Note: Descriptions are shown in the official language in which they were submitted.
2 ~
4070-7 PCT
METIIOD FOR SELE(~rlVÆLY CO~TII~C NON~'ONI)U(I'I'ORS
WITII CARI~ON PARTICI,ES AND TIIE US~ OF
COPPER-CON'r/~lNlNC SOLUTlONS'rllERElN
The invention relates to a method for selectively coating nonconductors wi~h carbon particles
and the use of copper-containing solutions therein.
The direct metallization of nonconductors has grea~ly gained in importance in the last ten years
within the printed circuit board industry. In this connection, the direct galvanizing methods
with polypyrrole and carbon particles, graphite and/or carbon black should be m~ntioned.
Oirect galvanizing methods by applying carbon particles on nonconductors are described, for
example, in the US patents 4,619,741, 4,622,107, 4,622,108, 4,631,117 and 4,684,560. A
common and central characteristic within the state of the art is a dipping solution, which
contains carbon particles (preferably acidic carbon blacks with particle sizes greater than 3 ~m)
dispersed in an alkaline surfactant solution. When a nonconductor (substrate) is dipped into
such a solution, a film of carbon remains adhered to the surface.
At the same time, relatively thick layers and corresponding amounts of carbon, which
afterwards must be removed once again, are deposited, for example, on the copper surface of
the printed circuit board.
The copper surface includes not only the external copper lamination of a printed circuit board,
but also the drilled inner layers, which are exposed in the case of multilayers and are contacted
by the copper sheath deposited later on galvanically.
Large amounts of carbon have a very disadvantageous effect, particularly in the case of fine
boreholes, which can become blocked. In addition, excess carbon must be remo\~ed from the
copper surfaces in a subsequent bath. In order not to remove the carbon from the
N:40707PPAT
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noncondllc~or surfaces, sucll as cpoxid~ resil1, glass, I -~Iylc~r.l~ o~o~lhiu~c~ polyilni(l~ .Idllcsive
and other materials used in ~hc mallllf~ctllring of llrinlcd circui~ boards, a coppcr c~ching
process is proposed, whicll takes away up ~o 5 ~lm of copper and, at Ihe same lime, praclically
frees the copper surface from carbon. By ~hese meal1s, however, the eleclrical contac~ to the
carbon Iying on the nonconductor is inlernlpted. In Ihe galv3nic bath, the copper layer must
first of all bridge the amount of sakl S ~Im by front growth, in order to conlact, for example,
an inner layer of a multilayer. However, since tlle multilayer consists of several layers, 8 to
16 layers being technically customary, there is such a phenomenon at each layer. As a result,
there are considerable fluctuations in the thickness of the copper layer in the borehole, which
lead to rejects or, at the very least, represent a significant disadvantage of the method. This
inadequacy limits the use of this advantageous technique.
A furlher disadvantage of the methods within the state of the art is the drying process after the
coating with carbon particles. In the case of vertical processing techniques, very much of the
carbon dispersion remains in the holes here, particularly in holes with a diameter of less than
0 4 mrn. Because the surface of the borehole is therefore difficult to dry and because of the
unusually thick coating with carbon, further processing is extremely problematical.
It is therefore an object of the invention to make available a selective method, for which there
is only a very slight deposition of carbon on the copper surfaces, such as those of a printed
circuit board, and for which the adhesion of the carbon particles to the nonconductor surface
is increased.
This objective is accomplished owing to the fact that the nonconductor is treated a.) with a
copper-containing solution and b.) a polyelectrolyte solution, preferably an aqueous gelatin or
polyacrylate solution, is c.) optionally rinsed with water subsequently~ and d.) the
nonconductor surface is brought into contact with a dispersiorl containing carbon. wetting agent
and an ionogenic metal compound and e.) subsequently optionally rinsed once again with
water. Furthermore, the accomplishment of the objective includes the use of copper-containing
solutions in the method.
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Preferred embodiments are dcscrihcd in Ihc dcl cn(l~nt claims.
The inventive method is based on a ~rcalmcnt of a coppcr surfacc whcrcin
1. the copper s~lrface is not covcred with carbon particles or covercd with carbon particles
that adhere only slightly, while thc adhesion of the carbon to the nonconductivesurfaces, that is, to the surfaces of the glass fibers and of the resin, remains unchanged
at a high level and
.,
2. the back-etching of the inner layers is avoided or, at the very least, decreased greatly,
because only mild etching solutions are used pursuant to the inventive method.
Pursuant to the invention, this is accomplished furthermore in the following way, owing to the
fact that copper compounds are produced on the copper surfaces of the printed circuit board.
These copper compounds hamper or make dimcult the adsorption of finely-divided carbon or
other conductive materials, so that very mild processes subsequently remove these copper
compounds and adhering carbon, without etching the copper layer underneath more strongly.
~1 The printed circuit boards, so treated, have an outstanding distribution of layer thicknesses of
.1 the galvanic copper in the borehole and, because of the intimate bond between the inner layers
`~' and copper hole sheath, withstand thermal processes, such as those required for the soldering
.~ shock test at 288C for 10 seconds.
Surprisingly, it was found that copper(l) compounds~ which are formed by the
disproportionation reaction of metallic copper with a divalent copper compound, hamper the
adsorption of gelatin and carbon.
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`I Compounds of univalent copper, which cannot be obtained directly. are prepared by the
', exchange reaction of the anions.
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As copper compollll(ls, hali(lcs~ pscl~ lulli~lcs, cllalcoecl1i(lcs. sulf.l~cs, hydroxides and
prefcrably phosphates come hlto collsideration.
The further step of the inventivc mcthod, the treatlllent of the nonconductor with an aque-)lls
gelatin solution, can be accomplished with sollltions, which contain 0.01% to 5.00% and
preferably 0.2% of gelatin. All commercial gelatin qualities. which are presenlly being
offered, are suitable for preparing this aqueolls gelatin sollltion. The flrst s~ep of the method
can also be carried out with an aqueous polyacrylate solulion ins~ead of a gelatin solu~ion.
Here also, all commercially obtainable polymer dispersions based on acrylate or on mixtures,
which contain polyacrylate, are suitable.
After this treatment with a gelatin solution or a polyacrylate solution. the nonconductor is
rinsed with water, preferably with distilled water.
Subsequently, there is contact between a nonconductor surface, so treated, and a dispersion
containing carbon (for example, carbon particles in the form of graphite and/or carbon black),
a wetting agent and an ionogenic metal compound (such as an alkali, ammonium or alkaline
earth halide).
As wetting agents added, especially phase-transfer catalysts, such as
hexadecyltrimethylammonium bromide, are suitable. Furthermore. all phase-transfer catalysts,
which contain a quaternary nitrogen atom and are commercially available. are suitable. In
addition, Aerosol OT (Cyanamid) and Cathodip~ are suitable as wetting agents.
As ionogenic metal compounds, which are to be added to the dispersion, the fluorides,
chlorides, bromides or iodides of lithium, sodium, potassium, magnesium~ calcium, barium,
strontium, ammonium or copper have proven their value.
\
The coating method is based on the principle of adjusting a carbon dispersion in such a
manner, that it is stable in the absence of the substrate that is to be coated. However, if this
dispersion comes into contact with the gelatin or polyacrylate layer adhering to the surface of
N:407071~PAT 4
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the nolIcolldllctol~ ~his carbon di~ elsi()n is d~ t~ c(l, wilh ~he rl sldl fl~ helc i.
coagulation and that carbon particles prccipilale ial thc solid/flllorin.l~d Pl1aSe bOlm(lary,
adhering firmly. ïhis coagulation is contlollcd by way of thc iono~cnic mctal compounds
(electrolytes) contained in the dispclsion.
At the present time, the role of lhe oligomeric ionophorcs of the substralc surfacc cannot yet
be defined. However, i~ is assumed that these lead to a high surface concen~ra~ion of ions,
which is then the cause for the desired coagulation. This coagulation takes place with
participation of the oligomeric ionophores, since the coagulation layer is resistant to rinsing.
The inventive method can be used to particular advantage for the direct galvanic metallizing
of nonconductors. In this connection, ceramic, glass or other polymeric materi31s, such as
fiber-reinforced plastics containing fillers or plastics that have not been reinforced, epoxides,
phenolic resins, cyanate esters, polyether imide, polyimide, fluorine-containing polymers
(PTFE) or similar materials can be named as nonconductors. Moreover, it can be used for
coating ABS plastic, polyphenyline sulfide, polyesters, polyacrylates and epoxide resins.
The method is also suitable for being used to produce conductor lines or structures on the
above-named polymeric materials. Especially emphasized is the treatmenl of boreholes in
printed circuit boards and the use for preparing electromagnetic shielding layers and printed
circuit boards.
The inventive method is suitable for use in vertical or horizontal continuous installations,
which are operated continuously within industrial galvanic production.
Printed circuit boards, electrodes, heating elements, chip carriers, electronic packages,
multichip modules, metallized plastic parts such as buttons, fittings or automobile parts can be
produced to advantage with the inventive method.
(
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The following Examples are intended to cxplain thc invcntivc mctl1o(1
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Outline of the Method
1. Cleaning agent; alkaline and acidic
` 2. Rinsing
` 3. Treatment in solution A
4. Rinsing
5. Treatment in solution B
6. Rinsing
7. Water-soluble polymer
. Rinsing
9. Carbon dispersion (graphite/carbon black)
10. Rinsing
~ 11. Removal of the copper(l) compound in a weak etching solution
il 12. Rinsing
13. Drying with air at 50C
14. Activating the copper surfaces in an acidic solution
3 15. Rinsing
1 16. Galvanic copper 0.5 4 A/dm2 (depending on the application)
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Example I
A printed circuit board, provided with boreholes, is treated as described above. Solution A contains 200 g of copper(ll) chloride per liter and
Solution B is skipped.
It was possible to clean the board by rinsing it in sprayjet rinsing equipment. so that the
exterior copper surfaces and the interior layers were freed from carbon (graphite). After
~ 40707~PA r 6
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g;llv~lnizillg ror S ~ c~ ci~lic copp~r ~ oly~ /(lln', 11~ hol~s w~rc copper
plated tighlly.
E~ample 2
A printed circuit board, provided wilh borcholes, is Ireated by ~he melhod oullincd above.
Solution A contains 200 g of copper(ll) chloride per liler and
Solution B contains 50 g of trisodium phosphale per liter.
As in Example 1, the graphite could easily be removed and the galvanizing result was also
good.
Example 3
A printed circuit board, provided with boreholes, is treated by the method outlined above.
Solution A contains 200 g of copper chloride per liter and
Solution B contains 50 g of potassium dihydrogen phosphate per liter.
The copper surfaces were free of carbon already after a few seconds of treatment in the weak
etching solution (step 11 in the Outline of the Method). After galvanizing for 5 minutes in an
acidic copper bath, the holes were copper plated tightly. No free regions could be identified
in the transmitted light test.
Example ~1
A printed circuit board, provided with boreholes, is treated by the method outlined above.
Solution A contains 50 g of copper(ll) bromide per liter and
Solution B contains 50 g of potassium hydrogen phosphate per liter.
After a short time, the copper surfaces were freed from graphite and the copper(l) layer was
removed. After 35 /lm of copper had been deposited in the center of the borehole, the
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multilaycr was subjccled to a sl~ock lest (288~(', 10 sccon(ls) .md a polishcd cr(l~s sccfion of
it was cxamined. The con~actillgs were not torn o~, thc bc)rchole shcalh was safisrilclory and
the layer thickness distribution was 85%, measured from borehole inlct to horchole cenler.
Exnmple S
A printed circuit board, pretreated as in Example 3, was treated with a conditioning solution
(water-soluble polymer) of 0.2% Mowoiol with a pH of 9 and treated further by the method
outlined above. The removal of the carbon also proceeded quickly and the through-plating was
free of defects after the given copper-plating time.
Example 6
.~
.~ printed circuit board, pretreated as in Example 3, was treated with a conditioning solution
of 0.2% gelatin with a pH of 9 and then by the method outlined above. The removal of the
carbon proceeded rapidly and without problems and the through-plating was without defects
after the given copper-plating time.
.~
No defects could be detected in the transmitted light test when the copper layer reached a
thickness of S ~m.
A printed circuit board, reinforced to 35 ~m copper, was subjected to a shock test (see above)
and found to be satisfactory.
Example 7
The adsorptive coating of nonconducting surfaces with conductive carbon blacks is suitable for
the through-plating of printed circuit boards based on glass fiber-reinforced epoxide resin
plastics and laminated with copper on both sides.
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The board, cleancd h~ 1% ~rkopal~D N 150 (Hocchst)/dil~lle slllfuric acid wilh ullr.l~l)-lnd, is
first pretreated for 15 seconds in a 0.2% aqucous gelalin solulioll wilh horizonlal movcmcn~
of the goods. For a bath balch~ the gelalhl~ af~er being allowed to swcll ror 10 minutes, is
first dissolved at an elevated tcmperature and subsequcnlly allowcd lo sland for S hours at
10C and then heated to 20C.
After the board is rinsed with deionized water, it is coated with graphite carbon black of the
Sigri company by adsorption from a 1% aqueous dispersion. The dispersing is brought about
with ultrasound. The dispersion is stabilized cationically with 2.5 x 103 moles/L of
hexadecyltrimethylammonium bromide (CTAB) and additionally contains 0.07 moles/L of
potassium chloride. The coating takes place at a bath temperature of 30C with horizontal
movement of the goods (stroke: 4 cm, frequency: 75 per minute) and is completed in 5
minutes.
The board is washed with deionized water and then dried with compressed air. The thickness
of the resulting carbon black layer is less than I m and the resistance, based on a square, is
of the order of 104~2. To remove the carbon black coating on the copper lamination, the plate
is etched anodically for 5 minutes with I A/dm in 0.5 moles/L of CuSO4/H2SO4 and rinsed
once again. After that, it is galvanized in the usual manner.
Example 8
The printed circuit board is coated with carbon black for the through-plating of printed circuit
boards as in Example 1. However, the carbon black dispersion is stabilized anionically with
Aerosol Ol~ (Cyanamid). A 1% dispersion of the EC carbon black. Printex~ L 6 (Degussa)
contains 3.4 x 10 13 moles/L of Aerosol OT and 0.04 moles/L of potassium chloride.
Example 9
Printed circuit boards, copper laminated on both sides, are through-plated as in Example 1,
here, however, by way of a coating with graphite. The aqueous graphite dispersion used (with
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a particle size of 0.~ Io 0.6 /lm) i~ a l~ro(hlcl of ~hc i~ch~on colnl).lny wi~ hC narnc of
"Aqua(lag0" and is used in a dillltion of 1: 6. rhC coalillg is carrie(l oul for 5 minlllcs wilh
a horizonlal movemcnl of Ihe goods (stroke: 4 cm, frc(lncllcy: 50 pcr minnlc.s) at a bath
temperature of 25C. Dcspilc Ihe facl Ihat Ihe rcsislance of Ihe graphile c-Jaling
(approximately 106n/square) is significanlly higller Ihall Ihal of carbon black laycrs, the
galvanic deposition of copper procceds bcner nll graphilc.
Example 10
The board is through-plaled over a coating with graphite, as in Example 3. The coating is
achieved, however, after a pretreatment of the printed circuit board by immersion in
Basoplast~ 280 D (BASF). Basoplast 280 D is a calionically stabilized, aqueous polymer
dispersion based on acrylate, which is used in a dilution of 1: 5. The immersion takes place
during a 15 second lifting motion at room temperature. The board is rinsed with deionized
water and then coated with graphite. Compared to the pretrealment with gelatin, the coating
admittedly is less, with a resistance of approximately 107S2/square. Nevertheless, the board
can be galvanized without dimculties.
Example 11
Because they are coated repeatedly with graphite, the epoxide resin boards can be galvanized
flat. As in Example 3, the epoxide board (2 cm wide, 2 cm high) is immersed in gelatin
solution and rinsed and then coated with graphite for a period of, however, 2 minutes. After
being rinsed, the coated board is immersed once again in gelatin solution, rinsed and coated
with graphite in the same way for a secon(l time. This type of coating is repeated twice more,
after which the board is dried with compressed air.
During the galvanizing, the contacting to the graphite layer is also immeried in the bath.
Starting with the contacting, the copper deposited spreads over the graphite layer.
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As in Example 5, glass can also be galvallizcd na,. Morcover, ~hc workpicces can havc any
shape. The adhesion of the metallizatioll to glass is, however, less than that of the
metalli~ation to epoxide resin.
Example 13
A preheated glass plate (2 cm wide, 2 cm high) is exposed at room temperature for 5 minutes
to gaseous hydrofluoric acid in a closed container. During this time the surface is roughed
uniformly. After the reaction products are rinsed from it, the plate is metallized as described
in Example 5. The adhesion of the galvanic coating is clearly better than that of a galvanic
coating on an untreated glass plate.
..
'I Example 14
An epoxide or glass plate is coated with graphite as described in Examples 5 to 8. After the
last rinsing, however, the plates are dried in an oven for 15 minutes and tempered. For
'epoxide boards the temperature is 120C and for glass plates 200C. The conductivity of the
graphite layers is increased by this treatment, so that the galvanic deposition of copper
proceeds more quickly. By these means, it is also possible to galvanize larger workpieces,
particularly of glass.
~1
Example 15
A glass plate (2 cm high, 2 cm wide) is coated with a polymer. As polymer the binder of the
BASF electrophoretic enamel "Cathodip~", which is a water-dilutable dispersion (product
number FT 83-0~70), is used as polymer. The dispersion is applied by immersing the plate
in the l: 1 diluted polymer dispersion and subsequently drying for 5 minutes at 80C. llle
transparer,t, adhering layer is water resistant and shows hydrophobic behavior. Thereupon,
the procedure of Example 5 is followed and, after the graphite coating, copper is deposited
N:407071!PAT 1 1
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galvanically. Ihe mc~ .alion Ol1 Ihis surf~ce shows a be~cr a(lll~sion s~r~llglh Ihan Ihe
mctallization on glass that has not bccn coalcd wilh polymcr. A fllrll1er incrc~ce in adhesion
is achicved due to the cross Ihlkil-g of thc polymcr after IhC galvani~alion. Il lakcs place while
stoving at a temperatllre of 180C for a pcriod of 15 minlltcs.
Example 16
A glass plate, 2 cm high, 2 cm wide, is coated wilh a water-insoluble gelatin layer from a
0.5% gelatin solutiol1, which contains 0.5% formaldehyde, by briefly immersing the plate in
the solution at a temperature of 20C and subsequently drying it with compressed air. Without
any further pretreatment, the plate is coated with graphite by adsorption from the dispersion
used in Example 3 at a temperature of 25C for 2 minutes with movement of the plates. The
plates are then rinsed and dried with compressed air. Afler that, the plates are dipped for a
second time, again for 2 minutes~ into the graphite dispersion and dried once more. This
procedure is repeated twice more. Subsequently the plales are copper plated galvanically in
the usual manner.
Example 17
The through-plating of a printed circuit board, copper laminated on both sides, is achieved
over a coating with graphite. For this purpose, the graphite dispersion described in Example
3 is used, however at a dilution of 1: 4. Furthermore, Arkopon0 T Plv, a Hoechst anionic
surfactant, is added at a concentration of 70 ppm.
The board, cleaned as described in Example 1, is coated by being immersed briefly, freeing
the boreholes by blowing compressed air through them and drying for 5 minutes at 80C. The
boards are etched as in Example I and subsequently copper plated galvanically.
N:40707P:PAT 1 2
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Through-Plating Prh~ted Circuit Boards: An cpoxidc rcsill mullilaycr wilh borcholcs less Ihan
I mm in diameter is cleaned in an aqueolls solution, which conlains 0.5% Arkopal NlS()
(HOECHST) and 5% sulfuric acid. Thc clcaning rcquircs ~ minutes, ultrasolllld bcing uscd
at the same time.
After being rinsed for 30 seconds with tap water, the board is immersed for I minute in an
aqueous solution, which contains 100 g/L of sodium peroxodisulfate and 20 g/L of sulfuric
acid, and rinsed once again. Subsequently, the board is treated for I minute in a hydrochloric
acid solution of 200 g/L copper chloride (pH of 1.8) at a temperature of 40C. After being
}insed with tap water, the board is immersed in a gelatin solution, rinsed once again and then
coated with carbon black as in Example 1, however for a period of 2 minutes.
The board is rinsed and subsequently immersed for 2 minutes at room temperature in an
aqueous solution, which contains 50 g/L of sodium peroxodisulfate and 50 g/L of sulfuric acid.
Aher being rinsed with a strong jet, the board is dried with hot air at 110C.
Finally, the board is copper plated electrolytically in Cupracid GS (Schering) at room
temperature with a current density of 4 A/dm2 for a period of 40 minutes.
Example 19
Through-Plating Printed Circuit Boards: A polyimide multilayer (Starr-Flex), which is
provided with boreholes having a diameter of less than I mm, is cleaned as in Example 18.
After being rinsed for 30 seconds with tap water, the board is immersed at room temperature
for 1 minute in an aqueous solution, which contains 100 g/L of sodium peroxodisulfate and
20 g/L of sulfuric acid and rinsed once more. Subsequently, the board is treated for 1 minute
in a hydrochloric acid solution of 200 g/L of copper chloride (pH of 1.8) at a temperature of
40C and after being rinsed once more, treated in a 10% solution of potassium dihydrogen
phosphate, also at 40.
~':40707PPAT 13
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~fter bcing rinscd wilh l~p wa~cr, Ihc boar(l is immcrsc(l in a gchltin solllliol1 as in l,xamplc
- 18, rh~sed once more and then coatcd wilh graphi~c as in l xan~plc 17, howcvcr for a pcriod
of 2 minutes.
The board is rinsed and subscqucntly hllmcrsed for I minlltc iat room tcmpcratllre in an
- aqueous solution, which contah~s 50 g/L of sodium pcroxodisulfate and 50 g/l, of sulfuric acid.
After being rinsed with a powerful strcam, the board is dried with hot air a~ 110C.
Suùsequen~ly, a~e board is copper plaled eleclroly~ically as in Example 18.
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