Electronics > Beginners
Double sided reflow soldering
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homebrew:
Hi,

I need to reflow a double sided board with components on both sides. I've done that in the past but only with some passives on the bottom and all the heavy stuff on the top. Obviously I went with the bottom side first and reflowed the top in a second pass.

However, this time, I do have an LQFP64 (an STM32) on the bottom side.

Question: Will it fall off during the second reflow? If so, how could I prevent this?

Best,
homebrew
0xfede:
Hi homebrew,

I'm pretty sure that this paper will help you:
https://www.jim.or.jp/journal/e/pdf3/47/06/1577.pdf

Best,
0xfede
wraper:
Yes it will fall off. You need to place SMT adhesive under the IC to prevent that.
johnmx:
You can use low melting temperature solder paste for the second pass (side).
This way the solder paste of the other side (first pass) will not melt.
Of course I don't recommend this for production, only for prototypes.
homebrew:
Thanks for the input.


--- Quote from: 0xfede on April 27, 2018, 08:37:52 am ---Hi homebrew,

I'm pretty sure that this paper will help you:
https://www.jim.or.jp/journal/e/pdf3/47/06/1577.pdf

Best,
0xfede

--- End quote ---

A scientific paper is always a nice answer to a question :-)


--- Quote from: wraper on April 27, 2018, 08:55:04 am ---Yes it will fall off. You need to place SMT adhesive under the IC to prevent that.

--- End quote ---

Classic practitioners vs. scientific debate - the paper mentioned came to the quite opposite conclusion, even for an QFP208. They deliberately needed to add weight in order to make the components fall.

Maybe I'll try it with one of the boards and the post the results here ...
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