There is a general shift in plastic package size towards largerand thinner dice. This can be seen in the dramatic increase in thenumber of QFP type packages produced in the semiconductor industry. Thisshift has pushed molding compound and die attach materials requirementstowards a lower modulus to comply with reliability requirements. Thishas brought with it a number of processability concerns. One of theforemost concerns is that of wirebondability of packages assembled witha thin die using low modulus die attach and overcoming the phenomenonwhich is commonly known as “bouncing”. In this paper, wereport on one such low modulus die attach material (JM2500 from JohnsonMatthey) which met reliability requirements but had a wirebondabilityissue when used with small, thin dice. This study used a dynamicmechanical analyzer (DMA) to study the bouncing phenomena. This was doneby first bonding the die to a leadframe with low modulus die attach.After cure, the DMA was used to observe die depression during asimulated wirebonding process. The effects of high and low filletheights on the bouncing effect was then studied. It was found thatincreased fillet height tends to act as a damper for the bouncingeffect. This observation was then tested on an actual bonding process ina production line where packages with fillet height <30% werecompared with packages with fillet height >50%. The results showed asignificant improvement in package wirebondability when fillet heightincreased. The merits and limitations of the technique for understandingwirebondability are also discussed
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