The failure behavior and modes of board level solder joints under coupling of vibration and thermal loads were studied based on the orthogonal experiment design method.The accelerated life tests with different temperature (T)

power spectral density (PSD) and frequency (V) were conducted by using a L

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(34) mixed-level orthogonal array.The results show that the degree of influence that the three factors have on the reliability of solder joints is TPSDV.The temperature is the main factor that can affect the failure modes of solder joints significantly.The crack initiates in the intermetalic compound (IMC) and propagates into the bulk solder gradually as the temperatu

re rise.The failure mode evolves from the brittle fracture to ductile fracture.Based on the analysis of the failure data

a fatigue life model of solder joint was developed by using the polynomial fitting method

according to the relationship between the logarithmic fatigue life value and the strain range of the back side of the printed circuit board.The fitting results indicate that the model can evaluate the fatigue life of solder joints under the coupling of the vibration and thermal loads accurately.