The Black Art of Reflowing

[bigbeark]

My buddy's Toshiba laptop died after 3 years. No video. The little shop around the corner wanted $200 to fix it. I smelled oven reflow and told him to just replace it.

I searched the web and found all kinds of people who successfuly resusitated their laptop boards by preheating an oven to 385F and cooking the board for 5 minutes, with the board resting on balls of tinfoil on a cookie sheet.

Now with the epidemic of failures caused by ROHS solder, I'm wondering if anyone here has done this with a desktop board? I'm thinking electrolytics would pop or have their life severely shortened. Wouldn't the PCI headers melt? One good thing, I guess, the heat would be uniform and controllable.

A heat gun could be deadly. I used to re-pad saxes with one, and was always impressed how quickly the thing could melt pad shellac.

Any experiences pro or con? Damage to the board? I know chips can run hot, but this seems too hot!

[stj]

Re: The Black Art of Reflowing

you try that shit with a board that has parts on both sides and you will end up with a pile of "spares" on your cookie tray.

[shovenose]

Re: The Black Art of Reflowing

I would be interested to know more about oven reflowing too...

[Th3_uN1Qu3]

Re: The Black Art of Reflowing

you try that shit with a board that has parts on both sides and you will end up with a pile of "spares" on your cookie tray.

Care to back up your claims? I did it on several boards including a DV9000 motherboard w/6150 and i haven't seen that laptop in 8 months. Come to think of it i also have to do my DV9000 w/8400GS since it's been acting up a lot lately, but i'm too lazy. As long as it still boots up i'll leave it alone. Anyway i've been using 210-230C, 390 seems a bit excessive and you could melt other things. If you see flux over the joints when you pull the board out, then the temperature was high enough.

Physics laws say there is something called surface tension. Look it up. Unless you're dumb enough to put the board in chipset side down, nothing will fall off. And actually, that's the very way they are done at the factory.

[mockingbird]

Re: The Black Art of Reflowing

Yes, he's wrong about dual-sided PCBs, people do it all the time with videocards.

Regarding devices with electrolytic caps, like motherboards for instance, many times it's only the northbridge that needs reflowing, so do you really want to desolder all the caps and then risk melting the plastic?

Regarding 6150, I blowtorched the northbridge, that was sufficient.

[Toasty]

Re: The Black Art of Reflowing

<snip>...Anyway i've been using 210-230C, 390 seems a bit excessive and you could melt other things...<snip>

He said 385°F which is 196°C

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Hot air with aluminum foil shields built to protect caps and other parts/plastics is far safer than oven reflow attempts.

[Th3_uN1Qu3]

Re: The Black Art of Reflowing

He said 385°F which is 196°C

Now that's more like it.

Hot air with aluminum foil shields built to protect caps and other parts/plastics is far safer than oven reflow attempts.

Have to disagree with you here, i've had a couple mess-ups with the hot air gun. On boards that were out of hope anyway, but still. The hot air gun is best for other SMD parts not BGAs.