JP2005336522A - Gold plating after heat treatment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the solder wettability because the soldering work is required to bond electrodes by solving a problem that a gold-plated wafer is heat-treated and soldering is performed after the heat treatment in order to improve adhesiveness of aluminum and aluminum-silicon alloy to nickel plating, and the solder wettability is considerably degraded after the heat treatment. <P>SOLUTION: To improve the adhesiveness of aluminum and aluminum-silicon alloy to nickel plating, the solder wettability is improved by performing displacement gold plating after the heat treatment of a gold-plated wafer. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to the field of surface treatment.

  Solder bonding is used to connect transistors and diodes.

  However, since the material of the connection part in the transistor or diode is aluminum or an aluminum-silicon alloy, surface oxidation is likely to occur and solder wettability is deteriorated.

  Usually, in transistors and diodes, solder wettability is improved by forming an electroless nickel / gold plating film in order to suppress oxidation of the electrode surface of aluminum or an aluminum-silicon alloy.

  The adhesion between aluminum or aluminum-silicon alloy and nickel plating in transistors and diodes is an important factor. If the electrode surface is nickel plated, the adhesion is insufficient. Therefore, heat treatment is applied to the wafer after gold plating in order to improve adhesion.

  However, when solder bonding is performed after the heat treatment, there arises a problem that the solder wettability of the nickel / gold plated electrode surface is remarkably deteriorated.

  Since the soldering work is necessary for joining the electrodes, it is necessary to improve solder wettability.

  In the present invention, in order to improve the adhesion between aluminum or an aluminum-silicon alloy and nickel plating, solder wettability is improved by performing substitution gold plating after heat treatment is applied to a gold-plated wafer.

  By performing displacement gold plating again after the heat treatment, the solder wettability is improved.

  The process of performing nickel plating and gold plating with aluminum or an aluminum-silicon alloy is as follows.

Surface oxide removal pretreatment-water washing-nickel plating-water washing-gold plating-heat treatment-argon plasma cleaning-degreasing-water washing-displacement gold plating are performed in this order.

  The metal composition of the pad on the wafer is pure aluminum or aluminum 98% -silicon 2% alloy, and the pad is subjected to nickel plating and gold plating.

The process is performed in the order of surface oxide removal pretreatment-nickel plating-gold plating-heat treatment-argon plasma cleaning-degreasing-displacement gold plating.

The surface oxide is removed with 1% HF at room temperature for 30 to 90 seconds.

Nickel plating was performed at 80 ° C. to 90 ° C. for 4 minutes to 300 minutes using a nickel plating solution having the composition shown in Table 1 to change the plating thickness from 1 μm to 30 μm.

  When the nickel plating thickness is 1 μm or less, the rust resistance is insufficient, and when it exceeds 30 μm, the stress is generated by the nickel plating and the wafer is distorted, so the nickel thickness is set to 30 μm or less.

After the nickel plating, the nickel plating solution residue was removed by a water washing step, and then the gold plating solution shown in Table 2 was applied at a thickness of 0.05 μm to 0.07 μm at 80 ° C. to 90 ° C. for 10 minutes to 25 minutes.

  When the gold plating thickness is 0.05 μm or less, the solder wettability is poor, and when the thickness is 0.07 μm or more, it does not adhere with displacement gold plating.

*ＦＥ−ＳＥＭによる断面観察
**金がニッケル内部に拡散しすぎる
評価：○：良好、×：不良 Thereafter, heat treatment is performed. Table 3 shows the relationship between heat treatment conditions and adhesion.

* Section observation with FE-SEM
** Gold diffuses too much inside nickel Evaluation: ○: Good, ×: Bad

After the heat treatment, argon plasma cleaning was performed at 200 W for 3 minutes with a plasma cleaner, and then treated with a degreasing solution shown in Table 4.

Next, the heat treatment temperature of 250 ° C for 15 minutes with good nickel plating adhesion was used for 15 minutes, using the displacement gold plating solution shown in Table 2 at 80 ° C to 90 ° C, 2 minutes to 6 minutes. Table 5 shows the relationship between the gold plating thickness and the solder wettability test after plating. In the solder wettability test, the Sn-Ag solder ball was heated at 270 ° C. for 1 minute, and then the solder wettability was observed.
As shown in Table 5, when the gold plating thickness is less than 0.01 μm, the solder wettability is poor, and when it is 0.04 μm or more, the solder wettability is good, but the color of the gold plating becomes red and the commercial value is lost.

In a transistor or a diode, a highly reliable product can be secured by forming a film having good solder wettability and ensuring adhesion between the electrode surface and nickel plating.

Claims (3)

The surface of the semiconductor electrode made of aluminum or aluminum-silicon alloy is subjected to 1 to 30 μm nickel plating, 0.05 to 0.07 μm gold plating is performed on the nickel plating, heat treatment is performed, and then 0.01 to the gold plating is performed. Product with gold plating of 0.03μm The surface of the semiconductor electrode made of aluminum or aluminum-silicon alloy is subjected to 1 to 30 μm nickel plating, 0.05 to 0.07 μm gold plating is performed on the nickel plating, heat treatment is performed, and then 0.01 to the gold plating is performed. ~ 0.03μm gold plated diode The surface of the semiconductor electrode made of aluminum or aluminum-silicon alloy is subjected to 1 to 30 μm nickel plating, 0.05 to 0.07 μm gold plating is performed on the nickel plating, heat treatment is performed, and then 0.01 to the gold plating is performed. Transistor with gold plating of 0.03μm