New mode crack of LSI package in the solder reflow process

A new cracking mode that cannot be explained by the conventional cracking mechanism has been observed under the current circumstance of surface mount components being smaller and thinner and having more stringent requirements in the solder reflow process. This type of crack is generated from the upper portion of the die pad corner, not caused by the delamination between the die pad and the plastic, and is attributed to absorbed moisture reaching the die attachment layer during storage and being vaporized by heat in the soldering. The vapor pressure pushes down the die pad, causing stress in the plastic of upper portion of the die pad corner, and cracks occur. A lead frame design that can prevent this type of crack is described