New mode crack of LSI package in the solder reflow process

A new mode crack that could not be explained by a general mechanism has been observed under the condition of the surface mount components being smaller and thinner, and requiring more severe characteristics in the solder reflow process. The mode crack is generated from the upper portion of the die pad corner, and is not caused by the delamination between the die pad and the plastic. This new mode crack mechanism is explained in the following way. Absorbed moisture reaches the die attachment layer during storage and is vaporized by heat in soldering; the vapor pressure pushes down the die pad and causes stress in the plastic of the upper portion of the die pad corner; then new mode cracks are generated. The authors also describe how a new lead frame design can prevent this crack