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

The authors have developed a face-down bonding technique for use in making an LCD (liquid-crystal-display) panel. The maximum bonding temperature is limited by the heat resistance temperature for the liquid-crystal materials and polarizer plates. The bonding temperature is approximately 150°C. Using a low-melting-point metal, such as the indium alloy, the IC electrodes and bonding pads on a glass substrate can be connected at a temperature less than 150°C. This technique is called the low-melting-point-metal connection (LMC) technique. Shallow-bowl-shaped bumps of low-melting-point metal, 10-20-μ high, were formed on the IC bonding pads by dipping, and the IC and the glass substrate were connected. This process was carried out at a pressure of 30 gf/bump or less and at a temperature of 150°C or less. Two kinds of reliability tests were then carried out. One was a thermal shock test, and the other was a high-temperature, high-humidity test (70°C, 90% R.H., 500 h). Stable results were obtained for both tests. Dot-matrix LCD panels with 640×400 dots were assembled using 20 driver IC chips and were shown to work well