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Conventional die attach adhesives are generally thermoset material. Thermoplastic adhesive is being used in linear circuits and large dice as this provides stress-absorbing action on the die. However, the thermoplastic nature of this adhesive tends to cause dampening of ultrasonic energy being applied to the bonding pad during thermosonic bonding. In this study, the effect of thermoplastic adhesive on thermosonic bonding was determined by comparing the ball shear strengths of ball bonds in dice attached using thermoplastic adhesive and those in dice attached using thermoset adhesive. The comparison was done at various bonding temperatures. Results revealed that ball shear strength increases proportionally with bonding temperature with thermoset adhesive. On the other hand, ball shear strength exhibited by dice attached with thermoplastic adhesive start to decline at 150 deg C. The study also showed at any given bonding temperature, the ball shear strength increases as bond power increases in dice attached with thermoplastic adhesive. However, for the same power, the ball shear strengths exhibited by dice wirebonded at high temperature (200 deg C) are lower than those bonded at low temperature (125 deg C). This study was therefore able to confirm that thermoplastic die attach can result in higher ball bond lifting occurrences, since its instability at the elevated temperature of thermosonic wirebonding dampens the ultrasonic energy being transmitted to the ball and the bond pad.
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