Anyone in here interested in electronics

... except that I want to keep the SOIC I am removing...

Well use lots of lead/tin and flux to soften it up and the moment your tweezers separate it, shut off the heat

I have had good results with a solder sucker.

I have loads of Germanium transistors.

I did originally consider something like this approach TBH; there are suggestions about using a length of thin 'non-solder-compatible' wire, pulling under the legs of the SOIC. I also considered using a scalpel blade.

Your suggestion of a thin needle is interesting; thanks. As you say, cutting the legs has other issues...

J^n

I'd say that once you have hot air available to you, all those other methods are obsolete. Hot air it and once it's moving, just pick up the component with tweezers (or a vacuum pick if you have one, they are handy).

Anything which involves mechanical force is at risk of damaging the tracks. If you need to use force, you haven't done the hot air right. The part should slide right off with no force.

There are fancy things you can do with different sized tips (prevents overspill and focuses the heat on a specific area), masking with bacofoil and bottom-heat from a hotplate (means the hot air needs to do less work) but after a bit of practice a simple hot air pencil moved around can be made to do a lot of the same jobs - not as well or as fast but good enough.

Vacuum picks are surprisingly cheap - a basic rubber bulb affair is under £2:

The nice thing about vacuum picks is you can move the component some distance without worry about it falling out of the tweezers, and they can pick up parts like QFPs where there is nowhere to grab without bending legs.

Theo

Hi Theo thanks for these useful (as always, from you) comments. I am a bit curious about the relative dissing of the use of a hot air gun here. I am aware there are lots of variables, and as mentioned I intend to do some practicing, but it does seem to be pretty much the standard approach 'out there'.

My recent employer was doing BGA soldering by hand, which was a surprise to me given the trouble I remember some years ago when BGAs were coming in, but that's progress for you. I do *not* intend to be doing any of that...

Cheers J^n

I have hot air available. No way would I use it for a SOIC, and really, honestly, I've done this hundreds of times.

I did one a few days ago. A 100 pin FPGA salvaged from a scrap PCB and used to replace one on my otherwise working PCB. It wasn't easy, but it wasn't a comparatively massive SOIC either.

I wouldn't call SOICs massive (up to what, 28 pins?) - if they're the same scale as the tip of the hot air pencil then it's possible to direct air at all sides together. Many SOICs are 0.15" wide SO-8, SO-16 etc which are smaller.

I can see more of a problem for jumbo 100+ pin QFPs that are a couple of inches on a side, which are too big to get air at all the pins at once. You need bottom heat, plus there are special tips which are a duct to just the four edges to avoid wasting air on the centre. With the pencil alone you're racing against one side cooling down as you heat the other side.

Theo

Some tips;

get some decent rework flux, and some capton tape so you can protect adjacent bits (desoldering an IC, and blowing lots of *tiny* passives off the board never to be seen again is a tad annoying (DAMHIK)).

I am quite a fan of the "ChipQuick" low melting point bismuth alloy solder. You apply that to the pins of the IC with an iron, and it mixes with the existing solder and allows it all to stay liquid long enough to remove a device without any hassle.

There is another trick that works well for this kind of thing. Grab some flat T&E cable of a decent size - say 2.5mm, and strip down a length of

(you can do it on DIL packages without the wire - just using a large mass of solder and two irons to heat both sides at once)

Thanks for the tips John. I have some Kapton tape and recently bought a syringe's worth of flux.

I had read mention of ChipQuick but had not yet read up on what it comprises; thanks for the info. There used to be a practical joke advertised in children's comics of a metal spoon which melted when used in a mug of hot tea etc. IIRC that was a bismuth alloy? To my surprise, I read that bismuth metal has very low toxicity.

I have found my faulty laptop motherboard for practicing on; I plan on reporting back here after I have done some practicing and had a go with my real microproject...

Cheers J^n

Another trick is to heat pins one by one, and slip the tape under them as you go along.

Thomas Prufer