Assembly process and solder joint integrity of the metal ball grid array (MBGA^TM) package

This paper first presents a brief overview of the MBGA^TM (Metal Ball Grid Array) package construction. Next, front-end die and wire bond manufacturing processes are reviewed. The development of a low volume encapsulation and ball attachment process is discussed in detail. Finally, the solder joint integrity of attached eutectic balls to the MBGA package is discussed. A low volume liquid encapsulation process was developed using a semi-automated dispensing system. In developing the process, a positive-displacement rotary valve was used to achieve a dispense consistency of ±2 percent by weight. Corresponding encapsulant heights averaged 0.0096 in, with an average standard deviation of ±0.0011 in. The development of a low volume ball attachment process included semi-automated flux dispensing of no-clean solder flux, ball placement with mechanical alignment fixtures, and solder ball reflow. The reflow process yielded high quality solder joints resulting in solder balls that sheared about 1.8 kg. A minimum ball shear of 1.5 kg, well above the industry requirement of 1 kg, was achieved after heat ageing at 175°C