The improvement of PBGA solder ball strength under high temperature storage

Plastic Ball Grid Array (PBGA) is a surface mount type high pin count package. It adopts solder balls for external terminals. Currently, the package´s specific character has determined that the ball shear strength between package substrate and solder ball terminals is weakened under the condition of high temperature storage. To overcome this problem investigations and an experiment were completed. As a result, it is seen that the gold plating thickness on solder ball pads has a major influence on degradation of solder ball shear strength under high temperature storage; thinner gold thickness is effective to strengthen the joints. At the same time, the case which used copper for solder ball pad was also examined. The point was that the copper pad forms an oxidized film on the surface which interferes with the solder joint. This fact requires pre-cleaning process before solder ball attach. Concerning more suitable PBGA manufacturing process, ultra-thin gold film is the most effective measure to strengthen solder balls and pad joints