Mechanical properties study of lead free solder joint material used in semiconductor packaging subjected to thermal condition

摘要

The effect of high temperature storage (HTS) on lead free solder joint material for ball grid array application using pull test method were studied in this paper. Some statistical analysis base on the pull test data also discussed. Three samples of different lead free solder joint material were selected in this experiment namely Sn3.8Ag0.7Cu (SAC387), Sn2.3Ag0.08Ni0.01Co (SANC), and Sn3.5Ag. After the thermal condition test, all the lead free solder joint material samples were tested using Dage 4000 pull test machine. Each pull test will be 5 units and each unit contain 8 balls. From all the samples, result shows that the mean pull strength for high temperature storage are 2847.66g, 2628.20g and 2613.79g for Sn3.5Ag, SANC and SAC387 respectively. Thus Sn3.5Ag shows a significantly better solder joint performance in terms of joint strength compare to SANC and SAC387. Hence, intermetallic compound (IMC) thicknesses were measured after cross-sectioning. Sample size for cross-sectioning was 3 units per read point, 2 balls per unit, and 3 maximum IMC peaks per ball and the measurement using high power scope of 100× and Image Analyzer software to measure the IMC thickness. For high temperature storage, result show that the mean IMC thicknesses for SAC387, SANC and Sn3.5Ag are 3.9139μm, 2.3111 μm and 2.3931 μm. It was found that IMC thickness for SANC and Sn3.5Ag does not show significant growth after high temperature storage but SAC387 demonstrated significant growth. Lower intermetallic thickness implies less brittle joint effect, thus from this part of study, better joint reliability is expected for the Sn3.5Ag solder system. In summary pull test method is feasible to be used in characterization in terms of solder joint strength of lead free solder joint material for semiconductor packaging. It also determined ball pull test results provide correlation of the IMC thickness and solder joint strength material.