Influence of the BGA solder joint microstructure on the thermal cycling reliability

Abstract

In this paper,Sn62Pb62Ag2 solder paste was used for reflow of SAC305 ball BGA and Sn63Pb37 ball BGA after removing lead-free ball. Different reflow processes were selected to obtain three types of solder joints ，including mixed solder joints with homogeneous structure(solder joint A)，mixed solder joints with inhomogeneous structure(solder joint B)，lead-tin solder joints which re-soldering Sn63Pb37 ball after removal lead-free ball(solder joint C).The reliability of solder joints after optimization was studied with an accelerated thermal cycling(ATC) test in the temperature range from -40°C to 125°C in accordance with IPC 9701A standard.200, 400, 500 and 1200 times thermal cycle tests were performed, and electrical performance tests were carried out after the different times test. Except that BGA of solder joint C appeared electrical performance failure after 500 times, the rest passed the electrical performance test. The results showed that the size of Ag-Sn compound in the solder joint A e was more refined and mainly distributed at grain boundaries, while the Pb phase gradually changed from a reticular structure to a smaller and more uniform island shape. With the increase of the number of cycles, the thickness of IMC layer at the interface of solder joint A did not change in detail, and the Pb-rich phases remained dispersed and always remained island, with cracks in the joint but less than 25%. When the number of thermal cycles reaches 500, it can be found that the reliability of BGA of solder joint A is better than that of BGA solder joints of other two structures. At this time, the crack of older joint B is more than 25%, while solder joint C is 100% cracked and appears in the stress concentration area on the side of components