Signal Transmission Of The Lead-free Solder Joint Failure Criteria

The relationship between lead-free solder joint's damage and signal transmission property is a hot-spot problem for a long time in the field of today's electronic packaging research. In this paper, under direct current (DC), the failure properties of single lead-free solder joint were explored with in situ resistance strain measurement under three different load conditions including shear creep testing at room temperature, shear creep testing at 125℃and shear creep testing during thermal cycle between 40℃and 125℃by a tailor-made electronic testing system. And the quantificational relationship between resistance strain and damage was deducted. The results show that resistance strain curves include a long time linear period and a shorter time exponential period. The resistance strain value at the critical point of the two periods is about 0.05. And the time of the exponential period accounts for 20% to 30% of solder joint's life. Under thermal cycle, the critical point of 40℃curve lags behind the 125℃curve, and the lagged time accounts for 8% of the solder joint's life. At high frequencies, the resistance, inductive reactance and capacitive reactance with solder joint degradation were investigated. And, transmission properties of signal through the damaged solder joint were simulated. The results show that when signal transmits through cracked solder joint, the output signal shows ring phenomenon. With the increase of solder joint's crack, the amplitude of the ring increases exponentially. Comparing the DC resistance curve and ring amplitude curve, it is found that the ring amplitude curve increases in response to cracking of the solder joint earlier than DC resistance curve, which indicates that signal transmission properties offers an improved means of sensing solder joint degradation. Besides, signal transmission properties with different frequencies were simulated when the signal transmitted through solder joint with a crack length of 0.05mm. The results show that with the increase of the signal frequency, the output signal show ring phenomenon. And the higher of the frequency, the larger of the output signal ring amplitude. This clearly shows that higher frequency signals are more sensitive to the degradation of the solder joint.