Silver electroplating composition and method for electroplating rough matte silver

Abstract

To provide a silver electrical plating composition and a method for electrical plating of rough surface dull silver.SOLUTION: A silver electrical plating composition makes coarse dull silver with a needle-like particle structure deposited. The deposition of the coarse dull silver enables good adhesion to dielectric materials even in environments with high relative humidity.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a silver electroplating composition and a method for electroplating matte silver with a rough surface. More specifically, the present invention relates to a silver electroplating composition and a method for electroplating matte silver with a rough surface having a needle-like or conical particle structure in order to improve the adhesiveness with a dielectric material.

Background Art

[0002] Lead frames are used for mounting and processing semiconductor dice or chips in the manufacture of semiconductor devices. The lead frame electrically connects the chip to an external device via the leads of the lead frame. In the industry, there are certain types of lead frames such as spot silver / hard solder coated lead frames and palladium pre-plated lead frames (PPF).

[0003] Conventionally, silver plating has been applied to all or part of the lead frame-based surface. The lead frame base is made of copper or a copper alloy in order to be firmly and well joined to metal wires (such as gold wires and copper wires) used when joining with a semiconductor element. In order to minimize the undesirable diffusion of copper in the underlying lead frame base made of copper or a copper alloy, silver or a silver alloy is directly formed on the lead frame base made of copper or a copper alloy without an underlying plating layer such as a nickel underlayer. The silver or silver alloy layer can have a thickness of 2 μm or more, typically 2.5 to 3.0 μm.

[0004] A semiconductor chip is implemented on a lead frame base, and after making bonding wire connections between the chip and the lead frame base, the semiconductor chip is encapsulated with a plastic molding compound called an epoxy molding compound (EMC) to form a package. For high reliability requirements, good adhesion between the lead frame base and the EMC of the package is the key to ensuring the proper functioning of the integrated circuit (IC) device. Delamination, cracking in the package, and even the so-called "popcorn" phenomenon can also cause device malfunctions.

[0005] During the life of the package, ambient moisture may be absorbed at the interface between the EMC and the lead frame base. When the moisture is absorbed and retained inside the device, the moisture is trapped and then evaporates at high temperatures. The evaporated moisture can exert a very large stress inside the package and may cause delamination at the interface between the EMC and the lead frame base.

[0006] To estimate the delamination tendency of a given package, the Institute of Printed Circuits (IPC) and the Semiconductor Technology Association of the United States have defined a standard classification for the moisture sensitivity level (MSL) of lead frame IC devices. According to this standard (J-STD-020D), which is an IPC and Semiconductor Technology Association of the United States standard, there are eight levels to represent the moisture sensitivity of the package. MSL1 corresponds to packages that are not affected by delamination even when exposed to moisture, while MSL5 and MSL6 devices are most prone to damage by moisture. To ensure sufficient adhesion under actual conditions, lead frame IC packages are tested according to the J-STD-20 MSL standard.

[0007] Due to the recent trend of introducing advanced electronics technologies into automobiles, the number of in-vehicle semiconductors is steadily increasing. On the other hand, in order to reduce the cost of semiconductor packages, it has become increasingly common to replace conventional gold wires with low-cost copper wires. However, copper wires have the drawback of being easily corroded by additives containing sulfur atoms that are used to improve the adhesion to the lead frame. To meet the strict conditions of the reliability test for in-vehicle conductors specified in Automotive Electronics Council-Q006 (AEC-Q006), it is important to prevent delamination between the EMC and the lead frame in the reflow process. Furthermore, in other fields such as 5G / Telecom and storage, the requirements for compliance with MSL-1 (moisture sensitivity level-1, 85 °C, 85% relative humidity for 168 hours, J-STD-20) are also increasing. In summary, the demands of the final market for IC packages are for higher reliability and a strong adhesive force between the EMC and the lead frame base.

[0008] Typically, the surface of most lead frame structures consists of two metals, such as copper or a copper alloy, which is the material of the lead frame body structure, and silver or a silver alloy present on the surface of the lead frame body structure. Silver or silver-containing alloys often have weak adhesion to the EMC. To address the adhesion between the lead frame base and the EMC, the industry has mainly focused on the surface of copper or a copper alloy. This can be achieved by a chemical etching process. For example, since a metal oxide surface generally exhibits better adhesion to the EMC than a metal surface without an oxide, the adhesion can be improved by generating a metal oxide layer on the surface of copper or a copper alloy through a chemical etching process. In addition to the chemical etching process, electrochemical treatments such as applying an anodic current to a copper or copper alloy material can also improve the adhesion by roughening the surface.

[0009] In recent years, the industry has focused on miniaturization and cost reduction of semiconductor packages. The demand for high-density packaging, which requires lighter and smaller components, has been increasing. High-density packages will further deteriorate the adhesion between copper, copper alloys and silver or silver alloys, especially within the EMC encapsulation. As a result, the adhesion between the lead frame base and the EMC, as well as the reliability of the package, especially the moisture sensitivity of the package, is significantly impaired. Summary of the Invention Problems to be Solved by the Invention

[0010] Therefore, there is a need for a method to improve the adhesion between the lead frame and the EMC in semiconductor packaging. Means for Solving the Problems

[0011] The present invention relates to a silver electroplating composition containing silver ions, a conductive compound, and a compound having the following formula:

Chemical Formula

[0012] The present invention further provides a) preparing a substrate; b) contacting the substrate with a silver electroplating composition containing silver ions, a conductive compound, and a compound having the following formula:

Chemical Formula

[0013] The present invention further relates to an article comprising a matte silver layer with a rough surface adjacent to the surface of a substrate, wherein the matte silver layer with a rough surface has Sa of 0.1 - 0.4 μm and Sdr of 5 - 50%.

[0014] The silver electroplating composition of the present invention enables the electroplating of a matte silver deposit with a rough surface onto a substrate. As a result, the matte silver with a rough surface provides good and reliable adhesion to dielectric materials (such as, but not limited to, epoxy molding compounds) even in an environment with relatively high humidity. The matte silver with a rough surface of the present invention enables reliable adhesion within semiconductor packaging, suppresses delamination or cracking between layers of the package and the "popcorn" phenomenon, and prevents defects in IC devices.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0016] Abbreviations used throughout this specification have the following meanings unless the context clearly indicates otherwise: °C = degrees Celsius; g = gram; ppm = parts per million; Kg = kilogram; L = liter; mL = milliliter; mm = millimeter; cm = centimeter; dm = decimeter; μm = micron; nm = nanometer; DI = deionized; A = ampere; ASD = ampere / dm 2=Plating rate; DC = Direct current; N = Newton; mN = Millinewton; R.O. = Reverse osmosis; R.T. = Room temperature; v = Volt; s = Second; sec. = Second; 3D = Three-dimensional; rpm = Revolutions per minute; 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; C.D. = Current density; Ag = Silver; Cu = Copper; S = Sulfur.

[0017] The term "adjacent" means that two metal layers are in direct contact such that they have a common interface. The abbreviation "N" means Newton, the SI unit of force, equal to the force that gives a 1-kilogram mass an acceleration of 1 meter per second per second, and equal to 100,000 dynes. The term "Ra" means the arithmetic mean deviation of the profile roughness. The term "Sa" means the arithmetic mean height and is substantially equal to Ra. The term "Sdr" means the developed interface area ratio corresponding to the surface area ratio and has a correlation of Sdr = (surface area ratio - 1) × 100%. The term "aqueous" means water or an aqueous system in which an organic solvent may be added to assist in solubilizing one or more components in the plating composition or plating bath. The terms "composition" and "bath" are used interchangeably throughout this specification. The terms "deposit" and "layer" are used interchangeably throughout this specification. The terms "electroplating", "plating", and "deposition" are used interchangeably throughout this specification. The term "matte" means dull or lacking luster but not having a cloudy or hazy appearance. The term "semi-gloss" means that the surface of an article has a visually hazy or slightly hazy appearance but still reflects light parallel. The term "bright" means that the surface of an article reflects light parallel and has a visually distinct appearance. The term "morphology" means the shape, size, texture, or topography of a surface or article. The term "dielectric" means an insulating material with a sufficiently low conductivity. The term "haze" means a cloudy or hazy appearance. The term "aliquot" means a part of a large whole, particularly a sample taken for chemical analysis or other processing. In the chemical structure [Chem.] means an optional shared chemical bond. The term "thio" means an organic compound containing -S- or -SH in the chemical structure. The articles "a" and "an" can refer to both singular and plural throughout this specification. Unless otherwise specified, all percentage (%) values and ranges refer to weight percentages. All numerical ranges are inclusive and can 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 relates to a silver electroplating composition comprising silver ions, a conductive compound, and a compound having the following formula: [Chem.] (wherein R1 is hydrogen or C1-C4 alkyl, R2 is C1-C4 alkyl or phenyl, preferably, R1 is hydrogen or C2-C4 alkyl, R2 is C2-C4 alkyl or phenyl, more preferably, R1 is hydrogen or C4 alkyl, and R2 is C4 alkyl or phenyl) and a compound having the same.

[0019] The silver ion source can be supplied by silver salts such as, but not limited to, silver halides such as chlorides, bromides, and fluorides, silver gluconate, silver citrate, silver lactate, silver nitrate, silver sulfate, silver alkanesulfonate, alkanol sulfonic acid, potassium silver cyanide, or mixtures thereof. When silver halide is used, preferably the halide is chloride. Preferably, the silver salt is potassium silver cyanide, silver nitrate, silver alkanesulfonate, or a mixture thereof, and more preferably, the silver salt is potassium silver cyanide, silver nitrate, or a mixture thereof. The silver salt is generally commercially available or can be prepared by methods described in the literature. Preferably, the silver salt is readily soluble in water. The silver electroplating composition of the present invention does not contain an alloying metal or metal for the purpose of brightening the silver deposit.

[0020] Preferably, the silver salt is included in the composition to provide silver ions at a concentration of at least 10 g / L, more preferably, the silver salt is included in the composition in an amount that provides a silver ion concentration in the range of 10 g / L to 100 g / L, still more preferably, the silver salt is included in an amount that provides a silver ion concentration in the range of 20 g / L to 80 g / L, even more preferably, the silver salt is included in an amount that provides silver ions at a concentration of 20 g / L to 60 g / L, and most preferably, the silver salt is included in the composition in an amount that provides a silver ion concentration in the range of 30 g / L to 60 g / L.

[0021] As the conductive compound contained in the silver electroplating composition of the present invention, there is mentioned a water-soluble salt for assisting the current in the silver electroplating composition during silver electroplating. Examples of the conductive salt include, but are not limited to, potassium dihydrogen phosphate, sodium dihydrogen phosphate, potassium phosphate, sodium phosphate, ammonium phosphate, sodium pyrophosphate, potassium pyrophosphate, ammonium pyrophosphate, sodium nitrate, nitrite, citrate, tartrate, salts of organic acids, salts of inorganic acids, and mixtures of one or more of the aforementioned conductive salts. Preferably, the conductive salt is potassium dihydrogen phosphate, potassium phosphate, sodium phosphate, ammonium phosphate, sodium nitrate, or a mixture thereof. More preferably, the conductive salt is potassium dihydrogen phosphate, sodium nitrate, or a mixture thereof. Most preferably, the conductive salt is potassium dihydrogen phosphate.

[0022] Examples of the organic acid that can be included in the silver electroplating composition of the present invention include, but are not limited to, acetic acid, citric acid, malonic acid, arylsulfonic acid, alkanesulfonic acid such as methanesulfonic acid, ethanesulfonic acid, and propanesulfonic acid, arylsulfonic acid such as phenylsulfonic acid, tolylsulfonic acid, and 5-sulfosalicylic acid. The salts of the aforementioned acids can also be included in the silver electroplating composition of the present invention.

[0023] Examples of the inorganic acid that can be included in the silver electroplating composition of the present invention include, but are not limited to, sulfuric acid, sulfamic acid, hydrochloric acid, phosphoric acid, hydrobromic acid, and fluoboric acid. The water-soluble salts of the above acids can also be included in the silver electroplating composition of the present invention. A mixture of an acid and its salt can be used. The acids are generally commercially available for both organic acids and inorganic acids, or can be prepared by methods known in the literature.

[0024] Preferably, the conductive compound is contained in an amount of at least 50 g / L, more preferably 50 g / L to 250 g / L, even more preferably 50 g / L to 150 g / L, and most preferably 80 g / L to 125 g / L.

[0025] The compound having the above formula (I) is included in the silver electroplating composition of the present invention as a roughening agent for providing a matte silver deposit with a rough surface. Such a compound is preferably included in the silver electroplating composition of the present invention in an amount of at least 1 ppm, more preferably 5 - 100 ppm, even more preferably 5 - 50 ppm, and most preferably 5 - 20 ppm.

[0026] The most preferred compound has the following formula.

Chemical formula

[0027] Optionally, one or more buffering agents and pH adjusting agents can be included in the silver electroplating composition to maintain the desired pH. Examples of buffering agents include, but are not limited to, boric acid and its salts, such as disodium borate, potassium borate, ammonium borate, and mixtures thereof, citric acid and salts of citric acid, such as potassium citrate, sodium citrate, ammonium citrate, or mixtures thereof.

[0028] Examples of optional agents for adjusting pH include, but are not limited to, potassium hydroxide, sodium hydroxide, ammonium hydroxide, citric acid, salts of citric acid, such as potassium citrate, sodium citrate, and ammonium citrate, phosphates, carbonates, phosphoric acid, and mixtures thereof.

[0029] Preferably, the buffering agent and pH adjusting agent are included in the silver electroplating composition in an amount of 10 g / L or more, more preferably 15 g / L - 100 g / L, even more preferably 15 g / L - 70 g / L. Most preferably, boric acid and its salts can be included in an amount of 15 g / L - 25 g / L. Most preferably, the pH adjusting agent can be included in an amount of 30 g / L - 70 g / L.

[0030] Preferably, the pH of the silver electroplating composition of the present invention is in the range of 6 to 14, more preferably 7 to 13, even more preferably 8 to 12, and most preferably 8 to 10.

[0031] Optionally, the silver electroplating composition of the present invention contains one or more silver complexing agents. Such complexing agents include, but are not limited to, potassium cyanide, hydantoin, hydantoin derivatives such as 5,5-dimethylhydantoin, succinimide and its derivatives, maleimide and its derivatives, and nicotinic acid. A preferred silver complexing agent is potassium cyanide.

[0032] Such silver complexing agents are included in conventional amounts well known to those skilled in the art. Preferably, the silver complexing agent is included in an amount of at least 5 g / L, more preferably 5 to 100 g / L, even more preferably 5 to 50 g / L, and most preferably 5 to 25 g / L.

[0033] Optionally, the silver electroplating composition of the present invention can contain one or more conventional grain refiners. Such grain refiners include, but are not limited to, thiomalic acid, 2-mercaptosuccinic acid, 3-mercapto-1-propanesulfonic acid, 1-[2-(dimethylamino)ethyl]-1H-tetrazole-5-thiol, and one or more of their salts. Preferably, the silver electroplating composition of the present invention does not contain such grain refiners.

[0034] When grain refiners are included, they can be included in an amount of 5 g / L or more, more preferably 10 g / L to 100 g / L.

[0035] The silver electroplating composition of the present invention contains water as a solvent, which is preferably at least one of deionized water and distilled water in order to suppress accidental impurities.

[0036] Optionally, the silver electroplating composition of the present invention can include one or more organic solvents to assist in solubilizing the composition components in water. Such organic solvents include pyridine, pyridine compounds, or mixtures thereof. Preferably, such pyridine compounds consist of 2-pyridinemethanol, 3-pyridinemethanol, 2-pyridineethanol, 3-pyridineethanol, and mixtures thereof combined with water. Preferably, when the solvent contains a pyridine compound, the solvent of the silver electroplating composition consists of 3-pyridinemethanol and water. Preferably, such compounds are included in the silver electroplating composition of the present invention in an amount of 0.1 g / L to 2 g / L, more preferably in an amount of 0.2 g / L to 1 g / L, and even more preferably in an amount of 0.2 g / L to 0.5 g / L.

[0037] Optionally, one or more surfactants can be included in the silver electroplating composition of the present invention. Such surfactants include, but are not limited to, ionic surfactants such as cationic and anionic surfactants, nonionic surfactants, and amphoteric surfactants. The surfactant may be included in a conventional amount such as 0.05 g / L to 30 g / L.

[0038] Examples of anionic surfactants are sodium di(1,3-dimethylbutyl)sulfosuccinate, sodium 2-ethylhexyl sulfate, sodium diamyl sulfosuccinate, sodium lauryl sulfate, sodium lauryl ether-sulfate, sodium di-alkylsulfosuccinate, and sodium dodecylbenzenesulfonate. Examples of cationic surfactants are quaternary ammonium salts such as perfluorinated quaternary amines.

[0039] Other optional additives can include, but are not limited to, leveling agents and biocides. Such optional additives can be included in conventional amounts.

[0040] Preferably, the silver electroplating composition comprises water, optional pyridine, 2-pyridinemethanol, 3-pyridinemethanol, 2-pyridineethanol, 3-pyridineethanol, or a mixture thereof, silver ions, a counter anion, a conductive compound, a compound of formula (I), an optional buffer, an optional pH adjuster, an optional acid, an optional grain refiner, an optional surfactant, an optional leveling agent, and an optional biocide, and the pH is from 6 to 14.

[0041] More preferably, the silver electroplating composition comprises water, optional 2-pyridinemethanol, 3-pyridinemethanol, 2-pyridineethanol, 3-pyridineethanol, or a mixture thereof, silver ions, a counter anion, a conductive compound, a compound selected from the group consisting of 6-(dibutylamino)-1,3,5-triazine-2,4-dithiol, 6-amino-1,3,5-triazine-2,4-dithiol, and mixtures thereof, an optional boric acid or its salt, an optional potassium hydroxide, sodium hydroxide, ammonium hydroxide, or a mixture thereof, an optional acid, an optional surfactant, an optional leveling agent, and an optional biocide, and the pH is from 7 to 13.

[0042] Even more preferably, the silver electroplating composition comprises water, optional 3-pyridinemethanol, silver ions, a counter anion, a conductive compound, a compound selected from the group consisting of 6-(dibutylamino)-1,3,5-triazine-2,4-dithiol, 6-amino-1,3,5-triazine-2,4-dithiol, and mixtures thereof, an optional boric acid or its salt, an optional potassium hydroxide, sodium hydroxide, ammonium hydroxide, or a mixture thereof, an optional surfactant, an optional leveling agent, and an optional biocide, and the pH is from 8 to 12.

[0043] Most preferably, the silver electroplating composition consists of water, optional 3-pyridinemethanol, silver ions, a counter anion, a conductive compound, a compound selected from the group consisting of 6-(dibutylamino)-1,3,5-triazine-2,4-dithiol, 6-amino-1,3,5-triazine-2,4-dithiol, and mixtures thereof, optional boric acid or a salt thereof, optional potassium hydroxide, sodium hydroxide, ammonium hydroxide, or mixtures thereof, optional surfactant, optional leveling agent, and optional biocide, and the pH is 8 to 10.

[0044] The silver electroplating composition of the present invention can be used to deposit a matte silver layer with a rough surface on various substrates. Preferably, the substrates on which the matte silver layer with a rough surface is deposited include copper and copper alloy layers. Such copper alloy layers include, but are not limited to, brass and bronze. Preferably, the silver electroplating composition of the present invention is used to electroplate a matte silver layer with a rough surface adjacent to the copper and copper alloy layers. Preferably, such copper and copper alloy layers are included in lead frame manufacturing and IC semiconductor packaging. Preferably, the matte silver layer with a rough surface is electroplated adjacent to a silver strike layer adjacent to the copper or copper alloy of the lead frame base or substrate. Such a silver strike layer preferably ranges from 10 to 20 nm. The silver strike layer is deposited adjacent to the copper or copper alloy by using a conventional silver electroplating bath or an electroless silver metal plating bath. To wrap the lead frame with a silver layer and copper or copper alloy and complete the lead frame and IC semiconductor package, a dielectric material called an epoxy molding compound is used. The IC package containing the matte silver layer with a rough surface of the present invention can prevent delamination of the molding compound layer by enabling good adhesion with the epoxy molding compound and is expected to have MSL-1 compliance (moisture sensitivity level-1, 85 °C and relative humidity 85%, 168 hours, J-STD-20).

[0045] The silver electroplating composition of the present invention can be electroplated at a temperature from room temperature to 70 °C, preferably from 30 °C to 60 °C, more preferably from 40 °C to 60 °C. The silver electroplating composition is preferably continuously stirred during electroplating.

[0046] The silver electroplating method of the present invention includes preparing a substrate, preparing a silver electroplating composition, and bringing the substrate into contact with the silver electroplating composition, such as by 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 electroplate silver and deposit it adjacent to the surface of the substrate.

[0047] The current density for electroplating matte silver with a rough surface can be in the range of 5 ASD or more. Preferably, the current density is in the range of 10 ASD to 180 ASD, more preferably 20 ASD to 150 ASD, and even more preferably 100 ASD to 150 ASD. Preferably, a high current density is used for silver plating to achieve the desired deposition of matte silver with a rough surface.

[0048] The silver electroplating composition of the present invention enables the deposition of a rough, matte, and uniform silver layer. The silver content of the deposit is 99% or more silver on a metal basis.

[0049] The rough matte silver layer preferably has an Sa of 0.1 to 0.4 μm, more preferably 0.2 to 0.3 μm, and an Sdr of preferably 5 to 50%, more preferably 25 to 30%. Sa and Sdr can be measured for the silver layer using conventional methods and apparatus known to those skilled in the art for measuring surface roughness. One method is to use an Olympus 3D Laser Microscope - LEXT OLS5000 - LAF (available from Olympus Scientific Solutions Americas). The surface roughness can be scanned, for example, at a surface area of 256 μm × 256 μm with a 50x objective magnification.

[0050] The deposit of matte silver has a needle-like or pointed structure, with a peak height of 1-4 μm and a diameter at the bottom of the peak of 0.2-0.4 μm. Such parameters can be measured using an Olympus 3D Laser Microscope-LEXT OLS5000-LAF. Other methods and devices well known to those skilled in the art can also be used.

[0051] Preferably, the thickness of the matte silver layer ranges from 0.1 μm or more. More preferably, the matte silver layer has a thickness range of 0.1 μm to 10 μm, more preferably 0.5 μm to 5 μm, even more preferably 2 μm to 4 μm, and most preferably 2 μm to 3 μm. The thickness can be measured by conventional methods known to those skilled in the art. For example, the thickness of the silver layer can be measured using a Bowman Series P X-ray fluorescence spectrometer (XRF) available from Bowman, Schaumburg, IL. The XRF can be calibrated using a pure silver thickness standard from Bowman.

[0052] The following examples are included to further illustrate the present invention but are not intended to limit its scope.

Example

[0053] Example 1 Button shear test A plurality of copper coupons having side dimensions of 0.27 dm × 0.06 dm × 2 were prepared such that the area of each coupon was 0.032 dm 2 . The Sa and Sdr of the copper coupons were determined using an Olympus 3D Laser Microscope-LEXT OLS5000-LAF. Sa ranged from 0.076 to 0.085 μm. The average was 0.08 μm. Sdr ranged from 1.26 to 1.49%. The average was 1.40%.

[0054] An aliquot of the copper coupon was roughened according to the procedure described in Tables 1 and 2.

[0055]

Table 1

[0056]

Table 2

[0057] The Sa and Sdr of the roughened copper coupons were measured using an Olympus 3D Laser Microscope - LEXT OLS5000 - LAF. The Sa values were in the range of 0.199 - 0.242 μm, and the average value was 0.218 μm. The Sdr values were in the range of 18.5 - 23.9%, and the average value was 20.7%.

[0058] The second and third aliquots were electroplated with a silver layer from a conventional silver plating bath or electroplated with a matte rough silver layer using the silver electroplating bath of the present invention described below. The fourth aliquot of the copper coupon was neither roughened nor silver electroplated.

[0059]

Table 3

[0060] The silver strike was electroplated on the copper coupon to a thickness of 0.1 - 0.2 μm. The thickness of the silver strike layer was measured using a Bowman Series P X - ray fluorescence spectrometer (XRF). The silver plating was carried out in a 1 L plastic container using an insoluble stainless steel anode.

[0061]

Table 4

[0062] Silver electroplating was carried out at pH 9 - 9.5. A jet plating apparatus (1010 spot plating apparatus of Kam Tsuen Mechanical & Electrical Ltd.) for high-speed silver plating was used. The silver layer had a thickness of 2.5 - 3 μm when measured using a Bowman Series P X-ray fluorescence spectrometer (XRF) available from Bowman, Schaumburg, IL. The XRF was calibrated using a pure silver thickness standard from Bowman.

[0063]

Table 5

[0064] Silver electroplating was carried out at pH 9 - 9.5. The silver layer had a thickness of 2.5 - 3 μm when measured with a Bowman Series P X-ray fluorescence spectrometer (XRF). The XRF was calibrated using a pure silver thickness standard from Bowman.

[0065] Sa and Sdr were measured for silver layers from each of two types of silver electroplating baths. The surface roughness was analyzed using an Olympus 3D Laser Microscope - LEXT OLS5000 - LAF (available from Olympus Scientific Solutions Americas). The surface roughness was scanned at a surface area of 256 μm × 256 μm with a 50x objective magnification.

[0066] The semi-bright silver layer plated from a Silverjet (trademark) 220SE silver electroplating bath had Sa values in the range of 0.09 - 0.12 μm and Sdr values in the range of 0.5 - 1.7%. Figure 1 is a 5000x SEM of the surface of the silver layer from one of the silver plating coupons taken with a Zeiss microscope.

[0067] In contrast, the Sa value of the silver surface plated on the copper coupon from the silver electroplating bath of the present invention was in the range of 0.15 to 0.3 μm and had an Sdr in the range of 12 to 30%. Figure 2 is a 5000-fold SEM of the surface of the silver layer from one of the silver-plated coupons photographed with a Zeiss microscope. The silver surface in Figure 2 has a rough tip morphology, in contrast to Figure 1. The silver electroplating bath of the present invention had a significantly rougher silver deposit than the silver layer plated from a conventional silver electroplating bath.

[0068] Next, all the coupons were coated with a molding compound EME-, a mixture of epoxy resin (5 - 10%), phenolic resin (1 - 5%), amorphous silica A (70 - 80%), amorphous silica B (5 - 10%), and carbon black (0.1 - 1%). The molding compound was formed into a button shape and cured in a conventional oven at 175 °C for 120 seconds. Then, post-mold cure was performed on the coupons having the button-shaped molding compound at 175 °C for 4 hours. The coupons were cooled to room temperature. Half of the coupons having the button-shaped molding compound were exposed to a humidity level of -1, 85 °C, and 85% relative humidity for 168 hours using an ESPEC benchtop type thermo-hygrostat, model SH-221. The coupons were placed in a stainless steel basket inside the chamber and set at 85 °C and 85% relative humidity for 168 hours (7 days). Then, the coupons were taken out of the chamber and dried in the ambient environment.

[0069] Next, a button shear test was performed on all the coupons. The conditions of the button shear test were as follows: a) Shearing device: 4000 Multipurpose Bondtester available from Nordson b) Cartridge: DAGE-4000-DG100KG c) Height of the button: 3 mm d) Diameter of the button: 3 mm e) Shearing height: 20% of the button = 600 μm f) Shearing speed: 85 μm / s g) Temperature: Room temperature

[0070] The results of button shear tests of silver-plated copper coupons, roughened copper, and non-roughened copper are shown in Table 6 below.

[0071]

Table 6

[0072] For the treatment w / o MSL-1, the shear force of the matte rough silver was 31.3 Kg, while the shear force of the conventional silver was 19.6 kg. The increase rate was (31.3 Kg - 19.6 Kg) / 19.6 Kg × 100 = 59.7%. For the treatment w / MSL-1, the shear force of the matte rough silver was 27 Kg, and the conventional silver was 16.5 Kg. The increase rate was (27 Kg - 16.5 Kg) / 16.5 Kg × 100 = 63.6%. The results showed that the matte rough silver plated from the matte rough silver bath had improved molding shear force higher than that of the silver plated from the conventional silver bath. For w / o MSL-1, the shear force of the matte rough silver had an improved molding shear force of approximately 60%. For w / MSL-1, the shear force of the matte rough silver of the present invention had an improved molding shear force of 63.6%. Also, the shear force of the matte rough silver was higher than that of the rough copper surface and the untreated copper surface.

[0073] Although there was a decrease in adhesion after the MSL-1 treatment of the matte rough silver, it was still higher than that of the conventional silver deposit, the roughened copper surface, and the untreated copper surface. The matte rough silver enhanced the adhesion between the molding material and the silver surface coating even in a high humidity environment.

[0074] Example 2 Roughness analysis of the silver layer at a high electroplating speed A plurality of C194 copper coupons having dimensions of 0.27 dm × 0.25 dm were prepared. The C194 coupon is a type of semiconductor material used for the formation of lead frames. The C194 coupon was composed of copper (>97%), iron (2.1 - 2.6%), phosphorus (0.015 - 0.15%), and zinc (0.05 - 0.2%). The silver plating area on the coupon was 0.0256 dm 2 (0.16 dm × 0.16 dm).

[0075]

Table 7

[0076]

Table 8

[0077] The pH of the bath was 9.5. Electroplating was performed using a jet plating apparatus in the same manner as in Example 1 above. The control bath 1 and Baths 1 - 2 of the present invention were plated at 150 ASD, and the control bath 2 and Baths 3 - 4 of the present invention were plated at 180 ASD. Semi-bright silver deposits were plated on the copper coupons plated in the control baths 1 and 2. Matte silver deposits with a rough surface were plated on the copper coupons plated in Baths 1 - 4 of the present invention. The thickness of the silver deposits was 2.5 - 3 μm.

[0078] The surface roughness was measured using the Olympus 3D Laser Microscope - LEXT OLS5000 - LAF described in Example 1 above. The Sa values and Sdr values of the plated coupons are shown in the following table.

[0079]

Table 9

[0080] The results of the roughness analysis showed that when plated at current densities of 150 ASD and 180 ASD, the silver deposits plated from the baths of the present invention had a significantly rougher surface than the silver deposits plated from the control or conventional silver baths.

[0081] Example 3 Hull Cell Test of Silver Electroplating Bath Containing Thio-Organic Compound as Roughening Agent A plurality of brass panels with dimensions of 10 cm × 7.5 cm and a plating area of 10 cm × 5 cm were prepared for silver electroplating in a Hull Cell within a current density range of 20 - 50 ASD. The brass panels were plated according to the process described in Table 10 below to perform silver electroplating.

[0082] [Table 10]

[0083] [Table 11]

[0084] [Table 12]

[0085] After the panels were silver-plated and dried, their appearance was inspected with the naked eye. The silver layer that appeared to have semi-gloss to gloss and haze showed a substantially smooth surface. The silver layer that appeared matte or dull showed a substantially rough surface. The plating results are disclosed in Table 13.

[0086] [Table 13]

[0087] [Table 14]

[0088] Only the silver electroplating bath containing 6-anilino-1,3,5-triazine-2,4-dithiol and 6-(dibutylamino)-1,3,5-triazine-2,4-dithiol gave a substantially rough and matte silver deposit.

Claims

1. Silver ions, a water-soluble salt, and the following formula: 【Chemical 1】 (wherein, R １ is hydrogen or C １ - C ４ alkyl, and R ２ is C １ - C ４ alkyl or phenyl) and a silver electroplating composition containing the compound.

2. The silver electroplating composition according to claim 1, wherein the compound is selected from the group consisting of 6-(dibutylamino)-1,3,5-triazine-2,4-dithiol, 6-anilino-1,3,5-triazine-2,4-dithiol, and mixtures thereof.

3. The silver electroplating composition according to claim 1, wherein the amount of the compound is at least 1 ppm.

4. The silver electroplating composition according to claim 1, wherein the water-soluble salt includes potassium dihydrogen phosphate, potassium phosphate, sodium phosphate, ammonium phosphate, sodium nitrate, salts of organic acids, salts of inorganic acids, or mixtures thereof.

5. The silver electroplating composition according to claim 1, further comprising a buffering agent.

6. The silver electroplating composition according to claim 1, further comprising a pH adjuster.

7. The silver electroplating composition according to claim 1, further comprising a silver complexing agent.

8. The silver electroplating composition according to claim 1, further comprising an organic solvent selected from pyridine and pyridine compounds.

9. The silver electroplating composition according to claim 8, wherein the pyridine compound consists of 2-pyridinemethanol, 3-pyridinemethanol, 2-pyridineethanol, 3-pyridineethanol, and mixtures thereof.

10. The silver electroplating composition according to claim 1, wherein the pH of the silver electroplating composition is 6 to 14.

11. [[ID=2 ​ ​ ​ ​ ​ ​ ​ ​

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