Board level reliability assessments of package on package

In spite of a great success of stacked package (PoP) in the market, some reliability issues about package on package (PoP) have been raised by several customers. To guarantee a high reliability in board level performances, many process and material developments are attempted. In the material developments, low silver contented solder alloys are adopted for higher board level drop performances. In OSP substrate pad finish, Sn/1.2Ag/0.5Cu/0.05Ni solder is applied and in Ni/Au substrate pad finish, Sn/1.0Ag/0.5Cu solder is adopted for higher reliabilities. 2nd level underfill is also adopted for higher drop performances but in this case, board level temperature cycle performance is deteriorated. To accomplish of higher board level performances both in temperature cycle and drop test, higher Tg & low CTE underfill materials are developed In the process developments, stacking materials and processes are developed. Board level reliabilities of pre- stacking & SMT stacking process is evaluated and paste and flux materials for top package stacking process are also evaluated. This paper discusses about board level reliabilities in temperature cycle and drop tests with various material and process combinations - especially, solder alloys, substrate pad finish, 2nd level underfill, stacking method and stacking materials.