On Fri, Aug 27, 2004 at 02:39:35PM -0600, Sean McLachlan wrote:
And a similar question I have: What is the best way to remove chips that are soldered to the board? Getting all 12 or 16 legs completely free of solder is almost impossible (can't get to the back of the legs). Is there a tip for a soldering iron that will heat all the legs on a side at once? It took me a solid hour to remove 2 chips, and it left the chips unusable. The chips were bad, but I'd hate to wreck a good chip pulling it out to test it.
Well, there are a couple of ways. One way is to use professional desoldering tools (always a plus!). Note that just having the tools doesn't mean you can do a professional job -- there are lots of tricks for using them "right".. Another way is to use the standard solder sucker. Even though I do own the above mentioned "professional" tools, I still use the solder sucker at times. You can do a great job with it as long as you take your time. - BE CAREFUL! There are a lot of really crappy boards out there that if you pump too much heat onto (or are too rough) you'll lift the traces.. - make sure there is enough solder in the joint. It sounds weird, but if you're not getting good heating around the pin in the thru-hole you will do better to add MORE solder on. Then it'll suck out a lot easier. If you suck the solder out and are left with a small amount in the hole that is closing it up, flow some more solder in and try again. - when you're initially applying heat use the tip of the iron to press the leg into a position in the middle of the socket (i.e., a lot of them are bent against one side of the hole). NOTE! If the leg has been bent over you're probably going to want to decide whether to sacrifice the chip or the trace -- see below about clipping leads. - DON'T press the tip of the iron hard onto the board. Be gentle. - pay attention to the "internal plane" traces. It takes a lot more heat to melt the solder on a leg that is connected to the power or ground plane -- since the plane is doing its best to dissapate the heat -- so be careful. And pay attention to that.. - once you've sucked all the solder out of the holes typically the pin is still a little stuck to one side of the hole. I like to go back with the iron tip and push each leg to make sure it is moving freely in the hole. - when you attempt to lift the chip BE VERY CAREFUL. These older boards are sometimes really cheap and you'll be able to see traces sticking to the pins. Lift the chip up just a little and look under it with a flashlight and see if it is truly coming up without traces... I like to wiggle the chip and make sure it is free -- if not figure out which pin(s) are still tacked down. If worse comes to worse go to the below section about clipping the chip leads.. - I like to take a screwdriver and put it under the chip and GENTLY lift one side and then the other - just a small amount -- either the chip lifts easily or a SMALL amount of pressure and you'll feel a *crack* as the bits of solder let go -- any greater pressure and you'll feel a bigger crack as you rip the board apart... - after you've got the chip out you're not done -- go back and clean up the holes (check both sides of the board). Repair any damaged traces. Now depending on the board/your skills/your tools you might not be able to remove the chip. If you're willing to sacrifice the chip (I'd rather sacrifice the chip over the board usually) you can use another technique. Take a pair of clippers and cut the pins from the chip (closest to the chip packaging). Then take a pair of needlenose in one hand, a soldering iron in the other, and hold the board with your last available hand. (*snicker*) Work your way around heating each leg and pulling it out. Then take some compressed air and heat each hole and blow the solder out (or use a solder sucker). By using a decent soldering iron and a solder sucker (I like the blue ones) you should be able to remove 40 pin chips easily with a little practice -- and be able to remove the chips without damaging the board or the chip. Just gotta be patient. As you get the feel of things your speed will get better. It's also good since these days it is important to replace a lot of the big processor/rom sockets you find on older boards -- since they have a bad habit of dying. Kurt -- /** * Kurt Mahan kmahan@xmission.com * * "Did I say that out loud?" */