Special characteristic of future flip chip underfill materials andthe process

摘要

New materials and process for future flip chip packaging have beenstudied. Three types of new concept materials with suitable process arediscussed in this paper. First is the preset underfill (PUF) process. Anon-conductive underfill film is used in this process by a flipchip-bonding machine with lamination capability. Throughput andreliability are mainly studied for this process. Basic reliabilityrequirements such as Thermal Shock Test -40 C to +125 C/1000 cycles,Pressure Cooker Test 121 C×2 atm/168 hrs, and Moisture SensitivityLevel/JEDEC Level 3, have been achieved with high throughput. Second isthe transfer underfill (TUF) material. A modified transfer moldingmachine instead of a liquid underfill dispensing machine does underfillin this process. The required characteristics for the transfer underfillmaterial are no volatiles in the material pellet and good flow abilitywith gap below 100 μm. New TUF material has successfully clears therequirements with newly developed clean tablet (CT) technology, andfiller particle distribution control. Third is an underfill paste (UFP)material. This new material has high thermal stability at operatingtemperatures up to 80 C, and rapid curing characteristics such as 150C×20 min or 175 C×5 min, due to the special reaction controlof the epoxy and phenol curing system. This material can be used in acurrent dispensing process with a minor adjustment in the heatingparameter. Coating or printing processes are also available options forthis UFP material. In this paper, the future of flip chip packages isdiscussed with these three materials and processes