Thermomechanical and electrochemical reliability of fine-pitch through-package-copper vias (TPV) in thin glass interposers and packages

This paper reports reliability of copper-plated through-package-vias (TPVs) in glass interposer by modeling and experimental validation using accelerated life tests. In this paper, both thermomechanical reliability and electrochemical reliability of fine-pitch TPVs in glass interposer were investigated. Thermomechanical reliability was investigated by developing finite element models to calculate the thermomechanical stresses and strains inside TPVs during thermal cycling tests with several glass and polymer liner combinations. Fatigue lifetime of TPVs in glass is predicted based on these simulation results and then validated using experiments. Test samples with daisy chains of TPVs are fabricated with different glass and polymer material combinations and subjected to accelerated temperature cycling tests to assess the thermomechanical reliability of TPVs in glass interposer. Resistance of each daisy chain is monitored using 4-point probe during cycling. It is observed that majority of test samples passed 1000 thermal cycles without any significant changes in electrical resistance. Cross-sectioning of TPV daisy chains that showed significant changes in resistance, revealed that failures were related to defects induced during copper plating in TPV side walls. Electrochemical migration reliability of TPVs in glass was investigated to study conductive anodic filament (CAF) resistance of glass at very small via spacing. Test samples with different material combinations were subjected to biased and highly accelerated stress temperature-humidity test (HAST) to assess electrochemical migration reliability of TPVs. After biased-HAST for 100 hours at 130°C, 85% relative humidity (RH) and 5 V DC, no CAF failures were detected in either of the two material combinations, indicating good insulation reliability under high temperature and humidity conditions.