I am trying to swap dead capacitors in my motherboard. Removing them was relatively easy, but I can not insert the new ones. The solder melted into the vias and the desoldering wire does not suck it out of the hole. Is there any safe method to remove the blocking solder from the vias?
Sometimes you can just push the majority of the stuff out, by quickly pushing a couple inches of un-heated solid wire through the hole while the solder is melted. If you do it fast enough, you end up with the solder frozen on the wire sticking out the other side of the board, and you can break the solder off and then just pull the wire back through.
Another thing that sometimes works is to heat the via and then quickly tap the board against the edge of a bench, moving the board in a short swing in the direction of the via. The inertia of the molten solder will cause it to keep going forward (and probably onto the floor) when the rest of the board stops. And (obviously, I had thought) you don't want use this technique on any but the sturdiest of boards.
Like the blowing technique, the down-side of these is that they can produce tiny, loose bits of conductive material to watch out for, which can cause shorts if you don't get them all. Suction is really the way to go.
Have you tried a desoldering pump?
Beyond what has already been answered, you can try to use wick solder remove.
There is a great article at wikipedia: http://en.wikipedia.org/wiki/Desoldering
And Youtube has many videos about: http://www.youtube.com/results?search_query=desoldering&aq=f
Thanks for your tips. Here are my observations:
- desoldering pump - After cleaning and oiling my pump I had still no luck with it. Maybe I have to practice more :)
- desoldering braid - Adding some fresh solder before using this definitely improves the cleaning effect, but it leaves the solder inside the hole. I've tried three different types of solder wick without success.
- tap-tap method - It seems usable for smaller boards but not for a computer motherboard so I have not tried it.
- Pushing out - I had no thin solid wire here, so I added a little extra solder and heated the via while pushing in the new capacitor from the opposite side. Sometimes worked but this thing has two legs and I have only 1 soldering iron :)
- Blowing out - I tried to blow with my mouth without any effect. Then I tried a dust blower, but I cannot aim it precisely into the hole.
Then I found something in my drawer:
It is a plastic bottle with metal needle head, 1 USD from DX. I inserted it to the hole from the opposite side then I heated the hole. After removing the soldering iron I quickly squeezed the bottle. It cleaned out the via! 8 of 10 times I was able to insert the new component to the hole without problem. For the remaining two holes I used a sewing needle to broaden the hole.
Still not the best method, but it worked for me better than any others mentioned here. However I am considering to buy a vacuum desoldering tool to save a whole day next time :)
If you can justify it, look into a desoldering iron, such as the Pace SX-90. I've found them very useful because you don't have to remove your heat source to suck out solder, they're temperature-controlled, and they also can pull vacuum indefinitely. (They use a vacuum pump, instead of a spring piston.) Granted, the Pace iron requires a controller, but that controller can also control a temp-regulated iron as well.
What soldering Iron are you using?
This sound suspiciously like the pad's your having a problem with are tied directly to the ground plane and your iron isn't transferring enough heat effectively. Or more specifically the ground plane is sinking enough heat to not get the solder up to the proper temperature.
I use a metcal MX500 and when i have this issue stepping up to a larger tip usually transfers enough heat to solve the problem. As a last step you can try a hotter tip, or if your using an adjustable iron, turn the heat up, just be careful not to go too high, if it gets too hot the pad will separate from the board.
Failing that, hold the board on edge, apply heat to the back side of the pad while pushing the cap in the top side, move the cap in as you move the iron out. This usually works for me.
Here's a cheap and easy technique which works better than any other method I've tried. First, get a good quality turkey baster which can withstand high heat. Amazon sells silicone hear resistant ones for cheap under $5.00. Make sure you are using an iron capable of a wide heat range. Most simple plug in type irons just can't deliver enough heat.
Apply a blob of solder to both sides of the via. Add paste flux to both blobs, but wait until they are sufficiently cool. You don't want the flux to liquify and run off the hot blob.
Anchor the PCB vertically between vice jaws or two heavy objects. Using the iron at a high setting, heat one side until it melts and immediately place your turkey baster's tip over it and hold it there. Then immediately heat the other side of the with the iron. As soon as both sides liquified suction in quicky squeeze the turkey baster's blub to blow out the solder.
Make sure you cleanup and solder droplets when you're done. You could use a vacuum action, but unless you form a really good seal around the via, it doesn't work very well.
I wanted to avoid spending a lot of money on special equipment, but already had a heat gun and this worked for me. My PCB had 10 holes filled with solder due to a mistake. I heated the area with the heat gun and tapped the pcb onto the table and all the solder came out. It made a mess of the table, so maybe put down some sacrificial surface first!