The Influence of Reflow Cycles on the Microstructure and Properties of mini-LED Solder Joints
XU Huizhi
TANG Jiansheng
WANG Shanlin
LU Peng
Abstract：In response to the multiple reflow failure issues of SnCu0.7 solder joints in flip-chip LED packaging,this study employed X-ray tomography,SEM-EDS analysis,and push-pull strength testing to reveal the thermal cycling failure mechanisms.The experimental results show that:after a single reflow,a(Ni,Cu)3Sn4 layer with a thickness difference of 3.2 μm forms on the chip/pad side;subsequent(Cu,Ni)6Sn5 phase transformation occurs on the pad side,while the growth rate on the chip side slows down.The interfacial fracture mode shifts from ductile to brittle,and the shear strength decreases to 52.4 MPa.The void ratio increases to 18.5％,with the maximum single-pore area fraction reaching 4.7％,leading to junction temperature rise.Thermal accumulation effects cause a reduction in refractive index,resulting in 1.8％luminous flux loss and 3.55％photoelectric efficiency degradation.The study indicates that uneven IMC growth,void aggregation,and thermal dissipation failure form a vicious cycle,providing a quantitative basis for the microstructure-performance correlation in high-density flip-chip packaging processes.
Keywords：flip-flop LED packageSnCu0.7 solder jointsthermal cycling failureinterfacial metal compound(IMC)optical performance degradation
Publication Date：2025-10-31
Online Publishing Date：2025-11-27(First online date of this platform, not the publication date of the document)
Pages：7( 27-33 )