On Mon, Jun 21, 2010 at 7:10 PM, Roger Weichert wrote: > Hi guys, this is a great thread and very helpful. Thanks. > > > > So you're saying that once you've soldered the device in, you then apply > more flux, and reflow it. > > What sort of hot air pencil are you using? > > What flux do you use? > > How long does it take to get hot enough to reflow the device so that it > aligns? I would be nervous about overheatin the ic. > > How big (how many pins) are the devices you use this technique with. > > Thanks again for the education. > > Regards, Roger > Roger, Yes, I'm soldering the package, allowing it to cool then reflowing with hot air. If the ceramic under the metalization of the "leads" on the LCC packages isn't up to temp, wetting seems to be poor at times I'm using the Weller HAP200 that came with the WR3000M I use at work, with the airflow usually around ~15-30% no real way to quantify that, just low enough to not blow the chip around :o) I use a bigger tip in it ( ~4 or 5 mm) and it looks as if this accelerometer is in the same package http://www.sparkfun.com/commerce/product_info.php?products_id=843 I'm using some kester RMA flux, since I'm using 63/37 Sn/Pb solder, It may not be the best for high production stuff (easier to clean, or no clean may work in some applications) but lets not get side tracked onto a flux debate, whatever works for someone works. On just a bare board, without heavy ground planes or heat sinking, I'd say 16 SOIC is about as big as you want to go without specialized tips, and just a big nozzle and a lot of hot air, as for overheating and how long, your IC manufacturer should have at least some profiles for reflow, to get at least a rough idea on how long you can heat it and you can actually heat too fast, you don't want to just max the hot air pencil out and burn the crap out of it. Some of the fancy pants hot air rework stations have a thermocouple to put on and it makes the chip follow the programmed temp profile. If you're fighting with big ground planes or thermal pad on the bottom of an IC, preheating can work wonders. If you're populating a bare board, then a simple hot plate can get the chips and board up to a warm but safe temp (I.e. the chip is fine at that temp for a while, it wont be damaged) and just use the hot air to get the chip to reflow. IR is a lot better for preheating populated boards, but its $$$$ With a WR3000M, a microscope, and some good tweezers, I've been able to rework anything from 0402 passives, small chip-scale stuff, and some smaller (10-12 mm ) BGA chips. Weller makes a shroud/pickup kit for the WR3000M that has a few different metal shrouds, and a spring loaded plunger with a silicone suction cup on the end, hook it up to the vacuum pickup on the base station, and add flux, and heat until all the leads flow, and the plunger gently lifts the chip off the board. With the shrouds, you can work larger chips, but if you're doing a lot, I'd suggest a proper hot-air station that accepts tips for different packages to direct heat at the leads. Time and practice :) Plus if you're using rosin flux, when smoke starts pouring off the board, you're probably a little on the hot side :o) -Jon H. -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist