mashersmasher

what's the best technique for desoldering chips. i want to take a some chips out of a board (not sure where it came from) and experiment with there usage. i however do not know how to desolder them effectively

dknguyen

The "best" and easiest way would probably be hot air. BUt it's expensive. I have a really hard time desoldering chips once they're on without using multiple soldering irons.

A soldering iron and copper wick is probably your best bet as far as cost goes.

ericgibbs

If you want to try the 'wick' method, strip down a length of aerial coaxial cable and use the screening braid.
If you have some water based flux lightly smear a little on the braid before you use it.

Place the braid on the joint you want to desolder and apply heat to the braid while pressing down with the soldering iron tip,
the excess solder should run up the braid.

When you have desoldered all the ic pins and the ic still wont come out of the pcb
use a pair of small pliers to ease the ic pin away from the track hole..

Do you follow this.?

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jpanhalt

A variation of the hot air method is to use a "soft" flame from a portable propane (or similar mix. ) torch on the back side. I have done that for SMD. Just let the chips drop onto something. Through-hole devices get stuck by their pins and you need to be more aggressive.

Some people have used broiler and/or toaster ovens the same way as the torch, but for me, the torch was easy and available. You can also play the torch on the component side to help the process along. John

killivolt

(Only if you do not plan to use the chip again)
I prefer to use a sharp razor and carefully cut at the edge to the center of the processor. Cutting all the way thru right away is not the best just score it to the center then turn around and score it back repeat this process until you have cut thru them all reverse and begin on the opposite side of the processor.

I do it this way on surface or thru hole if it is thru hole an if the pins have been bent on the other side then use the iron and new flux and solder to bend back to straight as possible.(applying new flux and solder will speed the heating process the old solder will flow much quicker and will keep you from damaging the pads.

It works best if you first used water soluble flux. Never attempt to use water soluble on rosin core or vise versa always stick to one or the other.


Afterward you simply just use the iron tip to remove the leads. Then clean up with braid and wash.


"I've never tried hot air but it sounds good" (all though I have a lot to spare.)

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Blueteeth

I just use a hot air gun, the sort used for paint stripping/heat shrink...as long as its powerful enoug and has some form of temperature contol (ie: more than one setting) it works a treat for completely wiping PCB's of SMT components. Also works for through hole but can be trickier as a lot of the time the pins are bent so that they held in 'mechanically'.

Just my two cents, picked one of these up for 9UKP and I've done a few PC motherboards with them (parts for my bits box).

Blueteeth

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mashersmasher

thanks yalls. i have a propane torch and a small butane pencil so i'll give that a shot. i'll have to practice the braid method on some junk though since that sounds like a good skill for adjustments

3v0

I have been beat up for this by the poeple on the EDA board so use at your own risk.

In some cases I find it useful to apply MORE solder prior to desoldering.

It seems wrong but the solder help conduct heat to the pins where it is needed. Solder is a much better conductor of heat then the board itself. The additional solder may prevent the board from cooking.

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mashersmasher

i've actually tried this on some smaller chips. it works out well sometimes especially when i use my 90w gun instead of the iron. i havn't done this in so very long though that i forgot about it.

Nigel Goodwin

Perfectly standard procedure, I almost always use it, it's particularly good for lead-free solder, apply extra leaded solder and it comes off MUCH easier.

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killivolt

This was my attempt at the same thing but it was lost in all my many words.

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BeeBop

I think this is most useful, especially when the solder you are trying to heat up is old, and don't know why they pounded you for it?

This was an answer expected on a test I did for a job application - the company rebuilt CNC controllers. - Didn't get that one though.

For the OP, it depends on what you are interested in, the board, or the part you are removing. If you are keeping the board (replacing the part) then I would do as killivolt says, and cut the leads to the chip off, then clean up. If you want to keep the part, then if you have through hole parts, either a solder sucker, or braid will work, both work well, if you practice. If the parts are surface mount, then hot air is your best bet. I wish I had a heat gun, but my little butane torch works, if I take care with how much flame, and how close to the underside of the board that flame is. Your butane pencil should work well for this.

crust

There was a post on hackaday a while back about building a hot air rework gun from a bulb type desoldring iron and a air source (which I seem to recall was a fish pump, but not sure).

Bob Scott

I saw that somewhere too. They stuffed the cavity at the end of the iron with solder braid to help conduct heat to the air moving through the cavity.