Date: Thu, 18 Sep 2003 01:55:58 -0400 From: Benjamin Berry <[EMAIL PROTECTED]>
I don't know what it would do to the rest of the components but I've found 5 minutes of exposure to a heat gun ( for paint stripping ) to loosen solder right up. Works great on multi pin through hole components.
I like that method, but there are some things to watch out for.
First, know your heat gun. A professional strength heat gun may burn your board, because it seems to put out a much higher temperature than other guns. I use a Milwaukee brand heat gun I bought at Home Depot which has a dial on the back for adjusting temperature. I don't know how good this one would be for stripping much paint, but it's great for desoldering.
Second, limit your time. I've found that most through-hole and surface mount stuff will come off in one to three minutes of exposure, but it varies greatly and, of course, depends on the temperature setting on the heat gun. So, when I'm doing through-hole stuff, I poke at the solder with a dental pick every fifteen seconds or so. When the dental pick starts penetrating the solder, it's almost done. When I'm doing a large surface mount chip, I gently (very very gently) pry at a corner of the chip with the dental pick, until it lifts with next to no force. I usually put a digital watch nearby so that I know how long I've been heating the board.
Third, don't blow away neighboring components. The first time I used a heat gun on a circuit board was on a PCC Power 120 with a bad CPU. I got the CPU off okay, but I literally blew away half a dozen surrounding components. They came loose and flew away with the hot air. I spent three months trying to get a detailed look at another Power 120 so I could figure out what went where*. Cover neighboring components with modeling clay so that they don't blow away. It only takes a thin layer, so a small box of modeling clay will last you most of forever. It's not a terrible idea to make a high resolution scan before starting, but that won't show you the tiny markings on a surface mount resistor.
Oh, and having a ~5x magnifying cup handy doesn't hurt either. That's the kind you can hold in place with the skin around your eye. It gives you magnification on your work with your hands free. This useful for soldering and usually not needed for desoldering. One of those lamps/magnifiers on an arm is probably better, but they can be expensive, and the magnifying cups are under $5 in the jewelry section of Ebay. Oh, but your depth perception goes, so be careful with the soldering pencil. I had a very hard to explain burn mark across my nose for a while...
* I finally managed it at the PCC going out of business auction. A really nice security guard there let me open one of the Power 120s up and sit there on the floor and copy down the values of the various resistors and such that I needed. He even moved one of the heavy floor lamps over to provide light for me. That was a really nice guy.
Jeff Walther
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