SMD chip soldering



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SMD chip soldering

Postby WORMDIRT » Thu Jan 31, 2019 6:06 pm

I'm trying to put a new CPU in a broken microkorg I bought. And it's just not working. Anybody want to take a shot at it? I'll pay kinda handsomely.
Maybe some advice is in order as well.
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Re: SMD chip soldering

Postby crochambeau » Thu Jan 31, 2019 6:45 pm

Have you tried solder paste and a heat gun? Are you using flux?

Depending on what kind of package it is, a lot of SMD is hand solderable. Is it showing you any leg?

I've also had success with the old "solder bridge around the entire fucking thing and then wick the legs clean" approach. The key to any hand operation is to stitch, or pull your iron away from the part, this will draw material away/off the PCB resist instead of across it.
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Re: SMD chip soldering

Postby WORMDIRT » Thu Jan 31, 2019 7:19 pm

crochambeau wrote:Have you tried solder paste and a heat gun? Are you using flux?

Depending on what kind of package it is, a lot of SMD is hand solderable. Is it showing you any leg?

I've also had success with the old "solder bridge around the entire fucking thing and then wick the legs clean" approach. The key to any hand operation is to stitch, or pull your iron away from the part, this will draw material away/off the PCB resist instead of across it.


I'm using a nice Weller station and flux. Lining it up and not bending pins is my problem right now. I'm a little ham fisted for delicate work like this. I'll try the flood and wick approach
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Re: SMD chip soldering

Postby crochambeau » Thu Jan 31, 2019 7:54 pm

I've done some stuff like this:

Make sure the PCB footprint is clean, then apply flux.
I'll tin one corner pad, drop and align the IC, and then tap that leg with the iron to make a TEMPORARY joint.

At this point I'm not concerned about a good or clean solder joint, I just want to pin the part so it doesn't move.

I'll bust out whatever optics I have on hand (I like using an old 50 mm lens from a camera, but anything that lets you SEE should work) and adequate light. Then I'll inspect everything for lining up. MINOR stuff can usually be nudged, but you want to avoid stressing that leg out too much.

Everything good? I'll tack down an opposing corner, maybe a few pins worth, then redo the first solder joint I did to release any stress on the joint and to make sure I don't forget the half assed joint. Then I'll rip through each side, usually ignoring any solder bridges until the everything is connected, then I'll flux some solder wick and clean up any excess.

The biggest PITA aspect is handling and lining stuff up.

For denser packages, laying in some solder paste across the strip of pads is easier, as it'll sort of stick the legs into place, then you can apply heat. I don't have a whole lot of experience doing that, as most of my work is still through hole, but that's the direction I'll go when I catch up to the density of SMD.
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