JP2005517814A - Electroplating solution containing organic acid complexing agent - Google Patents

Abstract

A solution for use in connection with deposition of one or more metals on an electroplatable substrate surface. The solution includes water; metal ions; complexing agent. The complexing agent is preferably an organic compound having 5 to 6 carbon atoms containing a 5 or 6 membered ring containing at least two hydroxyl groups and at least one oxygen atom. The compound is present in an amount sufficient to form a complex with the metal in solution and inhibit metal oxidation. If necessary, a suitable pH adjusting agent can be included in the solution to maintain the pH of the solution within the range of 2 to 10, preferably about pH 3.5 to 5.5. In the most preferred pH range, the solution is particularly useful for electroplating composite articles having electroplatable and non-electroplatable portions without adversely affecting the non-electroplatable portions. .

Description

  The present invention relates to metal deposition, in particular tin or tin-lead alloys on the surface of a composite article having an object or an electroplatable substrate, for example an article composed of metal, or an electroplatable and non-electroplatable part. Relating to the precipitation. The present invention also describes a method of inhibiting fusion during electrodeposition of a plurality of such composite articles. This is related to electroplating of small electrical components that have a large surface area / unit mass and are easy to fuse. Of particular interest herein are surface mount capacitors and resistors having, for example, metal parts and ceramic, glass, or plastic parts of electrical components.

  The size of electronic components has decreased dramatically in recent years. This reduction in size made it much more difficult to electroplate such parts. In addition, many surface mount technology (SMT) components have sensitive ceramic parts that can be damaged by highly acidic or highly alkaline solutions. In order to avoid this problem, neutral or near neutral pH electroplating solutions are desirable.

  Neutral or near neutral pH tin and tin / lead alloy electrolytes specifically formulated to be compatible with sensitive ceramic SMTs are disclosed in US Pat. Nos. 4,163,700, 4,329,207, 4,640,746, This is described in US Pat. Nos. 4,673,470 and 4,681,670. The formulations described in these patents include complexing agents such as citrate, gluconic acid, which are complexed with tin and / or lead at the required high pH to make them soluble in solution. Contains salt or pyrophosphate.

  The use of prior art solutions has the permanent problem of joining or assembling parts during electrodeposition. This is quite common when plating tin or tin alloys on small parts with flat surfaces where the parts tend to gather together during plating. When barrel plating SMT parts, it is not uncommon for up to 10% of the load to bond (ie, stick together). Under some conditions, the full load merges together into a large mass. The extent of this problem depends on the plating solution composition and the plating method and part geometry. This problem is particularly noticeable in tin-lead alloy electroplating.

  While neutral or near neutral pH tin and tin / lead alloy electrolytes specifically formulated to be compatible with sensitive ceramic SMT have some utility, this does not address the problem of component fusion. In addition, it has been found that the attack on the ceramic is strongly influenced by the electrolyte composition as well as the pH. Prior art electrolytes have been found to attack new low temperature fired ceramics even at nearly neutral pH. In addition, there are concerns regarding tin whisker growth on thin plated component surfaces. Therefore, tin deposits that are resistant to whiskers are desirable. The present invention solves this problem and provides a solution and method for forming the desired precipitate.

  The present invention relates to a solution for use in connection with the deposition of one or more metals on an electroplatable substrate surface. The solution includes water; a sufficient amount of metal ions to form metal deposits on the plateable substrate; and a complexing agent. The complexing agent is preferably an organic compound having 5 to 6 carbon atoms containing a 5 or 6 membered ring containing at least two hydroxyl groups and at least one oxygen atom. The reagent is present in an amount sufficient to form a complex with the metal and solubilize it in solution. In addition, the reagent inhibits the oxidation of metal ions in solution. The complexing agent prevents oxidation of the metal from a lower valence state to a higher valence state when the metal ion has the ability to exist in solution in at least two different valence states. If necessary, a suitable pH adjusting agent can be included in the solution to maintain the pH of the solution within the range of 2-10. In the most preferred pH range, the solution is particularly useful for electroplating composite articles having electroplatable and non-electroplatable portions without adversely affecting the non-electroplatable portions. .

  The complexing agent preferably has the following structure:

Wherein each R is the same or different and is hydrogen or a lower alkyl group having 1 to 3 carbon atoms, T is R, OR, or O═P (OR) ₂ —, and Z is O═ Or RO-, n is 2-4, Z can be the same or different each time it appears in the structure, and m is 1-3. ]
Or the complexing agent is a soluble salt of such structure. Most preferred compounds include ascorbic acid, isoascorbic acid (also referred to as erythorbic acid), dehydroascorbic acid, glucoascorbic acid, galacturonic acid, glucoronic acid, and glucose-6-phosphate, or salts thereof Is mentioned. Typical salts include alkali metals or alkaline earth metals. Such reagents are generally present in an amount of about 25-200 g / l.

  The present invention also relates to a method of electroplating metal deposits on the surface of a composite article comprising electroplatable and non-electroplatable portions. The method contacts a plurality of such articles with one of the solutions described herein and causes the current to pass through the solution to adversely affect non-electroplatable portions of the article. Forming a metal electrodeposit on the surface of the article that can be electroplated without. The preferred metal electrodeposit is tin metal or a tin-lead alloy, and the preferred article is an electronic component.

  It has been discovered that by using an electrolyte solution comprising one or more of the complexing agents disclosed herein, fusion of composite article electronic components can be largely eliminated. In particular, ascorbic acid and related compounds are most preferred for use as such complexing agents.

  Complexing agents are preferably utilized in solutions for electroplating tin or tin-lead deposits, but are also used in solutions for electroplating other metals, particularly metals having multiple valence states can do. Such complexing agents help maintain the metal in one of its lower valence states in solution, thus facilitating the electroplating process and reducing the oxidation of the metal that can affect the proper use of the solution. avoid. Stannic tin also forms complexes in these systems.

  Any of the complexing agents of the formula given above can be used in the present invention. An advantageous complexing agent is an organic acid, and preferred reagents include ascorbic acid, isoascorbic acid, dehydroascorbic acid, glucoascorbic acid, galacturonic acid, and glucolonic acid. Such acid salts can also be used, with the preferred salts being alkali or alkali metal salts. Ketogluconate can be used because these compounds convert to ascorbic acid in the bath. Heptagluconate is also suitable because it converts to a similar acidic species in solution. Any of these reagents can be used at a typical amount of about 25-200 g / l. The most preferred complexing agent is ascorbic acid or ascorbate since such compounds are relatively low cost and readily available.

  Ascorbic acid is included in the solution as simple ascorbic acid, an ascorbate salt such as sodium or potassium ascorbate, and / or an ascorbic acid-metal complex (such as tin ascorbate). The last is preferred when it is desirable to utilize other acidic components such as organic acids or organic acid salts to maintain the desired solution pH. The amount of ascorbic acid present should be sufficient and minimal to solubilize the metals present in the solution at the given pH of the solution. As such, the amount of ascorbic acid required is proportional to the metal concentration. A preferred ascorbic acid concentration is about 45-200 g / l with a tin concentration of 15 g / l.

  The solution of the present invention can be used to plate any electroplatable substrate. In general, such substrates are made of metals such as copper, nickel, steel or stainless steel. In today's commercial products, many parts that require electroplating are being produced in increasingly smaller sizes. In particular, electronic components are typical examples of such components. In addition, such parts are composite articles having electroplatable and non-electroplatable portions. The metal part is metallic or metallic, while the non-electroplatable parts are typically ceramic, glass or plastic. This solution is particularly useful for electroplating such composite articles.

  The electroplating solution can have any pH between 2 and 10, but is preferably about 3 to 7.5, more preferably about 4 to 5 so that the solution is compatible with the electronic component to be plated. Within the range of .5. When the part has metallic and inorganic parts, the preferred pH range allows the metal to be deposited on the metallic part surface without adversely affecting the inorganic part. In general, very high or very low pH solutions will damage the ceramic portion of the composite article to be plated.

  Such a solution preferably contains no appreciable amount of free acid or free base, but essentially any acid or base can be used for pH adjustment. Generally, since the solution is acidic, the base or basic component is utilized to convert the free acid to its corresponding salt. Preferred bases for this purpose include sodium hydroxide or potassium hydroxide as well as many others.

  The solution is formulated so as to be compatible with the substrate to be plated, preferably so as not to adversely affect the substrate. If a composite article having electroplatable and non-electroplatable parts is to be plated, the solution should be formulated so as not to attack or break the non-electroplatable parts of the substrate. It is. Simple tests can be used to determine substrate / solution compatibility. The article to be plated can simply be immersed in the proposed solution for a length of time that is longer than the length to be used for the plating process. The temperature of the solution can approximate that of the solution during the plating process, or high temperatures can be used for accelerated testing. The part is immersed in the solution for the desired time, then recovered and weighed to determine the weight loss that occurs due to attack of the article by the solution during immersion.

  For example, composite articles currently used for capacitor manufacture are being manufactured using low temperature fired ceramics. Such ceramics contain a greater proportion of glass than conventional ceramics and are more prone to attack during the plating process. A simple comparative test was performed to determine the suitability of various commercial solutions and to determine with the solutions according to the invention. The capacitor was placed in a beaker containing the same amount of such solution and the weight loss of the part after 5 hours immersion was measured. The results are shown in the table below.

This table shows that the present invention has essentially no effect on the capacitor and is a substantial improvement to the plating of such components compared to conventional baths.
A particularly useful apparatus for electroplating such electrical components is disclosed in US Pat. No. 6,193,858 and need not be described further herein. To the extent necessary, the entire contents of this patent are specifically disclosed herein for reference.

  Improvements to the previously patented system are disclosed in published international application W002 / 053809, the entire contents of which are specifically incorporated herein by reference. Immersion of the plating chamber in the electrolyte represents a significant improvement in that an external soluble electrode can be used, as disclosed in this application.

  Electrolytes containing the complexing agent of the present invention can electrodeposit tin or tin-lead alloys, while minimizing the fusion or bonding of electroplated parts and adversely affecting non-electroplatable parts of the article It was found that there was nothing to do. In this respect, such electrolytes are superior to those of the prior art, particularly citrate based baths. The complexing agent serves to maintain tin and / or lead in solution at the pH of the electrolyte. Certain complexing agents, particularly ascorbic acid, also serve as stabilizers to prevent oxidation of stannous tin to stannic.

  L-ascorbic acid (AA) is readily converted to L-dehydroascorbic acid (DAA). In addition, DAA can be easily returned to AA by converting two ketone groups on adjacent carbon surfaces into hydroxyl groups and converting the single bond connecting these atoms into a double bond. The ease with which AA is converted to DAA makes AA a powerful reducing agent. In the plating solution of the present invention, AA helps form a complex with both divalent and tetravalent tin ions. This prevents or at least minimizes the formation of tin oxide that would precipitate and form sludge that adversely affects the performance of the solution.

  Preferred solutions according to the present invention include water, divalent tin salts, and ascorbic acid as complexing agents, optionally divalent lead salts, salts to increase electrical conductivity, surfactants, or promote anodic dissolution. Contains reagents to do.

  As a stannous salt that may be used in the present invention, any suitable one of stannous sulfate, stannous chloride, stannous oxide, stannous methanesulfonate, stannous ascorbate or stannous Sources are mentioned. The stannous concentration in the solution is probably 5-100 g / l, most preferably 10-50 g / l. As mentioned above, the complexing agent of the present invention also forms a complex with the stannic salt, so it is possible to add the stannic salt to the solution instead of or together with the stannous salt without concern. It is.

  Lead salts that may optionally be included to form tin-lead precipitates include any solution-soluble divalent lead salts, such as lead methanesulfonate, lead acetate, or lead ascorbate. It is done.

  Perhaps the conductivity of the solution is increased by adding salt if necessary. If a pure tin solution is desired, a simple salt such as potassium sulfate may be used. Where a tin-lead alloy is desired, potassium methanesulfonate or potassium acetate may be appropriate. Metal sulfide salts can also be used if desired. Any of these salts may be used to promote anodic dissolution and aid electrodeposition.

  Surfactants typically utilized in tin or tin alloy electrolytes may be included in the solution to improve the crystal structure of the precipitate and to improve the quality of the precipitate at high current densities. Preferred surfactants include solution-soluble alkylene oxide condensation compounds, solution-soluble quaternary ammonium-fatty acid compounds, solution-soluble amine oxide compounds, solution-soluble tertiary amine compounds, or mixtures thereof. Can be mentioned. One preferred surfactant is an alkylene oxide condensation compound that is present in an amount of about 0.01 to 20 g / l. Other conventional surfactants can be used because there is no criticality to this component with respect to the deposit appearance, but some additives are better than others for bonding the articles to be plated May work. One of ordinary skill in the art can perform routine tests to determine the most appropriate surfactant for any individual plating solution.

  If a glossy precipitate is desired, the aromatic aldehyde can be added in an amount sufficient to act as a brightener. If desired, other conventional brighteners can be used instead.

  The substrate to be electroplated is preferably a composite article having conductive and non-conductive portions. The metal part is metallic or metallic, while the non-conductive parts are typically ceramic, glass or plastic. The solution is particularly useful for electroplating such composite articles and does not adversely affect non-metallic parts of the article and does not cause fusion of such parts.

  When it is desired to plate the surface of the composite substrate electronic component, the pH of the electrolyte is preferably kept within the range of about 4 to 5.5. The pH can be increased by adding caustic such as potassium hydroxide, ammonium hydroxide, sodium hydroxide or the like, or can be lowered using an acid such as sulfuric acid or methanesulfonic acid. . Alkane or alkanol sulfonic acids such as methane sulfonic acid are preferred for tin-lead alloy solutions because sulfuric acid can yield lead sulfate which is insoluble in the solution and appears to tend to precipitate. As mentioned above, a pH of about 4 to 5.5 results in the strongest inhibition of such metal assembly. Moreover, the amount of ascorbic acid should not be in large excess over what is needed to complex with tin to inhibit and minimize assembly.

  Typical antioxidants used in tin and tin-lead solutions may be included in the solution of the present invention (eg, catechol or hydroquinone as disclosed in US Pat. No. 4,871,429), but neutral Or, ascorbic acid has been found to be effective in preventing oxidation of stannous to stannic in plating solutions at near neutral pH. As such, ascorbic acid serves the dual function of acting as both a complexing agent and an antioxidant in the solution.

  It has been discovered that the plating solution of the present invention can be formulated to have a low throwing power to minimize or largely eliminate plating of non-conductive portions of composite articles and fusion of composite articles. It was done. Such a solution is particularly formulated so as not to deposit metal at a low current density. This is contrary to the conventional practice of blending the electrolyte so that the metal is deposited in the widest possible current density range. In fact, for most conventional tin electroplating solutions, anything is done to expand the current density range of electrodeposition by adding various additives. It has been found that component fusion can be minimized by limiting the current density range of electrodeposition to higher current densities. Fusion is believed to occur due to metal deposition in the electrolyte membrane between two closely contacting parts or between a part and a current feeder. Precipitation occurs in a thin film between two conductive surfaces, so it necessarily occurs at a low current density. By blending so that the electrolyte does not plate at a low current density, fusion can be minimized.

  It has been found that component fusion is strictly dependent on the plating bath composition, and the selection of an appropriate grain refiner or surfactant is a necessary requirement to minimize fusion. In this regard, it has been found that a simple electrolyte containing only a metal salt and a complexing agent electroplates surface mount technology (SMT) components without fusing. The resulting tin deposit is a dark gray matte and is unacceptable for commercial use. When a typical surfactant or grain refiner is added to the electrolyte to improve the quality of the precipitate, very strong coalescence is observed in almost all cases. Cathode surface polarization resulting from surfactants and grain refiners appears to strongly affect component fusion. Furthermore, it has been found that electrolytes containing additives that provide a limited coating at low current density are less prone to coalescence than additives that provide a high coating at low current density.

  Solutions formulated for plating individual parts in barrels or other suitable equipment have high throwing power so that the current penetrates the load and deposits the metal inside the bulk of the load It is widely thought that it must be. Also, the plating rate is very negligible at low current densities, so a substantial amount of metal does not deposit under these conditions, but rather most of the metal is deposited near the plating barrel circumference at high current density. it is obvious. Therefore, if the part itself does not have a low current density area, such as hollow or blind holes, use a solution with high throwing power for plating of individual parts in a barrel or other suitable equipment Was found unnecessary.

  In addition, plating solutions that do not deposit metal at low current densities will minimize metal deposition on the non-conductive portion surface of the composite article. The phenomenon of metal deposits extending from the conductive end of the article onto the nonconductive portion is commonly referred to as creep or bridging. The degree of this phenomenon depends mainly on the composition of the nonconductive material. For example, a ceramic material having a certain electrical conductivity is more prone to metal creep than a ceramic material that is a perfect insulator. Creep is believed to be caused by current leakage from the conductive portion of the article during electrodeposition to the “nonconductive” composite portion. By limiting metal deposition to high current density conditions, metal deposition on non-conductive portions can be minimized or eliminated.

  The plating solution of the present invention also helps to reduce or eliminate the presence of whiskers in the deposit. These are caused by the growth of filaments in the precipitate under certain thermal conditions after plating. Such whiskers have been found to be the cause of short circuit failures in low voltage devices. In addition, whiskers can move away from deposits and accumulate in other areas, causing further short circuit problems or impeding mechanical operation. By using the electroplating solution disclosed herein, the degree of whisker formation can be significantly reduced and eliminated altogether.

The plating solution of the present invention can be blended so as to have the following characteristics and advantages, and is preferably blended.
1. This will deposit from white mats to semi-gloss deposits.
2. This will not damage the parts that are to be coated.
3. This will not deposit metal at low current densities.
4). This can reduce or even eliminate whisker formation if the precipitate is later subjected to thermal conditions.

  If the part to be plated is a composite article containing a ceramic or leaded glass part, the acid or alkali solution will damage the ceramic or glass part during electroplating. Components such as SMT resistors, inductors and capacitors are of this type. The pH of the electroplating solution for the SMT part should be about 2.5-9 to minimize damage to the ceramic or glass portion of the article. In order to achieve this pH, the tin must be in complex form. Typically, prior art complexing agents include citrate, gluconate, and pyrophosphate. However, one or more organic additives are typically used to plate the semi-gloss deposit. The most common additives greatly increase the low current density coating of the solution, resulting in fusion of the parts to be plated and overplating of the non-conductive parts of the parts.

  By using an electrolyte at a high metal concentration, at an elevated temperature, selecting an additive that does not increase low current density coating (LCDC) or reduce LCDC and / or any combination thereof The low current density coating may be reduced. For example, when tin is the metal to be electroplated, a high metal ion content of at least about 25 g / l is preferred. Since high temperatures have generally been found to increase component fusion, high bath temperatures are the least desirable way to reduce LCDC.

  The selection of the organic additive in the bath is particularly important in maintaining uniform electrodeposition at a low level. The most desirable additive can be determined by routine testing on the particular plating solution under consideration. Such additives include conventional surfactants and grain refiners such as organic compound condensation compounds, such as single or multiple aromatic rings and other organics that have dye-like properties but are not surfactants. Condensation or reaction products are mentioned. Such compounds are generally well known in the prior art and are simply tested to ensure they do not give the plating solution a high throwing power.

  Other additives may be used in combination with surfactants and grain refiners to reduce the throwing power of the electrolyte. Ammonium chloride, ascorbic acid, and M-nitrophenol have been found to reduce throwing power when used with various surfactants and grain refiners. Obviously many other additives appear to function in this way, and the use of such other additives is the subject of the present invention. One of ordinary skill in the art can perform routine testing to determine whether the best combination of additives should be used for any individual electroplating solution.

  When plating composite articles, this solution can be used in the apparatus disclosed in US Pat. No. 6,193,858 and published international application W002 / 053809. The plating solution of the present invention can also be used in the rotary plating apparatus described in US Pat. Nos. 5,487,824 and 5,565,079 to obtain improved results because tin on the current feeder ring surface This is because the deposition of is substantially reduced, resulting in a significant reduction in maintenance required to replace and remove the current feeder.

  Therefore, it is also the subject of the present invention to use an electrolyte with reduced LCDC in a rotary plating apparatus. The use of the present invention is also advantageous when using plating barrels because less metal will deposit on the dangler surface, reducing metal creep and component fusion. Thus, the use of LCDC electrolyte in barrel plating is also the subject of the present invention.

  While the present invention is particularly advantageous when plating composite parts without a medium, the use of the present invention to plate individual articles mixed with a medium reduces the plating on the surface of the current feeder, and the composite article There is a considerable advantage of reducing or eliminating metal deposition on the surface of the non-conducting part.

  A useful method for testing electrolytes for LCDC is to use the standard 265 ml Hull Cell test. Use standard procedures for operating the hull cell. Typical conditions appear to be 5 minutes at 1A, 5 minutes at 0.5A or 5 minutes at 0.25A, each using paddle agitation. The hull cell panel made in 1A has an LCDC when the back of the hull cell panel is largely unplated except for a portion extending less than 1 cm from the panel edge. In addition, the most preferred electrolyte will have an unplated portion on the front low current density edge surface. This unplated portion may be 1/8 inch to 3/4 inch wide. Electrolytes that normally show the results of this type of hull cell panel are much less prone to coalescence than electrolytes that produce significant plating on the rear surface of the hull cell panel. Limiting the current density that would not deposit metal was measured by making a hull cell panel at 0.25A and determining the current density at the edge of the metal deposit using an appropriate hull cell panel scale. You can do it.

  In addition, when using an electrolyte with LCDC in an SBE device for modern SMT without media, current feeders are generally not plated with tin at the end of the plating cycle, and the parts are It has been found that it does not fuse with the current feeder. On the other hand, when using a commercially available neutral tin plating electrolyte and plating SMT without medium in SBE, the parts will not move within 3 minutes from the start of plating and the current feeder is completely tin. It is found to be coated. Therefore, the use of tin or tin alloy electrolytes with LCDC is necessary for the successful plating of SMT without medium in the SBE apparatus.

The following examples illustrate useful embodiments of the invention.
Example 1 :
Pure tin electrodeposition is obtained from the following solution under the following electroplating conditions.

  The above solution will deposit semi-bright tin at current densities up to 20 ASF.

Example 2 :
By adding 1.5 g / l of lead methanesulfonate to the solution of claim 1 and plating under the same conditions, a semi-bright tin-lead precipitate is obtained.

  This solution will also deposit semi-gloss 90% tin at current densities up to 20 ASF.

Comparative example :
Using the example formulation, tin was plated on 250 8 mm diameter plain washer surfaces in a 2.5 inch × 4 inch barrel and 140 ml of 2.5 mm diameter conductive balls were used as the medium. . The load was plated at 5 A, 6.5 V for 15 minutes. At the end of the plating cycle, none of the flat washers fused together.

  The same plating cycle was performed using an electrolyte with the following formulation.

  The load was plated at 5A, 9V for 15 minutes at the end of the plating cycle and only 12 were not bonded together. The remaining ones gathered in groups of up to 10 and were difficult to separate. This example clearly demonstrates the superiority of the solution of the present invention.

Example 3 :
The following examples show a reduction in tin whisker formation in precipitates produced by the electroplating solution of the present invention compared to prior art electroplating solutions.

  As mentioned above, whisker formation problems can occur when the deposits are subjected to heat treatment or conditions that arise when, for example, starting to use plated parts. Whisker can take from one week to five years to grow, in which case it can cause short circuits or other problems. An accelerated test was developed to determine if whisker formation occurs in the precipitates described above. For thermal cycle testing, the plated parts are placed in a controlled temperature chamber at -55 ° C for 15 minutes, then transferred to another temperature chamber within 20 seconds, where they are exposed to a temperature of 125 ° C for an additional 15 minutes. The cycle is repeated 500 times to see if whiskers occur on the precipitate surface.

  The substrate is plated with tin using the solution of Example 1 and then subjected to 500 cycles of the thermal cycling test referred to above. Another substrate was plated with tin from a conventional sodium gluconate plating solution, and the plated substrate was also subjected to 500 cycles in the same thermal cycling test.

  The results are shown in FIGS. 1 and 2, the surface of the plated part according to the invention shows a very small and very short whisker that is relatively harmless. In comparison, plated parts according to the prior art show much longer and much more whisker production, and therefore plated articles that are likely to cause possible mechanical interference if shorted or longer whiskers are removed. Produce. Thus, the plated deposits of the present invention are much more desirable, especially when tin deposits are required for small components such as electronic components.

It is a microscope picture of the board | substrate plated with tin with the plating solution of a prior art. 2 is a photomicrograph of the same substrate plated with tin with a plating solution according to the present invention. 2 is an enlarged micrograph of a portion of the surface of a substrate plated with tin with a prior art plating solution. It is an enlarged micrograph of a part of surface of the board | substrate plated with tin with the plating solution of this invention.

Claims (12)

A solution for use in connection with the deposition of one or more metals on an electroplatable substrate surface comprising:
water and;
A sufficient amount of metal ions to form metal deposits on the plateable substrate;
An organic compound having a 5 to 6 membered ring containing at least two hydroxyl groups and at least one oxygen atom and having 4 to 18 carbon atoms, forming a complex with the metal, A complexing agent present in an amount sufficient to solubilize and inhibit oxidation of the metal;
If necessary, with a suitable pH adjusting agent to maintain the pH of the solution within the range of 2-10;
Containing solution. The complexing agent has the structure:

Wherein each R is the same or different and is hydrogen or a lower alkyl group having 1 to 3 carbon atoms, T is R, OR, or O═P (OR) ₂ —, and Z is O═ Or RO—, n is 2-4, Z can be the same or different each time it appears in the compound, and m is 1-3. ]
The solution of claim 1, wherein the complexing agent is a soluble salt of such structure.   The complexing agent is derived from ascorbic acid, isoascorbic acid, dehydroascorbic acid, glucoascorbic acid, galacturonic acid, glucaronic acid, or salts thereof, or ketogluconate or heptagluconate, about 25-200 g / The solution of claim 2 present in an amount of l.   The metal is tin and is added to the solution as stannous alkyl sulfonate, stannous sulfate, stannous chloride, stannous ascorbate, or stannous oxide, about 5-100 g The solution of claim 1 present in an amount of / l.   The solution of claim 4 further comprising a divalent lead salt in an amount sufficient to precipitate a tin-lead alloy from the solution.   One or more of the conductive salts in an amount sufficient to increase the conductivity of the solution, a surfactant in an amount sufficient to improve precipitate quality and grain structure, or anodic dissolution The solution according to claim 1, further comprising an agent for promoting aging.   The conductive salt is an alkali or alkali metal sulfate, sulfonate, or acetate compound, and the surfactant is an alkylene oxide condensation compound, present in an amount of about 0.01 to 20 g / l, or the anode The solution according to claim 6, wherein the agent for promoting dissolution is potassium methanesulfonate, ammonium chloride or a metal sulfide salt.   The substrate is a composite article having electroplatable and non-electroplatable portions, the pH adjusting agent is an acid or base, and the pH is adjusted to a range of about 3.5 to 5.5; The solution of claim 1 that allows electroplating of the electroplatable portion of the article without adversely affecting the non-electroplatable portion.   A method of electroplating a metal deposit on a surface of a substrate, wherein the substrate is brought into contact with the solution according to claim 1, and a current is passed through the solution to form a metal electrodeposit on the surface. , Including methods.   A method of electroplating metal deposits on the surface of a composite article comprising electroplatable and non-electroplatable parts, the method comprising contacting a plurality of such articles with the solution of claim 1 and a current Passing the solution to form a metal electrodeposit on the electroplatable portion surface of the article without adversely affecting the non-electroplatable portion of the article.   A method for reducing whisker formation of metal precipitates on a substrate surface, wherein the substrate is brought into contact with the solution according to claim 1, and the solution is passed through an electric current to form a metal electrodeposit on the substrate surface. Forming and simultaneously reducing or eliminating whisker formation of the precipitate.   The substrate is a composite article comprising electroplatable and non-electroplatable parts, and a plurality of such articles are contacted with the solution to determine whether there are whiskers on the electroplatable part surface of the article 12. The method of claim 11, further comprising forming a reduced precipitate of whiskers.

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