KR102459744B1 - Plating bath composition and method for electroless plating of palladium - Google Patents

Abstract

The present invention relates to a water-based plating bath composition and method for depositing a palladium layer by electroless plating on a substrate. The aqueous plating bath composition according to the present invention includes a source of palladium ions, a reducing agent for palladium ions, and an aldehyde compound. The water-based plating bath composition has an increased deposition rate on palladium while maintaining bath stability. The water-based plating bath composition also has an extended life. The aldehyde compounds of the present invention allow the deposition rate to be controlled over the life of the bath, and the electroless deposition of the palladium layer at low temperatures. The aldehyde compound of the present invention activates electroless palladium plating baths with low deposition rates and reactivates old electroless palladium plating baths.

Description

Plating bath composition and method for electroless plating of palladium

The present invention relates to an aqueous plating bath composition and method for electroless plating of palladium for metallization of semiconductor wafers in the manufacture of printed circuit boards and IC boards.

In the metallization of semiconductor wafers, as well as in the manufacture of printed circuit boards, IC boards, etc., the electroless deposition of palladium is a well-established technique. The palladium layer is used, for example, as a barrier layer and/or as a wire-bondable and solderable finish.

An electroless palladium plating bath composition comprising a source of palladium ions, a nitridation complexing agent, and a reducing agent selected from formic acid and derivatives thereof is disclosed in US 5,882,736. The electroless palladium plating bath composition is suitable for depositing pure palladium, unlike the plating bath composition comprising hypophosphite as a reducing agent to form the palladium-phosphorus alloy layers.

US Pat. No. 4,424,241 describes an electroless plating solution comprising palladium, an organic ligand and a reducing agent, namely formaldehyde and formic acid. The reducing agent is used in high concentration. According to US Pat. No. 4,424,241, concentrations that are too low reduce the deposition rate.

Most of the prior art literature teaches palladium plating bath compositions, but the plating rates obtained therefrom cannot satisfy the current demand for steadily increasing the plating rates required to achieve economical production.

Also, the deposition rate constantly decreases over the life of the bath, and if the deposition rate is too low, the life of the electroless palladium plating bath will eventually end. This is due to the catalytic effect of the already deposited palladium and the autocatalytic deposition mechanism. Typically, varying the temperature of the electroless palladium plating bath is used to control the deposition rate and bath life. Increasing the bath temperature also increases the deposition rate. However, operating the bath at a higher temperature simultaneously increases the risk of the bath becoming unstable.

The safety of such a plating bath means that the plating bath is stable against decomposition, ie against undesired precipitation of metallic palladium in the plating bath itself. Thus, the instability of the electroless palladium plating bath ultimately shortens the bath life. Due to the high cost of palladium, early disposal of the electroless palladium plating bath is also undesirable for economic reasons.

It is an object of the present invention to provide a plating bath composition and method for electroless plating of palladium with a further increased deposition rate. Another object of the present invention is to provide a plating bath composition and method for electroless plating of palladium which allows to control the deposition rate to a desired high value. Another object of the present invention is to provide a plating bath composition and method for electroless plating of palladium, wherein the deposition rate is further increased while the bath is still in a stable state. It is a particular object of the present invention to provide a plating bath composition and method for electroless plating of palladium which allows to maintain a constant high deposition rate over the life of the plating bath. It is a further object of the present invention to provide a plating bath composition and method for electroless plating of palladium which allows to increase the life of the plating bath.

These objects are addressed with a water-based plating bath composition for the electroless deposition of palladium comprising;

(i) at least one source for palladium ions;

(ii) at least one reducing agent for palladium ions, and

(iii) at least one aldehyde compound according to formula (I)

wherein R is -H; unsubstituted or substituted, linear alkyl groups containing 1 to 10 carbon atoms; and unsubstituted or substituted, branched alkyl groups containing 3 to 10 carbon atoms; and unsubstituted or substituted aryl groups; and

The at least one aldehyde compound according to formula (I) has a concentration in the range from 0.01 to 25 mg/l.

These objects are further solved by a method for electroless palladium plating comprising the following steps:

(a) providing a substrate;

(b) depositing a layer of palladium on at least a portion of the substrate by contacting the substrate with a water-based plating bath composition as described above.

The water-based plating bath composition according to the present invention is referred to herein as a composition or a composition according to the present invention. The terms “plating” and “deposit” are used interchangeably herein.

The aldehyde compounds according to formula (I) provide water-based plating bath compositions according to the present invention with increased deposition rates and extended lifetimes on palladium, in particular pure palladium. Although increasing the deposition rate, the aldehyde compound according to formula (I) does not impair the stability of the water-based plating bath composition according to the present invention against undesirable degradation. The addition of the aldehyde compound according to formula (I) to the electroless palladium plating bath allows to control the deposition rate over the life of the bath to a certain range. The aldehyde compounds according to formula (I) of the present invention activate an electroless palladium plating bath with a low deposition rate even when an old electroless palladium plating bath is newly prepared and reactivated. The aldehyde compounds according to formula (I) of the present invention allow the electroless deposition of palladium layers at low temperatures.

1 depicts the deposition rate of a water-based plating bath composition containing formaldehyde.
2 depicts the deposition rate of a water-based plating bath composition containing n-propanal.
3 depicts the deposition rates of water-based plating bath compositions containing n-pentanal in the concentration range of 0.25 to 1.25 mg/l.
4 depicts the deposition rates of water-based plating bath compositions containing n-pentanal in the concentration range of 1 to 10 mg/l.

The water-based plating bath composition comprises (iii) at least one aldehyde compound according to formula (i).

wherein R is -H; unsubstituted or substituted, linear alkyl groups containing 1 to 10 carbon atoms; and unsubstituted or substituted, branched alkyl groups containing 3 to 10 carbon atoms; and unsubstituted or substituted aryl groups; and

The at least one aldehyde compound according to formula (I) has a concentration in the range from 0.01 to 25 mg/l.

In one embodiment, R may be -H. In another embodiment, R is preferably not -H.

In a preferred embodiment, R is -H; unsubstituted or substituted, linear alkyl groups containing 1 to 10 carbon atoms; and unsubstituted or substituted, branched alkyl groups containing 3 to 10 carbon atoms.

In another preferred embodiment, R is an unsubstituted or substituted, linear alkyl group containing from 1 to 10 carbon atoms; and unsubstituted or substituted, branched alkyl groups containing 3 to 10 carbon atoms.

In another preferred embodiment, unsubstituted or substituted, linear alkyl groups preferably contain from 1 to 8 carbon atoms, more preferably from 1 to 5 carbon atoms, even more preferably from 2 to 5 carbon atoms. unsubstituted or substituted, linear alkyl groups. More preferably, the unsubstituted or substituted linear alkyl group is preferably selected from the group comprising n-pentyl group, n-butyl group, n-propyl group, ethyl group and methyl group; more preferably selected from n-butyl group, n-propyl group, ethyl group and methyl group; Most preferably it is selected from n-butyl group, n-propyl group and ethyl group.

In another embodiment, unsubstituted or substituted, branched alkyl groups are selected from unsubstituted or substituted, branched alkyl groups, preferably containing 3 to 8 carbon atoms, more preferably 3 to 5 carbon atoms. do. Even more preferably, the unsubstituted or substituted branched alkyl groups are 2-pentyl (sec-pentyl) group, 3-pentyl group, 2-methylbutyl group, 3-methylbutyl (iso-pentyl) group, 3-methylbut -2-yl group, 2-methylbut-2-yl group; 2,2-dimethylpropyl (neo-pentyl) group, iso-butyl group, sec-butyl group, tert-butyl group and iso-propyl group; Most preferably it is selected from an iso-butyl group, a sec-butyl group, and an iso-propyl group.

In another embodiment, the unsubstituted or substituted aryl group is an unsubstituted or substituted aryl group, preferably containing 6 to 10 carbon atoms; more preferably an unsubstituted or substituted phenyl group and an unsubstituted or substituted naphthyl group; Most preferably selected from unsubstituted or substituted phenyl groups.

In a further embodiment, the linear alkyl group, branched alkyl group or aryl group is preferably substituted. Preferably, the substituents are amino, carboxyl, ester, mercapto, hydroxyl, methoxy, ethoxy, methyl, ethyl, halogen such as fluorine, chlorine, bromine, iodine; independently of each other from the group comprising allyl, vinyl and aryl groups; preferably amino, carboxyl, ester, hydroxyl, methoxy, ethoxy, methyl, ethyl, halogen such as fluorine, chlorine, bromine, iodine; and an aryl group; more preferably carboxyl, ether, hydroxyl, methoxy, ethoxy, methyl, ethyl, halogen such as fluorine, chlorine, bromine, iodine; and an aryl group.

In a more preferred embodiment, the at least one aldehyde compound according to formula (I) is hexanal (hexanealdehyde), pentanal (valderaldehyde), butanal (butyraldehyde), propanal (propionaldehyde), etanal ( acetaldehyde), methanal (formaldehyde), phenylmethanal (benzaldehyde) and 2-phenylacetaldehyde; preferably n-hexanal, n-pentanal, n-butanal, n-propanal and etanal; more preferably n-pentanal, n-butanal, n-propanal, and etanal, even more preferably n-hexanal, n-pentanal, n-butanal and n-propanal selected from the group.

As used herein and in the claims, the term “alkyl” refers to a hydrocarbon radical having the general formula C _n H _2n+1 , where n is an integer from 1 to 10. The alkyl moieties according to the invention may be linear and/or branched, preferably saturated. For example, a linear alkyl group comprising 1 to 10 carbon atoms means a linear alkyl group having a total number of C atoms in the range of 1 to 10 each. A branched alkyl group comprising 3 to 10 carbon atoms means a branched alkyl group wherein the sum of the C atoms of the backbone and the C atoms of the branched chain results in a total number of C atoms in the range of 3 to 10, respectively. A linear alkyl group containing 1 to 8 carbon atoms or a branched alkyl group containing 3 to 8 carbon atoms includes, for example, methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl or octyl. A linear alkyl group comprising from 1 to 5 carbon atoms or a branched alkyl group comprising from 3 to 5 carbon atoms includes, for example, methyl, ethyl, propyl, butyl or pentyl.

To the extent that the term “aryl” is used herein and in the claims, it refers to a cyclic aromatic hydrocarbon radical such as phenyl or naphthyl.

In addition, the alkyl and/or aryl may in each case be substituted by replacing the H atom with a substituent as described above for the linear alkyl group, branched alkyl group and/or aryl group.

the at least one aldehyde compound according to formula (I) has a concentration in the water-based plating bath composition according to the invention in the range from 0.01 to 25 mg/l; Preferably it is 0.01-10 mg/l, More preferably, it is 0.1-10 mg/l.

Surprisingly and in contrast to the prior art, it has been found that aldehyde compounds increase the deposition rate of electroless palladium plating baths when included in concentrations lower than those used in the aldehyde reducing agent.

A water-based plating bath composition according to the present invention comprises at least one source of palladium ions. Preferably, the at least one source of palladium ions is a water-soluble palladium compound. More preferably, the at least one source of palladium ions is selected from the group comprising palladium chloride, palladium acetate, palladium sulfate and palladium perchlorate. Optionally, instead of forming these complexing compounds in the plating bath by adding the palladium salt and complexing agent for palladium ions as separate components to the plating bath, a complexing agent for palladium ions and palladium ions, preferably nitrogenated A complexing compound comprising a complexing agent may be added to the plating bath. Complexing compounds suitable as a source for palladium ions include, for example, complexing compounds comprising palladium ions and a complexing agent; preferably nitrogenated complexing agents; More preferred are ethane-1,2-diamine and/or alkyl substituted ethane-1,2-diamine. Suitable complexing compounds may further comprise counter ions to palladium ions; Preferred are chloride, acetate, sulfate or perchlorate. Suitable nitrogenated complexing agents and alkyl substituted ethane-1,2-diamines are defined below as complexing agents. Preferably, complexing compounds suitable as a source of palladium ions include, for example, dichloro ethane-1,2-diamine palladium diacetato ethane-1,2-diamine palladium; dichloro N ¹ -methylethane-1,2-diamine palladium; diacetato N ¹ -methylethane-1,2-diamine palladium; dichloro N ¹ ,N ² -dimethylethane-1,2-diamine palladium; diacetato N ¹ ,N ² -dimethylethane-1,2-diamine palladium; dichloro N ¹ -ethylethane-1,2-diamine palladium; diacetato N ¹ -ethylethane-1,2-diamine palladium, dichloro N ¹ ,N ² -diethylethane-1,2-diamine palladium; and diacetato N ¹ ,N ² -diethylethane-1,2-diamine palladium.

The concentration of palladium ions in the composition ranges from 0.5 to 500 mmol/l, preferably from 1 to 100 mmol/l.

The aqueous plating bath composition according to the present invention further comprises at least one reducing agent for palladium ions. The reducing agent makes the plating bath autocatalytic, ie an electroless plating bath. The palladium ions are reduced to metallic palladium in the presence of the reducing agent. This plating mechanism provides a plating bath according to the present invention, 1) an immersion type palladium plating bath containing no reducing agent for palladium ions, and 2) for the electroplating of palladium which requires an external current to deposit the palladium layer. Distinguish from plating baths.

The at least one reducing agent is preferably a chemical reducing agent. The reducing agent reduces the metal ion to its metal form and provides the electrons needed to form a metal deposit on the substrate.

More preferably, the at least one reducing agent is a reducing agent for depositing pure palladium deposits. A pure palladium deposit is a deposit containing palladium in an amount of at least 98.0 to 99.99% by weight, preferably at least 99.0 to 99.99% by weight.

Even more preferably, the at least one reducing agent for palladium ions is selected from the group consisting of hydrazine, formic acid, derivatives thereof and salts thereof.

Even more preferably, the at least one reducing agent for palladium ions is selected from the group consisting of formic acid, derivatives of formic acid and salts thereof. Even more preferably, the formic acid derivative is selected from esters of formic acid. Even more preferably, the ester of formic acid is selected from the group consisting of formic acid methyl ester, formic acid ethyl ester and formic acid propyl ester. Suitable counter ions for the formic acid salt are, for example, selected from hydrogen, lithium, sodium, potassium and ammonium. The aqueous plating bath composition according to the invention is particularly suitable for depositing a palladium layer in the presence of formic acid, their derivatives and salts as reducing agent.

Preferably, the at least one reducing agent is not formaldehyde.

Preferably, the concentration of the at least one reducing agent in the water-based plating bath composition according to the invention ranges from 10 to 1000 mmol/l.

Preferably, the molar ratio of the reducing agent to palladium ions in the composition according to the present invention to palladium ions is 1: 10 to 10: 1; more preferably 1: 5 to 5: 1; More preferably, it is 1:3 to 3:1.

The water-based plating bath composition according to the invention is particularly suitable for depositing pure palladium layers. The pure palladium layer allows for sufficient thermal stability of the bonded or brazed connections, so the pure palladium layer is particularly suitable for high temperature applications such as in motor control devices.

Hypophosphite ions and/or amine borane compounds and/or sodium borhydride are not suitable as reducing agents because palladium alloy layers are deposited from such plating bath compositions.

The aqueous plating bath composition according to the present invention may further include at least one complexing agent for palladium ions. Complexing agents (also referred to as chelating agents) keep metal ions dissolved and prevent unwanted precipitation from solution.

Preferably, the at least one complexing agent is a nitrogenated complexing agent for palladium ions. More preferably, the at least one nitrogenated complexing agent is selected from the group comprising primary amines, secondary amines and tertiary amines. More preferably, the at least one nitrogenated complexing agent is selected from the group comprising diamines, triamines, tetraamines, and higher homologs thereof.

Suitable amines are, for example, ethane-1,2-diamine (NH ₂ -CH ₂ -CH ₂ -NH ₂ , ethylene diamine); alkyl substituted ethane-1,2-diamine; 1,3-diamino-propane; 1,2-Bis(3-amino-propyl-amino)-ethane; diethylene-triamine; diethylene-triamine-penta-acetic acid; N-(2-hydroxy-ethyl)-ethylene-diamine; ethylene-diamine-N,N-diacetic acid; 1,2-diamino-propyl-amine; 1,3-diamino-propyl-amine; 3-(methyl-amino)-propyl-amine; 3-(dimethyl-amino)-propyl-amine; 3-(diethyl-amino)-propyl-amine; bis-(3-amino-propyl)-amine; 1,2-Bis-(3-amino-propyl)-alkyl-amine; diethylene-triamine; triethylene-tetraamine; tetra-ethylene-pentamine; penta-ethylene-hexamine and mixtures thereof.

Suitable alkyl substituted ethane-1,2-diamines are, for example, N ¹ -methylethane-1,2-diamine (CH ₃ -NH-CH ₂ -CH ₂ -NH ₂ ); N ¹ ,N ² -dimethylethane-1,2-diamine (CH ₃ -NH-CH ₂ -CH ₂ -NH-CH ₃ ); N ¹ ,N ¹ -dimethylethane-1,2-diamine ((CH ₃ ) ₂ -N-CH ₂ -CH ₂ -NH ₂ ); N ¹ ,N ¹ ,N ² -trimethylethane-1,2-diamine ((CH ₃ ) ₂ -N-CH ₂ -CH ₂ -NH-CH ₃ ); N ¹ ,N ¹ ,N ² ,N ² -tetramethylethane-1,2-diamine ((CH ₃ ) ₂ -N-CH ₂ -CH ₂ -N-(CH ₃ ) ₂ ); N ¹ -ethylethane-1,2-diamine (C ₂ H ₅ -NH-CH ₂ -CH ₂ -NH ₂ ); N ¹ ,N ² -diethylethane-1,2-diamine (C ₂ H ₅ -NH-CH ₂ -CH ₂ -NH-C ₂ H ₅ ); N ¹ -ethyl-N ² -methylethane-1,2-diamine (C ₂ H ₅ -NH-CH ₂ -CH ₂ -NH-CH ₃ ); N ¹ -ethyl-N ¹ -methylethane-1,2-diamine ((CH ₃ )(C ₂ H ₅ )-N-CH ₂ -CH ₂ -NH ₂ ); N ¹ ,N ¹ -diethylethane-1,2-diamine ((C ₂ H ₅ ) ₂ -N-CH ₂ -CH ₂ -NH ₂ ); N ¹ -ethyl-N ¹ ,N ² -dimethylethane-1,2-diamine ((CH ₃ )(C ₂ H ₅ )-N-CH ₂ -CH ₂ -NH-CH ₃ ); N ¹ ,N ² -diethyl-N ¹ -methylethane-1,2-diamine ((CH ₃ )(C ₂ H ₅ )-N-CH ₂ -CH ₂ -NH-(C ₂ H ₅ )); N ¹ ,N ¹ -diethyl-N ² -methylethane-1,2-diamine ((C ₂ H ₅ ) ₂ -N-CH ₂ -CH ₂ -NH-CH ₃ ); N ¹ ,N ¹ ,N ² -triethylethane-1,2-diamine ((C ₂ H ₅ ) ₂ -N-CH ₂ -CH ₂ -NH-C ₂ H ₅ ); N ¹ -Ethyl-N ¹ ,N ² ,N ² -trimethylethane-1,2-diamine ((CH ₃ )(C ₂ H ₅ )-N-CH ₂ -CH ₂ -N-(CH ₃ ) ₂ ) ; N ¹ ,N ² -diethyl-N ¹ ,N ² -dimethylethane-1,2-diamine ((CH ₃ )(C ₂ H ₅ )-N-CH ₂ -CH ₂ -N-(CH ₃ )( C ₂ H ₅ )); N ¹ ,N ¹ -diethyl-N ² ,N ² -dimethylethane-1,2-diamine ((C ₂ H ₅ ) ₂ -N-CH ₂ -CH ₂ -N-(CH ₃ ) ₂ ); N ¹ ,N ¹ ,N ² -triethyl-N ² -methylethane-1,2-diamine ((C ₂ H ₅ ) ₂ -N-CH ₂ -CH ₂ -N-(CH ₃ )(C ₂ H ₅ )); N ¹ ,N ¹ ,N ² ,N ² -tetraethylethane-1,2-diamine ((C ₂ H ₅ ) ₂ -N-CH ₂ -CH ₂ -N-(C ₂ H ₅ ) ₂ ) and these are mixtures of

Preferably, the molar ratio of complexing agent and palladium ion to palladium ion in the composition according to the invention ranges from 1:1 to 50:1.

The aqueous plating bath composition according to the present invention may further include at least one stabilizer. Stabilizers, also called stabilizers, are compounds that stabilize the electroless metal plating solution against unwanted outplating in bulk solutions and spontaneous decomposition. The term "outplating" means the undesired and/or uncontrolled deposition of metal on a surface other than the substrate surface.

The at least one stabilizer is selected from the group consisting of selenium, tellurium, copper, nickel and iron elements and/or compounds of mercapto-benzothiazole, seleno-cyanate, thiourea, saccharin, ferrocyanate; 4-nitrobenzoic acid; 3,5-dinitrobenzoic acid; 2,4-dinitrobenzoic acid; 2-hydroxy-3,5-dinitrobenzoic acid; 2-acetylbenzoic acid; 4-nitrophenol and their corresponding ammonium, sodium and potassium salts.

Preferably, the concentration of such additional stabilizers in the composition according to the invention is from 0.01 to 500 mg/l, more preferably from 0.1 to 200 mg/l, even more preferably from 1 to 200 mg/l, most preferably is in the range from 10 to 100 mg/l.

Preferably, the water-based plating bath composition according to the present invention is an acidic plating bath. The pH-value of the aqueous plating bath composition is more preferably in the range of 4 to 7 because the composition is unstable at a pH-value of less than 4. More preferably, the pH-value of the composition ranges from 5 to 6. At pH-values greater than 7, the composition tends to deposit palladium on the substrate by immersion type plating resulting in weak adhesion between the palladium layer and the underlying substrate. Furthermore, plating bath compositions having a pH-value greater than 7 will also attack organic resist materials that may be part of the substrate, such as solder mask materials.

The present invention relates to a method for electroless palladium plating comprising the steps of:

a) providing a substrate;

b) contacting the substrate with a water-based plating bath composition according to the present invention to deposit a layer of palladium on at least a portion of the substrate.

Preferably, the steps of the method are performed in the order described above. Preferably, the substrate has a metal surface.

The palladium plating or deposition of palladium is preferably carried out by contacting the composition according to the invention with a substrate having a metal surface, whereby a layer of palladium is deposited on at least a portion of the metal surface of the substrate. Preferably, the metal surface or a portion thereof coated with palladium is selected from the group comprising copper, copper alloys, nickel, nickel alloys, cobalt, cobalt alloys, platinum, platinum alloys, gold, gold alloys and gallium arsenide. The metal surface or part thereof to be coated is, for example, part of a printed circuit board, an IC substrate or a semiconductor wafer. Palladium layers are used on semiconductor wafers as, for example, semiconductor chips, light emitting diodes (LEDs) or precious metals in solar cells, wire bondable and solderable finishes.

Suitable methods of contacting the substrate with the aqueous-based electroless plating bath composition are, for example, dipping the substrate into the composition, or spraying the composition onto the substrate.

Preferably, the substrate is subjected to a water-based plating bath composition according to step b) at a temperature of 30 to 95 °C, more preferably 30 to 85 °C, still more preferably 50 to 85 °C, even more preferably 30 to 65 °C. contact with Preferably, the substrate is contacted with the composition for 1 to 60 minutes, more preferably 10 to 20 minutes. Preferably, the substrate is contacted with the water-based plating bath composition to provide a palladium plating layer in a thickness range of 0.01 to 5.0 μm, more preferably 0.02 to 2.0 μm, still more preferably 0.05 to 0.5 μm.

The thickness of the palladium layer was measured by x-ray fluorescence (XRF), which is well known to those skilled in the art. XRF measurements use characteristic fluorescence radiation emitted from samples (substrates, deposits) excited with x-rays. By evaluating the wavelength and intensity and assuming the layer structure of the sample, the layer thickness can be calculated.

In one embodiment of the invention, a thin activation layer of palladium is first deposited on a substrate by an immersion-type plating method (exchange reaction), preferably on a substrate having a metallic surface, and then Palladium deposition occurs from the water-based plating bath composition.

Methods of activation for metal surfaces prior to electroless palladium deposition are known in the art and can be applied in practicing the present invention. Suitable water-based activation baths include palladium salts such as palladium acetate, palladium sulfate and palladium nitrate, complexing agents for palladium ions such as primary amines, secondary amines, tertiary amines and ethanolamines, and acids, for example nitric acid, sulfuric acid and methane sulfonic acid. Optionally, such activating bath further contains an oxidizing agent such as nitrate ions, perchlorate ions, chlorate ions, perborate ions, peroxate ions, peroxo-disulfate ions and peroxide ions.

The concentration of the palladium salt in the aqueous activation bath ranges from 0.005 to 20 g/l, preferably from 0.05 to 2.0 g/l. The concentration of the complexing agent for palladium ions is in the range from 0.01 to 80 g/l, preferably from 0.1 to 8 g/l.

The pH value of the aqueous activation bath is preferably in the range from 0 to 5, preferably from 1 to 4.

Typically, the substrate is immersed in a water-based activation bath at 25-30° C. for 1-4 minutes. Before the substrate is immersed in the water-based activation bath, the metal surface of the substrate is cleaned. For this purpose, etch cleaning is usually carried out in oxidizing, acidic solutions, for example solutions of sulfuric acid and hydrogen peroxide. Preferably, this is followed by another washing in an acidic solution, for example a sulfuric acid solution.

The aldehyde compound according to formula (1) of the present invention increases the deposition rate of the aqueous plating bath composition on the electroless deposition of palladium, in particular on the electroless deposition of pure palladium. Thus, the water-based plating bath composition is activated and the deposition process is accelerated. This contributes to the acceleration of the manufacturing process.

The deposition rate of known electroless palladium deposition baths usually continues to decrease over the life of the bath. Therefore, in the case of plating using an old palladium deposition bath compared to a newly prepared palladium deposition bath, a longer plating time is required to obtain palladium layers of the same thickness and quality. Addition of an aldehyde compound according to formula (I) to an electroless palladium plating bath to control the deposition rate to a constant range over the life of the bath, in particular to a constant high range of the deposition rate over the life of the bath allow This ensures the deposition of constant thickness palladium layers over the life of the electroless palladium plating bath and facilitates process control of the manufacturing process.

If the deposition rate of a known electroless palladium deposition bath is too low, the deposition bath is no longer suitable for depositing palladium and must be discarded. Controlling the deposition rate to a constant range over the life of the bath, particularly to a constant high range, also extends the life of the electroless palladium plating bath.

In addition, the aldehyde compounds according to formula (I) of the present invention activate electroless palladium plating baths with low deposition rates even when freshly prepared. In addition, the aldehyde compounds according to formula (I) of the present invention reactivate the old electroless palladium plating bath. An old electroless palladium plating bath refers to an electroless palladium plating bath already used for plating herein whose deposition rate has already dropped during such use. Reactivating also means that the aldehyde compounds according to formula (I) increase the deposition rate of the old electroless palladium plating bath.

In known electroless palladium plating baths and deposition methods, controlling the deposition rate and duration of bath life is achieved by increasing the bath temperature to 55-95° C. during deposition. However, the temperature rise of the electroless palladium plating bath has several disadvantages. Operating the bath at a higher temperature increases the risk of the bath becoming unstable. Higher energy consumption is required. There are drawbacks to some metal layers present on the substrate to be plated. For example, an aluminum or copper layer undergoes corrosion when present on a substrate that is plated with palladium from a deposition bath at high temperatures. The aldehyde compounds according to formula (I) of the present invention allow the electroless deposition of the palladium layer at low temperatures of 30 to 65 °C. Thus, the stability of the water-based plating bath composition of the present invention is maintained and corrosion of the metal layer also present on the substrate during the deposition of palladium from the composition is prevented.

The present invention also relates to a method for controlling the deposition rate in a range over the lifetime of any electroless palladium deposition bath, the method comprising the steps of:

c) providing an optional electroless palladium deposition bath, and

d) adding to the electroless palladium deposition bath at least one aldehyde compound according to formula (I) as defined above.

The electroless palladium deposition bath may be any electroless palladium deposition bath, for example any water-based electroless palladium deposition bath. In one embodiment, the electroless palladium deposition bath is a water-based plating bath composition according to the present invention.

In one embodiment of the present invention, the electroless palladium deposition bath may be a freshly prepared electroless palladium deposition bath.

In another embodiment, the electroless palladium deposition bath may already be used for some time for plating.

Also in a preferred embodiment, the electroless palladium deposition bath is a bath for the electroless deposition of pure palladium.

The deposition rate or concentration of the at least one aldehyde compound according to formula (I) may be determined during plating or storage. If the deposition rate or concentration of the at least one aldehyde compound according to formula (I) is below a threshold value, the at least one aldehyde compound according to formula (I) is replenished. Replenishment is carried out by adding at least one aldehyde compound according to formula (I) to the electroless palladium deposition bath.

The at least one aldehyde compound according to formula (I) may be added as a solid or powder or may be dissolved in a solvent prior to being added to the electroless palladium deposition bath. Examples of suitable solvents include water; acids such as sulfuric acid, hydrochloric acid, phosphoric acid; alkaline solutions such as solutions of sodium hydroxide or potassium hydroxide; and organic solvents such as propanol, ethanol, and methanol.

In another preferred embodiment, the electroless palladium deposition bath can already be used for a period of time for plating, the deposition rate dropping relative to the initial deposition rate. In this embodiment, the present invention relates to a method of reactivating an aqueous-based electroless palladium deposition bath, comprising the steps of:

e) providing a previously used aqueous-based electroless palladium deposition bath, the deposition rate of which drops in relation to the initial deposition rate;

f) increasing the rate of its deposition by adding at least one aldehyde compound according to formula (I) not defined above.

The present invention also relates to the use of at least one aldehyde compound according to formula (I) for

accelerating palladium deposition from any electroless palladium deposition bath, and/or

adjusting the deposition rate to a range over the life of any electroless palladium deposition bath, and/or

Reactivating an electroless palladium deposition bath already used during plating, the deposition rate of which dropped relative to its initial deposition rate.

examples

The invention is further illustrated by the following non-limiting examples.

general procedures

substrates and pretreatment;

A test chip made of silicon covered with a SiO ₂ layer and having four dies each was used as the substrate. Each die had several isolated pads of aluminum-copper alloy on its surface. The diameters of the pads varied from 10 μm to 1000 μm, and the distance between the pads ranged from 20 μm to 1000 μm.

The test chips were already pretreated with double-zinccation. Thereafter, the test chip is nickel-plated using an electroless nickel plating bath (Xenolyte Ni MP, product of Atotech Deutschland GmbH) containing a nickel(II) salt, a reducing agent for nickel ions, a complexing agent for nickel ions and a stabilizer. plated. The nickel plating bath had a pH value of 4.5 and was maintained at 87° C. during plating. The test chip was immersed in a nickel plating bath for 10 minutes and a nickel layer with a thickness of 3 μm was plated on the test chip. The test chips were then rinsed in deionized water and placed in a palladium plating bath.

Palladium plating bath matrix and palladium plating:

A plating bath matrix (Xenolyte Pd LL, product of Atotech Deutschland GmbH) having a pH value of 5.5 and comprising water, palladium ions, sodium formate as reducing agent for palladium ions and ethylene diamine as complexing agent for palladium ions was prepared throughout all examples was used. Different production batches of sodium formate with different purities were used in the examples.

Different amounts of aldehyde compounds according to formula (I) of the present invention were added over Examples 1-4 to 2 I of individual palladium plating bath matrix. The water-based plating bath composition was maintained at 55° C. during plating. The substrate was immersed in the water-based plating bath composition for 6 minutes. After that, the substrate was rinsed with deionized water for 1 minute and air dried.

Determination of Deposition Rate:

The thickness of the palladium layers deposited on the various water-based plating bath compositions tested was determined by X-ray fluorescence (XRF; Fischer, Fischerscope® X-Ray XDV®-11). Thickness was measured on four palladium pads for each substrate. The deposition rate for each water-based plating bath composition was calculated by dividing the measured thickness of the deposited palladium layer by the plating time of 6 minutes. The average values of the deposition rates for each substrate are presented in Examples 1-4 below.

Example 1

Example 1 was performed with a plating bath matrix containing different batches of sodium formate: batch 2 with high purity and batch 3 with lower purity. 0-10 mg/l of formaldehyde was added to the plating bath. The water-based plating bath composition and plating results are summarized in Table 1 and shown in FIG. 1 .

Deposition Rate of Aqueous Plating Bath Compositions Containing Formaldehyde
Concentration of formaldehyde [mg/l] Deposition rate [nm/min] Batch 2 reducing agent Batch 3 reducing agent compare 0 49 71 according to the invention One 51 72 10 68 81

Example 2

Example 2 was performed with a plating bath matrix containing different batches of sodium formate: batch 2 with high purity and batch 3 with lower purity. 0-10 mg/l of n-propanol was added to the plating bath matrix. The water-based plating bath composition and plating results are summarized in Table 2 and shown in FIG. 2 .

Deposition Rate of Aqueous Plating Bath Compositions Containing n-Propanal
Concentration of n-propanal [mg/l] Deposition rate [nm/min] Batch 2 reducing agent Batch 3 reducing agent compare 0 48 69 according to the invention One 53 71 10 65 79

Example 3

0-1.25 mg/l of n-pentanal was added to the plating bath matrix. The plating bath matrix contained the sodium formate of production batch 1 with the highest purity. The water-based plating bath composition and plating results are summarized in Table 3 and shown in FIG. 3 .

Deposition Rate of Water-Based Plating Bath Compositions Containing n-Pentanal
Concentration of n-pentanal [mg/l] Deposition rate [nm/min]
Batch 1 reducing agent compare 0 35.1 according to the invention 0.25 38.6 1.25 43.2

Example 4

0-10 mg/l of n-pentanal was added to the plating bath matrix. The plating bath matrix contained sodium formate of production batch 2 with high purity. The water-based plating bath composition and plating results are summarized in Table 4 and shown in FIG. 4 .

Deposition Rate of Water-Based Plating Bath Compositions Containing n-Pentanal
Concentration of n-pentanal [mg/l] Deposition rate [nm/min]
Batch 2 reducing agent compare 0 44 according to the invention One 50 5 53 10 58

Summary of Results for Examples 1-4

Examples 1 to 4 showed that the deposition rate of the aqueous plating bath composition containing the aldehyde compound according to formula (1) was higher than that of the composition lacking the aldehyde compound. As the concentration of the aldehyde compound increased, the deposition rate increased. The deposition rates for the composition containing no aldehyde compound therein (the comparative composition of Examples 1 to 4) are different from each other due to the different batches of sodium formate used.

Deposits obtained from water-based plating bath compositions with or without an aldehyde compound according to formula (I) were 98-99.99 wt.-% pure, ductile, gray-white in color, and adhered very well to substrates.

Example 5

0-50 mg/l of n-pentanal was added to the plating bath matrix. The plating bath matrix contained sodium formate of production batch 2 with high purity. The water-based plating bath compositions and plating results are summarized in Table 5.

Deposition Rate of Water-Based Plating Bath Compositions Containing n-Pentanal
Concentration of n-pentanal [mg/l] Deposition rate [nm/min]
Batch 2 reducing agent compare 0 43 according to the invention 5 52 10 58 50 42

Example 6

0-1.25 mg/l of n-hexanal was added to the plating bath matrix. The plating bath matrix contained the sodium formate of production batch 1 with the highest purity. The water-based plating bath compositions and plating results are summarized in Table 6.

Deposition Rate of Water-Based Plating Bath Compositions Containing n-Pentanal
Concentration of n-pentanal [mg/l] Deposition rate [nm/min]
Batch 1 reducing agent compare 0 36.1 according to the invention 0.25 37.9 1.25 41.4

Claims (15)

A water-based plating bath composition for electroless deposition of palladium, comprising:
(i) at least one source for palladium ions;
(ii) at least one reducing agent for palladium ions, said at least one reducing agent selected from the group consisting of hydrazine, formic acid, derivatives thereof and salts thereof, and
(iii) at least one aldehyde compound according to formula (I),

wherein R is an unsubstituted or substituted, linear alkyl group containing 1 to 10 carbon atoms; and unsubstituted or substituted, branched alkyl groups containing 3 to 10 carbon atoms; and substituted or unsubstituted aryl groups; and
wherein said at least one reducing agent (ii) is not formaldehyde,
A water-based plating bath composition for the electroless deposition of palladium, wherein the at least one aldehyde compound according to formula (I) has a concentration ranging from 0.01 to 25 mg/l. The method of claim 1,
wherein the unsubstituted or substituted, linear alkyl groups are selected from the group comprising an n-pentyl group, an n-butyl group, an n-propyl group, an ethyl group and a methyl group. The method of claim 1,
The unsubstituted or substituted, branched alkyl groups include 2-pentyl group, 3-pentyl group, 2-methylbutyl group, 3-methylbutyl group, 3-methylbut-2-yl group, 2-methylbut-2-yl group; A water-based plating bath composition for electroless deposition of palladium, selected from the group comprising 2,2-dimethylpropyl, iso-butyl, sec-butyl, tert-butyl and iso-propyl. The method of claim 1,
wherein the unsubstituted or substituted aryl groups are selected from unsubstituted or substituted phenyl groups and unsubstituted or substituted naphthyl groups. 5. The method according to any one of claims 1 to 4,
The linear alkyl groups, the branched alkyl groups, or the aryl groups are substituted and the substituents are independently of each other amino, carboxyl, ester, mercapto, hydroxyl, methoxy, ethoxy, methyl, ethyl, halogen, allyl , a water-based plating bath composition for electroless deposition of palladium, selected from the group comprising vinyl and aryl groups. 5. The method according to any one of claims 1 to 4,
wherein the at least one aldehyde compound according to formula (I) is selected from hexanal, pentanal, butanal, propanal, etanal, phenylmethanal and 2-phenylacetaldehyde in water-based for the electroless deposition of palladium Plating bath composition. 5. The method according to any one of claims 1 to 4,
The at least one source for the palladium ions is palladium chloride, palladium acetate, palladium sulfate, palladium perchlorate, dichloroethane-1,2-diamine palladium, diacetatoethane-1,2-diamine palladium; dichloro N ¹ -methylethane-1,2-diamine palladium; diacetato N ¹ -methylethane-1,2-diamine palladium; dichloro N ¹ ,N ² -dimethylethane-1,2-diamine palladium; diacetato N ¹ ,N ² -dimethylethane-1,2-diamine palladium; dichloro N ¹ -ethylethane-1,2-diamine palladium; diacetato N ¹ -ethylethane-1,2-diamine palladium, dichloro N ¹ ,N ² -diethylethane-1,2-diamine palladium; and diacetato N ¹ ,N ² -diethylethane-1,2-diamine palladium. A water-based plating bath composition for electroless deposition of palladium. 5. The method according to any one of claims 1 to 4,
A water-based plating bath composition for electroless deposition of palladium, further comprising at least one complexing agent for palladium ions selected from the group consisting of primary amines, secondary amines and tertiary amines. The method of claim 1,
wherein the derivatives of formic acid are selected from esters of formic acid. 5. The method according to any one of claims 1 to 4,
wherein the concentration of the at least one reducing agent is in the range of 10 to 1000 mmol/l. A method for electroless palladium plating comprising:
(a) providing a substrate;
(b) contacting the substrate with the water-based plating bath composition of any one of claims 1 to 4 to deposit a layer of palladium on at least a portion of the substrate. way for. 12. The method of claim 11,
wherein the substrate is contacted with the water-based plating bath composition at a temperature of 30 to 65° C. in step (b). A method of regulating a deposition rate in a constant range over the life of an electroless palladium deposition bath, the method comprising:
c) (i) at least one source for palladium ions; and (ii) providing an electroless palladium deposition bath comprising at least one reducing agent as defined by claim 1;
d) adding to said electroless palladium deposition bath at least one aldehyde compound according to formula (I) as defined by claim 1,
wherein the at least one aldehyde compound according to formula (I) has a concentration in the bath ranging from 0.01 to 25 mg/l. A method of reactivating an aqueous electroless palladium deposition bath comprising:
e) providing a previously used aqueous-based electroless palladium deposition bath, wherein said previously used aqueous-based electroless palladium deposition bath comprises (i) at least one source for palladium ions; and (ii) at least one reducing agent as defined by claim 1 , wherein the deposition rate is dropped relative to its initial deposition rate; and
f) adding at least one aldehyde compound according to formula (I) as defined by claim 1 to increase its deposition rate,
wherein the at least one aldehyde compound according to formula (I) has a concentration in said bath ranging from 0.01 to 25 mg/l. delete

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