Electronics > Manufacturing & Assembly

Advise needed in fixing poor PCBA service soldering

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V_King:
Hello,
Got a bad batch of boards from a chineese PCBA service (well known to everybody!). Good 1 out of 3 of boards are not working and looking at the solder joints through microscope you can see the solder joints look cold. Worry is the rest will fail soon too. I don't want to discuss the chineese supplier issues or any rants, just want to see if this batch could be somehow saved inhouse? I don't have time and energy to deal with chineese "customer service".

I wonder if it would work just putting the boards into one of those cheap reflow ovens to get through the heat cycle again, where solder joints properly heat up? I don't know if it is ok to keep reheating boards after initial assembly. Would components or PCB board itself get affected going through heat cycle again?  There are too many components to do it by hand.
Or any other suggestions?

Also, I wonder if there is anybody Leicestershire/Nottinghamshire/Derbyshire way in UK with a reflow oven, whom could help in this case? I do not see myself using the reflow oven again, so better pay for the beers while the oven reflows the handful boards I've got.

Please keep comments relevant to the subject. Thanks

Shonky:
A good photo would help.

You might even get away reflowing with just some hot air.

Reflow of the whole board may be feasible too.

Psi:
If you do a reflow, add a good amount of flux.

DavidAlfa:
Start with a thin flux layer, if you add too much it'll boil and scramble the parts making it much worse than before.

SMTech:

--- Quote from: DavidAlfa on September 13, 2023, 01:00:44 pm ---Start with a thin flux layer, if you add too much it'll boil and scramble the parts making it much worse than before.

--- End quote ---

Choose your flux wisely, when put through a reflow oven some make an almighty sticky black mess, the flux in solder paste is unlike the fluxes often used for rework.

As per @Shonky, a picture would help, people frequently diagnose things like cold joint, poor reflow, or dry joint when in fact they mean something else entirely. Putting something back through reflow will melt solder that didn't quite melt the first time, it won't magically solder a joint with insufficient solder or rectify a tombstoned device (in fact they'd probably get worse).

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