Study on Ag-Plated Cu Lead Frame and Its Effect to LED Performance Under Thermal Aging

Abstract

A systematic study about the effect of thermal aging time on lead frame morphology and LED optical performance was demonstrated in this paper. Three different lead frames for LED manufacturing were chosen to execute thermal aging test for reliability qualification. An evolution about Ag recrystallization, Cu diffusion, Cu nucleation, and growth on lead frame surface was comprehensively explained. The relationship between surface morphology and lead frame reflectance was first established by experimental characterization and comparison. After that, theoretical analysis based on diffusion theory reasonably explained the copper diffusion and nucleation process, which matches well with the morphology changes. Later on, optical simulation on various commercial LED packages was implemented to evaluate the effect of lead frame reflectance on the optical output. In conclusion, centering on Cu diffusion induces reflectance decrease, the connection initializes from thermal aging to final LED lumen performance was successfully built up in this paper. The findings can be directly applied as guidance to facilitate industrial LED manufacturing and reliability qualification.