Advice on removing and replacing an IC in a PLCC package

[motocoder]

I am working on repairing an Agilent multimeter. One of the ICs on the board is bad and needs to be replaced. I’ve sourced a replacement part, and am planning on swapping it out this weekend.

I’ve desoldered a number of ICs, but I’ve not worked with a relatively fine-pitched surface mount part like this before. I also have concerns about the traces and pads on this particular PCB being relatively fragile.

I do have access to a hot air station, as well as a traditional soldering iron, solderwick, flux pen etc. If anyone here feels they have some expertise in the area of SMD repair, I would appreciate any advice you can share on how best to go about swapping this part out. Some approaches I have seen are:

1.   Cut the pins on the existing PLCC. Remove package, then use soldering iron to remove pins. Use solder wick to remove solder from pads. Resolder each individual pin with iron or using lots of flux and drag soldering.
2.   Use hot air station to melt solder on existing part, then lift part with a pair of tweezers. Use solder-wick to clean up pads, then resolder using soldering iron (drag soldering).
3.   Same as #3, except use hot air station to solder in replacement. Could I just leave the existing solder on the board and reflow it with the hot air station, or am I better off removing the existing solder?

Thanks

[TheSteve]

Cutting the pins always has some risk of pulling pads off as the leads are cut if you're not really careful. If you have used hot air before I'd remove it using the hot air. I would then clean the pads with solder wick, then alcohol, and then hand solder the replacement device in. For PLCC devices I generally solder pin by pin as the pitch is still quite large by SMD standards. For really small devices I have wiped the solder on or soldered 2/3 pins in one shot and it works quite well.

[wraper]

I personally most likely would do number 2, probably 3 if difficult to access the pins with soldering iron.
Cutting the leads of PLCC may be tricky (if no very fine side cutters available) and there is high possibility to lift the pads with mechanical stress.

[McBryce]

If you go for hot air you'll need to well protect any nearby components with Kapton tape. Otherwise you'll end up with a mess. I wouldn't advise cutting the pins, you could easily damage tracks under the IC.

McBryce.

[amyk]

I'd definitely use hot air.

[orion242]

Use hot air station to melt solder on existing part, then lift part with a pair of tweezers.

For the fine pitch, I use preheater/hot air and don't lift it if possible.  Lightly bump it and very carefully slide it off the pads if space allows.  If space is tight, keep the heat to it and lift, after it sides off as many pads as possible.

[edpalmer42]

Search Youtube for 'bios replacement'.  There are lots of videos about replacing motherboard bios chips in PLCC packages.  You'll find demonstrations of your three methods plus a fourth - cut the pins with a scalpel.  I had to replace a PLCC44 chip.  I decided to cut the pins with fine tip cutters.  It worked out fine.  I decided to solder in a socket since the chip doesn't have a good reputation.  That is also covered in the Youtube videos.  The unit is now working fine.

[MarkL]

Another option is Chip Quik.  It works at low temperatures and dramatically reduces the risk of damage to the pads or slipping with a knife.

I usually use it with nothing more than a board pre-heater at 150C positioned underneath the target chip.  150C won't cause other components in the area to reflow, but it's more than enough to melt the removal alloy.

It can take several minutes for the removal alloy to combine with the solder, but eventually the chip lifts off with a suction-cup tool.  Pushing the blobs of alloy around the pins with a toothpick can speed up the mixing process.  And use LOTS of flux.

Can be purchased direct, but the usual distributors (Mouser, DigiKey, etc) carry it too:

  http://www.chipquik.com

[motocoder]

Thanks to everybody who replied. Based on what I heard, here is the plan:

1) Use copious amounts of flux and ChipQuick to lower the melting temperature of the existing solder.
2) After applying the ChipQuick, I'll use my hot air station set to a low temp (150C) and a small suction pick-up tool to remove the chip.
3) Remove solder from pads using solder wick
4) Place some solder on one pad, then place the new chip down and melt the solder on that pad to hold the chip in alignment. Tack down a pin on the other side of the chip, then apply lots of flux and either solder the pins individually or drag solder them.

[wraper]

Thanks to everybody who replied. Based on what I heard, here is the plan:

1) Use copious amounts of flux and ChipQuick to lower the melting temperature of the existing solder.
2) After applying the ChipQuick, I'll use my hot air station set to a low temp (150C) and a small suction pick-up tool to remove the chip.
3) Remove solder from pads using solder wick
4) Place some solder on one pad, then place the new chip down and melt the solder on that pad to hold the chip in alignment. Tack down a pin on the other side of the chip, then apply lots of flux and either solder the pins individually or drag solder them.

This sounds weird. If you have a hot air station, using chipquick makes no sense. Moreover, chipqiuck will contaminate solder on the pads. Solder remains will need to be thoroughly removed by cleaning the pads from solder, then applying new solder and then cleaning one more time. Otherwise solder joints will be dull and brittle. In the end it will be more stress on the PCB than just removing the part without chipquick.

[kripton2035]

I would use #2

[motocoder]

Thanks everyone. I went with the ChipQuick approach. I planned on applying it with my soldering iron and then using hot air to do the final melt and lift the part. However, while I was apply the ChipQuick, the chip came off on its own. The new chip went on fine, but unfortunately, there is another IC that is bad, and that one is no longer sold by Agilent...

[fluxcapacitor]

whats the other bad chip, any part numbers .