HALTを模擬した負荷下で2軸ラチェット変形を示す銅－はんだ接合体の疲労寿命評価

抄録

Highly Accelerated Limit Test (HALT) gives a product a severe loading which combines fast thermal change with mechanical vibration until the product fails, to identify its weak point in a short time. Since it takes a long time to evaluate the strength reliability of the solder joint in electronic equipment experimentally, HALT is expected to be employed for the evaluation. To achieve such an evaluation, the deformation and the fatigue behaviors of solder joints during HALT must be clarified by conducting some simplified test reflecting the essence of HALT. Then, the authors have conducted HALT simulation tests using a copper-solder joint specimen, in which the specimen is subjected to cyclic torsion with a superimposed tensile stress. The biaxial ratchetting strain was generated at the solder joint of the specimen in the test, and the ratchetting strain rate had a high correlation with the fatigue life of the solder joint. This means that the ratchetting strain rate will become an effective parameter for predicting the fatigue lives of solder joints in the HALT simulation tests. However, in the test, the solder joint is subjected to cyclic torsion at the same time, and therefore a parameter concerned with the cyclic loading is also needed for predicting the fatigue lives consistently. Then, we proposed a prediction method based on Miner's law, which considered the effect of both the ratchetting strain and the cyclic loading on the fatigue life of the solder joint. The validity of the proposed method was discussed using the fatigue test results.