Influences of fan-in/fan-out structure and underfill fillet on TCT reliability of flip chip BGA

The reliability of two types of flip chip ball grid array (BGA) was investigated using temperature cycling tests (TCT). It showed that the reliability of the fan-out structure was higher than that of the fan-in structure. The fan-in structure broke more easily at the die edge than the fan-out structure. The highest region of thermal stress on the fan-out structure package was different from that of the fan-in structure package. Therefore, the crack modes were also different. FEM analysis makes the difference of the maximum principal stress on the backside clear. The higher stress region of each structure influences the TCT reliability. The use of a ceramic substrate, as opposed to BT resin, improved the lifetime of the fan-in structure under thermal stress.