Recently, many new kinds of fine pitch bonding techniques have been developed. Among these is the authors' face down bonding technique for use in manufacturing liquid crystal display (LCD) panels. The maximum bonding temperature must be low because of the low heat resistance temperatures of the liquid crystal materials and polarizer plates (approximately 150°C). By using a low melting point metal, such as an indium alloy, the integrated circuits (IC) electrodes and bonding pads on a glass substrate are connected at a temperature lower than 150°C. The technique, named the low melting point metal connection (LMC) technique, was developed as follows. First, using the dipping method, low melting point metal bumps were formed on the IC bonding pads with gold bumps. Shallow-bowl-shaped bumps, 10–20 µ m high, were the result. Next the IC and the glass substrate were connected at a pressure of 30 gf/bump or less and a temperature of 150°C or less. Two kinds of reliability tests were performed on this sample. One was a thermal shock test (TST): a repetition of — 40 and 100°C for 30 min each, for 300 cycles. The other was a high temperature and high humidity test: 70°C, 90% relective humidity (RH) for 500 h. Both tests obtained stable results. Finally, dot matrix LCD panels, with 640 by 400 dots, were assembled with 20 driver IC chips. The panels displayed test patterns perfectly. The LMC technique makes it easy to test and repair the IC bonds. The results of the trial manufacturing and testing show that the LMC technique can be readily applied in manufacturing LCD panels and many other kinds of electronic equipment. © 1990 IEEE
