JPH10270836A - Solder plating method for spherule - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solder plating method for spherules by which the amount of hydrogen gas stored in a solder plated film can be reduced by suppressing the occurrence of hydrogen itself during plating through a simple process. SOLUTION: When electroplating is performed by maintaining the total ion concentration at a high value of 20-50 g/l and the current density at a low value of 0.03-0.3 A/dm<2> , the occurrence of hydrogen can be suppressed and a solder film which is reduced in hydrogen content to <=0.05 ppm, particularly, <=0.03 ppm can be formed. When the spherules are coated with such a solder plated film, the occurrence of such a problem that the spherules come off and are scattered from a substrate or voids are formed in the film can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method for manufacturing
In connection with the improvement of the solder plating method of providing a solder plating film on the outer peripheral surface of a microsphere of about 1.0 mm, particularly a metal sphere, electroplating is performed at an extremely low current density using a plating solution having a high ion concentration. The present invention relates to soldering of microspheres having a predetermined thickness of a solder plating film having a small hydrogen content on the surface.

[0002]

2. Description of the Related Art Conventionally, BGA (Ball Grid A)
The microsphere used as a pump core material of a (rray) type semiconductor package has a diameter of 0.1 mm to 1.0 mm.
In addition to solder having a predetermined composition, recently, Kovar (Ni) is used in consideration of electrical characteristics and mechanical characteristics.
-Co-Fe alloy), a chip carrier coated with a brazing material using metal spheres such as Cu and 42Ni-Fe alloy as a core material has been proposed (Japanese Patent Application Laid-Open No. 62-112355).

As a method for producing the above-mentioned microspheres, a so-called liquid dropping method in which a molten metal is dropped into a liquid at a predetermined temperature, and the molten metal is formed into a sphere by the surface tension of the molten metal itself and solidified as it is (Japanese Patent Laid-Open No. 7-252510). , A so-called mechanical plastic working method such as forming with a die (Japanese Patent Laid-Open No. 4-354)
No. 808), a vibration heating method in which a metal particle or a metal piece is placed on a flat plate in a non-oxidizing atmosphere and heated and melted while applying vibration to form a sphere by its surface tension and solidify as it is (Japanese Patent Publication No. 2-50961). No.) has been proposed.

[0004] The brazing material for the outer peripheral surface of the microsphere manufactured as described above is appropriately selected depending on the required dimensional accuracy, the bonding strength between the semiconductor package and the printed board, and the like. For example, a solder (Pb-Sn-based) having a thickness of 5 to 50 μm and having various compositions is coated, and a base layer of Ni or the like may be formed as necessary.

[0005] Method conventional solder plating, the case of using a barrel type, ion concentration 5~13g / l, performed at a current density 0.5~3.0A / dm ^2. (For example, it is described in Plating Kyomoto Electroplating Research Society, edited by Nikkan Kogyo Shimbun (1986, ninth edition, reprinted from P132 to P137).)

[0006]

The microspheres provided with the solder plating film on the outer peripheral surface in this way cause swelling of the solder plating film when being heated and welded to a package board. There has been a problem that the ball is peeled and scattered from the substrate, or a problem that voids (voids) are formed in the solder plating film after heating and mounting.

Conventionally, therefore, it has been necessary to heat the package board in a vacuum or in an inert gas to perform a degassing process before mounting the package board by heating. Further, when this process is performed, there is a problem that the solder is partially melted and the coating thickness becomes uneven.

Further, the present inventors have studied various conventional problems, and have a correlation with the amount of hydrogen gas occluded in the solder plating film of the microspheres. It is necessary to reduce the amount of hydrogen gas to be absorbed as much as possible, and as a plating method that can reduce the amount of hydrogen gas absorbed in the solder plating film, an inert gas is introduced into the plating bath and plating is performed while bubbling. (Japanese Patent Application No. 8-188834) or a method of maintaining the entire plating bath at reduced pressure (Japanese Patent Application No. 8-215429).
No.).

However, the above-mentioned method has a problem that it is necessary to add a new processing step or to install various incidental reaction equipment at the time of the plating reaction, resulting in poor workability.

In view of the above problems, an object of the present invention is to provide a method for plating microspheres, which has a simple process and can reduce the amount of hydrogen gas absorbed in a solder plating film.

[0011]

Means for Solving the Problems The present inventors have analyzed the plating reaction in detail, and as a result of earnestly studying a method of suppressing the generation of hydrogen itself during the plating process instead of removing the generated hydrogen gas. By increasing the total ion concentration to a high concentration and performing electroplating at a low current density,
The generation of hydrogen can be suppressed, and the amount of hydrogen is 0.05 ppm or less,
In particular, it was found that a solder coating reduced to 0.03 ppm or less can be formed. When a solder plating coating is provided on microspheres, particularly metal spheres, by this plating method, the microspheres are separated and scattered from the substrate due to the swelling of the coating described above. It has been confirmed that the problem of the occurrence of voids and the problem of voids in the coating can be solved, and the present invention has been completed.

That is, the present invention provides a method for forming a solder coating on microspheres by electroplating, wherein a plating solution having a total ion concentration of tin and lead of 20 to 50 g / l is used, and By performing electroplating in a current density range of 3 A / dm ^2, the amount of hydrogen in
This is a solder plating method for microspheres, which is reduced to 5 ppm or less.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The plating method according to the present invention is intended to reduce the total ion concentration of tin and lead in a plating bath to 5 to 13 of a normal condition.
g / l, and by using a plating solution having a high ion concentration of 20 to 50 g / l, utilizing the fact that the tin-lead deposition potential shifts to a noble side, and 0.03 to 0.1 g / l.
By setting a low current density of 3 A / dm ² , the deposition potential of solder (tin-lead alloy) can be kept more noble than the generation potential of hydrogen, and the generation amount of hydrogen can be significantly suppressed. It is.

In the present invention, if the total ion concentration of tin and lead in the plating bath is less than 20 g / l, it is difficult to obtain a noble potential higher than the hydrogen generation potential.
If the amount exceeds g / l, it becomes difficult to control the composition of the solder coating (ratio of tin to lead), so the ion concentration of the plating bath was limited to 20 to 50 g / l. The preferred concentration range is 25
３５35 g / l.

The tin and lead ion concentrations in the total ion concentration of tin and lead in the plating bath vary depending on the desired solder plating composition and plating conditions. In order to obtain a total ion concentration of 30 g / l, 0.1 g using an alkanolsulfonic acid bath.
When plating at 1 A / dm ² , tin (Sn ²⁺ ) ion concentration is 24-27 g / l and lead (Pb ²⁺ ) ion concentration is 3-6 g.
/ L is preferably adjusted.

The cathode current density is 0.03
If it is less than A / dm ² , the productivity will be remarkably deteriorated, and the film surface will be rough and a good plated film cannot be obtained. Also 0.
If it exceeds 3 A / dm ² , the amount of hydrogen generated during the plating reaction increases, the hydrogen content in the plating film increases, and the desired product cannot be obtained. Therefore, the cathode current density is reduced from 0.03 to
It was limited to 0.3 A / dm ² . A more preferable cathode current density range is 0.06 to 0.15 A / dm ² .

As the solder plating solution used in the plating of the present invention, a plating solution containing tin alkanol sulfonate, lead alkanol sulfonate, tin phenol sulfonate, lead phenol sulfonate, or the like can be used.
As an electroplating method, various types of barrel systems can be used.

In the present invention, the microspheres are Cu,
In addition to metal spheres such as solder, spheres formed by coating a plastic sphere with a metal can be similarly plated.

[0019]

【Example】

Example 1 A Cu wire having a diameter of 0.6 mm was cut to a fixed size by a press machine to obtain a cylindrical piece (L / D = 1.07) having a diameter D = 0.6 mm and a length L = 0.64 mm. Cu pieces were prepared, degreased with a higher alcohol, placed in a hole formed in a carbon-made flat piece placing jig, placed in a hole, and then placed in an electric furnace at 1150 ° C. in a hydrogen atmosphere at 1150 ° C.
After heating and melting for 0 minute, it was cooled at a cooling rate of 25 ° C./min and solidified to produce a Cu ball having a diameter of 0.7 mm.

As a solder plating bath, tin (Sn ²⁺ ) 2
Electroplating was started at a bath temperature of 24 ° C. using a plating solution of pH <1 containing an alkanolsulfonic acid containing 5.2 g / l and 4.8 g / l of lead (Pb ²⁺ ) and a semi-brightening agent. Electroplating uses a horizontal barrel and a cathode current density of 0.06
Electroplating was performed for 22 hours at A / dm ² , Sn / Pb = 6/4 as a cathode plate, and the outer peripheral surface of the Cu ball was coated with a eutectic solder plating layer having a film thickness of 37 μm.

The swelling rate and the rate of peeling and scattering from the substrate were measured when 1000 pieces of the Cu balls having the solder plating layer according to the present invention were welded at 200 ° C. and 210 ° C. for 10 seconds each for 1000 seconds. . Table 1 shows the results. Further, the amount of released hydrogen gas was measured for each peak at the measurement temperature while increasing the temperature from room temperature to 600 ° C. by the TCD detector method. Table 2 shows the results.

Comparative Example 1 Using Cu balls produced in the same manner as in Example 1, Sn ²⁺
A eutectic solder plating layer having a film thickness of 37 μm was coated on the outer peripheral surface of a Cu ball under the same conditions as in the example using a plating solution having the same composition as in the example except for 8.3 g / l and Pb ²⁺ 1.5 g / l. . Thereafter, in the same manner as in Example 1, the occurrence of blistering, the rate of separation and scattering from the substrate, and the amount of released hydrogen gas were measured. The results are shown in Tables 1 and 2.

[0023]

[Table 1]

[0024]

[Table 2]

[0025]

According to the present invention, when a solder film is formed by electroplating, the total ion concentration of tin and lead is 20 to 5%.
0 g / l plating solution and 0.03 to 0.3 A /
By performing electroplating in an extremely low current density range of dm ^2, the amount of hydrogen absorbed in the solder plating film can be reduced to 0.05 ppm or less. As is clear from the examples, when the microspheres provided with the solder plating film are heated and welded to the package board, the swelling of the coating is drastically reduced, and the problem that the microspheres peel off and scatter from the substrate is solved.

Claims (1)

[Claims] 1. A method of forming a solder coating on microspheres by electroplating, wherein the total ion concentration of tin and lead is 20 to
Using a plating solution of 50 g / l and 0.03 to 0.3 A
/ Dm ^{2 is} a method for soldering microspheres in which the amount of hydrogen in a solder coating is reduced to 0.05 ppm or less by performing electroplating in a current density range of / dm ² .