree. C. 155.degree. C. PA.sup.2)
35.degree. 45.degree. 30.degree. 40.degree. Sn.sup.3) 29.degree.
42.degree. -- 18.degree. .sup.1)Soldering angle measured with
lead-containing solder (Sn/Pb 60/40) .sup.2)Electrically conductive
polyaniline .sup.3)Tin coating * Comparison Experiment
[0060] While the invention has been particularly shown and
described with reference to a number of embodiments, it would be
understood by those skilled in the art that changes in the form and
details may be made to the various embodiments disclosed herein
without departing from the spirit and scope of the invention and
that the various embodiments disclosed herein are not intended to
act as limitations on the scope of the claims.
* * * * *