Solid State Diffusion Bond
This bonding method is the joining of two metals by the solid state
diffusion process in which molecules interdiffuse along crystal
It is commonly used to join fine wire to the metallized target area
prepared on the semiconductor device. It is accomplished by applying a tool to exert force and to cause plastic deformation at the interface of the wire and the metallization, which extrudes and dispenses impurities. Ultrasonic agitation of the applied tool is used to aid this dispersal.
The metals at the interface now presented to each other, nascent
crystals where molecules interdiffuse along the crystal boundaries.
Metals most amenable to this process such as gold, aluminum, silver
and platinum are closely grouped in the periodic table. The only metals which will enter into this process readily are face centered cubic crystal structures and possible those others that are closely grouped in the periodic table.
Examination of a metallurgical section will show the interdiffusion
with no line of separation. The line of separations will be seen to
resume at the edges of the bonded zone. The function of heat in this process is simply to enhance these actions.