Nickel electroplating composition for crude nickel

Abstract

To provide nickel electroplating compositions for rough nickel.SOLUTION: A nickel electroplating composition comprises nickel ions, a thiourethane represented by formula (III), and a salt of the thiourethane and is free of alloying metals. The nickel electroplating composition deposits rough nickel on substrates. The rough nickel can be electroplated over wide current density ranges. The rough nickel deposits enable improved adhesion to other metal layers in contrast to many conventional nickel deposits.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a nickel electroplating composition for depositing rough nickel on a substrate. More specifically, the present invention relates to a nickel electroplating composition for depositing rough nickel on a substrate, which contains thiourea.

Background Art

[0002] A lead frame is used to mount and process semiconductor dice or chips in the manufacture of semiconductor devices. The lead frame functions to electrically connect the chip to an external device via the leads of the lead frame. Examples of lead frames include spot silver and solder-coated lead frames, and palladium pre-plated lead frames (PPF).

[0003] PPF is a three-layer lead frame containing nickel having a thickness range of 0.5 to 2 μm, palladium having a thickness range of 10 to 100 nm, and gold having a thickness range of 3 to 9 nm. The nickel layer prevents the diffusion of copper from the lead frame bulk to the palladium layer and is used as an underlying layer for bonding with solder. The palladium layer has a function of preventing the oxidation of the nickel surface and the diffusion of gold into the nickel layer, while the upper gold flash layer is designed to prevent the oxidation of palladium and the outgas absorbed by palladium.

[0004] A semiconductor chip is mounted on the lead frame, and a bonding wire connection is formed between the semiconductor chip and the lead frame. Each semiconductor chip is protected from the environment by encapsulation with a plastic molding compound, also called an epoxy molding compound (EMC). Good adhesion between the lead frame and the EMC is very important to ensure the high reliability and proper functioning of the interconnect circuit (IC) device. Poor adhesion causes peeling, cracking, and the "popcorn" phenomenon. This results in device failure, especially under harsh conditions such as high temperature, high humidity, and thermal cycling.

[0005] Various methods exist in the art to avoid delamination of epoxy molding compounds from lead frames or substrates. Such methods include the use of special lead frame designs, chemical bonding, and mechanical interlocks. Special lead frame designs include holes, grooves, and hemispheres created on the lead frame surface by mechanical or laser processing. Such methods may not be able to achieve the high reliability required to meet industry standards for adhesion between EMC and lead frames, or may not comply with MSL-1 (moisture resistance level -1, 168 hours at 85°C and 85% relative humidity, IPC / JEDECJ-STD-20).

[0006] Chemical bonding techniques include brown oxide, organic adhesion promoters, polymer primers, and coupling agents. The mechanism involves brown oxide and organic adhesives possessing one or two functional groups that connect to the EMC and lead frame. Therefore, adhesion is strengthened by chemical bonding. In the brown oxide method, copper on the substrate surface is oxidized to copper oxide or cuprous oxide. However, the brown oxide method is not applicable to Ni / Pd / Au pre-plated lead frames because the copper surface is not exposed. Furthermore, the micro-etching effect in brown oxide treatment can weaken the lead frame and lead to dimensional variations.

[0007] Organic treatments have several limitations that hinder their widespread adoption in mass production. For example, there can be compatibility issues between organic adhesion promoters and various types of EMCs. Regarding polymer primers, the process steps can become complex. Copper coupling agents can undergo hydrolysis under normal packaging conditions.

[0008] Because the gold and palladium layers of PPF (Ni / Pd / Au) lead frames are essentially inert metals, it is difficult to modify their chemical bonds to improve mold adhesion. The only feasible method is to utilize a mechanical interlocking effect by roughening the surface of the copper or nickel substrate. However, the palladium and gold layers are too thin to be roughened during the manufacturing process.

[0009] Patent documents 1 and 2 disclose nickel plating baths for depositing a crude nickel layer to improve adhesion between the nickel layer and resin sealant of a semiconductor package. Patent document 1 discloses a nickel plating bath comprising nickel chloride, sodium thiocyanate, and ammonium chloride for providing a crude nickel precipitate. Patent document 2 discloses a nickel plating bath comprising nickel sulfate, ammonium sulfate, sodium sulfate, sodium chloride, and boric acid for depositing a crude nickel layer. [Prior art documents] [Patent Documents]

[0010] [Patent Document 1] U.S. Patent No. 7,190,057 [Patent Document 2] U.S. Patent No. 7,285,845 [Overview of the Initiative] [Problems that the invention aims to solve]

[0011] While nickel plating baths exist that can deposit crude nickel, there is still a need for improved nickel electroplating baths that can enable the deposition of crude nickel. [Means for solving the problem]

[0012] This invention relates to nickel ions and the following formula: [ka] The present invention relates to a nickel electroplating composition that does not contain alloying metals and comprises a compound having (wherein R1 and R2 are independently selected from hydrogen, a linear or branched (C1-C6) alkyl, a linear or branched hydroxy(C1-C6) alkyl, a linear or branched carboxy(C1-C6) alkyl, a linear or branched amino(C1-C6) alkyl, or a (C5-C6) cycloalkyl ring, or R2 may be sulfur and G may be carbon or nitrogen), and a salt of thiourethane.

[0013] The present invention also, a) To provide a substrate; b) Nickel ions and the following formula: [ka] A nickel electroplating composition comprising a compound having (wherein R1 and R2 are independently selected from hydrogen, a linear or branched (C1-C6) alkyl, a linear or branched hydroxy(C1-C6) alkyl, a linear or branched carboxy(C1-C6) alkyl, a linear or branched amino(C1-C6) alkyl, or a (C5-C6) cycloalkyl ring, or R2 may be sulfur and G may be carbon or nitrogen), and a salt of thiourethane, and not containing alloying metals, is brought into contact with a substrate; c) Depositing a nickel layer containing Sa≧70nm and Sdr≧4% on the substrate. This also relates to a method of electroplating nickel metal onto a substrate, including the method described above.

[0014] The nickel electroplating composition of the present invention enables the deposition of a crude nickel layer having substantially granular or cabalstone-type morphology. The crude nickel improves adhesion between the crude nickel layer and adjacent metal layers, and also improves mold adhesion to epoxy molding compounds, such as those found in lead frames. [Brief explanation of the drawing]

[0015] [Figure 1] Figure 1 is a SEM at 10,000 times magnification of a conventional nickel layer having a substantially smooth surface. [Figure 2] Figure 2 is a SEM at 10,000 times magnification of a rough nickel layer electroplated from the nickel bath of the present invention, showing a cobblestone-type morphology.

Mode for Carrying Out the Invention

[0016] The abbreviations used throughout this specification have the following meanings unless otherwise clearly indicated in the context: °C = degrees Celsius; g = gram; Kg = kilogram; L = liter; mL = milliliter; m = meter; cm = centimeter; μm = micron; nm = nanometer; DI = deionized; A = ampere; ASD = ampere / dm 2 = current density or plating rate; PPF = palladium pre-plated lead frame, EMC = epoxy molding compound, XRF = X-ray fluorescence, AFM = atomic force microscope, KV = kilovolt, V = volt, LPM = liter / minute; min = minute; MSL = moisture sensitivity level; MSL-1 = moisture sensitivity level-1, 168 hours at 85 °C and 85% relative humidity; w / o MSL-1 = without MSL treatment; w / MSL-1 = with MSL treatment; S = sulfur; C = carbon; Ni = nickel; Pd = palladium; Au = gold; and wt% = weight%.

[0017] The term "thiourethane" means a compound containing the functional moiety N-C(S)-S. The term "moiety" means one or more atoms that make up a part of a molecule. The term "adjacent" means in direct contact such that two metal layers have a common interface. The term "aqueous" means water or water-based. The term "matte" means a dull appearance. The terms "composition" and "bath" are used interchangeably throughout this specification. The term "Ra" means the arithmetic mean deviation of the profile roughness. The term "Sa" means the arithmetic mean height within the evaluation area and is substantially equivalent to Ra, but Sa is less affected by scratches, contamination, and measurement noise, so Sa provides more stable results. The term "Sdr" means the developed interface area ratio corresponding to the surface area ratio having the correlation Sdr = (surface area ratio - 1) × 100%. The terms "electroplating", "plating", and "deposition" are used interchangeably throughout this specification. The term "morphology" means the shape, size, texture, or topography of a surface or an article. The term "ion" means a cation or an anion, depending on the context in which it is used herein and as understood by those skilled in the art. The dashed line "------" represents an optional covalent bond. The term "IPC / JEDECJ-STD-20" means the Institute for Interconnecting and Packaging Electronic Circuits (IPC) and the Solid State Technology Association regarding the standard classification of the moisture sensitivity level (MSL) of lead frame IC devices. The terms "a" and "an" may refer to both the singular and plural forms throughout this specification. All numerical ranges are inclusive and may be combined in any order, except when it is logical that the sum of such numerical ranges is restricted to 100%.

[0018] The present invention has the following chemical structure:

Chemical formula

[0019] Preferably, R1 and R2 are independently selected from hydrogen, linear or branched (C1-C6) alkyl, linear or branched hydroxy(C1-C6) alkyl, linear or branched carboxy(C1-C6) alkyl, linear or branched amino(C1-C6) alkyl, or R2 may be sulfur and G may be carbon or nitrogen.

[0020] A preferred thiourethane compound is given by the following formula: [ka] (In the formula, R1 and R2 are independently selected from hydrogen, linear or branched (C1-C6) alkyl, linear or branched hydroxy(C1-C6) alkyl, linear or branched carboxy(C1-C6) alkyl, linear or branched amino(C1-C6) alkyl, and G in formula (I) is carbon.)

[0021] More preferably, R1 and R2 in formula (I) are independently selected from hydrogen, linear or branched (C1-C3) alkyl, linear or branched hydroxy(C1-C3) alkyl, or linear or branched carboxy(C1-C3) alkyl, or R2 is sulfur and G is carbon or nitrogen. Even more preferably, R1 and R2 are independently selected from hydrogen, (C1-C2) alkyl, hydroxy(C1-C2) alkyl, or carboxy(C1-C2) alkyl, or R2 is sulfur and G is nitrogen. Even more preferably, R1 is selected from hydrogen, (C1-C2) alkyl, hydroxy(C1) alkyl, or carboxy(C1) alkyl or carboxymethyl, R2 is sulfur and G is nitrogen.

[0022] The most preferred thiourethane compound has the following formula: [ka]

[0023] Preferably, the salt of the thiourethane compound is not limited to alkali metal salts such as sodium salt, potassium salt, and lithium salt, more preferably sodium salt and potassium salt, and even more preferably sodium salt.

[0024] Preferably, thiourethane is included in the nickel electroplating composition in an amount of 5 ppm or more, more preferably 10 ppm to 100 ppm, even more preferably 20 ppm to 80 ppm, even more preferably 30 ppm to 60 ppm, and most preferably 45 ppm to 55 ppm.

[0025] The nickel electroplating composition contains nickel ions from one or more sources of water-soluble nickel salts. Such nickel salts include, but are not limited to, nickel sulfate and its hydrates, nickel sulfate hexahydrate and nickel sulfate heptahydrate; nickel sulfamate and its hydrate, nickel sulfamate tetrahydrate; nickel chloride and its hydrate, nickel chloride hexahydrate; nickel carbonate; nickel methanesulfonate; nickel bromide; nickel fluoride; nickel iodide; nickel oxalate; nickel citrate; nickel tetrafluoroborate; nickel hypophosphite; and nickel acetate. Preferably, the source of nickel ions is nickel sulfamate, nickel chloride, or a mixture thereof.

[0026] One or more sources of nickel ions are included in the aqueous nickel electroplating composition in an amount sufficient to provide the desired nickel ion concentration to achieve the desired crude nickel deposition. Preferably, the concentration of nickel salt in the nickel electroplating composition of the present invention is 20 g / L or more. More preferably, the concentration of nickel salt is 25 g / L to 750 g / L, even more preferably in the range of 30 g / L to 500 g / L, and most preferably 30 g / L to 300 g / L.

[0027] Chloride ions can be optionally included in the aqueous nickel electroplating composition of the present invention. One or more sources of chloride ions are preferably included in an amount of 0 g / L to 50 g / L, more preferably 0 g / L to 30 g / L, even more preferably 0 g / L to 20 g / L, and most preferably 3 g / L to 10 g / L.

[0028] Sources of chloride ions include, but are not limited to, nickel chloride, nickel chloride hexahydrate, hydrogen chloride, alkali metal salts such as sodium chloride and potassium chloride, magnesium chloride, calcium chloride, ammonium chloride, and organic hydrochlorides such as, but are not limited to, guanidine hydrochloride, ethylenediamine dihydrochloride, trimethylammonium chloride, pyridine hydrochloride, phenylammonium chloride, and hydrazine dihydrochloride. Preferably, the sources of chloride ions are nickel chloride and nickel chloride hexahydrate.

[0029] The nickel electroplating composition of the present invention is acidic. The pH is preferably in the range of 2 to 6, more preferably 2.5 to 4.5, and even more preferably 3 to 4.2. Inorganic acids, organic acids, inorganic bases, organic bases, and their salts can be used to adjust the pH of the aqueous nickel electroplating composition. Examples of such acids, but not limited to, include inorganic acids such as sulfuric acid, hydrochloric acid, sulfamic acid, boric acid, and their salts. Examples of organic acids, but not limited to, include acetic acid, aminoacetic acid, ascorbic acid, lactic acid, 5-sulfosalicylic acid, and their salts. Inorganic bases such as sodium hydroxide and potassium hydroxide, as well as organic bases such as various amines and ammonium acetate, can also be used to adjust the pH. Preferably, the pH adjuster is selected from boric acid, lactic acid, 5-sulfosalicylic acid, and ammonium acetate. Most preferably, the pH adjuster is boric acid, its salts, and ammonium acetate. The pH adjuster can be added in the amount required to maintain the desired pH range.

[0030] The aqueous nickel electroplating composition of the present invention may optionally contain one or more types of surfactants. Examples of such surfactants, though not limited to cationic surfactants and anionic surfactants, include ionic surfactants, nonionic surfactants, and amphoteric surfactants. Preferably, the surfactant can be used in conventional amounts such as 0.05 g / L to 150 g / L, more preferably 0.05 g / L to 15 g / L, and even more preferably 0.05 g / L to 5 g / L.

[0031] Examples of surfactants include, but are not limited to, anionic surfactants such as sodium di(1,3-dimethylbutyl)sulfosuccinate, sodium 2-ethylhexyl sulfate, sodium diamylsulfosuccinate, sodium lauryl sulfate, sodium lauryl ether sulfate, sodium dialkylsulfosuccinate, and sodium dodecylbenzenesulfonate, as well as cationic surfactants such as quaternary ammonium salts such as perfluorinated quaternary amines. An example of a commercially available anionic surfactant is AEROSOL-M-80 sodium dihexylsulfosuccinate, available from Solvay Chemicals.

[0032] The aqueous nickel electroplating composition of the present invention does not contain alloy metals or metals that can be added to a metal plating bath to increase or improve the luster of nickel metal deposits.

[0033] Furthermore, the aqueous nickel electroplating composition of the present invention does not contain cyanide or cyanide compounds.

[0034] Preferably, the aqueous nickel electroplating composition of the present invention comprises a nickel cation and a corresponding counteranion from one or more nickel salts, the following formula: [ka] The formula comprises a thiourethane having (wherein R1 and R2 are independently selected from hydrogen, linear or branched (C1-C6) alkyl, linear or branched hydroxy(C1-C6) alkyl, linear or branched carboxy(C1-C6) alkyl, linear or branched amino(C1-C6) alkyl, or R2 may be sulfur and G may be carbon or nitrogen), a salt of the thiourethane, optionally one or more chloride salts containing chloride anions and corresponding countercations, optionally one or more pH adjusters, optionally one or more surfactants, and water.

[0035] More preferably, the aqueous nickel electroplating composition of the present invention comprises nickel cations and corresponding counteranions from one or more nickel salts, The following formula: [ka] (wherein R1 and R2 are independently selected from hydrogen, linear or branched (C1-C3) alkyl, linear or branched hydroxy(C1-C3) alkyl, linear or branched carboxy(C1-C3) alkyl, linear or branched amino(C1-C3) alkyl, or R2 is sulfur and G is nitrogen) a thiourethane having a salt of the thiourethane, optionally one or more chloride salts of chloride anions and corresponding countercations, one or more pH adjusters, optionally one or more surfactants, and water.

[0036] More preferably, the aqueous nickel electroplating composition of the present invention comprises nickel cations and corresponding counteranions from nickel salts selected from the group consisting of nickel chloride, nickel sulfamate, nickel sulfate, and mixtures thereof, and a thiourethane having the following formula: [ka] The formula comprises a thiourethane having (wherein R1 and R2 are independently selected from hydrogen, (C1-C2) alkyl, hydroxy(C1-C2) alkyl, or carboxy(C1-C2) alkyl, or R2 is sulfur and G is nitrogen), a chloride anion and corresponding countercation from one or more chloride salts optionally selected from the group consisting of nickel chloride and sodium chloride, a pH adjuster selected from the group consisting of boric acid, lactic acid, 5-sulfosalicylic acid, their salts, ammonium acetate, and mixtures thereof, one or more surfactants, and water.

[0037] A method for electroplating crude nickel comprises providing an aqueous nickel electroplating composition and bringing a substrate into contact with the aqueous nickel electroplating composition by means of immersing the substrate in the composition or spraying the composition onto the substrate. A current is passed through a conventional rectifier, where the substrate functions as the cathode and a counter electrode or anode is present. The anode can be any conventional soluble or insoluble anode used to electroplat nickel metal adjacent to the surface of the substrate. The aqueous nickel electroplating composition of the present invention deposits a nickel metal layer having a rough, granular, or cabalstone-like form on the substrate.

[0038] Preferably, the current density is in the range of 1 ASD or more. More preferably, the current density is in the range of 2 ASD to 20 ASD. Even more preferably, the current density is in the range of 5 ASD to 15 ASD.

[0039] The temperature of the nickel electroplating composition for depositing crude nickel is preferably in the range of 30°C to 70°C, more preferably in the range of 40°C to 65°C, and even more preferably in the range of 45°C to 60°C. Preferably, the nickel electroplating composition is continuously stirred during electroplating.

[0040] The thickness of the crude nickel metal layer may be in the range of 0.5 μm or more. Preferably, the crude nickel layer has a thickness in the range of 0.5 μm to 50 μm, more preferably 0.5 μm to 10 μm, and even more preferably 0.5 μm to 5 μm. The thickness of the nickel metal layer can be measured by conventional methods known in the art, such as XRF. For example, the thickness of the nickel layer can be measured using a Bowman Series P X-Ray Fluorimeter (XRF), available from Bowman, Schaumburg, IL. The XRF can be calibrated using a pure nickel thickness standard sample from Bowman.

[0041] The nickel layer preferably has a coarse granular, cabalstone-like, or mound-like particle morphology, with particles having a height of 400 nm to 700 nm and a base diameter of 200 nm to 600 nm, and more preferably, particles having a height of 500 nm to 700 nm and a base diameter of 250 nm to 600 nm. The greater the thickness, the greater the coarseness and particle size of the nickel precipitate. These parameters can be measured using an Olympus 3D Laser Microscope-LEXT OLS5000-LAF (available from Olympus Scientific Solutions Americas). Other methods and apparatus known to those skilled in the art may also be used.

[0042] Preferably, the nickel layer surface has an Sa of 70 nm or more, and more preferably an Sa of 70 nm to 180 nm, which is substantially equal to the Ra. Preferably, the Sdr is 4% or more, and more preferably the Sdr is 4% to 10%. Such parameters can be measured using conventional methods known in the art, such as an Olympus 3D laser microscope or AFM. For example, Sa and Sdr can be measured using an Olympus 3D Laser Microscope-LEXT OLS5000-LAF. Surface roughness can be measured by scanning a surface area of, for example, 256 μm × 256 μm at a 50x objective magnification.

[0043] The aqueous nickel electroplating composition of the present invention can be used to deposit a nickel layer on various substrates, both conductive and semiconductor substrates. Preferably, the nickel layer is deposited adjacent to the copper, copper alloy, or nickel-iron layer of the substrate. Examples of copper alloys, but not limited to them, include brass, bronze including cupronickel, copper-tin alloys, and copper-bismuth alloys.

[0044] Adjacent to the crude nickel layer, preferably, a noble metal is deposited such that the crude nickel layer and the noble metal share a common interface. Examples of such noble metals, though not limited to gold, include gold and palladium. Preferably, palladium is deposited adjacent to the crude nickel, forming a common interface with it, and gold is deposited adjacent to the palladium, such that gold and palladium share a common interface. Preferably, the palladium layer has a thickness in the range of 5 nm to 20 nm, and preferably, the gold layer has a thickness in the range of 0.5 nm to 5 nm. Such a metal layer arrangement is called a PPF and is common in lead frames. Such lead frames are then sealed in an EMC.

[0045] The rough nickel layer improves the bonding between the substrate, such as the lead frame, and the EMC. The rough nickel also improves gold wire bonding to the PPF surface. The rough nickel surface increases the contact area between the lead frame and the EMC, and between the lead frame and the bonding wire.

[0046] The IC package containing the crude nickel layer of the present invention enables good adhesion with epoxy molding compounds, prevents delamination of the molding compound, and can be expected to comply with MSL-1 (moisture resistance level -1, 168 hours at 85°C and 85% relative humidity, IPC / JEDECJ-STD-20).

[0047] The following embodiments are included to further illustrate the present invention, but are not intended to limit its scope. [Examples]

[0048] Example 1 Hull cell test The following two types of aqueous nickel electroplating baths were prepared.

[0049] [Table 1]

[0050] [Table 2]

[0051] Hull cell testing was performed using the following operating parameters: applied current 5A, 3 minutes, 55°C, 4 LPM air agitation. The current density ranged from 2 ASD to 20 ASD in the longitudinal direction of the Hull cell panel. During plating, the pH of the nickel bath in Table 1 was 1.31, and the pH of the nickel bath in Table 2 was 1.25. The Hull cell panel was made of bronze (copper-zinc alloy). The panel was first cleaned by electrocleaning with 60 g / L of RONACLEAN® GP-300 (available from DuPont de Nemours, Inc.) electrocleaning solution at 4-6 V, 60°C for 30 seconds, and then activated with 100 g / L of pre-dip solution ACTRONAL® 988 (available from DuPont de Nemours, Inc.) at room temperature for 5 seconds. After plating, the panel was rinsed with DI water and air-dried at room temperature. The thickness of each panel was measured using a Bowman Series PX line fluorometer (XRF) at 10ASD, one of the most common current densities in actual production line applications. The XRF was calibrated using Bowman's pure nickel thickness standard. The nickel thicknesses at 10ASD plated from the nickel baths shown in Table 1 (Invention) and Table 2 (Comparison) were 5.15 μm and 5.43 μm, respectively.

[0052] Panels plated with the nickel bath of the present invention had a dull appearance at current densities of 2 to 10 ASD and exhibited some haze at the panel edges. In contrast, panels plated with the comparative nickel bath had an uneven surface with haze and slight reflection at all current densities from 2 to 20 ASD.

[0053] The roughness of the nickel layer on each panel was measured using an Olympus 3D Laser Microscope-LEXT OLS5000-LAF. Surface roughness was measured by scanning a 256 μm × 256 μm surface area at 10 ASD points on the Hull cell panel with an objective lens magnification of 50x. Surface roughness was characterized by an area roughness index including Sa (arithmetic mean height) and Sdr (unfolded surface area ratio). Sa is substantially equal to Ra (arithmetic mean deviation) of profile roughness, and Sdr corresponds to the surface ratio used industrially, with a correlation of Sdr = (surface ratio - 1) × 100%. Higher Sa or Sdr indicates greater roughness of the nickel deposit. The average Sa of the nickel layer plated from the bath of the present invention was 0.308 μm and the average Sdr was 29.68%. In contrast, the average Sa of the nickel layer plated from the bath of the comparative example was 0.068 μm and the average Sdr was 4.71%. The nickel layer plated from the nickel plating bath of the present invention showed a significantly increased surface roughness compared to the nickel layer plated from the comparative bath.

[0054] Example 2 Hull cell test The following two types of aqueous nickel electroplating baths were prepared.

[0055] [Table 3]

[0056] [Table 4]

[0057] Hull cell testing was performed using the following operating parameters: applied current 5A, 3 minutes, 55°C, 4 LPM air agitation. The current density ranged from 2 ASD to 20 ASD in the longitudinal direction of the Hull cell panel. During plating, the pH of the nickel bath in Table 3 was 4.05, and the pH of the nickel bath in Table 4 was 4.40. The Hull cell panel was made of bronze (copper-zinc alloy). As in Example 1 above, the panel was first cleaned by electrocleaning and then activated with a pre-dip solution. After plating, the panel was rinsed with DI water and air-dried at room temperature. The thickness of each panel was measured by XRF as in Example 1 above. The thickness of the nickel deposit plated at 10 ASD from the bath in Table 3 (invention) was 5.16 μm, and the thickness from the nickel bath in Table 4 (invention) was 5.79 μm.

[0058] Panels plated with the nickel bath of the present invention had a dull, matte appearance at current densities of 2 to 20 ASD, and a bright appearance at the edges at current densities of 0 to 2 ASD. In contrast, panels plated with the comparative nickel bath exhibited haze at current densities less than 10 ASD and appeared semi-glossy at current densities of 10 to 20 ASD.

[0059] The surface roughness of the nickel layer on each panel was measured at 10 ASD points on the Hull cell panel using an Olympus 3D Laser Microscope, as described in Example 1 above. Surface roughness was characterized by an area roughness index including Sa (arithmetic mean height) and Sdr (surface area ratio). The average Sa of the nickel layer plated from the bath of the present invention was 0.289 μm, and the average Sdr was 32.12%. In contrast, the average Sa of the nickel layer plated from the comparative bath was 0.073 μm, and the average Sdr was 2.47%. The nickel layer plated from the nickel plating bath of the present invention had substantially increased surface roughness compared to the nickel layer plated from the comparative bath.

[0060] Example 3 Beaker test Multiple copper alloy C194 coupons were used with a plating area of ​​2.7 cm × 3 cm. C194 coupons are a type of semiconductor material used for forming lead frames. The C194 coupons were composed of copper (≧97%), iron (2.1~2.6%), phosphorus (0.015~0.15%), and zinc (0.05~0.2%). Each coupon was pre-treated in the same manner as in Examples 1-2 above before nickel electroplating.

[0061] The following two types of aqueous nickel electroplating baths were prepared.

[0062] [Table 5]

[0063] [Table 6]

[0064] During electroplating, the temperature was maintained at 60°C, the pH at 3.5, and the paddle travel distance and speed at 8 cm × 30 cycles / min. The applied current density was set to 1, 5, 10, and 20 ASD. The target nickel coating thickness was 0.75 μm, but at a current density of 10 ASD, some coupons achieved nickel coatings of 1.5 μm or even 3.0 μm. The coating thickness was tested by XRF. Coating roughness was measured at points 1, 5, 10, and 20 ASD using an Olympus 3D Laser Microscope. Particle morphology was measured using a Zeiss Sigma 300, 20 KV, and a working distance of 10 cm SEM.

[0065] Coupons nickel-plated from a bath without 2,5-dimercapto-1,3,4-thiadiazole had low roughness and were dull or semi-glossy. On the other hand, coupons nickel-plated from a bath containing 2,5-dimercapto-1,3,4-thiadiazole had a significantly increased rough surface and a dull coating. The mean values ​​of Sa and Sdr for nickel-plated coupons with a thickness of 0.75 μm are shown in Tables 7 and 8.

[0066] [Table 7]

[0067] [Table 8]

[0068] Tables 9 and 10 show the average values ​​of Sa and Sdr for coupons plated with nickel to thicknesses of 1.5 μm and 3 μm using 10ASD.

[0069] [Table 9]

[0070] [Table 10]

[0071] Example 4 Button shear test and wire bonding test A lead frame substrate made of C194 copper alloy with dimensions of 6 mm x 27 mm was pre-treated by electrocleaning and pre-immersion in the same manner as in Example 1 above. This lead frame was electroplated using the crude nickel bath shown in Table 1 of Example 1 or the comparative nickel bath shown in Table 11.

[0072] [Table 11]

[0073] Nickel electroplating was performed at 10ASD for 30 seconds. The pH of the nickel plating bath was maintained at 3.5 during electroplating. The temperature of each bath was maintained at 60°C. A 0.75 μm nickel layer was deposited on the copper alloy of the lead frame. The thickness of the nickel layer was measured by XRF. Comparative nickel deposits had the morphology shown in Figure 1, and crude nickel deposits had the morphology shown in Figure 2. Particle morphology was characterized by SEM using a Zeiss Sigma 300, 20 KV, working distance of 10 cm, and 10,000x magnification. The nickel deposits in Figure 2 show characteristic cabalstone-like nickel deposits from the nickel plating bath of the present invention. In contrast, Figure 1 shows substantially smoother nickel deposits characteristic of many conventional nickel baths.

[0074] The surface roughness of the nickel precipitates was characterized by the area roughness index Sa (arithmetic mean height) and Sdr (surface area ratio). The coating roughness was measured using an Olympus 3D Laser Microscope. The average Sa of the nickel layer plated from the bath of the present invention was 0.11 μm, and the average Sdr was 8.32%. On the other hand, the average Sa of the nickel layer plated from the bath of the comparative example was 0.095 μm, and the average Sdr was 1.03%.

[0075] Next, a palladium layer was plated onto the nickel layer using a PALLADURE® 200 palladium electroplating bath (available from DuPont de Nemours, Inc.) at 0.75 ASD for 3 seconds. The bath temperature was 45°C. The palladium layer on each nickel layer was 10 nm thick. Then, a 3 nm thick gold layer was plated onto the palladium layer using an AURALL® 364 gold strike bath (available from DuPont de Nemours, Inc.). The gold plating was performed at 0.1 ASD at 45°C for 15 seconds. The PPF multilayer structure had layers of Ni 0.75 μm / Pd 10 nm / Au 3 nm.

[0076] Gold bonding wire (Heraeus AW-14) with a diameter of 25 μm was solder-bonded to the PPF surfaces of the comparative nickel and crude nickel described above using a K&S manual wire bonder model 4524. Subsequently, the adhesive strength of the various nickel precipitates was tested by button shear tests, wire tensile strength tests, and wire tensile failure mode tests.

[0077] Subsequently, all coupons were coated with molding compound EMC-G700LA (Sumikon bakelite Co.). To avoid unexpected hardening, the EMC was stored at -40°C and removed from the freezer 24 hours before the molding process. During the thawing process, the EMC was kept under vacuum to minimize moisture absorption. The molding compound was molded into buttons and cured in a normal oven at 175°C for 2 minutes. Coupons using the button-shaped molding compound were then post-molded and cured at 175°C for 4 hours. The coupons were then cooled to room temperature. Half of the coupons using the button-shaped molding compound were exposed to a moisture resistance level of -1, 85°C, and 85% relative humidity for 168 hours using an ESPEC benchtop temperature and humidity chamber, model SH-221. The coupons were placed in a stainless steel basket inside the chamber and set to 85°C and 85% relative humidity for 168 hours (7 days). The coupons were then removed from the chamber and dried in the ambient environment.

[0078] Subsequently, a button shear test was performed on all coupons. The conditions for the button shear test were as follows: a) Shearing device: Nordson Dage 4000 multi-purpose bond tester b) Cartridge: DS 100 c) Button height: 3mm d) Button diameter: 3-3.5mm e) Shear height: 20% of the button = 600 μm f) Shear rate: 85 μm / sec g) Temperature: room temperature

[0079] The results of the button shear test for comparative nickel PPF coupons and crude nickel PPF coupons are shown in Table 12 below.

[0080] [Table 12]

[0081] The reduction in shear strength of the crude nickel of the present invention was similar to that of the comparative nickel, but the crude nickel of the present invention showed improved adhesion compared to the comparative nickel with or without MSL-1 treatment.

[0082] A Nordson Dage 4000 multi-purpose bond tester was used for the wire pull test (cartridge WP100, test speed 200 μm / sec). In the wire pull and wire pull fracture mode tests, the fracture modes were stitch fracture and neck fracture. For the comparative nickel PPF, neck fracture was the fracture mode in 84.6% of cases, and stitch fracture was the fracture mode in 15.4% of cases. In contrast, for the crude nickel PPF, neck fracture was the fracture mode in 78.9% of cases, and stitch fracture was the fracture mode in 21.1% of cases. The wire pull and wire pull fracture mode tests were performed according to the IPC-TM-650 Test Methods Manual, No. 2.4.42.3, February 1998 (Originating Task Group MCM-L Substance Performance Task Group (D-33e)) The Institute for Interconnecting and Packaging Electronic Circuits (available from 2215 Sanders Road-Northbrook, IL60062-6135). The results are shown in Table 13.

[0083] [Table 13]

[0084] Both neck and stitch fractures in the crude nickel are industrially acceptable. The wire tensile strength of the crude nickel PPF did not decrease significantly. This was unexpected, as rough surfaces are expected to reduce tensile strength, and gold wire is not expected to adhere to rough surfaces. Wire tensile strength can be further optimized by adjusting the wire bonder and working parameters.

Claims

1. Sources of nickel ions and chloride ions, and the following formula: 【Chemistry 1】 (wherein, R ６ and R ２ are independently hydrogen, linear or branched hydroxy(C １ - C ６ )alkyl, linear or branched carboxy(C １ - C ６ )alkyl, linear or branched amino(C １ - C ６ )alkyl, (C ５ - C ６ )cycloalkyl ring, or R ２ can be sulfur and G is nitrogen), and salts of the thiourethane, and an acidic nickel electroplating composition free of alloying metals.

2. The aforementioned thiourethane is given by the following formula: 【Chemistry 2】 A nickel electroplating composition according to claim 1, having the following characteristics.

3. The nickel electroplating composition according to claim 1, wherein the amount of thiourethane is 5 ppm or more.

4. The nickel electroplating composition according to claim 3, wherein the amount of thiourethane is 10 ppm to 100 ppm.

5. The nickel electroplating composition according to claim 1, wherein the nickel ion source is selected from the group consisting of nickel sulfate, nickel sulfate hexahydrate, nickel sulfate heptahydrate, nickel sulfamate, nickel sulfamate tetrahydrate, nickel chloride, nickel chloride hexahydrate, nickel carbonate, nickel methanesulfonate, nickel bromide, nickel fluoride, nickel iodide, nickel oxalate, nickel citrate, nickel tetrafluoroborate, nickel hypophosphite, nickel acetate, and mixtures thereof.

6. The nickel electroplating composition according to claim 1, wherein the source of chloride ions is selected from the group consisting of nickel chloride, nickel chloride hexahydrate, hydrogen chloride, sodium chloride, potassium chloride, magnesium chloride, calcium chloride, ammonium chloride, guanidine hydrochloride, ethylenediamine dihydrochloride, trimethylammonium chloride, pyridine hydrochloride, phenylammonium chloride, hydrazine dihydrochloride, and mixtures thereof.

7. The nickel electroplating composition according to claim 1, wherein the pH of the nickel electroplating composition is 2 to 6.

8. The nickel electroplating composition according to claim 1, further comprising a pH adjusting agent.

9. The nickel electroplating composition according to claim 8, wherein the pH adjusting agent is selected from the group consisting of sulfuric acid, hydrochloric acid, sulfamic acid, boric acid, acetic acid, aminoacetic acid, ascorbic acid, lactic acid, 5-sulfosalicylic acid, and salts thereof.

10. The nickel electroplating composition according to claim 1, further comprising a surfactant.

11. The nickel electroplating composition according to claim 10, wherein the surfactant is selected from the group consisting of sodium di(1,3-dimethylbutyl) sulfosuccinate, sodium 2-ethylhexyl sulfate, sodium diamyl sulfosuccinate, sodium lauryl sulfate, sodium lauryl ether sulfate, sodium dialkyl sulfosuccinate, sodium dodecylbenzenesulfonate, perfluorinated quaternary amines, and mixtures thereof.

12. The nickel electroplating composition according to claim 1, wherein the nickel electroplating composition does not contain a cyanide compound.

13. A method for electroplating nickel metal onto a substrate, a) To provide the aforementioned substrate; b) bringing the substrate into contact with the nickel electroplating composition of claim 1; c) A method comprising depositing a nickel layer containing Sa ≥ 70 nm and Sdr ≥ 4% on the substrate.

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