suprising smd reflow fix

[peace brainerd]

My wireless usb card took a severe blow this morning. Something actually fell on top of it and it quit working. As I was removing/replacing it I noticed that the connection status in the system tray was erratic. Hmmm. Maybe I got lucky and just broke a connection at the usb port on the pcb. I got inside and prodded around. I microsurgically resoldered the pins on the usb socket. The card still connected to the laptop erratically as I very slightly flexed the pcb. I continued along each trace and gently pressed each smd component as I watched the system tray and could get none of the individual devices to indicate a broken junction.

I went ahead and carefully resoldered the resistors nearest the usb connection. Still no fix. Every time I gently flexed the pcb I'd get an erratic connection. I suspect that this pcb has an inner trace layer and something got jarred at a connection somewhere, or else a device got cracked and ruined. I tossed the card in the trash. About an hour ago I suddenly thought that gee, these whole boards go through an (albeit extremely well controlled) oven that flows solder on the whole board. What could it hurt after all to drag it out of the trash and giv'er a whirl with my heatgun? What are the odds that I'd get in the temp range to flow solder without destroying the ICs?

I'll be darned. I hit it with high heat for about four seconds, until I could actually see the solder shine, and then let it cool very gradually. It is an extremely small board so I was able to do both sides with a single shot each.

I'm using it right now. In fact in seems never to have worked better! Did I just get very lucky?

[TheMG]

That's the thing with SMD... solder joints are so small it can often take a microscope to spot a bad one.

Likely, an already weak solder gave way during the impact, and lifted off the board no more than a fraction of a millimeter.

[trodas]

Very lucky indeed.

I have bad connection like this on one of my old mainboards and I did not yet bought a hot air gun to attempt to fix it. It is also close the the connectors that are from plastic, so, I'm affraid that I have to shield them from the hot air somehow...

And on top of this, this faulty connection if bellow the chip itself (it looks like the DDRII ram's with BGA chips. I see nothing from the top.

I know that I have to desolder the caps around first to not overheat them, but these connectors... well, they must be protected