The mechanical reliability of 1mil Au wire bonds in different bond pad opening shapes, sizes and placement accuracy.

摘要

The semiconductor industry trend has been to shrink the sizes of ICs and packaging, while increasing the functionality and complexity of the designs. Wire bonding, an interconnection technology, has been pushed towards meeting the demand of increased I/Os, smaller pad openings and finer pitches. To investigate the reliability of bonding to these smaller openings, the mechanical strength of 1mil Au wire bonds were tested and compared in this research. Wire pull and ball shear tests were chosen to evaluate the strength after bonding to three pad opening designs: 70microm x 70microm square, 44microm diameter circle and 40microm diameter circle. Also, to study the effects of placement, bonds were placed 25% from the center of the pad in the 70microm x 70microm square and 44microm diameter circular design.;After bonding and package assembly, the units were exposed to reliability stress tests such as: High Temperature Storage (HTS) conditions at 150°C and 175°C, Unbiased Highly Accelerated Stress Test (UHAST) and Moisture Sensitivity Level (MSL-1). Mechanical tests were also performed after stressing to compare any degradation in the bond. Mechanical cross sectioning and Intermetallic Compound (IMC) check was executed to investigate the shape and weld, respectively. It was concluded that the bondable surface area is decreased by 26% from the square to circle design, but the average shear strength declined only by 4%. This relatively slight decrease in shear strength supports the idea that altering opening size and shape may be a comparable solution to the standard rectangle and square designs.