Palladium-nickel alloy plating solution

Abstract

The present application relates to a palladium-nickel alloy electroplating solution, which is composed of: tetraammine palladium sulfate 45-55 g / L, nickel sulfamate 30-40 g / L, ammonium sulfate 120-160 g / L, urea 20-40 g / L, complexing agent 20-30 ml / L, brightener 3-6 ml / L, and wetting agent 1-2 ml / L. The high-speed continuous plating process specification is: PH 6.8-7.5, temperature 50-60 DEG C, cathode current density 20-50 A / dm2, and titanium anode as anode. After pulse electroplating, the alloy plating layer contains 75-85% of palladium and 15-25% of nickel, and has excellent electrical properties and corrosion resistance, and can completely replace gold plating layer or hard gold layer, saving more than 20% of precious metals. The complexing agent used in the present application is divided into two categories: A type is hydroxyethyl and hydroxypropyl compound of organic amine; and B type is high molecular organic amine polyurea quaternary ammonium salt cationic compound. The brightener used in the present application is pyridine, thiazole, and imidazole heterocyclic derivative. Through the combined application of complexing agent and brightener, the technical problem of unstable palladium content in palladium-nickel alloy plating layer is solved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of electronic plating, and particularly relates to a palladium-nickel alloy plating solution. BACKGROUND

[0002] The palladium-nickel alloy plating layer (containing 80% palladium and 20% nickel) can replace pure gold plating layer or hard gold plating layer, and can reach the quality standard of gold plating layer in contact resistance, brazing property, wear resistance, ductility and corrosion resistance, etc. Meanwhile, about 25% of noble metal can be saved. Therefore, the relative stability of the content of the two metals in the palladium-nickel alloy plating layer is very important.

[0003] In recent years, with the vigorous development of electronic industry, various electrical properties, physical properties and corrosion resistance of electronic components are extremely high. While electronic plating is rapidly developing in scale and intelligence, cost reduction and efficiency increase are also the inevitable choice of the industry. At present, the price of gold is high, and the best plating layer to replace gold plating layer is still palladium-nickel alloy plating layer.

[0004] The stability of the traditional palladium-nickel alloy plating process is insufficient in the following aspects:

[0005] 1. Most of the palladium chloride (or ammonium palladium chloride) is used as the main salt, and its shortcomings are as follows: the chloride ion is oxidized to chlorine gas or other chlorate at the anode, which has an oxidizing effect on other organic matters in the plating solution; when the residual chloride ion on the plating layer is not completely cleaned in the washing tank, the corrosion resistance of the alloy plating layer is affected, resulting in unqualified salt spray test. Therefore, tetraammonium palladium sulfate is used as the main salt.

[0006] 2. The traditional process uses nickel chloride or nickel sulfate as the nickel salt, resulting in a large internal stress in the alloy plating layer, which is prone to cracking. The use of nickel sulfamate as the nickel salt reduces the internal stress of the plating layer and makes the plating layer crystallize more uniformly and finely.

[0007] 3. The traditional process rarely uses organic complexing agents. Instead, it mainly relies on ammonia water to stabilize the plating solution. In a 50-60℃ environment, the pH value is high, and the ammonia water is prone to volatilization, resulting in unstable plating solution. At the same time, the odor is large, and the production environment is poor.

[0008] 4. The traditional process generally uses weak brighteners such as benzenesulfonate, naphthalenesulfonate, sodium saccharin, and sulfonic acid sodium benzaldehyde, which are added in large amounts and are prone to fogging. The alloy plating layer has a high sulfur content and contains a large amount of organic inclusions, which affects the appearance and corrosion resistance of the plating layer.

[0009] 5. The traditional process has a fatal flaw due to the lack of complexing agents: after the newly prepared plating solution is used for a period of time or after it is stopped for a week, the palladium content in the plating layer will decrease significantly, sometimes to 30-40%. Even if more palladium chloride is added, the palladium content in the plating layer cannot be increased to about 80%, and the plating solution can only be scrapped, and the palladium salt needs to be recovered, resulting in great loss.

[0010] In summary, the traditional palladium-nickel alloy electroplating process cannot meet the process stability requirements of modern intelligent mass production. SUMMARY

[0011] The present application aims to provide a palladium-nickel alloy electroplating solution, which can produce a palladium-nickel alloy coating with various performances that can not only replace gold plating and meet the electrical properties and various physical properties of the coating, but also meet the process stability requirements of modern intelligent mass production.

[0012] The technical solution provided by the present application is a palladium-nickel alloy electroplating solution, which comprises: 45-55 g / L of tetraammine palladium sulfate, 30-40 g / L of nickel sulfamic acid, 120-160 g / L of ammonium sulfate, 20-40 g / L of urea, 20-40 ml / L of a complexing agent, 3-6 ml / L of a photoresist agent, 1-2 ml / L of a wetting agent, and the balance of water. The complexing agent is composed of an A component, a B component, and water. The A component is a hydroxyethyl or hydroxypropyl compound of an organic amine. The B component is a high-molecular-weight organic amine polyurea quaternary ammonium salt cationic compound.

[0013] The present application uses A.B two types of complexing agents to stabilize the plating solution. The A type complexing agent refers to a hydroxyethyl or hydroxypropyl compound of ethylenediamine, polyene polyamine, and polyethyleneimine. For example, penta-hydroxyethyl diethylene triamine, tetra-hydroxypropyl ethylenediamine, and polyethyleneimine hydroxyethyl compound (molecular weight of about 1500). The A type complexing agent is added in an amount of 5-15 g / L, and generally 8-12 g / L.

[0014] The B type complexing agent of the present application is an organic amine polyurea quaternary ammonium salt cationic compound with a molecular weight of 2000-3000. Its structure is as follows: N.N dimethylpropylamine or N.N dimethylethylenediamine reacts with urea to generate amine urea N(CH3)2-CH2-CH2-CH2-NHCONH-CH2-CH2-CH2-N(CH3)2, which then reacts with a crosslinking agent dichloroether or dichloroethane to generate a high-molecular-weight polyurea quaternary ammonium salt cationic compound. Based on screening, the present application selects N,N dimethylethylenediamine as the organic amine and dichloroethane as the crosslinking agent, which is named as B complexing agent and is contained in the electroplating solution in an amount of 3-4 g / L.

[0015] The A.B two types of complexing agents are mixed and used, and the composition is: 30-40% of A type, 10-20% of B type, and the balance of water. The addition amount in the electroplating solution is 20-40 ml / L. According to long-term experience, the consumption of the complexing agent is 1500-2000 ml / Kg of the A.H.

[0016] The brightener adopted by the present application is a pyridine, thiazole, imidazole heterocyclic derivative with very strong polarity and strong adsorption, such as benzyl nicotinic acid onium salt, fenugreek base, 2-vinyl-1-pyridine propane sulfonic acid end onium salt, trans-3-(3-pyridyl) allylic acid, tetrahydrothiazole thione, and methyl imidazole, etc. In the brightener, the total amount of various heterocyclic derivatives is about 15%, and the rest is water. The amount of the brightener in the electroplating solution is 3-6 ml / L.

[0017] According to long-term experience, the consumption of the brightener is 300-500 ml / KAH.

[0018] The present application adopts a low-foam wetting agent, which is composed of 20% sodium monoisooctyl succinate sulfonate, 5% sodium 2-ethylhexyl sulfonate, and the rest is water. The addition amount is 1-2 ml / L, and the consumption is 30-40 ml / KAH. The surface tension is lower than 45 mN / m. The porosity of the plated layer is reduced.

[0019] The palladium-nickel alloy plated layer produced by the palladium-nickel alloy electroplating solution can not only replace the gold plated layer to meet the electrical properties and various physical properties of the plated layer, but also meet the process stability requirements of modern intelligent large-scale production. The electrical properties and various physical properties of the gold plated layer are met. The use of the precious metal can be saved by about 25%. DETAILED DESCRIPTION

[0020] The present application is a palladium-nickel alloy electroplating solution, which is composed of 45-55 g / L tetraammonium palladium sulfate, 30-40 g / L nickel sulfamic acid, 120-160 g / L ammonium sulfate, 20-40 g / L urea, 20-40 ml / L complexing agent, 3-6 ml / L optical shell agent, 1-2 ml / L wetting agent, and the rest is water. The complexing agent is composed of A component, B component, and water. The A component is a hydroxyethyl or hydroxypropyl compound of an organic amine; the B component is a high-molecular organic amine polyurea quaternary ammonium salt cationic compound.

[0021] The present application adopts tetraammonium palladium sulfate instead of palladium chloride to prevent the oxidation of chloride ions on the anode to generate chlorine or other chlorates. The residual chloride ions after the subsequent water washing affect the corrosion resistance of the plated layer.

[0022] The present application adopts nickel sulfamic acid as a nickel salt. In the field of electronic electroplating, the plated layer obtained by using nickel sulfamic acid is dense and fine, and has better ductility and solderability.

[0023] The present application adopts ammonium sulfate as a conductive salt, and the content is 120-160 g / L. The design is to maintain the production operation of the plating solution with a low ammonia content (30-50 g / L). Under the neutral condition of pH 6.8-7.5, ammonia is not easy to volatilize and lose. At the same time, ammonium sulfate serves as a coordination source of palladium and nickel to preliminarily form palladium ammonia complex ions and nickel ammonia complex ions, thereby avoiding the formation of hydroxide precipitates under the neutral condition.

[0024] The present application adopts urea as buffer and stabilizer, urea has certain reducibility, which is beneficial to the reduction of palladium ammonia complex ion; its decomposition product is beneficial to the stability of plating solution pH. In the existing literature, urea is not found as a buffer and stabilizer in palladium-nickel plating solution. According to long-term experience, the consumption of urea is about 2000g / KAH (KAH is kiloampere hour, the same below).

[0025] The present application adopts A.B two types of complexing agents to stabilize the plating solution, the A type complexing agent (complexing agent A) refers to ethylenediamine, polyene polyamine, polyethylene imine hydroxyethyl, hydroxypropyl compound. Such as penta-hydroxyethyl diethylene triamine, tetra-hydroxypropyl ethylenediamine, polyethylene imine hydroxyethyl compound (molecular weight about 1500). This kind of substance has small molecular weight, easy to form mixed coordination ion with nickel ammonia complex ion, inhibit the deposition of nickel. Because the stability constant of palladium ammonia, nickel ammonia complex ion and many complexing agent ligands cannot be found, only can be screened by experiment. The experiment proves that among the mixed ligand system formed by citrate, tartrate, maleate, EDTA disodium, sodium nitrilotriacetic acid, HEDP, trisodium trithiocyanate and palladium ammonia complex ion, nickel ammonia complex ion, there is no obvious deposition advantage of palladium. The adding amount of A type complexing agent is 5-15g / L, generally 8-12g / L.

[0026] The B type complexing agent of the present application is an organic amine polyurea quaternary ammonium salt cation compound, its molecular weight is between 2000-3000. Its structure is as follows: N.N dimethylpropylamine or N.N dimethylethylenediamine, reacts with urea to generate amine urea N(CH3)2-CH2-CH2-CH2-NHCONH-CH2-CH2-CH2-N(CH3)2, then reacts with crosslinking agent dichloroether or dichloroethane to generate high molecular weight polyurea quaternary ammonium salt cation compound. On the basis of screening, the present application selects N,N dimethylethylenediamine as organic amine, and selects dichloroethane as crosslinking agent. The B type complexing agent is named as complexing agent B, its content in the plating solution is 3-4g / L. Complexing agent B has good dispersing ability to mixed coordination system, can significantly expand the current density distribution range: 1. Increases the upper limit of current density, avoids burning, peeling and cracking in high current area; 2. Widens the lower limit of current density, makes the plating in low current density area (deep hole of workpiece) good. Complexing agent B guarantees the stable operation of high speed plating. The content of B type complexing agent cannot be too high, which will affect the overall current efficiency and the stability of PH.

[0027] A.B two types of complexing agents are used together, the composition is: A type 30-40%, B type 10-20%, the rest is water, the adding amount in the plating solution is 20-40ml / L. According to long-term experience, the consumption of complexing agent is 1500-2000ml / KAH.

[0028] The brightener adopted by the present application is a pyridine, thiazole, imidazole heterocyclic derivative with very strong polarity and adsorption, such as benzyl nicotinic acid onium salt, fenugreek base, 2-vinyl-1-pyridine propane sulfonic acid end onium salt, trans-3-(3-pyridyl) allylic acid, tetrahydrothiazole thione, and methyl imidazole, etc. Traditional phenyl sulfonate, naphthalene sulfonate, and benzaldehyde sulfonate can only plate a misty or semi-bright palladium-nickel alloy coating, and the dosage is very large, generally 5-10 g / L, which causes the coating to have a large amount of sulfur and many organic inclusions, affecting the appearance and corrosion resistance of the coating. The brightener adopted by the present application can increase cathode polarization and refine the grain, making the alloy coating smooth and bright. In the brightener, the total amount of various heterocyclic derivatives is about 15%, and the rest is water. The amount of the brightener in the electroplating solution is 3-6 ml / L.

[0029] According to long-term experience, the consumption of the brightener is 300-500 ml / KAH.

[0030] The present application adopts a low-foam wetting agent, which is composed of 20% sodium monoisooctyl succinate sulfonate, 5% sodium 2-ethylhexyl sulfonate, and the rest is water. The addition amount is 1-2 ml / L, and the consumption is 30-40 ml / KAH. The surface tension is lower than 45 mN / m. The porosity of the coating is reduced.

[0031] The present application utilizes the above-mentioned palladium-nickel alloy electroplating solution to electroplate palladium-nickel alloy, and the electroplating process comprises the following steps: terminal substrate degreasing, acid activation, electroplating semi-bright aminosulfonic nickel, electroplating aminosulfonic nickel-phosphorus alloy, electroplating palladium-nickel alloy, sealing, and drying. Titanium anode is used as the anode to electroplate the treated terminal substrate, and the pH of the electroplating solution is 6.8-7.5. The process specification is as follows:

[0032] High-speed palladium-nickel alloy electroplating process specification

[0033] Temperature 50-60℃

[0034] PH 6.8-7.5

[0035] Anode Insoluble titanium anode

[0036] Cathode current density 20-50A

[0037] Stirring Strong air stirring and liquid flow

[0038] Deposition rate 20A / dm20.9 microns / min

[0039] Current efficiency 90~95%

[0040] Maintenance method:

[0041] 1. Tetraammonium palladium sulfate, aminosulfonic nickel, and ammonium sulfate are supplemented daily according to the analysis results, or supplemented at any time according to the online monitoring data.

[0042] 2. Temperature and pH value are monitored and adjusted on-line. Dilute sulfuric acid and ammonia are used to adjust the pH value.

[0043] 3. Complexing agent, brightener, wetting agent and urea are replenished according to the setting of the automatic adding machine.

[0044] 4. The control of current is based on the complexity of the workpiece and the thickness requirement, and is controlled by the experience of the technician.

[0045] 5. When the proportion of complexing agent and brightener is out of adjustment, the amount is adjusted by Hull cell experiment.

[0046] The performances of the palladium-nickel alloy coating obtained by the present application and the pure gold coating are compared in Table 1

[0047] Table 1

[0048] Test item Palladium nickel alloy Common hard gold Test instrument and condition or standard Alloy composition (wt%) Pd 75-85% Ni 15-25% 99.9% Optical EDX fluorescence spectrometer Appearance Silver-white plating layer Gold-yellow plating layer Visual observation Contact resistance mΩ 2.5~5 1.5~2 Gurley resistance tester Ductility ＞8% Superior ASTM 489 Hardness (HV) 400-500 110 Microhardness tester Density g / cm³ 11.3~11.6 17 Mettler density tester Weldability Good Very good 260°C solder bath immersion 3-5 seconds Corrosion resistance 500 times / 2 μm No bare spots No bare spots Use gold-plated socket, manually plug and unplug Anti-H2S test No discoloration No discoloration 1% H2S gas, temperature 25°C, humidity 90% for 1 hour Neutral salt spray test 24 hours passed 24 hours passed Substrate 68 brass, no primer and closed thickness 4 μm

[0049] As shown in the above table, the palladium-nickel alloy coating produced by the present application can completely replace the gold coating and meet the electrical performance and physical performance of the gold coating. It can also save about 25% of the noble metal.

[0050] The following five examples of the present application are carried out under standard electroplating solution and the same operation specification. Different combinations of complexing agent and brightener are detected to obtain the performances of the palladium-nickel alloy coating.

[0051] After the five example experiments are completed, the plating solution is placed for 15 days, and then the same experiment is carried out again. The two alloy coatings are detected at the same time to obtain the best ratio of complexing agent and brightener.

[0052] Standard electroplating solution

[0053] Palladium tetraammonium sulfate 50g / L

[0054] (metallic palladium) (20g / L)

[0055] Nickel sulfamate 34g / L

[0056] (metallic nickel) (8g / L)

[0057] Ammonium sulfate 130g / L

[0058] Urea 30g / L

[0059] Wetting agent 2ml / L

[0060] PH value 7.0

[0061] Standard operation conditions

[0062] Temperature 55℃

[0063] Cathode current density 20A / dm²

[0064] Stirring air agitation and liquid flow

[0065] Titanium anode

[0066] Cathode 0.3mm x 30mm x 100mm 68 brass sheet

[0067] Time: 3-5 minutes, depending on the required thickness for the experiment.

[0068] Current efficiency 90-93%

[0069] In the following five examples, the preparation of electroplating solutions...

[0070] 1. Add 70% pure water to the plating bath, heat to approximately 55℃, and add the required amount of water.

[0071] Mix complexing agent A and complexing agent B thoroughly.

[0072] 2. Add the calculated amounts of ammonium sulfate, urea, tetraamminepalladium sulfate and nickel aminosulfonate in sequence, and stir to dissolve.

[0073] 3. Finally, add the calculated amount of brightener and wetting agent, and add water to the set volume.

[0074] 4. Adjust the pH value to the specified range using ammonia and alkyl sulfuric acid, and then you can perform a trial plating.

[0075] In the following five examples, the preparation methods of complexing agent B are described.

[0076] 1. Synthesis of urea-dimethylaminoethane: The urea is synthesized using an N,N-dimethylaminoethylenediamine:urea molar ratio of 2:1.

[0077] Add the ammonia gas to the reaction vessel while stirring, and simultaneously add nitrogen gas. Heat the vessel to 80-90℃ and maintain the temperature for 10 hours, then raise the temperature to 120℃ for 2 hours to recover the ammonia gas released during the reaction.

[0078] Synthesis of the copolymer: Urea-dimethylaminoethane: 1,2-dichloroethane: water were synthesized in a molar ratio of 1.1:1:10.

[0079] Add the solution to the reaction vessel while stirring. Reflux at 80°C for 10 hours, then add a small amount of molecular weight regulator (nicotinic acid, approximately 0.03% of the total weight of the reaction solution), maintain the temperature for 3 hours, and check the molecular weight range (2000-3000). If it meets the requirements, add activated carbon for decolorization. Then distill off the excess water.

[0080] The solid content is 50%, which is the complexing agent B.

[0081] In the following five examples, the complexing agent B is the same.

[0082] The wetting agent used in the following five examples is formulated as follows

[0083] Sodium cumenesulfonate (Sasol Chemicals) 20%

[0084] Sodium ethylhexyl sulfonate (BASF) 5%

[0085] The remainder is pure water.

[0086] Example One, Complexing Agent: Complexing Agent A Tetrahydroxypropyl ethylene diamine 12 g / L

[0087] Complexing Agent B 3 / L

[0088] Brightener: 2-Vinyl-l-pyridine propane sulfonic acid

[0089] Merocyanine 300 mg / L

[0090] Methoxsalen 5 mg / L

[0091] Example Two, Complexing Agent: Complexing Agent A Pentaethylenediamine

[0092] Complexing Agent B 4 g / L

[0093] Brightener: Benzyl nicotinic acid ylide 300 mg / L

[0094] Trigonelline 300 mg / L

[0095] Tetrahydrothiazoline thione 0.5 mg / L

[0096] Example Three, Complexing Agent: Complexing Agent A Pentaethylenediamine 10 g / L

[0097] Complexing Agent B 3.5 g / L

[0098] Brightener: Trans-3-(3-pyridyl) allylic acid 400 mg / L

[0099] Tetrahydrothiazoline thione 0.5 g / L

[0100] Example Four, Complexing Agent: Complexing Agent A Tetrahydroxypropyl ethylene diamine 10 g / L

[0101] Complexing Agent B 3.5 g / L

[0102] Brightener: Trans-3-(3-pyridyl) allylic acid 400 mg / L

[0103] Methoxsalen 5 mg / L

[0104] Tetrahydrothiazoline thione 0.2 g / L

[0105] Example 5, Complexing agent: Complexing agent A polyethyleneimine hydroxyethyl compound 10 g / L

[0106] Complexing agent B 3.5 g / L

[0107] Brightener: trans-3-(3-pyridyl)allyl acid 400 mg / L

[0108] 2-vinyl-1-pyridine propane sulfonic acid

[0109] Internal ylide 200 mg / L

[0110] Methimazole 5 mg / L

[0111] Table 2 Performance table of palladium-nickel alloy coating of Example 1 to Example 5

[0112] Test item Example 1 Example 2 Example 3 Example 4 Example 5 Alloy composition Pd 73.8% Ni 26.2% Pd 75.6% Ni 24.4% Pd 78.3% Ni 21.7% Pd 80.5% Ni 19.5% Pd 81.7% Ni 18.3% Sample after 15 days Pd 72.3% Ni 27.7% Pd 75.2% Ni 24.8% Pd 77.7% Ni 22.3% Pd 80.0% Ni 20.0% Pd 81.5% Ni 18.5% Plating layer appearance Uniform and bright Uniform and slightly dark bright Bright and good vibration flatness Bright and good vibration flatness Bright and good vibration flatness Sample after 15 days Uniform and bright Uniform and slightly yellowish bright Bright and good vibration flatness Bright and good vibration flatness Bright and good vibration flatness Contact resistance mΩ 4.8 5.6 4.6 4.5 4.2 Sample after 15 days 4.6 5.4 4.5 4.5 4.1 Ductility 7.6 7.4 8.2 8.3 8.5 Sample after 15 days 7.6 7.4 8.1 8.3 8.5 Hardness (HV) 460 450 460 490 460 Sample after 15 days 460 440 450 480 450 Density g / cm³ 11.5 11.3 11.4 11.5 11.6 Sample after 15 days 11.5 11.3 11.4 11.5 11.6 Weldability Good Good Good Good Good Sample after 15 days Good Good Good Good Good Wear resistance 500 times / 2 μm No bare spots No bare spots No bare spots No bare spots No bare spots Sample after 15 days No bare spots No bare spots No bare spots No bare spots No bare spots Anti-H2S test thickness 2 / μm 1 hour No discoloration Slightly dark No discoloration No discoloration No discoloration Sample after 15 days No discoloration Slightly dark No discoloration No discoloration No discoloration Neutral salt spray test thickness 4 / μm 24 hours passed 24 hours passed 24 hours passed 24 hours passed 24 hours passed Sample after 15 days 24 hours passed 24 hours passed 24 hours passed 24 hours passed 24 hours passed

[0113] Conclusion: 1. Under the action of urea and two types of complexing agents, the palladium-nickel alloy electroplating solution can be stable for a long time, ensuring the normal operation of high-speed electroplating. High-quality palladium-nickel alloy coating can completely replace gold coating.

[0114] 2. It has been proven that trans-3-(3-pyridyl)allyl acid, 2-vinyl-1-pyridine propane sulfonic acid internal ylide, and methimazole are excellent brighteners with small addition amount and excellent performance.

Claims

1. A palladium-nickel alloy electroplating solution, comprising: tetraammine palladium sulfate 45-55 g / L, nickel sulfamate 30-40 g / L, ammonium sulfate 120-160 g / L, urea 20-40 g / L, complexing agent 20-30 ml / L, brightener 3-6 ml / L, wetting agent 1-2 ml / L, and the balance being water; wherein the complexing agent is composed of component A, component B and water, component A is tetrahydroxypropyl ethylenediamine, pentaethylenediamine or polyethylenimine with a molecular weight less than 1500, component B is an organic amine polyurea quaternary ammonium salt cationic compound generated by reacting urea amine with crosslinking agent β, β' dichlorodiethyl ether or 1.2 dichloroethane, the molecular weight of which is between 2000-3000, wherein the urea amine is generated by deamination of dimethylaminopropylamine or dimethylaminoethylenediamine with urea; the weight percentage of component A in the complexing agent is 30-40%, and the weight percentage of component B is 10-20%; the brightener is a 10-20 wt% aqueous solution of pyridine, thiazole or imidazole heterocyclic derivative; and the wetting agent is composed of 20 wt% sodium monoisooctyl sulfosuccinate, 5 wt% sodium ethylhexyl sulfonate and the balance being water.

2. The palladium-nickel alloy electroplating solution of claim 1, wherein: The urea content is 20-30 g / L.

3. The palladium-nickel alloy electroplating solution of claim 1, wherein: The heterocyclic derivative in the brightener is 2-vinyl-1-pyridine propane sulfonic acid ylide, trans-3-(3-pyridyl) allylic acid, trigonelline, tetrahydrothiazole thione or imidazole. The heterocyclic derivative in the brightener is 2-vinyl-1-pyridine propane sulfonic acid ylide, trans-3-(3-pyridyl) allylic acid, trigonelline, tetrahydrothiazole thione or imidazole.