Low-stress leadframe design for plastic IC packages

Abstract

This paper describes a method of leadframe design which reduces thermal deformation and stress in the chip, and improves moldability of leadframe-based plastic encapsulated IC packages. The design works by splitting the die-pad into several sections joined together by flexible expansion joints. The split die-pad allows relative motion between the sections of the pad and breaks down the total die-pad length that is rigidly attached to the chip into smaller segments. These two factors reduce the magnitude of coefficient-of-thermal-expansion (CTE) mismatch and out-of-plane deformation of the assembly, resulting in reduced chip stress and improved moldability.