JPH0422991B2 - - Google Patents

Description

Claim 1: In water, a soluble divalent tin compound, a soluble divalent lead compound, and as a complexing agent gluconate, pyrophosphate, malate, tartrate, malonate, and phosphonate. acids, malic acid, malonic acid,
An electrolytic solution for tin-lead alloy plating is prepared by adding at least one compound selected from hydroxyacetic acid or an alkali salt thereof, or further at least one compound selected from crystal atomizers and brighteners. A seed compound is added to prepare an electrolytic solution for tin-lead alloy plating, and the pH value of the electrolytic solution is adjusted to a range of substantially 1.5 to 5.5, and the ammonium compound content is substantially 30 g/ A plating bath for a tin-lead alloy, characterized in that the plating bath for a tin-lead alloy is prepared so as not to exceed 5% by weight or 5% by weight.

2. The plating bath for tin-lead alloy according to claim 1, wherein the phosphonic acid is hydroxyethylidene diphosphonic acid or nitrilotrimethylphosphonic acid.

3. The plating bath for tin-lead alloy according to claim 1, wherein the crystal grain refiner or brightener is an alkylene oxide or an imidazoline compound.

4. The plating bath for tin-lead alloy according to any one of claims 1, 2, and 3, characterized in that the PH value is in the range of 3 to 4.

5. The above-mentioned conductive metallic part of a composite substrate is composed of a conductive metallic part made of a metal or alloy that can be electroplated, and a non-conductive inorganic part that cannot be electroplated. In the method of electroplating a tin-lead alloy, a soluble divalent tin compound and a divalent lead compound are added and dissolved in water as an electrolytic solution along with a complexing agent to form an electrolytic solution for plating the tin-lead alloy. The electrolytic solution for tin-lead alloy plating can be prepared by preparing a liquid or adding at least one of an electrodeposited crystal atomizing agent and a brightening agent as an additive to the electrolytic solution for tin-lead alloy plating. and further adjust the PH value of the above electrolyte to substantially
The above electroplating is carried out using a tin-lead alloy plating bath adjusted to a range of 1.5 to 5.5 and in such a manner that the ammonium compound concentration does not substantially exceed 30 g/% or 5% by weight. To form the desired tin-lead alloy electroplating only on the conductive metallic part without adhering electrodeposit to the non-conductive inorganic part or corroding the inorganic part, which is impossible. An electroplating method for composite substrates characterized by:

6. A composite board that has an electronic component with a metallic part that can be electroplated and a glass or ceramic part that cannot be electroplated, where cracks or solubilization occur in the glass or ceramic part of the board. 6. The electroplating method according to claim 5, wherein desired electroplating is formed only on the metallic portion of the substrate without depositing plating metal on the glass or ceramic portion of the substrate.

7. Electroplating according to claim 5 or 6, in which a soluble salt solution of at least one of gluconate, pyrophosphate, malate, tartrate, and malonate is used as the complexing agent. Method.

8. The electroplating method according to claim 5 or 6, wherein at least one of carboxylic acid, phosphonic acid, or an alkali salt thereof is used as the complexing agent.

9. Claims 5 or 6 in which at least one of malic acid, malonic acid, hydroxyethylidene diphosphonic acid, nitrilotrimethylphosphonic acid, hydroxyacetic acid, or an alkali salt thereof is used as a complexing agent. Electroplating method described.

10. The electroplating method according to claim 9, wherein an alkylene oxide or an imidazoline compound is used as the crystal finer or brightener.

11. The electroplating method according to any one of claims 5 to 10, wherein the PH value of the plating solution is in the range of 3 to 4.

TECHNICAL FIELD The present invention relates to a plating bath and a plating method for electroplating a tin-lead alloy or solder onto a composite substrate having a metal part that can be electroplated and an inorganic part that cannot be electroplated.

BACKGROUND OF THE INVENTION The electronic component industry is constantly searching for new composite materials for use as electrical and electronic components. Such new composite materials are
It is developed based on the need for miniaturized components that can perform a variety of functions.

Many of these composite materials contain metallic portions that are readily electroplated by themselves using state-of-the-art electrolytic baths. If such an electroplatable part is combined with a non-conductive, non-electroplatable part of an inorganic material such as glass, ceramic, etc. to form a composite material, the inorganic part of the composite material. It has become extremely difficult to selectively electroplat only the electroplatable metallic portions of the composite material without degrading or electroplating the composite material.

For example, when conventional tin-lead boron fluoride electrolytic baths are used to perform such selective plating, the fluoroboric acid is seen to attack the inorganic portions of the composite material. This attack is usually solubilized (i.e. etching or dissolving the inorganic material).
Or it will appear in the form of Kratzking. If the inorganic portions of the composite material are etched to a significant extent, the tin-lead alloy will adhere to the inorganic portions and thus cause shorting of the metallic (electroplatable) portions.

It is also not suitable to use tin-lead electrolytes that do not contain boron fluoride, such as those disclosed in U.S. Pat. No. 4,459,185. Although plating baths such as these do not cause cracking of the inorganic parts, tin and lead are deposited on the inorganic parts of the composite material, resulting in short circuits in the metallic parts. A special type of electronic component that uses a composite structure is the dual inline package (DIP).

These components, which are well known in the industry, typically have a die or chip attached to the surface;
Created by coupling circuits to multiple pins. The die is then encapsulated by a small piece of ceramic that is deposited with lead oxide glass containing approximately 50% soft lead oxide, which melts at relatively low temperatures.

The soft glass binder used to encapsulate the circuit oozes around these pieces and solidifies during processing, becoming part of the package. As such, the structure consists of a metal pin, a ceramic encapsulation and a solidified capsule. To continue processing these packages, the metallic portion (usually an iron-nickel alloy) must be electroplated to facilitate soldering to the pins.

The method commonly practiced in the industry today is to plate DIPs with these composite structures with stannous sulfate and pure tin from solutions containing sulfuric acid, since soft oxidized glass parts This is because the plating solution does not accept deposits from such solutions, or because such plating solutions do not attack soft lead glass parts. However, pure tin electrodeposit is known to produce whiskers extending in various directions from the surface. These whiskers are made of tin metal in the form of extremely thin hairs, which bridge adjacent metallic parts and cause short circuits. For this reason, the industry prefers to avoid using pure tin deposits in such packages.

Tin with DIP of 5% or more lead
Some attempts have been made to plate with lead alloys, since these tin-lead alloys do not tend to form whiskers. The tin-lead electrolytic baths commonly used in the industry today cannot be used for this purpose, as discussed above. This is because the soft lead-glass bond has a tendency to electroplat, thus causing a short circuit in the pin circuit. As also mentioned above, yet another problem is that the soft lead glass bond dissolves in or is attacked by conventional plating solutions.

Summary of the Invention The present invention provides a composite substrate having an electroplatable metallic portion and a non-electroplatable inorganic portion.
This relates to a method of electroplating using a tin-lead alloy electrolyte that does not plate or attack the inorganic parts of the composite material, but does not plate the metal parts of the composite material. . The inorganic parts (ie ceramic or glass) are not entirely inert in the electrolyte, and some of these parts are very slightly dissolved. However, this degree is within the range allowed in the electronic industry.

The plating solution used to plate these substrates in accordance with the present invention contains a divalent soluble tin compound, a divalent soluble lead compound, and has a pH of about 1.5 to 5.5. . These plating solutions also contain at least a minimum of metallic tin and metallic lead.
Contains a complexing agent to keep the pH above the level. These plating solutions also do not contain appreciable amounts of free acid or free base components. These plating baths may also contain alkylene oxide compounds or imidazoline compounds.

The invention also relates to a method of making the electroplating solution of the invention, which electroplating solution comprises adding tin and lead compounds together with a complexing agent to water to remove all free acids and free bases from the electrolyte. The method consists of adjusting the pH between about 1.5 and 5.5 by adding a suitable base or acid compound.

Using such an electrolyte to electroplat substrates with electroplatable metallic parts and non-electroplatable, non-conductive inorganic parts does not tend to produce whiskers, and does not tend to produce whiskers. This results in a tin-lead electrodeposit being plated onto the metallic part without attacking the part. In this way, the problems of the prior art, such as shorting of pins and attack of glass or ceramic parts, are overcome by the plating bath of the present invention.

[Brief explanation of drawings]

The nature, advantages, and various other additional features of the invention will be better understood with reference to the embodiments of the invention, which are illustrated in detail in the accompanying drawings. In this embodiment, Fig. 1 is a perspective view showing the structure of one type of DIP made of ceramic, and Fig. 2 is a perspective view with a partial cross section showing the structure of a multilayer ceramic chip capacitor (capacitor). It is.

DETAILED DESCRIPTION OF THE EMBODIMENTS In the following description, "composite material" generally refers to a material having one or more electroplatable parts and one or more non-electroplatable parts. means. Electroplatable parts are generally metallic, ie, have metallic properties. These parts may be fabricated metal, or metal coatings, or electroplated deposits.

The parts that cannot be electroplated are usually made of inorganic materials. The term “inorganic materials” refers to ceramics,
It refers to glass or refractory materials primarily containing various metal oxides such as lead oxide, aluminum oxide, silicon oxide, zirconium oxide, or titanium oxide.

First, what is shown in FIG. 1 is an electrical component commonly known as a dual in-line package or DIP. The circuit (not shown) is constructed by ceramic pieces 1 and 2.
It is also enclosed in a capsule made of soft lead oxide glass. The circuit within the encapsulation is suitably connected to a pin 4 made of metal alloy. The bonding bar 5 is removed after electroplating.

The soft lead oxide glass used in these DIPs is well known. The melting point of these glasses is determined primarily by the percentage of lead oxide contained in the glass. An example of a soft lead oxide glass commonly used in the electronics industry to encapsulate DIPs is approximately 50% lead oxide, 25% silicon dioxide, 10% aluminum oxide (alumina Al ₂ O ₃ ), It contains 10% boron oxide (B ₂ O ₃ ) and 5% of various oxides such as zinc oxide, lithium oxide and manganese oxide.

Next, what is shown in FIG. 2 is an example of a composite electrical component known as a multilayer ceramic chip capacitor. In manufacturing these chips, a ceramic 11 containing an electrode 12 and a dielectric 13 is used.
It is formed into a cube with a monolithic structure. Both ends of these chips are metallized 14 for insertion into a circuit. This type of chip can be used as a capacitor, while it can also be used as a similar type of chip resistor or other electronic component.

The plating method of the present invention is suitable for generally all composite materials having an electroplatable (i.e. metallic) part and an inorganic (i.e. ceramic or glass) part, especially for conventional boron fluoride currently on the market. When attempting to plate metal parts of composite materials with a tin-lead plating solution, are the inorganic parts attacked by tin-lead deposits?
Alternatively, it can be used for composite materials that are plated at least to some extent by tin-lead deposits.

Selective application of tin-lead alloy plating on the electroplatable portions of these composite substrates is accomplished using the plating bath of the present invention. These plating baths generally have at least one soluble tin compound, one soluble lead compound, one complexing agent, and preferably a PH between about 1.5 and 5.5. Furthermore, these plating baths must not contain significant amounts of free acid or base components.

The compound of tin and lead can be added to the plating solution in its divalent state and in the form of any soluble salt. Some, but not all, examples include tin sulfate, tin pyrophosphate, tin alkanes or alkanol tin sulfonates, tin boron fluoride, tin gluconate, tin tartrate, lead acetate, lead alkane or tin alkanol sulfonates, etc. Contains lead gluconate, lead tartrate, lead pyrophosphate, etc.

A wide variety of complexing or chelating agents can be used to maintain the plating solution at the desired PH value. Some examples of these complexing or solubilizing agents include gluconate, pyrophosphate,
Included are solution-soluble salts such as malonate, malate or tartrate, organic acids such as malic acid or malonic acid, and alkali salts of these organic acids.

Particular desirable compounds include sodium gluconate, potassium pyrophosphate, potassium sodium tartrate (Rotziel's salts), hydroxyethyldenediphosphonic acid, nitrotrimethylphosphonic acid, and hydroxyacetic acid or one of its alkali salts. . Other compounds, such as glucose, can also be used as complexing agents, but the amounts required do not make them practical or economical. Certain compounds are effective in certain plating baths, while others, such as EDTA (ethylenediaminetetraacetic acid),
Lactic acid, glycine, etc. do not work very well to maintain the solubility of metals in the presence of sulfonate alkanes or sulfonate alkanols. The most advantageous complexing agent for a particular plating solution can be determined by routine experimentation.

The PH of the plating solution of the present invention can vary depending on the amount and type of additives used. The pH is sufficient to create the desired tin-lead deposit without adversely affecting glass or ceramic parts or creating bridging or shorting with adjacent metallic parts. Must. Desirably, the pH of the plating solution is at least about 1.5.
and it is particularly advantageous to operate between about 3 and 5. Higher PH's, up to about 5.5, can also be used, but lower PH values make the cathode more efficient.

When the pH of the plating solution is about 5.5 or higher, the inorganic parts are more likely to be activated by the plating solution. In this way, the pH of the Metsuki solution is kept below a value that does not have any negative effects (for example, solubilization) on this inorganic part.
At the same time, it must be maintained below a value that does not cause crosslinking. As a supplement, about 6 or more
At pH values, it becomes extremely difficult to retain metallic lead and metallic tin in the plating solution.

After adding the metals and complexing agent to the plating bath, the pH of the resulting electrolyte is adjusted to the desired range of about 3 to 4 by adding a base or basic compound. This PH adjustment is accomplished by largely eliminating the free acid in the plating bath by converting it to the corresponding salt of the free acid. Preferred bases for pH adjustment include alkali hydroxides such as sodium hydroxide or potassium hydroxide. Ammonia or ammonium salts can be used for pH adjustment, provided the amount used does not provide excess ammonia in the plating bath.

Thus, it is important to avoid using large amounts of ammonia in the plating bath to achieve the selective plating required for these composite substrates. With ammonia, there are free ammonia and various ammonia salt complexing agents to make the plating bath alkaline. Representative patents disclosing the use of excess amounts of these additives include U.S. Patent No. 4,163,700 and British Patent No.
There is issue 2007713. High ammonia and ammonium contents in these plating baths cause the problems mentioned above.

The base or basic component used for pH adjustment must be relatively low for the following reasons.

(a) A large amount of base will cause the pH to exceed 6, which will make the plating bath unstable and metals will precipitate, or (b) A large amount of base will have an adverse effect on the inorganic parts of the substrate as mentioned above. give.

The inventors have found that the maximum concentration of ammonia or ammonium compounds in a plating bath without causing the problems described above is about 30 g/or about 5% by weight based on the total composition weight of the plating bath. . If the plating bath contains more ammonia or ammonium compounds than this concentration, the plating bath will become unstable and the inorganic parts of the substrate will be eroded and solubilized or cracked, making it impossible to achieve the objectives of the present invention. Can not.

Although dull deposits are acceptable, it is desirable to obtain shiny or glossy deposits by adding atomizing agents or brighteners to the plating solution. In this regard, the same types of atomizers or brighteners commonly used in conventional fluoroboric acid plating bath solder plating are suitable. Preferred additives include the well-known alkylene oxide compounds (ie, compounds containing condensates of methylene oxide or propylene oxide). Also suitable brighteners include:
There are surfactants that contain imidazolines. The amounts of these compounds used are similar to those used in conventional tin-lead plating solutions and will be well known to those skilled in the art.

EXAMPLES The scope of the present invention will be illustrated by the following examples, which are set forth solely for the purpose of illustrating embodiments of the present invention.
Nor should it be construed in any way to limit the scope of the invention.

The plating bath shown below was prepared for plating a composite substrate made of glass and metal.

Example 1 (Comparative Example) Plating bath disclosed in Example 4 of US Pat. No. 4,163,700. The solubilizer or complexing agent is ammonium citrate. This plating bath produces tin-lead deposits with or without the addition of brighteners (as matte deposits are acceptable);
Due to its high ammonia content it attacked the leaded glass parts of the substrate and the resulting deposit showed severe crosslinking.

Example 2 (Comparative Example) Plating bath disclosed in Example 1 of US Pat. No. 3,984,291. In this plating bath, tin is added as stannous pyrophosphate and lead is added as lead tartrate or lead pyrophosphate. Potassium pyrophosphate and Rossiul salt are present as solubilizers or complexing agents. The pH of this bath is 8.5
It is adjusted to. As in Example 1, the tin-lead alloy adhered to the metallic part of the substrate, but the leaded glass part was exposed to the relatively high temperature of the plating bath.
Severely affected by PH and high ammonia/ammonium concentrations.

Example 3 Metallic tin as boron tin fluoride 15g/,
3 g/metal lead as lead acetate, and 100 g/ sodium gluconate. The bath is adjusted to a pH of about 3 with sodium hydroxide or gluconic acid.

Example 4 15g of metal tin as stannous gluconate/
, metallic lead as lead acetate 3 g/, sodium gluconate 100 g/, and sodium malate
55g/, the pH of the plating bath is adjusted to about 3 with sodium hydroxide.

These DIP (Dual Inline Packages)
The plate is then plated to a thickness of 200 microinches at 10 to 15 ASF at room temperature with gentle agitation in the above-described plating bath by hanging plating on a trellis. The appearance of the deposits in Examples 3 and 4 was uniform and matte. The lead glass bond did not accept much plating and no crosslinking was observed between the pins. Furthermore, the glass portion of the substrate was hardly attacked by the plating baths of Examples 3 and 4 above.

Although it is clear that the invention disclosed in this example is well calculated to achieve the desired results, numerous modifications and embodiments may be devised by those skilled in the art. It seems possible. It is intended, however, that the appended claims cover all such modifications and embodiments as fall within the true spirit and scope of the invention.