JPS62247094A - Silver plating solution for high-speed electroplating - Google Patents

Abstract

PURPOSE:To increase plating speed and to improve uniformity in plating and covering power by adding alcohol and an alkali metallic cyanide to a product prepd. by reacting selenium dioxide with acetylacetone and by adding a specified amount of the resulting additive to a silver plating soln. CONSTITUTION:An additive contg. selenium is added to a silver plating soln. contg. silver cyanide, an alkali metallic cyanide and an alkali metallic carbonate or hydroxide so that the concn. of selenium in the plating soln. is regulated to 0.1-5.0ppm. The additive is prepd. by adding 1-3C alcohol and an alkali metallic cyanide to a product prepd. by reacting selenium dioxide with acetylacetone. The resulting plating soln. enables plating at high current density and can give a smooth and lustrous finished surface.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a high-speed electrolytic silver plating solution that can provide a smooth and glossy finished surface even when electrolytic silver plating is performed at high current density and high speed.

[Prior Art] Conventionally, silver plating for semiconductor electronic components such as transistor headers, lead frames, and substrates for the purpose of wire bonding, brazing, and soldering has been carried out using cyan-type silver plating based on silver cyanide and potassium cyanide. Plating is performed using a silver plating solution using the rack method, barrel method, or partial plating method.

These silver plating solutions contain 25 to 50 g/fJ of silver cyanide.
It contains potassium cyanide 30~Boa/j and sodium carbonate or potassium carbonate 10~5h/j, and the current density is 0°1~1 for rack method and barrel method.
G, 5A/ds2, 2-3A/d for partial plating method
It is operated at about 1. In addition, in order to shorten the time required for plating in the rack method and barrel method, a surfactant, ethyl xanthate, and potassium selenite are added to these silver plating solutions by 0.5 to 2. OA/dm2
In some cases, smooth plating is performed using a current density of about 100 mL.

[Problems to be Solved by the Invention] Conventional silver plating solutions, for example, silver cyanide, are
When performing matte silver plating with a plating thickness of 5 at a current density of 0.5 A/dm2 using a silver plating solution containing approximately J/1, the theoretical time required for plating is approximately 20 minutes. . Therefore, in order to shorten this time, the silver concentration was set to 80~
Attempts have been made to perform plating at temperatures as high as 120o/41, but in this case, there are drawbacks such as increased loss of liquid and poor throwing power. In addition, silver plating solutions containing surfactants and ethylxanthate increase the plating speed, but the surfactants make the solution foamy, and the concentration and current density of the plating solution must be precisely controlled during the plating process. It has the disadvantage that if it is not managed, it tends to cause unevenness in the finish.

[Means for Solving the Problems] The present invention has been made to solve the above-mentioned problems. For example, when silver plating with a thickness of 5 mm is applied using the rack method, the silver concentration is 30111. /Jl level is 4.0
~5. Plating is possible at a high current density of approximately OA/dm2, the time required for plating is as short as approximately 2.5 minutes, and a plating solution with low foaming property is used in the plating process, and it is possible to reduce unevenness in plating and reduce throwing power. The purpose is to obtain a plating solution with improved plating solution, in which selenium dioxide and acetylacetone are reacted with a silver plating solution consisting of silver cyanide, alkali metal cyanide, alkali metal carbonate, or alkali metal hydroxide. Additives made by adding an alcohol having 1 to 3 carbon atoms and an alkali metal cyanide to a plating solution with a selenium concentration of 0.1 to 5, Opp
1m.

[Function and Examples] Various components other than additives that can be used in the high-speed electrolytic silver plating solution of the present invention may be any of those conventionally used in electrolytic silver plating solutions. Any conventional alkali metal cyanide such as silver cyanide, potassium cyanide or sodium cyanide, alkali metal carbonate such as potassium carbonate or sodium carbonate, or alkali metal hydroxide such as potassium hydroxide or sodium hydroxide may be used.

The concentration of the silver cyanide in the plating solution is 20 as AQ.
The range is preferably 500/41. The concentration is 2
If it is less than 0o/j, it is difficult to obtain a high current density;
If you use a high current density, it is easy to get burnt due to plating,
Moreover, if it exceeds 50 o/j, there is no particular technical problem, but silver loss tends to increase.

Moreover, the concentration of the alkali metal cyanide in the plating solution is 50 to 10G! ; l/J is preferable.

If the concentration is 50a/fl without swirling, the throwing power tends to be poor.

Further, the concentration of the alkali metal carbonate in the plating solution is preferably in the range of 10 to 5 h/j.

If the concentration is less than 1 h/j, the submerged conductivity tends to be a little low, and if it exceeds 50 a/1, the liquid temperature will drop to 15
Carbonate crystals tend to form in the liquid below ℃.

When an alkali metal hydroxide is used instead of the alkali metal carbonate, the concentration is also preferably in the range of 10 to 50 Q/fl.

Additives produced by the following method are also added to the high speed electrolytic silver plating solution of the present invention. That is, selenium dioxide 1
Add 1 to 1.2 moles of acetylacetone to the mole to make 50 to
The reaction is carried out at 65°C, preferably about 60°C, with stirring for 10 to 15 minutes in a flask with a lid, and then an alcohol having 1 to 3 carbon atoms such as methyl alcohol, ethyl alcohol, or isopropyl alcohol is added, and if necessary, The additive is diluted with water, further dissolved with alkali metal cyanide such as potassium cyanide and sodium cyanide, heated at about 10°C for about 1 hour, added activated carbon if necessary, and filtered. can be obtained. There are no particular limitations on the concentration of additives that can be obtained.

The additive has a selenium concentration of 0.1 to s, o in the plating solution.
It is added so that it becomes pp-. Selenium concentration is 0, lp
When it is less than pm, it is difficult to obtain smoothness, and plating with high current density tends to cause plating and discoloration, and 5. O
If it exceeds pp■, the smoothness will not change, but the hardness of some of the precipitated silver may increase.

When the additive is added so that the selenium concentration in the plating solution is 0.1 to 5.0 ppl, the additive usually becomes a colloid and adheres to the plating surface. This colloidal material reduces the crystal size of electrolytic deposited silver, effectively forming a smooth, semi-glossy surface, and also reduces the occurrence of discoloration due to the generation of hydrogen gas even during electrolysis with high current density, resulting in a smooth and smooth surface. is retained.

It is thought that these effects are due to the fact that the additive, although added in a small amount, efficiently adheres to the plated surface.

When silver plating is performed using the high-speed electrolytic silver plating solution of the present invention, the preferred current density range is 0 in the case of a rack method.
．． 1~4.5A/dm2, especially 2~3^/d
It is s2. If the current density exceeds 4.5 A/ds2, plating and discoloration are likely to occur even if additives are added.

Further, the preferred temperature of the plating solution is 20 to 50°C.

If the liquid temperature is less than 20°C, it is difficult to maintain a high current density, and plating discoloration is likely to occur.If it exceeds 50°C, evaporation of the liquid is large and the liquid concentration is likely to change.

Next, the high-speed electrolytic silver plating solution of the present invention will be explained in more detail by giving experimental examples, working examples, and comparative examples, but the present invention is not limited only to these experimental examples and working examples.

Experimental Example 1 (Synthesis of additives) 25 d of acetylacetone for analysis was added to 2 g of selenium dioxide, and the mixture was reacted at 60°C for 10 minutes with stirring in a flask with a lid. Next, 15 M1 of ethyl alcohol was added, and the mixture was diluted with water. It was set to 2fJ. After 2 g of potassium cyanide was dissolved in this, it was heated at 70°C for 1 hour, and after adding activated carbon 3 to 5Q, it was filtered to obtain 1900 M1 of additive.

Examples 1-2 and Comparative Examples 1-2 Silver cyanide, potassium cyanide 800/j and potassium carbonate 10 weighed to give 30 o/j as 80
A plating solution was prepared using A/1, and further Experimental Example 1
The resulting additives were added as shown in Table 1 to prepare plating solution 21 of the present invention.

Next, as a test piece, length 5cm, width 5cm,
Thickness 0.5 - After degreasing the copper plate and applying silver strike plating, it was fixed on a rack in a 2J beaker, and the current density was 4A/dm2, and the liquid! ! Plating was carried out at 35°C for 3 minutes.

Note that the 7 nodes and the cathode were covered with silver plates of the same size.

The generation of air bubbles at the cathode during plating and the appearance of the plated test piece were observed. Furthermore, Example 1
A detailed study of the quality of the plating deposits in 2 and 2 revealed that the plating thickness was 7.0 to 1.6-1, the purity of silver was 99.99%,
Wire bonding using gold wire with a diameter of 25ρ is good.
The product had good throwing power (during stirring) and was of excellent quality with no blistering or discoloration even when heated in air at 500° C. for 1 minute.

Examples 3 to 4 and Comparative Example 3 Silver cyanide, potassium cyanide 50a/fl, and potassium carbonate 1 weighed to give 2Qa/j as Ag
A plating solution was prepared using 0Q/fJ, and further Experimental Example 1
The resulting additives were added as shown in Table 2 to prepare plating solution 2j of the present invention.

Next, as a test piece, length 15+e+e, diameter 1■
After degreasing about 1,000 silver lead wires (2), open type plating was applied for 10 minutes at a current density of 2 A/dm2 and a liquid temperature of 30°C.

The generation of air bubbles at the cathode during plating and the appearance of the plated test piece were observed. The results are also listed in Table 2.

Furthermore, when we examined the quality of the silver-plated test pieces in Example 3.4 and Comparative Example 3 in detail, we found that Example 3.
Test pieces 4 and 4 corresponded extremely well to wire bonding, in which gold wire with a diameter of 25 cm was bonded by heat, and there was no peeling at all, and there was no discoloration even when heated at roughly 450°C for 1 minute. The test piece of Example 3 did not undergo the wire bonding at all, and changed color when heated at 450° C. for 1 minute.

Examples 5 to 6 and Comparative Example 4 A plating solution was prepared using silver cyanide, potassium cyanide 60111/j, and potassium carbonate 10Q/1, which were weighed so that the AQ was 30 o/j, and further Experimental Example 1
The resulting additives were added as shown in Table 3 to prepare plating solution 21 of the present invention.

Next, a copper plate was degreased and silver strike plated as a test piece, and then the jet was sprayed using a jet nozzle at a speed of 10-7 seconds and an electron density of 40A/d12.
, partial plating of buttons -x5-■ was performed at a liquid temperature of 35°C for 15 seconds.

The appearance of the plated test piece was observed.

The results are also listed in Table 3.

Table 3 Further detailed examination of the quality of the silver-plated test pieces in Example 5.6 and Comparative Example 4 revealed that Example 5.
Test pieces No. 6 and 6 gave good results when thermocompression bonded with gold wire (25ρ) and silicon chips were welded with solder, and did not change color even when heated at 450°C for 1 minute. The test piece of Comparative Example 4 had 20X peeling due to wire bonding and die bonding.
More than one occurrence occurred. Further, the color changed when heated at 450° C. for 1 minute.

[Effects of the Invention] As described above, the high-speed electrolytic silver plating solution of the present invention contains an additive made by reacting selenium dioxide and acetylacetone with an alcohol having 1 to 3 carbon atoms and an alkali metal cyanide. By adding selenium to a concentration of 0.1 to s, oppm, the plating speed can be increased 4 to 8 times compared to conventional methods, and the surface of the plating applied using this plating solution is smooth. It is semi-glossy and corresponds well to wire bonding and soldering, so it greatly contributes to improving the productivity and yield of semiconductor electronic components.

Claims (1)

[Claims] (1) Silver plating solution consisting of silver cyanide, alkali metal cyanide, alkali metal carbonate or alkali metal hydroxide is reacted with selenium dioxide and acetylacetone, alcohol with 1 to 3 carbon atoms and cyanide. 1. A high-speed electrolytic silver plating solution, characterized in that an additive containing an alkali metal is added so that the selenium concentration in the plating solution is 0.1 to 5.0 ppm.