Investigation of the Adhesion Strength of Underfill/Solder Mask/Substrate Joints Under Thermal Cycling

Chi-Hui Chien*, Yung-Chang Chen, Chi-Chang Hsieh, Yii-Der Wu, Yii-Tay Chiou a Professor, Department of Mechanical and Electro-Mechanical Engineering, National Sun Yat-Sen University, Taiwan b Graduate Student, Department of Mechanical and Electro-Mechanical Engineering, National Sun Yat-Sen University, Taiwan c Instructor, Department of Vehicle Engineering, National Pingtung University of Science and Technology, Taiwan d Deputy Manager, Electronics Research & Service Organization, Industrial Technology Research Institute, Taiwan ABSTRACT With the increasing application of flip-chip technology in the microelectronics industry, the adhesion strength of interfaces in the flip-chip structures is becoming an important issue for manufacturing and operation. This paper presents an experimental investigation of the adhesive strength of underfill material to solder mask coated FR-4 substrate under thermal cycling. In this study, effects of the number of thermal cycles on interfacial strength were investigated by using button shear test. The relationship between interfacial strength and the thickness of solder mask was also examined. Furthermore, the morphologies of fracture surfaces of the test specimens were analyzed by scanning electron microscopy. The results of this study show that the interfacial strength of the underfill/solder mask/substrate joint was significantly reduced by thermal fatigue. Finally, the degradation behavior and possible mechanisms were then determined on the basis of these observations.