Hi to all, I'm a small repairer and almost always all the repair go ok. Sometime I try to re-weld one pcb. I add flux and then use soldering iron or hot air. The pcb is working fine for a couple of days and then stop again. Afretr repeat the job it turn ok for some days and then stop working again.
Any suggestions?

 

Hi to all, I'm a small repairer and almost always all the repair go ok. Sometime I try to re-weld one pcb. I add flux and then use soldering iron or hot air. The pcb is working fine for a couple of days and then stop again. Afretr repeat the job it turn ok for some days and then stop working again.
Any suggestions?

Yes.
First thing is you tell us what is the instrument, make and model.
Second thing to do is to locate a circuit drawing.
Third thing to do is to document what you see, hear, smell, feel by touch, history and condition of the unit, what it does and does not do.
Fourth thing, for help on AAC, is to post photographs.

 

We would need a lot more information and exact details and nature of what you are trying to achieve by the repair.

 

Hi to all, I'm a small repairer and almost always all the repair go ok. Sometime I try to re-weld one pcb. I add flux and then use soldering iron or hot air. The pcb is working fine for a couple of days and then stop again. Afretr repeat the job it turn ok for some days and then stop working again.
Any suggestions?

I would suggest diagnosing specifically what does not work, then implementing a means of effective repair. A ‘not working’ item often needs to be handled carefully, as it suddenly working, without our understanding, might be luck, but not a repair.

 

they was 2 instrument panel of different car. One of them was off at all the second have many check lamp on without any reason.
After reweld both them start working for a wail then die again. After a second reweld work for some days and die again. then I just stop trying. they are smd. I usually are able to handle without any problem with lqfp, tssop, and other small package.

 

Hi to all, I'm a small repairer and almost always all the repair go ok. Sometime I try to re-weld one pcb. I add flux and then use soldering iron or hot air. The pcb is working fine for a couple of days and then stop again. Afretr repeat the job it turn ok for some days and then stop working again.
Any suggestions?

I would also consider damage to one or more of the PCBs via holes.
Welding causes an enormous z-axis strain on the board and if you can locate the path that has the defect, it would be worth checking continuity on the vias that you can see (if there are blind/u vias, than the checking gets tougher.

 

some of them are multilayer

 

some of them are multilayer

Multilayers are certainly more susceptible to innerlayer separations due to thermal excursions. A small crack that forms can close and open even as a result of card bending or even small mechanical pressure