[patricklang]

I'm looking for a good method to remove and later resolder a SMD chip on my Sonica (see sonica mod thread) and am looking for suggestions.

From the instructions, chip-quik sounds like it is well-suited for cheap removal, but it sounds like the chip-quik 'alloy' is left in a glob on the removed chip, making reattaching difficult.

Does anyone have other suggestions? I don't think I'd trust my old 15w radio shack to do a good job. I can probably borrow a friend's metcal w/ fine tip in a few weeks if nothing else...

 

[MisterX]

I am assuming you're talking about removing the DAC.
Fill the spaces between the legs of the chip with solder.... You want to end up with a big blob of solder that covers all of the legs on one side of the chip.
Heat that solder blob and lift one side of the dac off the board. Repeat for the other side and remove the excess solder with a desoldering bulb.
Clean up the solder pads with desoldering braid and you should be all set to solder in the replacement.

 

[hadron]

I use an old heavy duty Weller that takes 1/4" tips, made a chisel tip out of a strip of copper sheet. Worked pretty good the few times I've used it since you can heat all the pins on one side at once, a small screwdriver helps to lift the pins for removal.

 

[Wodgy]

IMHO none of the techniques suggested so far will allow you to remove the chip undamaged, unless you're very lucky. SMD devices have much less area to dissipate heat than through-hole devices, and if you heat all the pins on one side at once, you really do risk roasting the chip.

Your greatest chance of success is to desolder pin-by-pin, in the same order that you'd solder it, i.e. pin 1, then the pin on the far opposite side of the chip, then pin 2, etc.

 

[beamrider]

Quote:

Originally posted by patricklang I'm looking for a good method to remove and later resolder a SMD chip on my Sonica (see sonica mod thread) and am looking for suggestions. From the instructions, chip-quik sounds like it is well-suited for cheap removal, but it sounds like the chip-quik 'alloy' is left in a glob on the removed chip, making reattaching difficult. Does anyone have other suggestions? I don't think I'd trust my old 15w radio shack to do a good job. I can probably borrow a friend's metcal w/ fine tip in a few weeks if nothing else...

I've used chip-quik, and it is a godsend to me. Doesn't glob up on the chip at all here, it seems to glob on the board itself, but a solder sucker makes short work of that.

 

[hadron]

I find that doing pin-by-pin desoldering leads to holding the iron on each pin for many seconds too often, and you still sometimes have to bend the pin off the board, this is a real pain for the inner ones. Doing each side all-at-once has the advantage of needing no more than 2-3 seconds with minimal bending. In fact, Weller makes tweezer stations for SMD with tips up to 18.5 mm that heat all the pins at once. This is not a problem as long as you're quick about it, if you do this often and are burning chips then it might be worthwhile to get a small rework station.

 

[greyhorse]

The method we used at work for anything up to a 16 pin IC was basically the same as hadron's. Our soldering iron tips were a little more professional of course; we used Hakko's K(knife)-type tip.

We’d dollop some solder across the blade, and run the blade back and forth across one side of an IC till all the joints on that side were melted. Then we’d do the same on the other side, and quickly return to the original side to repeat the process again. If all went well, by this time both sides were hot enough that all the joints on the IC were still melted. All that was needed to remove the IC at this point was to lift the blade; surface tension would carry the IC along with the blade.

The K-type tip is also probably the best tool for removing chip type parts like resistors and capacitors because you can apply heat to both sides of the devices at once. You simply put a bit of solder on the blade, and lay it across both pads of the PCB and slide the blade to the side. Surface tension does the rest.

Once you get used to using the K-type tip, it’s faster and more consistent than using SMD tweezers, which are near useless when they wear out even a little. This is of course only true for smaller ICs, but the K-type tip definitely has its place.

The K-type tip is also my favourite tip for soldering SMD ICs. You put a bit of solder on a corner pad, align the IC, and solder that corner pin to properly position the IC. Then you feed solder to the blade while running it along the IC legs, and then pull the tip away. The large surface area of the tip does a great job of pulling off excess solder, so the amount of solder you use becomes largely irrelevant. Using this method, you get perfect joints pretty much every time. You should be able to solder anything down to QFPs with this technique, though these require a bit more care.

*edit* Please be aware that this desoldering technique requires a lot of practice. At first your movements are clumpsy, and you end up applying too much heat. When you finally do remove the IC, you end up splashing solder all over the PCB. Find junked boards at any place you can, and practice. A lot.
*edit ends*

 

[JohnFerrier]

Quote:

Originally posted by patricklang I'm looking for a good method to remove and later resolder a SMD chip on my Sonica (see sonica mod thread) and am looking for suggestions.

I work with a guy that uses a heat gun for soldering and desoldering (even over a nice RF MetCal setup with lots of tips and dual element devices). He can't do everything that way, but prefers it when possible. And he has a reputation for quality work. I think a heat gun would be okay for desoldering. Soldering with one just doesn't seem to work for me.

For desoldering, he slowly works the small nozzled heat gun around and around (starting away from the board and then draws near). He watches for the solder to liquify then pops the chip off with tweezers. He does this with 176 pin PLDs with pins on all four sides.


JF