On 1 February, Victor wrote: > Hi, > I am looking for info. or prices of the low temperature solder pastes? > Are these solder pastes used in shop floor at all? What is your opinion > in using this ? > Thank you very much. > Best regards, > Victor Hi Victor! The last time I looked into using a low temperature solder paste was a few years ago on a dense double-sided board that had J-leaded parts on both sides. I was worried about losing parts on the second-side, so I was thinking about doing a "step-solder" process. I was going to do the second-side with a low melting temperature alloy so that I didn't have to worry about the first side becoming liquidous. That's until I started checking the prices out...whooo-doggies! The two metals that I was looking at to alloy with cost BIG BUCKS! It was Indium and Bismuth. To give you an idea what it was going to cost, I weighed the board with and without paste to get an idea of how many grams of paste I was going to print on each board, and it worked out to around $20-30 per board using either Indium or Bismuth! MAN! So needless to say, I didn't use it. I've heard a few negative things too about using bismuth or indium alloys...for one thing, the joints will be real dull, gray looking...not shiny at all, and I've also heard that the joints will be pretty brittle. One of the neatest things I've seen a bismuth alloy used for is with a little kit called "Chip-Qwik" (I think that's how it's spelled). It's basically a bismuth alloy that you can use to remove parts with. You can use a single tipped soldering iron and remove say a 208-pin QFP! You take this special bismuth alloy and bridge all the leads together with it, and that mixes with the solder fillets that were already formed, which lowers the melting temperature so much that the residual heat left from bridging all the leads together keeps everything liquidous for a couple of minutes, and you can pick the part up with your fingers and set it in the palm of your hand without it burning you. The liquid solder can be put into your hand too...it kinda' acts like mercury until it cools...you could probably win some bar bets with this stuff (GRIN ;^D) "Why would someone want to use this alloy to remove parts?" you may ask. I think it might be useful if the PCB was very, very expensive and you don't want to risk heat damage to the PCB removing a defective part, or vice versa...removing an expensive part without damage. __\/__ . / ^ _ \ . |\| (o)(o) |/| #------.OOOo----oo----oOOO.-----# # Steve Gregory # # SMT Process Engineer # # The SMT Centre Incorporated # # [log in to unmask] # #________________Oooo.__________# .oooO ( ) ( ) ) / \ ( (_/ \_) *************************************************************************** * TechNet mail list is provided as a service by IPC using SmartList v3.05 * *************************************************************************** * To unsubscribe from this list at any time, send a message to: * * [log in to unmask] with <subject: unsubscribe> and no text. * *************************************************************************** * If you are having a problem with the IPC TechNet forum please contact * * Dmitriy Sklyar at 847-509-9700 ext. 311 or email at [log in to unmask] * ***************************************************************************