Operation of a Vacuum Reflow Oven with Preliminary VOID REDUCTION Data

摘要

Vacuum reflow has been around for some time with only slight interest but is now gaining attention in electronics assembly because of a desire to lower and even eliminate voids in solder joints and thermal pads. Initially, vacuum reflow was a batch operation in which boards were placed in a vacuum chamber and heated to melt the solder. During the heating process the chamber was evacuated and the void level was reduced or, in some cases, removed from the solder joint. Sometimes the vacuum was applied when solder approached liquidus, and at other times vacuum was applied during the entire heating cycle. The equipment was expensive to purchase and operate, but the biggest detriment was throughput. Therefore, vacuum reflow was not appropriate for high-volume production. Additionally, there were questions about the need to eliminate voids, with some claiming a small number of voids in joints actually increases their apparent strength. Preliminary results of this trial show vacuum reflow is an excellent way to decrease the void level in thermal pads of MFLs. Levels below 5% were obtained with hold times of 20 sec. and vacuum levels of 20 Torr. Additionally, it was a surprise to learn relatively soft vacuum levels of 120 Torr and short hold times can significantly lower void levels. Additional results will be published by BTU International, The AREA Consortium and the Advance Process Laboratory at Universal Instruments Corp.