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Browse Prior Art Database

Flip Chip Solder Ball Rework Process

IP.com Disclosure Number: IPCOM000050493D
Original Publication Date: 1982-Nov-01
Included in the Prior Art Database: 2005-Feb-10
Document File: 3 page(s) / 57K

Publishing Venue

IBM

Related People

Erickson, AJ: AUTHOR [+2]

Abstract

The flip-chip solder ball contact structure shown in Fig. 1 has been described, for example, in U.S. Patent 3,401,055. As shown in Fig. 1, the aluminum conductor line 2 on the surface of the semiconductor substrate 1 is exposed through a via hole in the polyimide layer 3, so that a sequence of the chromium layer 4, the copper layer 5, and the gold layer 6 may be deposited thereon, forming the ball limiting metallurgy (BLM) contact. A molybdenum mask 7 having a hole 8 therein is juxtaposed over the ball limiting metallurgy, and the assembly is inserted in a vacuum evaporator.

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Flip Chip Solder Ball Rework Process

The flip-chip solder ball contact structure shown in Fig. 1 has been described, for example, in U.S. Patent 3,401,055. As shown in Fig. 1, the aluminum conductor line 2 on the surface of the semiconductor substrate 1 is exposed through a via hole in the polyimide layer 3, so that a sequence of the chromium layer 4, the copper layer 5, and the gold layer 6 may be deposited thereon, forming the ball limiting metallurgy (BLM) contact. A molybdenum mask 7 having a hole 8 therein is juxtaposed over the ball limiting metallurgy, and the assembly is inserted in a vacuum evaporator. A tin lead alloy is evaporated by means of an RF induction heater or other high temperature technique, and the evaporated tin and lead atoms are rendered incident on the molybdenum mask 7 and through the window 8 so as to deposit the tin-lead solder pad 9, as shown in Fig. 1. The substantially trapezoidal cross-sectional shape for the tin-lead solder pad 9 shown in Fig. 1 is the desired contour.

Occasionally, a malfunction in the vacuum evaporator apparatus will occur which will cause the overheating of the tin lead solder pad 9 during the deposition process. Fig. 2 illustrates a common consequence of this malfunction which is the reflow of the solder in the pad 9 so as to cause the inadvertent projection 10 of the solder pad 9 to overlap the knife edge 11 in the window 8 of the molybdenum mask 7. This will effectively rivet the molybdenum mask onto the surface of the semiconductor substrate 1, thereby rendering the assembly useless. If the semiconductor substrate 1 is a high volume part, it can be scrapped by merely mechanically pulling the molybdenum mask 7 from the substrate 1, destroying the substrate in the process. However, where engineering parts are being fabricated in limited quantities, the unnecessary sacrifice of semic...