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47309Re: [SeattleRobotics] SMT toaster oven problems

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  • Randy Carter
    Oct 25, 2012
      The aging factors in solder paste are the solvent in the flux evaporates and the solder corrodes. The solvent evaporating is slowed by chilling the container. The corrosion of the solder is going to make it a little more difficult to solder. Requiring a little more heat and time. Also you may be using too much paste. It's difficult when applying it manually but stencils etc. are difficult to use and expensive for just 2 copies of a PCB.

      The process I use is to heat the board to 95C for 30 minutes to chase out any moisture that may have been absorbed by the components. (I don't have the facilities to reseal moisture packs.) Then I crank it all the way up and wait until 220C is reached then I turn off and open the door, letting the oven cool down. If I'm in a hurry I set a small fan to blow into one side of the oven and allow the heat to escape out the other side until I can pick up the boards with my hands.

      I do have a fair amount of solder balls stuck to the board that are easily knocked off with a pick. I also have a fair amount of solder bridges especially on the finer pitched IC's. Solder wick is my friend here.

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      ---------- Original Message ----------
      From: Tony Mactutis <tony@...>
      To: SeattleRobotics@yahoogroups.com
      Subject: Re: [SeattleRobotics] SMT toaster oven problems
      Date: Wed, 24 Oct 2012 21:15:17 -0700

      Peter, I don't think the solder paste would go bad in a few months if it has been in the fridge. I've used much older paste than that.

      I would make sure to leave the board in the oven until all the solder is melted. Don't worry about the profile. I just turn my oven up all the way (the dial goes up to 500 F) and wait for it to hit temperature. I then put the board in and wait for the paste to melt. When it has all melted (maybe 4 to 5 minutes), I give it perhaps 20-30 seconds and then take the board out to cool. No timing required.

      There may be scattered beads when you are done; just use a soldering iron to clean them up. All you usually have to do is touch them with the tip.

      On 10/24/2012 9:50 AM, Peter Balch wrote: Whe I first tried SMT soldering user a toaster oven it worked wonderfully.

      But now it doesn't. Most of the solder more-or-less melts and the components
      are stuck down but there's a lot of grey goo (i.e. solder paste) left on the
      pcb near to the pads.

      I'm pretty sure I 'm using the same I'm using the same temperature profile -
      it's the same oven and it doesn't have any sort of temperature control. It's
      the same solder paste. So what's going wrong?

      Am I seeing an effect of the solder paste ageing? I've kept it in the fridge
      as one is supposed to but it is now a few months old.

      Peter
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