Development of a rectangular dual-beam optical unit for YAG laser soldering of fine pitch flat package IC's.

摘要

We have developd a new optical unit for YAG laser soldering of high-density, super-multiple-pin LST 's. The unit enablesus to irradiate facing lines of LST 's lead arrays simultaneously with two rec -tangular cross-section laser beams. We evaluated the unit by using an experimental assembled systemcomposed of two rectangular robots, a velt conveyor, and a mounting system with pattern recognitioncapability. The following results obtained with 100 pin flat package IC 's are summerized asfollows (1) The most suitable solder amount was 2.5mg/cm-7mg/cm when solder paste was continuouslydispensed across lead pad arrays and subsequently fused by rectangular laser beams. (2) Four lines of flat package IC lead arrays were soldered in 4 seconds, which is less than half of thatfor a previously developed conventional laser soldering method. (3) The photographs taken duringlaser soldering revealed that the flux in the solder paste evaporated in the first quarter of a unitsoldering time; the dispensed solder then fused and flowed to leads and pads during the next quar-ter, and subsequently they got wet completely with the fused solder in the following half of the unitsoldering time. (4) Suitable laser irradiation time for the FPIC 's having different pitch and volume ofleads was found to be approximately proportional, at a constant laser power to their lead volume perlead pitch.