Isothermal Fatigue of LCC/PWB Interconnections

Abstract

This paper describes the isothermal fatigue of leaded chip carrier to PWB interconnections. A split board technique was used to test the behavior of the Kovar leads and Sn63 solder joints made between a 64 IO leaded chip carrier and a PWB. The leads and solder joints were subjected to proscribed deflections at 35°C or 125°C and at frequencies of 0.33 Hz or about 0.002 Hz. At 35°C and 0.33 Hz, the failures were primarily in the Kovar lead, but when the cycling frequency was decreased to about 0.002 Hz, the failures developed in the Sn63 solder joint between the lead and the PWB. At 125°C, the failures were in the solder, even when the cycling frequency was 0.33 Hz. In addition to studying the influence of temperature and cycle frequency, this paper also compares the behavior of leaded joints to that of leadless joints and illustrates the superiority of the leaded joints.