Kwan-yu Lai, Micralyne, and Jeffrey G. Stark, Sensor Products, describe the use of color-coded pressure-indicating film to ensure uniform, correct pressure during wafer bonding. Wafers are bonded by applying precise combinations of physical pressure, temperature, and/or voltage. Pressure is measured as an average, assuming perfectly flat pressure plates. In practice, the pressure plates are often non-ideal, or they may have degraded over time. Applied pressure characterization is important for high yielding eutectic/thermocompression bonds.
Bond recipes are tested for consistency then adjusted based on the results from the pressure-indicating film. There are also specific benefits that are distinct to each type of bonding application: metal eutectic bonding, anodic bonding, fusion bonding, metal diffusion bonding, glass frit bonding, polymer adhesive bonding.