Mechanical bending fatigue reliability and its application to area array packaging

The drive to finer pitch assemblies is in part due to smaller portable products. As these products reduce in size, the thickness of the printed circuit board must also reduce in thickness in proportion to the product size. These assemblies have become more flexible. Many of these products are assembled with area array packaging, which require numerous low-frequency mechanical deflections. The reliability emphasis has become more focused on isothermal bending fatigue. This paper will discuss a test method to evaluate bending fatigue reliability of 1.0 and 0.8 mm pitch area array packaging, the effect of printed circuit board (PCB) thickness, fatigue fracture morphology and its relation to solder joint location. Finite element results will also be presented to support and expand upon the findings in this study.