Development of BGA under-fill process

(July 4th 2006)

As a result of a particular customer requirement, Ultra CEMS has developed an on-site BGA under-filling process.

Stuart Vanstone, Ultra CEMS Production Engineer states "BGA under-filling is carried to improve the mechanical stability, resistance to vibration, exposure to high G-forces etc. on ball grid array devices.

In essence, an epoxy type adhesive is flowed under the BGA device and cured. The adhesive is "pulled" under the device by capillary action. Curing of the adhesive is achieved by the application of controlled heat. After the recommended curing time the board can then be processed in the normal way.

Under-fill is best done after test, although BGA's which have been under-filled can be reworked.

To test and improve the process our first trials were done on 4 mm thick, 100mm square glass plates. The results were very good. It proved possible to track the progress of the under-fill and inspect the results of the process through the glass plate for air entrapment. Different techniques were then tried; the best results obtained being from the dam & fill method".