[log in to unmask] wrote: > > Hello, > > Many articles recommend rapid cooling rate during rework for reliable > solder joints. What cooling rate can be readily achieved with most > rework stations? One article recommended 100 C in 5 seconds, is it > reasonable? I thought it would be hard to achieve such a rapid > cooling. > > Thanks, > > Yuan Yuan, I have recently completed characterization of our Air Vac DRS22 machine for replacement of Amkor's 352-ball and 432-ball Super BGA packages. I was able to force cool from 212 C (measured against the underside of the BGA with a 5-mil diameter coaxial thermocouple) to 185 C in the first 1/2 minute; 185 C to 176 C in the next 1/2 minute; 176 C to 141 C in the next 1/2 minute and 141 C to 119 C in the next 1/2 minute. I am restricted by company guidelines to 30 PSIG air pressure on the machine which impacts maximum air flow rate available. The nozzle for the super-BGA package is quite large, which supports maximum air flow, thus a "fast" cooling rate for this machine. A quick calculation shows a cooling rate of 36 C in the first minute (it took 2-minutes to cool 93 C which is about 24 times as long as your target of 100 C in 5 seconds). My experience...our DRS22 rework machine can't get close to that cooling rate. My opinion... none of the others can either. Maybe some of those metallurgists out there will tell us just what the tradeoffs are between cooling rates of 100 C per 120 sec. vs 100 C per 5 sec. Gary P. -- Gary D. Peterson _/_/_/ _/ _/ _/ SANDIA NATIONAL LABORATORIES _/_/_/ _/ _/_/ _/ _/ P.O. Box 5800, M/S 0503 _/_/ _/_/_/ _/ _/ _/ _/ Albuquerque, NM 87185-0503 _/_/_/_/_/_/ _/ _/ _/_/ _/ Phone: (505)844-6980 _/ _/_/ _/ _/_/_/ _/ _/ _/_/_/_/ FAX: (505)844-2925 _/ _/_/ _/ E-Mail: [log in to unmask] _/_/_/