BUMP STRUCTURE FOR REFLOW BONDING OF IC DEVICES

摘要

In a semiconductor device tape assembly bonding process the fingers (22) of a copper tape are reflow soldered to metal bumps (19) located on the semiconductor device (10). First, the semiconductor wafer is covered with a conductive film composed of thin layers of aluminum (14), nickel-vanadium alloy (15) and gold (16). The bumps are then created by electroplating gold through openings in a photoresist mask. The gold bumps (19) are overcoated with a contolled thickness tin layer and the tin is overcoated with a thin gold anticorrosion layer. The copper assembly tape is coated with a thin gold layer (23) and are lightly pressed against the bumps by means of a thermode. The thermode is quickly heated to a temperature well above the gold-tin eutectic melting temperature and then rapidly cooled. The tin layer on the bump will combine with the adjacent gold to form a liquid phase eutectic (24) which will form and contact both the copper finger and the gold bump. Upon cooling the eutectic melt will solder the finger to the bump. Since all of the tin is combined with the gold there is no metallic tin left in the system and the problems of tin whiskers and tin electromigration are avoided.