The Reliability Of Lead.free BGA Balls And Failure Analysis Under Random Vibration

Due to the advantages, more density of packaging, more friendlily to environment etc.,lead-free ball grid array (BGA) packaging is becoming the mainstream packaging technique.Existing literatures are mainly focused on the thermal cycle reliability. The reliability ofBGA balls is one of the urgent problems, which constrains the development of packagingtechnique currently. It is inevitable for electronic products to suffer from vibration loadingin the process of shipping and using. Therefore vibration reliability couldn’t be ignored. Tosolve the problems, a numerical assessment mechanical was established combining randomvibration test with FEM method in this paper. The effect of under-fill used in the electronicpackaging widely to vibration reliability is also discussed in this paper. Chip location andboundary conditions of PCB were taken into consideration in the discussion. Additionally,comparison analyses between mixed solder joints contained low-temperature solder Sn58Biand SnAgCu solder joints was performed.Print circuit board was designed using Protel DXP and was assembled using reflowtechnique. Based on the designed clap and dynamic voltage monitor system, randomvibration test platform was established in this paper. The lifetime of Sn3Ag0.5Cu solderjoints and mixed solder joints was obtained through vibration test. The numeric assessmentmechanical was established based on theory of cumulative damage in fatigue, three brandtechnique and modified Masson high. cycle fatigue equation. And CDI was calculated usingthis method,3D histogram of CDI was also proposed.The structure of packaging, location of chips and constraint conditions of PCB wereprincipal factors affecting the vibration reliability of packaging. Therefore FEM randomvibration analyses were performed on packaging with under-fill, packaging with under-filland additional constraint condition and packaging with mixed solder joints and theiraffection were also discussed in this paper. This indicates that under-fill, additionalconstraint condition, and combination of the two measures are all beneficial to improve thevibration reliability, and the last method works best.Sn3Ag0.5Cu package was assembled using Sn58Bi low temperature solder, duing toadvantages of low weld temperature and low cost. Through the comparison the resultsbetween experiment and finite element analysis, random vibration reliabilities were evaluated. It have been found that joints with single solder have better vibration reliability.