Like any solid material, the conductor becomes soft within a certain range of temperature. This range of temperature is different for each material, and when reached, it enables the atomic structure of the two element to join together by diffusion. This rate of diffusion is almost nil at ambient temperatures, so the application of heat is necessary in order to accelerate the process so sufficient diffusion is achieved to produce a bond within approximately some tenths of second. Pressure applied to the materials being bonded ensures an excellent contact between their two surfaces to further promote atomic diffusion process. The wire and the pad are then strongly linked together by the atomic connections created during the diffusion process.
Diffusion of the blue atoms (ex: Copper wire) and white atoms (ex: Gold plated pad) during the process of Thermocompression Bonding. |