DE2132003A1 - Solution for electroless copper plating - Google Patents

Description

The present invention relates to improved, stabilized solutions for electroless copper plating and a method of use these solutions, for copper-plating substrates which have a surface that is catalytically active and the deposition caused by copper from the solutions for electroless copper plating.

It is an object of the present invention to provide improved baths to create for electroless separation that are easy to use, extremely stable, very reliable, economical to use and which can be used for long periods of time,

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to deposit any desired copper thickness and where the Chemicals that are consumed by the deposition reaction can easily be replenished again to make an extended one To enable use of the solutions.

Another object of the invention is to provide a new and improved To provide methods of electrolessly depositing an improved quality of copper on various substrates, e.g. insulating substrates for electrical circuits, metals, ceramics or other desired carrier surfaces. The improved Quality is generally revealed by the physical properties of the copper layer, e.g. its ductility, Color etc

There is already a multitude of baths and methods for electroless Copper plating has been described and many of them have been used commercially to coat copper on various substrates knock down, be it for decorative or useful purposes. The baths for electroless copper plating had to be due to their special Nature can be somewhat unstable in order to deposit copper on the catalytically active surface. Many of the known solutions were very unstable and after a relatively short period of use they decomposed with random copper deposition. Around To avoid catastrophic decomposition during use, various techniques have been developed to ensure the stability of the To enlarge the bath, e.g. by using copper (II) ions and copper (I) ions form very strong complexes or chelates Agents, by adding various additives, etc.

Although such techniques increase the stability of the bath against self-decomposition, they have the undesirable effect of greatly increasing the time required to deposit a given thickness of a copper layer, since the stability of the bath is generally directly related to the The speed at which copper is separated from the bath . Aue for this reason is the electroless copper plating

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in many applications only for depositing very thin copper films used to create an electrically conductive surface, which by electrodeposition of copper up to the desired thickness is built. Where the entire surface of a substrate is plated, this generally causes it no difficulties. However, if required, relatively thick layers of copper on a variety of insulated metal surfaces to apply, for example, to produce a board with multiple circuits on an insulating substrate on which

en hundreds of isolated copper areas the need to connect an electrical lead to each of these j areas for electrolytic copper deposition To make it possible in all these areas represents an almost unsolvable and, at best, very costly task. It would be highly desirable when building the entire circuit to its desired thickness using electroless deposition techniques could make, thereby avoiding the need to make electrical connections.

A method of stabilizing solutions for electroless Copper plating, which has found widespread use in industry, was the aeration of the solution for electroless deposition Air or another gas containing oxygen. This kind of Stabilization avoids many of the disadvantages associated with other f means of stabilizing electroless plating solutions are connected, since this does not have the opposite effect on the speed, with the copper from the stabilized Solutions is deposited. This stabilization process is described and claimed in U.S. Patent 2,938,805, to which reference is hereby made.

The speed with which copper is deposited from solutions for electroless copper plating also depends on the respective Copper ion concentration in the solution. This means that after a partial consumption of the copper ion concentration through use, the deposition rate becomes so low that

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it is no longer economical to use the solution v / o it or, although, even at this point, there are still considerable copper ions remained in the solution. In the past it was common at this point replace the solution with a fresh one. Try to bring the copper ion concentration up to its original one Content to replenish, as well as that of other chemical constituents consumed by the deposition fraction have been undertaken. In general, however, the stability of these reconstituted solutions is less than that of the original solutions, so that regeneration is only marginally economical.

Some electroless copper plating solutions are sufficiently stable that it is economical to replenish the chemicals used. However, the chelating agents or additives used to provide the necessary stability are so effective that deposition on the catalytically active surfaces does not occur at ambient temperature and heating of the solution is required to initiate deposition. And even then, it takes extremely long times, on the order of 2 hours and more, to electrolessly deposit a copper layer approximately 0.025 mm (1 mil) thick.

In the invention it has been found that extremely stable baths for electroless copper plating by adding some Hydroxysulfonates can be obtained for all known electroless plating solutions which have a copper (II) ion source and a source of hydroxyl ions sufficient to provide that required for electroless copper plating To create a pH value, generally a pH value greater than 10 and preferably from 12 to 13, furthermore an agent which contains copper ions in alkaline solution can reduce to copper metal, generally formaldehyde or a formaldehyde-generating substance, e.g. paraformaldehyde, etc., in the presence of a surface; which is catalytically active and the precipitation να; K ^ pf-si-

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from an electroless copper plating solution, in general either a metal surface itself or a non-metallic surface, which is created by deposition of metallic Particles either from colloidal metal solutions or by absorption of metal particles, in one treatment first with a reducing solution, e.g. an acidic, aqueous solution of tin (II) chloride, followed by rinsing and a treatment with an acidic, aqueous solution of a noble metal salt, e.g. palladium or platinum chloride, etc. in catalytically active Form was transferred.

The solutions for electroless copper plating that can be improved according to the invention are known. They are described in both patent and technical literature. Typical but not limiting Examples of this are US patents 2 87 ^ 072, 2,938,805, 2,996,408, 3,075,855, 3,075,856, U.S. Patent Application Serial No. 8II 012 of March 27, 1969 and the various References and patents cited for these patents. To the teachings of all these scriptures as far as theirs Compositions and usage techniques is concerned hereby referred to.

The stability described above is achieved by adding a water-soluble Salt of a hydroxysulfonate to the solution for "electroless copper plating obtained, the hydroxysulfonate selected are made from dithionites, bisulfite addition products lower alkyl aldehydes and bisulfite addition products of unsaturated, lower aliphatic hydrocarbonols. With the designation "Unsaturated, lower, aliphatic hydrocarbonols" are intended to mean hydroxyl-substituted hydrocarbons of the aliphatic Series containing 1 to 8 carbon atoms and contain either an olefinic or acetylenic bond. These compounds are olefinic and acetylenic alcohols, including multi-hydroxyl alcohols of the aliphatic series.

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These substances are well known as chemical compounds and in terms of their manufacturing processes. Dithionites are too known as hyposulfites or hydrosulfites, commonly made as the sodium salt and used in dyeing. they react with formaldehyde to form an equimolar mixture of the corresponding hydroxymethanesulfinate salt and the hydroxymethanesulfonate salt. The latter compound is the same as the bisulfite addition compound of formaldehyde.

The addition of bisulfites to ketones and aldehydes is one Equilibrium reaction that is shifted by the pH value. A high pH causes a shift to the free one Aldehyde or ketone and the bisulfite and is much more pronounced for ketones than for aldehydes. If there is a bisulfite If an olefinic double bond attaches to it, it forms a saturated sulfonate and when a bisulfite is attached to an acetylenic one Bond attaches, it can form either an olefinic sulfonate or a saturated disulfonate, depending on whether a or add two molecules of bisulfite to the triple bond. The reaction products are likely to be one in both cases Mixture of possible stereoisomers, since the sulfonate group can attach to one of the two unsaturated carbon atoms. These addition products with olefins and acetylenes are not in equilibrium, as is the case with the addition products of ketones and aldehydes is the case.

Because of the equilibrium reaction described above and because of the high pH value of solutions for electroless copper plating are the bisulfite addition products of ketones, if any, as Additions to solutions for electroless copper plating are of little value, and the addition products of the aldehydes are, although satisfactory, for the purpose of the invention not removed as effectively as the bisulfite addition products of the olefinic and acetylenijichen hydrocarbon alcohols. The exact function the hydroxyl group is not known, but it is necessary. It can also be added as a hydroxyl-supplying group

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e.g. as an ester group which hydrolyzes under the basic conditions of the bath and the hydroxyl group forms the part that also carries the SuIfonatgruppe. Polyhydroxy alcohols are better than alcohols containing a hydroxyl group. There can be more than one olefinic or acetylenic group in the alcohol molecule from which the bisulfite addition product is present will be produced.

Since the hydrocarbon portion of the Hydroxylsulfonats has no effect, it is not advisable to use has Hydroxylsulfonate, whose hydrocarbon part up more than 8 carbon atoms ί, that this half should be a lower aliphatic hydrocarbon. Likewise, the metal cation has no effect on the effectiveness of these hydroxyl sulfonates for the purpose of the invention as long as they do not render them insoluble in the plating solution. They can be alkali or alkaline earth metal cations, but preferably the former, especially sodium, because of its cheapness and accessibility.

Typical, but not exhaustive, of the literature describing various bisulfite addition products which can be improved according to the invention are U.S. Patents 2,793,229, 2,820,818, 2,857,427, 3,211,783, the British patents 756 105, 774 563, the article by Reppe et al in J. ( Liebip; s Ann. 5_9_6, 1 (1955) etc. and those in these publications cited literature. These teachings are hereby incorporated by reference. For as yet unexplained reasons, the bisulfite addition products, which were separated from the reaction mixture by filtration, apparently more effective for the inventive Use as the same material that has been further purified by recrystallization.

'Only a very small amount of the water-soluble salt of the above material is required to convert the solutions to the electroless Effectively stabilize copper plating against self-decomposition. In general, amounts of about 0.005 g / l plat-

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treatment solution had a noticeable stabilizing effect, with the best results being obtained in the range of O ₅ Ol g / l to 0.08 g / l. The optimum amount is in the range of about 0.02 to 0.0 ¹ I g / l. Higher amounts can also be used, but there is no need for this, since the rate of deposition is noticeably reduced when the amount of the additive according to the invention is increased and the quality of the copper deposit also decreases. However, even amounts of 1 g / l do not render the plating solution unusable.

It is actually surprising to find that these materials are effective stabilizers in such small amounts, but it was even more surprising to find that in addition to this, increased Stability has little, if any, effect on the rate of precipitation of the stabilized solutions became. The solutions easily deposit copper on activated surfaces at room temperature, stop depositing when the activated surface is removed from the solution and decompose if they stand for long periods of time, especially if they are ventilated. The chemicals used can can easily be replaced and precipitation for several days will not show signs of self-decomposition Bath. It was also surprising to find that the quality of the copper deposit also has an advantageous effect was, perhaps due to the controlled deposition of copper from the bath for electroless deposition. The secluded Copper is very light in color and has a very fine grain texture. If a very smooth metal surface, e.g. a plate made of stainless steel or a plastic laminate that had only been lightly blown off with steam, which is electrolessly copper-plated, which is allows the non-destructive removal of the copper deposit from the substrate, the result is a copper that is extremely flexible, much more than an electrolytically manufactured copper plate. When the solution according to the invention is used for electroless copper plating is used to divide precipitation into through holes ::: and electrical circuits on an insulating Subst-r-a'G hsp :: - u

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and the various electronic components in the holes mounted and soldered there by placing the circuit board over the surface of a molten solder bath in a Wave soldering machine, the components will work well with the electrical circuit with no faults Circuit board soldered. In addition, the circuit components can be unsoldered and new components soldered on in their place without failures and damage to the electrical circuit.

the
In the following, reference is made to / examples in which the invention is explained in more detail. Unless otherwise stated, 1 liter of the plating solution is used to coat both sides of a 3.8l cm χ 10.16 cm (1.5 x ^ inch) sheet of epoxy resin-soaked laminated glass with copper, after this, as usual, under Use of tin (II) chloride and palladium chloride had been activated. If used, the stainless steel plate was the same size and similarly activated.

Standard solution

In order to document the effect of the additives according to the invention, a typical known solution for electroless copper " selected from the following composition:

CuSO ^ '5H ₂ O 25th g / l NiCl ₂ '6H ₂ O 1 g / l Rochelle Salt '4H 2 ° 37.5 g / l NaOH 16 g / l Formaldehyde (37 %) 15th ml / 1

This solution easily deposits copper on metal or activated non-metallic surfaces. Generally this will Formaldehyde added immediately before use. However, this solution decomposes autogenously, as is typical of the

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known solutions for electroless copper plating and deposits copper in the solution and on the walls of the container after it has been used for a few hours and must therefore be eliminated at this time. The copper precipitate obtainable from this solution looks good when peeled off a mirror-smooth substrate such as stainless steel, it tears if it is sharply bent and kinked. While ventilation extends the life of this plating solution, but the solution also decomposes if it is left at room temperature overnight. Ventilation with "one stream of fine air bubbles was used in all examples, except where this was expressly denied.

example 1

Various hydroxyl sulfonates were added to the above standard solution, and samples of epoxy resin-impregnated glass fiber laminates, which had been only lightly blown off with steam prior to activation with the standard tin (II) chloride / palladium chloride treatment, were added to these solutions and left plate these samples overnight with approximately 0.038 mm (1.5 mil) layers of copper deposited on the surface of the laminates. The rate of deposition decreased with time due to the decrease in copper ion concentration as the plating progressed. Generally, a layer of copper about 0.025 mm (1 mil) thick was obtained in the first 5 to 7 hours. A fresh portion of the laminate was introduced into the solution and the plating reaction to a total time of 2 hours, ¹ J continued to determine the stability. In the invention, it was found that no decomposition occurs even using these Hydroxylsulfonate within 2 hours and ¹ I even later, regardless of VFE long as the deposition continues.

From the epoxy-impregnated fiberglass laminate that had been plated overnight, an approximately 2.5 ¹ J cm (1 inch)

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wide strip peeled off and subjected to a bending test. This For bids the copper strip was formed into a loop and placed inter a weight-loaded roller which ran in about 2.5 ¹ J cm (1 inch) wide web. A kink was formed by rolling over it with the roller. The strip was then opened and the crease smoothed out by running the roller over the strip again. These two operations create a bend in the measurement and were repeated until the copper separated at the kink. The designation of the test result as half a bend means that no destruction occurred during the kink formation, but did occur during j the second part of the test. For example, in the following table, a result of 1.5 in the bending test means that the strip was kinked once, smoothed out once and the kink was formed a second time, all without any damage occurring, which would then, on the second attempt to smooth out the kink, entered. The tempering was carried out by heating to 100 ^° C. in an air circulation oven for 15 minutes to 1 hour. The length of time within this range did not appear to affect the results. The temperature was chosen to avoid any decomposition of the plastic substrate and oxidation of the copper.

Table I below shows the results of testing various hydroxyl sulfonates, the designation “S” in the “Stability” column indicating that no sign of self-decomposition was found after separation for 2k hours. The designation "PS" means that although catastrophic decomposition did not occur, some negligible precipitate formed on the walls of the container. In the case of the known baths for electroless copper plating, such insignificant deposits were highly undesirable because they * led to fatal decomposition of the entire bath. However, this did not occur with the solutions investigated according to the invention. Such solutions marked with "PS" are still usable, although they are less satisfactory than those with

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Solutions designated "S" because they unnecessarily consume plating chemicals. Those marked with "U" in the stability column
Solutions decomposed during the 24 hour period and contained precipitated copper particles in the solution and did not result in further copper deposition on a catalytic surface. They are typical of a solution that is after
has suffered fatal decomposition in a period of use.

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Natural
blsulfite
Adduct of Table I. stability Bending test
not an-
let leave - Nitrium
salt - g / l added
to the Plattle
solution U - - 2-propane
sulfonate - 0.04 U - - 1-butane
sulfonate acetone 0.04 U - 1.5-2
2.5-3 2-hydroxy
2-propane
sulfonate Proprion
aldehyde 0.04 PS
PS 1.5-2
2.5-3 1.5
2.5 1-hydroxy
1-propane
sulfonate Allyl
alcohol 0.04
0.08 PS
3 1.5
2.5 1.5
1.5 3-hydroxy
1-propane
sulfonate Propargyl
alcohol 0.04
0.08 S.
S. 1.5
1.5 3.5 3-hydroxy
1.2-
propane-
disulfonate 2-butene
1,4-diol 0.04
0.005 S.
S. 2.5
8th 4th
4.5 I, ² * -
Dihydroxy
2-butane
sulfonate 1,4-butin-
dlol
(Dladdukt) 0.04
0.10 S.
S. 3
3 1.5 1.4-
Dihydroxy
2,3-butane
dlsulfonate 1,4-butyne
diol
(Hono-
adduct) 0.04
0.02 S. 1.5 1.4-
Dihydroxy
2-but-2-en-
sulfonate 0.02

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It should be noted that the first three statements are not covered by the invention. You were taken to to document that closely related compounds are not satisfactory Deliver results. The first two compounds in the "Sodium Salts" column do not have a hydroxyl group and show so that a hydroxyl group is present in the sulfonate molecule have to be. The third entry shows that the bisulfite adducts of ketones compared to aldehydes are also unsatisfactory are. Of all the ketones, acetone is the most stable bisulfite addition product.

Example 2

In Example 1, the bisulfite addition products were isolated as white crystalline compounds, but not prior to use purified by recrystallization. In this example the bisufite addition product is made, but not from solution isolated because enough water is used to keep it in solution. A solution of 20.8 g of sodium bisulfite and 8.6 g of 1,4-butynediol were heated to the boil in 200 ecm of water and then cooled to room temperature. No crystals formed after cooling. A fraction of 10 ml of this solution was added to one liter of the standard solution, which was increased by increasing of the formaldehyde part had been changed slightly to 20 g / l. This increase in formaldehyde has no effect on the stability or the quality of the copper deposit, it only allows more copper to be deposited. One plate each with epoxy resin impregnated fiberglass laminate and stainless steel were placed in this bath and plated overnight. That The bath remained completely stable and the copper plating survived after being removed from the stainless steel in the bending test, 2.5 bends before tempering and 5 bends after Tempering.

If instead of the 10 ml of the bisulfite addition product of the above Diol 10 ml of a solution of 8.6 g of 1,4-butynediol in 200 ml Vfesser used in the above solution, decomposed

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the plating bath after a plating time of 2 hours Completely. When this experiment is repeated using 10 ml of a solution of 20.8 g of sodium bisulfite in 200 ml v / ater did not decompose the bath as catastrophically, but did lead to some copper deposition on the container. It should be noted that the sodium bisulfite with the formaldehyde of the solution with formation of the llatrum bisulfite-formaldehyde addition product can react and that this is likely to be responsible for this stability. The strongly alkaline conditions of the bath for electroless copper plating are, however, not the ideal conditions for the sodium bisulfite addition product | of formaldehyde. As mentioned above, dithionites react with formaldehyde to form two products, one of which is the same as the bisulfite addition product of formaldehyde. The following example illustrates the usage this material.

Example 3

If an attempt is made to dissolve sodium dithionite in water, the solution will immediately become cloudy, but if it is placed in dissolves in a formaldehyde solution, the solution remains clear. A solution of 2 g of sodium dithionite in one liter of 37% aqueous Formaldehyde solution was prepared. A 15 ml fraction of this Solution was used to replace the 15 ml formaldehyde in the standard solution. The standard laminate was used in this solution plated overnight. The copper strip held two Bends out in the flex test and the bath was completely stable and showed no signs of degradation or negligence (extraneous) plating after 24 hours. If the standard solution was used and solid sodium dithionite was dissolved therein at a concentration of 20 mg / liter, was obtained also completely stable solutions. The copper films peeled from the laminate were of excellent quality and gave results of 2.5 to 7 bends without tempering. Increasing the concentration of sodium dithionite up to 40 mg / 1 also led to extremely stable solutions. That from the laminate

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removed copper survived 1.5 bends before tempering and 6.5 bends after tempering.

example k

This example illustrates the effect of the quantity variation of the addition product and the possibility of using the solution without aeration for an extended period of time. The addition product of sodium bisulfite was the addition product of 1, 1-butynediol used, which was dissolved in water at a concentration of 4 g / l. I-liter fractions of the standard solution were used in each case used, in which various amounts of the addition product solution were contained. The results are in the summarized below in Table II.

Table II

Duration of the bending test

ml of the solution plating thickness of the copper do not let the adduct (std,) fer plating be left

5 20 1.5 1.5

10 23.5 1.9 2.5 5-6

10 (not 19.5 1.65 1.5 8.5 ventilated)

30 23.5 1.75 1.5 2

Example 5

This example shows the extended life of the copper plating solutions of the present invention and the ability to replace the chemicals used to further extend the useful life of these plating solutions. One liter of the standard solution was admixed with 10 ml of the solution of the bisulfite diadduct des!, IJ-butynediol with a concentration of ^ g / l. The standard laminate was used and plated for 23.75 hours. One side of the laminate had a 0.042 mm (1.67 mil) layer of copper and the other side was 0.052 mm (2.0i} mil). After stripping the copper was _s to survive in the layer 3 * 5 bends without annealing and after annealing 4-5 bends.

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The chemicals consumed were made using the make-up solutions Replaces A and B of the following compositions:

Complementary solutions

A. 225 g / l B. NaOH 410 g / l g / l CuSO ₄ -5H, 9 g / l Rochelle salt • 4H ₂ 0 109 NiCl ₂ 6η! 164 ml / 1 HCHO (37 * ~ 0 '%)

The composition of these two supplementary solutions is based on calculations of the separation of a certain amount Chemicals required for copper. The amount of copper to be added can easily be determined using a colorimeter. In order not to let the volume get too large, a quantity of the used up is before the addition of the supplementary solutions A and B. Plating bath removed, which is equal to the volume of supplement chemicals. The concentration / of A and B are such that 2.5 parts by volume of A per 1 part by volume of B are used will.

After the above precipitation, the solution is made up by first removing 95.8 ml and then adding 68.4 ml of A, -27.4 ml of B and 5 ml of the adduct solution. The solution is then used again to deposit copper on the standard laminate for 23.75 hours. The copper thickness on one side was about 0.039 mm (1.56 mils) and on the other side about 0.042 mm (1.66 mils). After stripping from the laminate, the copper was able to withstand 1.5 bends before tempering and 7.5 BiegungAiach annealing for 20 minutes at 120 ⁰ C.

The solution would be replenished by removing 95.8 ml of the spent plating solution and adding 68.4 ml of solution A, 27.4 ml of solution B and 10 ml of the adduct solution. The standard epoxy resin impregnated fiberglass laminate

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was added and plated for 7.5 hours. The thickness of the copper plating was about Ο ₃ Ο254 mm (1 mil) on one side and about 0.0258 mm (1.02 mils) on the other side. This copper, when removed from the laminate, survived 5.5 bends both before and after tempering.

The solution was made up again by removing 92 ml of the solution and replacing it with 65.7 ml of solution A, 26.3 ml of solution B and 10 ml of the adduct solution.

After plating a standard fiberglass laminate for 17.25 hours, the solution was replenished by removing 100.9 ml of the solution and adding 78.5 ml of solution A, 31.4 ml of solution B and an additional 10 ml of the Adduct solution. A standard laminate was plated for 24 hours. The solution was renewed again by removing 116.6 ml of the solution and adding 83.3 ml of solution A and 33.3 ml of solution B and an additional 10 ml of the adduct solution. At the end of another 24 hours of plating on a standard laminate board the solution still showed no signs of degradation or negligible plating and allowed still the deposition of a very valuable copper on the glass fiber laminate.

Example 6

This example shows that the plating speed is initially greater and decreases as the chemicals in the solution are consumed. It also shows that ventilation is not essential, although it is advantageously used. The standard solution described above was used with the addition of 0.04 g / l of the sodium bisulfite diadduct of 1,4-butynediol. The standard activated laminate was placed in one liter of the solution for 5 hours without aeration. The copper-clad laminate was removed and had a light-colored, flexible copper sheet about 0.026 mm (1.03 mils) thick on its surfaces.

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layer. A second activated (seeded) standard laminate board was placed in the bath and plated overnight without aeration. The next day the bath was still stable with no evidence of decomposition. Although the copper ranks » which had been deposited overnight only formed a very thin copper film on the laminate, it was very light and flexible.

One of the critical requirements of electroless copper plating solutions is pH. If a solution with all the essentials Ingredients is produced, except for the alkali, generally sodium hydroxide, which is only added in an amount If the pH is 9.5, the solution separates out of copper. The pH value must be at least 10 can be increased before deposition occurs and at least to 32 before a reasonably fast deposition rate is reached. If the pH is increased above 13, this affects the stability of an otherwise stable solution.

During the deposition, one of the products of the chemical reaction must be acidic in nature as a control of the solution during plating shows a decrease in pH, causing the plating speed is decreased. In general, adding more alkali to raise the pH will result in a noticeable increase in plating speed from the speed just before the pH change was measured.

It would be desirable to be able to increase the amount of alkali that can be tolerated in the bath without on the other hand to influence the stability. It was found in the invention that this can be achieved by adding a salt raög-J.ich which, together with the alkali in the bath, has a buffering effect at the high pH values found in these baths are caused. All known buffers for a pH value greater than 10 can be used. A particularly good salt

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for this purpose is sodium borate. Boric acid or other metal borates can be used, but in the presence of the large amounts of alkali in these baths, these materials are _{converted, generally Sodium Hydroxide 3} , or act just like sodium borate in solution.

The following example shows the use of sodium borate, to be able to use higher alkali concentrations.

Example 7

Two 1 liter copper plating solutions are prepared using the standard solution, increasing the amount of sodium hydroxide to 25 g / l. Both solutions contain 0.0 ¹ l g / l of the sodium bisulfite diadduct of 1,4-butynediol. In addition, one of the solutions contains 38.1 g / l sodium borate. A standard activated laminate is introduced into each of the solutions. After 5 hours of plating with aeration, the average thickness of the plating on the laminate in the bath without borate was about 0.025 mm (1 mil) and about 0.018 mm (0.7 mil) from the solution with borate. Both solutions were perfectly stable and did not have a negligible copper precipitate. The copper that had precipitated from the bath with the borate was lighter and more flexible than that from the solution without the borate. A next set of standard laminates that had been activated for electroless plating were placed in the baths and plated for an additional 3 hours with aeration, during which time no evidence of instability of any of the baths was observed. The plating speed had decreased so that the average thickness of the copper plating on the laminates from both baths was about 0.007 mm (0.26 mils), showing a decrease in plating speed with time that was less in the solution containing the borate buffer was as in the solution without borate bufferο

Although the above examples all use Rochelle's salt as a complexing agent for copper C'IlQ ions, üur-den with üqp Εϊ? ™

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found also successfully stabilized other baths for electroless copper plating, the other complexing agents for the copper (II) ions have included, for example, those electroless copper plating solutions disclosed in the aforementioned patents. It was, however found that if the complexing agent contains nitrogen, e.g. ethylenedlamine tetraacetic acid or its alkali metal salts, Ethanol amines, nitriloacetic acid, etc., the copper is not as flexible as when nitrogen-free complexing agents be used. Of all the complexing agents investigated, the best results were obtained with those according to the invention Stabilizing agents obtained when Rochelle salt was used as complexing agent j for the copper (II) ions. It was

from also found that the inclusion of small amounts / nickel salt improves the quality of the copper, especially the ductility. Although nickel alone is not plated from such baths If the entire copper salt is replaced by a nickel salt, it was analytically determined that nickel is contained in small amounts in the copper deposited from the solution of the specific examples which Contain nickel. The above specific examples, therefore, represent the best mode of carrying out the invention.

In order to use the solutions according to the invention for preparing To document a circuit board containing plated holes, the following example is given.

Example 8

A fiberglass composite, which is on each of the two Main surfaces wearing copper foils and their individual layers by means of an epoxy resin that contains 2% by weight of tin (II) oxide, connected to each other was used. This laminate and its use for the manufacture of electrical Circuitry is disclosed and claimed in the aforementioned U.S. Patent Application No. 811,012. All kinds of electrical Circuits are made on both surfaces using a standard photosensitive process

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Etch is made by masking the desired areas and using standard etching techniques to produce the desired pattern. After the entire surface of the laminate has been coated with a protective layer, holes are drilled through the laminate at the desired points in the circuit, where circuit components are to be introduced or where connections to the circuit on the opposite side of the laminate are to be made. After blowing off the dust from the holes with air, the laminate is immersed for one minute in a 0.1 '% ± ge aqueous solution of palladium chloride containing about 10 g / l aqueous hydrochloric acid and heated to 60 ⁰ C (l40 ⁰ P ) is heated. This treatment only activates the walls of the drilled holes, since it is only in these that the tin (II) oxide is exposed so that it can reduce the palladium chloride to palladium metal. After rinsing, the palladium that has deposited on the edges of the copper foils that lie in the walls of the hole is removed by immersing the laminate in an aqueous solution of ammonium persulfate containing 2 ^ 0 g / l, which is brought to about 32 ^° C (90 ⁰ P) is eliminated / After rinsing in distilled water, the laminate is placed in a 2-liter bath, the composition of which was the same as that of a standard solution containing an additional 0.04 g / l of the sodium bisulfite Contained diadduct of 1,4-butynediol. The bath was ventilated and plating for 20 hours produced a very light and thick layer of copper in all of the holes drilled. The masking material was stripped from the panel and the copper was cleaned by immersing it in the above ammonium persulfate solution for 30 seconds, then rinsing and drying, after which the entire circuit was tinned using a conventional immersion tinning solution. The circuit components were then simply placed in the desired locations on the circuit pattern and soldered there using a standard wave soldering machine. If any defective components were found, either while testing the circuit or while it was being used

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these components easily unsoldered from the circuit board and replaced with a satisfactory component which can easily be soldered at this point without any danger to the electrical circuit of the de-energized deposited Interrupt copper.

Although the above examples illustrate many modifications that can be made within the scope of the present invention still further variations are readily apparent to the person skilled in the art. It has been found that the Rochelle salt, which is used in the above examples as a complexing | agent for copper (II) ions was used by each other known agents for the chelation of copper (II) ions can be replaced and that already in solutions for electroless Copper plating has been used. The ones used according to the invention Hydroxyl sulfonate compounds can be used in the same way to stabilize such solutions. The copper plating can be applied to the entire surface of the laminate or only to selected parts of it, to make either decorative or useful figures, e.g. electrical circuits. In addition to bare plating On the surface of a laminate, holes can be drilled into this laminate, the walls of which can be easily plated are, if desired, connections between two copper " areas on the two main surfaces of the laminate.

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Claims (10)

Claims Solution for electroless copper plating with a copper (II) ion source, a source of hydroxyl ions sufficient to create a pH value required for electroless copper plating is, an agent that can reduce copper ions to copper metal in the presence of a surface that is catalytic is active to cause the precipitation of copper from the solution and a sufficient amount of a complexing agent, to prevent the precipitation of copper (II) hydroxide from the solution, characterized that the solution is a water-soluble salt of a hydroxyl sulfonate selected from dithionites, Bisulfite addition products of lower alkyl aldehydes and bisulfite addition products of unsaturated, lower aliphatic Contains hydrocarbonols in an amount sufficient to maintain the stability of the plating bath as well as the Improve the quality of the copper plating obtained from the Bath is obtained, but less than the amount * which prevents the deposition of copper from the bath. 2. Solution according to claim i, characterized in that the bisulfite addition product together with a water soluble borate is present. 3. Solution according to claim 1, characterized that the hydroxyl sulfonate is the bisulfite addition product of an unsaturated, lower, aliphatic Is hydrocarbonols. 4. Solution according to claim 1, characterized in that the hydroxyl sulfonate is the bisulfite addition product of an acetylenic, lower, aliphatic Ifrodrocarbonol. 109883/1608 5. Solution according to claim 1, characterized in that the hydroxyl sulfonate is the bisulfite addition product des 1, ^ - butynediol. 6. Solution according to claim 1, characterized in that the hydroxyl sulfonate is the bisulfite addition product of 1,4-butynedioIs, which together with a water soluble borate is present. 7. Method for electroless copper plating, thereby characterized in that one has a catalytically active substrate, which the precipitation of copper from Solutions for electroless copper plating on at least selected parts thereof caused with the plating solution of Brings claim 1 in touch. 8. The method according to claim 7 »characterized that after the deposition of the copper from the substrate, the substrate is tempered, to further improve the quality of the copper plating. 9. Method for electroless copper plating, thereby characterized in that a catalytically active substrate, which the precipitation of copper | from solutions for electroless copper plating, at least on selected parts thereof, with the plating composition according to claim 6 brings into contact. 10. The method according to claim 9, characterized that after the deposition of copper on the substrate, the substrate is annealed in order to improve the quality to further improve the copper plating. "■» • _{Wed. INSPECrED} 109883/1608