A fracture mechanics approach to soldered joint cracking

Fracturing of a soldered joint, 60Sn-40Pb and beryllium copper, is investigated by a method that makes use of a double cantilever beam specimen where two symmetrical beams are soldered together. In this center line of solder layer, an initial crack is created. In one set of experiments, a monotonically increasing load is applied in the opening mode until the crack suddenly propagates. This procedure is repeated to obtain a set of load-deflection curves of different crack lengths which are used to calculate the J integral. The critical J integral is found to be 900-1200 J/m². In the second set of experiments, a subcritical load in the opening mode is applied and the corresponding displacement at the loading point is held constant. Subsequent load decrease and increase in the crack length are recorded with time. The rate of crack growth per unit time shows linear correlation with the third power of the J integral. Furthermore, there seems to exist a threshold J integral of 200-300 J/m² below which no crack growth is observed