Development of cost-effective high power 208HTQFP

The 208HTQFP (high power thin quad flat package) with exposed heat sink was developed, which is completely compatible with the standard 208TQFP in terms of process, equipment and reliability, and is also cost-effective. With biphenyl EMC, the thermal resistance of 208HTQFP was greatly decreased, down to 23.1°C/W compared to that of 208TQFP which was 45.9°C/W. The application of a high conductivity EMC reduced the thermal resistance down to 19.2°C/W. The adoption of a dimple on the top side of the heat sink played a key role in preventing package cracking under preconditioning of 30°C/60% RH for 192 hrs, but these dimples were not enough for preconditioning of 85°C/65% RH for 96 hrs. To minimize the cushioning effect of the thermoset polyimide tape during wire bonding, parameters such as die attach post-cure time, wire bonding temperature, ultrasonic power and force were evaluated. Shorter die attach post-cure time, low wire bonding temperature, and high ultrasonic power and force showed better wire bondability. A mould flash on the heat sink was observed, and was completely removed by dipping in film remover for two hours