Any advice on depopulating SMT boards?

[Mark Hammer]

Armed with those Wavefront/Alesis chips, a tube of SMT TL081's that Pete Snow graciously bequeathed me, and a box of old ISA cards that will doubtless never get sold in a garage sale, I thought I'd take a stab at the world of SMT/SOIP building.  My first step was to pick up some pretinned "surfboards" at a local place.  I'm ready to try and make my own (scanned the surfboards and converted them to a glossy photo paper mask, not etched yet, though, so I may well be wasting mytime).

I'm wondering how to safely get those tantalizing 386's off the modems, and the quad op-amps, caps and comparators off those old 8-bit soundcards.

Any advice?  I have a heatgun, dental picks, and assorted other implements.

[KE4NYV]

I usually use the hot air bonder/reflower I have at work, but I doubt you have one.  So, the heat gun is your next best option.  Basically heat the parts up to the point where everything is molten and then tip the board and tap on a hard surface and basically "knock" everything off.  You'll find most of the parts will survive this method, SOME may not.

Good luck.

[Mike Burgundy]

A gas-torch will also work, as long as you don't set it to too hot a flame. A friend of mine used to do this to (more fragile than yer regular opamp) memory chips in massive quentities - none suffered damage, or so he says.

[remmelt]

You could try making your own hot air pencil! Looks cool, huh?

If you are interested, I have some SMT chips I got in a TI sample that I'm never going to use anyway. Drop me a line. I have 10 TL074s and 10 4558s.

[Peter Snowberg]

I've tried just about every "hack" method available and they all pale in comparison to SMD tweezers & hot air rework pencils.

After removing a few 386s from modems, one thing they all seem to have in common is they're the low voltage versions of the chip which are of much less utility for amp building. The SOIC packages are also rated for lower power handling. That said... I drive my Leslie at GOOD volume with a modem amp running from 9V.

SMD is about reflow soldering and the solder coating of commercial PCBs is very helpful. Tinned off-the-shelf surfboards will give you much better luck than untinned DIY boards, but if you polish a DIY board with 0000 steel wool and then cover all the traces manually with an iron you get something very usable.

If you want to remove SOIC-8 packages, squish a cheap iron tip into a fan the same width as one side of the package. You might also consider using a big Weller gun style iron... one of the ones that contains a big transformer with the two prong tip/element. You can crush the tip with vice grips to increase the width and then file to finish. Heat the iron (a couple of seconds for the Weller gun), add enough solder to almost drip off the tip, bring that into contact with all the pins on one side of the device and then pry up with a little screwdriver to lift one side of the device. Now use some solder wick to remove any excess solder from that side. Heat the other side and the device falls off.

This will not work for resistors, caps, or other two lead devices. In these cases you can try heating both sides by alternating with a regular iron but heat damage comes to some of the caps quite easily. Tweezers are by far the best for these. I can't believe I held out this long without them. There is no going back! They also work wonderfully for desoldering regular resistors, diodes, capacitors, and transistors too!

With all soldering but with SMD especially, make sure you always have plenty of flux!!! I cover the bare PCB pads with flux paste on a Q-tip, place the part, and then touch the junction to reflow the solder already sitting on the board. The leads "sink" into place under the weight of the iron.

I prefer building in SMD. It's just easier.

Once you get smaller than 0603 packages it starts to get a bit silly for DIY, but 0603 and SOIC as well as even smaller IC packages are easily within the reach of anybody with a 1/32" or a 1/64" tip, some tweezers, some fine solder, some fine solder wick, and some flux paste.

I just saw a picture of what could be titled SMD Vero too! :shock: News at 11.

[Paul Marossy]

I forgot where I saw this page, but one guy split the end of his RadioShack soldering iron into a two-pronged fork for desoldering SMT devices. He claims that it works really well.

[The Tone God]

I'll second most of what Peter said. Use the right tools if your serious.

The heat gun does not work that great for this application. You have to heating the whole board to the tempature for the solder to melt. You can damage componets, the board, and yourself at that point. It could also release some chemicals which I would suspect are not good for your health. It may also set off your fire alarms depending on which type you have. :roll:

Andrew

[puretube]

imho, there are 2 diff. problems: melting/absorbing the "sodder",
and: "loosening" the (possible) glue.


One (2) thing(-s) I like about SMD: reduced goop-amount neccessary for obscuring circuits, @ reduced shipping costs!  

[Johan]

when repairing Mackie/phonic/behringer/presonus mixers/modules I've usualy used a Weller "pyropen" ( butandriven soldering pen )with the hotair "tip" and tweesers when removing the faulty/suspect SMD ICs and transistors
I guess buying a pyropen for that specific jobb unless you use it in your daily work, wouldnt make much sence, but that is one way to do it and still be able to use both the pcb and any ICs/transistors again...

..biggest chip removed and cuccessfully reused this way by me...140pin Hammond/suzuki "MUSE"-chip for Hammond BX-2...tock a while but worked..

johan

[Paul Marossy]

Here's that page I was mentioning earlier: http://www.storm.ca/~rheslip/recyclin.htm