Study On Reliability Of QFP Devices Solder Joints Under Large Temperature Range

With the development of science and technology, human’s ability is strong enough to make more achivements, especially in the area of deep-space detection, where global competition has been focusing on. Compared to the near-earth detection area where China has quite a lot achievements, the harsh environment of deep-space aerospace demonds more on electronics reliability. Compare with NASA’s 15 years systematic study on the influence of enviroment on electronic product reliability,our country’s relevant research on extreme environment is still in its infancy,which may delay our long-life deep space detection tasks, so we need to carry out a series of basic researches to fill out this blanks immediately.According to the requirements mentioned above, this research choose Sn-based solder Sn63Pb37, Sn3.0Ag0.5Cu and QFP chips that assemblied by these solders as the research objects, analyzing the influence of extreme environment on solder and pin’s mechanical property through 0~300 cycles extremely temperature test(-196°C ~+150°C). The aims of this research are to reveal the solder and pin failure mode in extreme environment and to evaluate the reliabilities of these two kinds of solder.The low and high speed strain tensile test results show the Sn63Pb37 solder tensile is stronger than that of SAC305. With the same test periodic, Sn63Pb37 solder tensile increased by 59.1% and 48.0% respectively. The Sn63Pb37 solder has better mechanical stability, while organization also maintains uniform durning temperature cycling test. Fracture analysis shows that ductile fracture is the main failure mode in the test, but it turns to embrittlement tendency,which belongs to the mixed fracture, in the high strain rate and high cycle(Sn63Pb37:100~300 cycles, SAC305:250~300 cycles).Mechanical properties test of QFP pin shows that with test cycles increasing, the strength of the corner and middle pins assemblied by two kinds of solder are both on the decline, while both of them meet the standard requirements. As a whole, SAC305’s pin mechanics performance is slightly better than Sn63Pb37’s. Fracture analysis shows that two solder pin’s fracture mode both transfers from ductile fracture to brittle fracture during the temperature test.Pin’s profile analysis through the inspection of cracks and hole defects shows that SAC305 solder’s performance of resisting fatigue is better. The morphology of solder pad side IMC changes from scalloped to stratiform gradually, and SAC305’s IMC is thicker than Sn63Pb37’s. The intermetallic compound growth index of Sn63Pb37/pad interface and SAC305/pad interface are 0.3723 and 0.3357, belong to the boundary diffusion type. But since SAC305 solder has better CTE matching with pad and IMC, it has excellent anti-fatigue performance. The results also shows that ENIG solder pad can inhibit the growth of intermetallic compounds by comparing the thickness of upper and lower compound.