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Is it possible to place components on both sides of the board if I'm doing DIY toaster-oven style reflow soldering? I would think that doing the reflow twice (for the other side) might overheat the components already soldered on.

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    \$\begingroup\$ Any particular reason? \$\endgroup\$ – Thomas O Oct 20 '10 at 14:59
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    \$\begingroup\$ It's always going to be difficult, either needing careful application of heat or some kind of glue. \$\endgroup\$ – Toby Jaffey Oct 20 '10 at 15:02
  • \$\begingroup\$ I've decided it will be best to place the majority of components on the top side, but the occasional component on the bottom side which will be added by myself manually using my temp-co soldering iron. \$\endgroup\$ – Thomas O Oct 22 '10 at 22:05
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    \$\begingroup\$ We do double sided boards in a toaster oven. No need for epoxy at all. The components won't fall off even if the solder melts. \$\endgroup\$ – Rocketmagnet Mar 31 '12 at 16:36
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    \$\begingroup\$ Double sided boards here too, no epoxy. Takes a pretty heavy component to fall off. 100 pin qfp won't fall off in my experience. \$\endgroup\$ – Erik Friesen May 23 '14 at 22:56
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I have seen this done with a two step method.

The most professional way I have been taken part in involved all of the components have a bit of glue sticking them down(technically epoxy). The oven then would heat the top side to the correct temp, then the board was flipped and the board had the top heated. This was being used by a firm that created products exclusively for the military and I believe had strict requirements on reliability and I believe their oven method was very reliable.

I have also seen methods where people use high temp epoxy and then just bake the whole thing at once. You need things lined up carefully because the epoxy will stop things from moving around and normally during reflow parts move into their proper position on the board almost automatically.

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  • \$\begingroup\$ So. Reflow one side, apply epoxy, reflow other side. Sounds simple enough. :) \$\endgroup\$ – bjarkef Oct 20 '10 at 15:01
  • \$\begingroup\$ Can't hurt to try it. I hope it works well for you. \$\endgroup\$ – Kortuk Oct 20 '10 at 15:09
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    \$\begingroup\$ Is that right? Wouldn't the steps be 1. Apply epoxy to components on side A 2. Reflow side A 3. Reflow side B? If the first side doesn't have epoxy, the parts are going to fall off. It doesn't matter if the second side has epoxy. \$\endgroup\$ – endolith Oct 20 '10 at 20:28
  • \$\begingroup\$ I had a feeling that he was not going to place the second set of components until he had reflowed one side. there are 8 million ways to approach this. \$\endgroup\$ – Kortuk Oct 20 '10 at 21:10
  • \$\begingroup\$ I have heard of people trying to using solders that have different melting points and using a different heat profile for each side, but I haven't actually seen any success doing it this way in house. \$\endgroup\$ – Kellenjb Oct 21 '10 at 2:59
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I've found that most components will be held in place just by the surface tension of the liquid solder, when run through the re-flow oven inverted. You can get about 30g per square inch of pad area before the component will actually drop. If you do have a larger component on one side you run that side second. You only have to brace components if you have large components on both sides.

Use Kapton tape or a Teflon tape wrapped around a larger component to thermally shield it and prevent re-flow.

Make Jigs out of scrap FR-4 from the edges of your panelized boards. Components that won't be held by surface tension are usually taller than most of the components on a board. This means you might be able to jig it so that the boards weight rests on your heavy component pinning it in place.

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