In this paper, a new method was proposed for evaluating the high-cycle fatigue strength of BGA (Ball Grid Array) packages with Pb-free solder and Pb solder due to a vibration. Attaching a weight induced mixed mode stress in the solder ball of a package. To consider the effect of a mixed mode stress occurred in a solder ball and a frequency to fatigue strength of solder ball, a test was carried out with the four kinds of weights which induced the different ratio of nominal normal stress and nominal shear stress in a solder ball (σn/τn=2, 4, 5, and 6) at various frequencies (10-27 Hz). Based on the nominal shear stress in solder balls, a new evaluation equation to consider the effect of a mixed mode stress in a solder ball was proposed and the scatters of the fatigue strength in Pb-free packages and Pb packages were evaluated with a Weibull distribution. From a successive observation of a cross section during a fatigue test, a position of crack initiation and a propagation path were found out. Although an intermetallic compounds in both of packages were confirmed by an EDX microprobe analysis, they don't contribute to the initiation of a crack in a solder ball.
|ジャーナル||Nihon Kikai Gakkai Ronbunshu, A Hen/Transactions of the Japan Society of Mechanical Engineers, Part A|
|出版ステータス||出版済み - 12 2004|
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