Capillary wedge bonding technology for stacked die packages

BSOB is currently widely used in flash memory BGA packages, which use fine gold wire to connect each layer of stacked flash chips, that can be 2, 4, 8 or even 16 layers, and finally connect them to BGA substrate. Due to its special process characters, dummy stud balls are needed for continuous wire bonding process to link different layers of flash chips. This special process occupies quite big capacity of wire bonding equipment. In this paper, a new wire bonding method, called Capillary Wedge Bonding (CWB), is introduced to perform interconnection for different layers of flash chips without or reducing the dummy stud balls. UPH is one of the key factors to be studied and compared, also ball shear, wire pull IMC and cratering test are included. The final packages reliability level with different wire bonding methods are also evaluated and compared.