Mechanical Property of SAC305 Ball-Grid Array and Epoxy Sn-58Bi Solder Joints with 85 °C/85% Relative Humidity Environmental Conditions.

The ball-grid array (BGA) is widely used to reduce component size and it had advantages such as high I/O pins and fine pitch. Typical Sn-Ag-Cu (SAC) solder alloys are used for formation of BGA because SAC solder has excellent characteristics among lead-free solders. However, the electronic components assembled by SAC solder were easily damaged by heat during manufacture process because SAC solder had high melting point of 220 °C. To prevent these thermal damages, SAC305 BGA component assembled by Sn-58Bi solder paste has been studied because Sn-58Bi solder had low melting point of 139 °C. In generally, Sn-58Bi solder was improved by additional elements or polymer such as epoxy because Sn-58Bi had a brittle property. However, the epoxy Sn-58Bi solder did not guaranteed high environmental reliability such as high-temperature high-humidity (HTHH) test. Thus, we evaluated the shear strength of solder joints assembled by SAC305 BGA components with Sn-58Bi solder paste and epoxy Sn-58Bi solder paste. The shear strength of solder joints was evaluated by die shear test after HTHH test at the 85 °C/85% RH conditions. The Cu6Sn5 intermetallic-compound (IMC) at the interface of solder joints was observed by scanning electron microscope (SEM). The IMC thickness of Sn-58Bi solder joints was smaller than that of epoxy Sn-58Bi solder. The shear strength was improved up to 20% by epoxy addition. The shear strength of epoxy Sn-58Bi solder joints dramatically decreased after HTHH test for 100 h.