Assembly and reliability study for the micro-ball grid array

The μBGA is a die-sized, testable package designed for applications requiring high density and power dissipation. It has an area array of contacts beneath the chip, and is assembled in a flip-chip configuration using Surface Mount Technology (SMT). However, it differs from flip-chip in that it has an elastomeric layer between the bump array and the silicon. This layer provides compliance for socket normal forces and allows for thermal expansion mismatches between the silicon and the substrate. The bump pitch ranges from 0.5 to 1.5 mm so that registration tolerances for testing are relatively loose. Initial assembly work on the μBGA has shown that SMT is an applicable process. The test chip used was a Texas Instruments (TI) daisy chain die, 12.5 mm×12.5 mm, with 188 I/O on a 0.5 mm (20 mils) bump pitch. The substrate was specifically designed for solder assembly and test with four TI land patterns. The assembled die were placed with standard pick and place machines