A new face down bonding technique using a low melting point metal

A description is given of a face-down bonding technique, the low-melting-point metal connection (LMC) technique, for use in manufacturing liquid-crystal display (LCD) panels. By using a low melting point metal, such as an indium alloy, it is possible to connect the integrated circuit (IC) electrodes and bonding pads on a glass substrate at a temperature lower than 150°C. 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 μm 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% relative humidity (RH) for 500 h. In both tests, stable results were obtained. Finally, dot matrix LCD panels, with 640×400 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