Thermocompression Attach. Using this technique, there are no adhesives to join the die and the package. Instead, heat and force are applied to the die in a process called "thermocompression bonding". The bumps are forced against their opposing pads and a second metallic bond is formed where the bond comes into contact with the package metallization. This technique typically requires the use of heat as high as 350° to 400°C, and forces of as much as 100 g/bump.
During this process, a die is subjected to high force and temperature. Dies that are thinner, brittle or intolerant of high heat may not be suitable for attaching using this method.
Thermosonic Attach. This process is nearly identical to the thermocompression solution, with the exception that an ultrasonic transducer is used to induce another form of energy to the bonding process. In this way, the heat and force requirement may be reduced substantially.
The challenge to this process is determining how the application of ultrasonics will affect the die structurally. One determining factor will be the mechanism used to hold the die while the forces are being applied. Collet selection is critical in minimizing the stresses.