Thin QFP design and development

The challenges presented by the low profile thin quad flat packages (TQFPs) are the design of the mold, control of the assembly operations of wire bonding and molding, moisture performance characteristics, and thermal and mechanical performance. The authors describe the design, modeling for manufacturability, and characterization of a TQFP. The design issues of the TQFP include package symmetry, die thickness, and wire bond loop height. Thermal, mechanical, and electrical modeling results are presented. The assembly process characterization and material selection are discussed. The package performance testing includes moisture weight gain studies, moist package cracking (popcorn) and delamination evaluation, temperature cycle, thermal shock, and autoclave. It is apparent from the moisture preconditioning data that care must be taken to keep the packages in a humidity-controlled environment. A preconditioning bake of 125°C for 8 h hours should be mandatory if packages are exposed to a high humidity environment for a long time period. However, it is clear that when preconditioned appropriately, the TQFP package should have a reliability performance comparable to that of a standard QFP package