The mechanics of the solder ball shear test and the effect of shear rate

A test rig was developed to do high speed solder ball shear tests on a servohydraulic testing machine. Shear tests were conducted over a range of shear rates on eutectic tin–lead and lead-free solder balls that were mounted on a chip scale package (CSP) with a solder mask defined (SMD) ball grid array (BGA) configuration and on the Cu pads in a maskless printed wire board (PWB). The high speed ball shear test was found to induce a brittle solder/pad interface fracture that resembles the fracture in lead-free interconnects of board mounted microelectronic devices that have been subjected to mechanical shock. An approximate static analysis of the solder ball shear test has been developed that enables the plastic, fracture, and friction work to be separated. This analysis suggests that the specific work after maximum load obtained for low shear rate is closely related to the toughness of the solder. Provided the fracture was stable, the specific work after maximum load was relatively insensitive to shear rate suggesting that the solder toughness is also rate insensitive. The shear strength and total specific shear work all increase with shear rate.