removing parts from PCBs
chenmel at earthlink.net
Fri Nov 11 19:51:20 CST 2005
On Fri, 11 Nov 2005 21:03:39 -0800
"Chuck Guzis" <cclist at sydex.com> wrote:
> On 11/11/2005 at 8:31 PM compoobah at valleyimplants.com wrote:
> >I've seen several references to using torches to remove DIPs from PCBs.
> Are there any specific things to keep in mind to avoid heat damage &cet?
> Are you talking propane plumber's blowtorches?
> Yes, I hold the board component-side down and flame it from above--a lot
> of components will simply drop out of the board once the solder has
> melted--do this out-of-doors as the fumes from the epoxy or phenolic can be
> pretty noxious. Keep the flame moving. Sometimes just tapping the board
> will cause quite a few components to to fall out. DIPs usually require a
> pair of needle-nosed pliers or small screwdriver to remove.
> Some invert the arrangement and do it component side up with the fame from
> below. I'm not convinced that one method is any better than the other.
> An old propane barbeque grill might also be another approach. Another
> might be to use a heat gun. Leave the oxyacetylene torch in the
> shop--it's way too hot.
> You won't get everything--small 1/8w resistors and small bypass caps don't
> tolerate heat very well, but you're after the expensive stuff, after all,
To add my comment- I always use one of those 'chip puller' tweezers made of stamped sheet metal. Get a grip on the chip before applying the heat so it's exposed to as little as possible. Be CAREFUL about breathing any of the nasty smoke that may kick in if the board material burns. A face mask isn't a bad idea. I bolt the board in a Black&Decker 'benchmate' so its pointing up in the air. I don't usually bother to try to salvage two leaded passives. Move fast, and plan the zones you will be heating, as the 'side heat' moving up and around on the board means you'll be pulling lots of chips in sequence once things start to melt.
We used to get all our DRAM this way back when the 256K parts were 'big bucks' (in the $7 apiece range for parts that had been salvaged this way.) I used to frequent a surplus store that sold a lot of RAM salvaged this way. A few times when I went in, there was an employee behind the counter 'cleaning up' parts stripped this way by dipping them in a well-regulated and fluxed solderpot.
A solderpot is another way of accomplishing this kind of stripping, I used to have a small one and recovered a lot of SRAM parts off little module boards they were mounted on by trimming the boards down to fit in the pot, floating the board on the molten solder and lifting the chip off. If you can find a big solderpot to float in this is a better method than the torch. If you have a medium solderpot and the boards you're salvaging off are bipolar (not ESD sensitive stuff) you can cut the board into sections that will fit onto the solder surface.
I salvaged a bunch of stuff just this summer using the torch method. From some scrap communications hardware (big card cages full of boards, one board for each channel). If you have a lot of the same board to 'strip' it goes fast once you have a routine down and know which parts you're keeping and which you're ignoring. If you frequent surplus gear auctions, the kind of equipment with good salvagable chips falls in the 'haul it away after paying $5 for a whole skid full of it' category.
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