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I had given a few boards for manufacturing and this is how they’ve come back from the fab. Do I need to reflow these again? Would it be safe to do so? I checked and the pins are not shorted but what is that white substance around the pins? Solder flux?

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enter image description here

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    \$\begingroup\$ Looks like solder paste that did not fully reflow. Try a bit of hot air and see if it reflows to confirm. \$\endgroup\$
    – Unimportant
    Commented Apr 10, 2021 at 12:32
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    \$\begingroup\$ Looks like the board was way too cold. The fab should seriously look into their process and you could consider another fab, given the additional hassle. \$\endgroup\$
    – tobalt
    Commented Apr 10, 2021 at 13:12
  • \$\begingroup\$ Would it be okay to reflow the full board again? \$\endgroup\$
    – user3418620
    Commented Apr 10, 2021 at 14:43
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    \$\begingroup\$ I would say yes. Most Components will survive many rounds of reflow. If you have VLSI logic ICs with very fine structures, those are most susceptible and could be damaged. \$\endgroup\$
    – tobalt
    Commented Apr 10, 2021 at 16:24
  • \$\begingroup\$ It doesn't look GREAT, but it may be OK. I assume it is lead free solder. Lead free solder does not shine as much as leaded solder does, and no-clean flux sometimes leaves a powdery white residue which I think you have on your board. But a few of the SMT passives look like they might have been hand reworked, so that could be a sign that problems occurred during assembly that had to be corrected (which is not unheard of or necessarily cause for alarm...). \$\endgroup\$
    – user57037
    Commented Apr 11, 2021 at 1:23

2 Answers 2

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Reflow a very small lot and inspect the solder joints.

Yes, it's solder flux not completely evaporated.

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  • \$\begingroup\$ Evaporate? Flashed away may be. \$\endgroup\$
    – user263983
    Commented Apr 10, 2021 at 13:53
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You can normally reflow a board like this again without damage, but that looks like it's just flux and probably won't help much (I'm not seeing unflowed solder balls).

I would heat the board up a bit (you don't need to heat it the whole way to solder flow) to soften the flux, and then clean it with appropriate flux remover. Acid brushes and Kimwipes are helpful for this.

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  • \$\begingroup\$ Agree. If you do reflow it, though, it may be a good idea to clean it first with high purity alcohol to see if you can remove any flux residue, and also maybe add some more liquid flux to help insure good flow and no solder bridging. \$\endgroup\$
    – user57037
    Commented Apr 11, 2021 at 1:24

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