Advise needed in fixing poor PCBA service soldering  - Page 1
Forum section: electronics / general

author: V_King
author_rank: Regular Contributor
timestamp: September 13, 2023, 09:55:01 am
content: 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

author: Shonky
author_rank: Frequent Contributor
timestamp: September 13, 2023, 10:06:00 am
content: 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.

author: Psi
author_rank: Super Contributor
timestamp: September 13, 2023, 10:18:31 am
content: If you do a reflow, add a good amount of flux.

author: DavidAlfa
author_rank: Super Contributor
timestamp: September 13, 2023, 01:00:44 pm
content: Start with a thin flux layer, if you add too much it'll boil and scramble the parts making it much worse than before.

author: SMTech
author_rank: Frequent Contributor
timestamp: September 13, 2023, 01:57:08 pm
content: Quote from: DavidAlfa on September 13, 2023, 01:00:44 pmChoose 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).

author: jmelson
author_rank: Super Contributor
timestamp: September 13, 2023, 03:42:02 pm
content: Assuming this is some kind of gull-wing parts, like SOIC or leaded flat pack, apply water-soluble flux everywhere that needs fixing, then allow to dry most of the way. (The flux has alcohol solvent, so dries in a few minutes.) Then, reflow in oven, and wash in running water after cooling. I assume there is solder on the pads already, just that it didn't wet well.Jon

author: Jackster
author_rank: Frequent Contributor
timestamp: September 14, 2023, 12:41:33 am
content: Quote from: V_King on September 13, 2023, 09:55:01 amI am in Longford, Derbyshire. It is a few miles West of Derby city.You are welcome to come over when I have the oven running and throw them in.I don't think this will fix your issues but if you want to give it a go, you are welcome to try.

author: V_King
author_rank: Regular Contributor
timestamp: September 14, 2023, 06:52:12 pm
content: Quote from: Jackster on September 14, 2023, 12:41:33 amThanks, I had a look at your website, it looks good. We might be able to send work your way to avoid the issues above, if the cost is vene remotely comparable. How is it best to reach you?

author: Jackster
author_rank: Frequent Contributor
timestamp: September 20, 2023, 10:31:46 am
content: Quote from: V_King on September 14, 2023, 06:52:12 pmYou can email me via jackpcba.uk