The Recapping FAQ

[Paul S]

Re: The Recapping FAQ

I corrected the problem with the images in the Word version of this How-To. But now the file is 8.6MB and way too huge to upload. The PDF version is still 1.7 MB

Moderator: If a file (PDF) version of this thread is something that you would like to add, please contact me. Also, you can remove my last two posts, as they are no longer relevant.

[Scenic]

Re: The Recapping FAQ

upload the .pdf version at http://upload.wozzap.de (10MB Filesize limit ; not allowed file extensions are listed there) and post the link here. i will then upload it to my private webspace and post the link here.

edit: my private webspace is paid webspace... not some free hoster crap that could disappear without a warning

[Paul S]

Re: The Recapping FAQ

upload the .pdf version at http://xxx.xxx.x.xxx(10MB Filesize limit ; not allowed file extensions are listed there) and post the link here. i will then upload it to my private webspace and post the link here.

edit: my private webspace is paid webspace... not some free hoster crap that could disappear without a warning

Done.

Thanks, I hope that I did it correctly. My Deutsch is a little rusty. Just because my last name is Schmidt doesn't mean I know the language.

[Paul S]

Re: The Recapping FAQ

I don't know if you needed me to give you the url for the uploaded file, but here it is;
http://upload.wozzap.de/up/The%20Recapping%20FAQ.pdf

[zandrax]

Re: The Recapping FAQ

I don't know if you needed me to give you the url for the uploaded file, but here it is;
http://upload.wozzap.de/up/The%20Recapping%20FAQ.pdf

Nice collection, Paul
I noticed only a minor error: Asus brand is spelled As us in page 15, below the picture.

Zandrax

[Paul S]

Re: The Recapping FAQ

Nice collection, Paul

Willa did all of the work, I just copied and pasted.

I noticed only a minor error: Asus brand is spelled As us in page 15, below the picture.

Zandrax

Dam spell check got me! There was one time when I accidently double-clicked and accepted something that I didn't check. I guess that was it.

[Scenic]

Re: The Recapping FAQ

http://bambooz.pytalhost.net/badcaps...apping_FAQ.pdf



BTW: all files uploaded to upload.wozzap.de will be deleted automatically after 1 month.

[zandrax]

Re: The Recapping FAQ

http://bambooz.pytalhost.net/badcaps...apping_FAQ.pdf



BTW: all files uploaded to upload.wozzap.de will be deleted automatically after 1 month.

Like Rapidshare. So thank you Scenic, your link should last.

Zandrax

[ratdude747]

Re: The Recapping FAQ

6.2. Mechanical Solder Pumps

It is NOT recommended to use a mechanical pneumatic solder pump in order to clean the hole, they really have far too much power. There is a possibility to damage the lead port by sucking it out at the same time as the solder. This would mean that you would have to carefully solder in the new cap, making sure that solder flowed all the way through the hole in order to meet the right traces in the layers of the board. It will be quite difficult so forget about mechanical solder pumps. Additionally the recoil can impact the board and damage a trace or the pump can spray solder debris on the board that can cause a short when you power up the board.

i beg to differ. first, if you spray wd40 in the barrel form both ends, then you have virtually zero recoil. the debris issue is taken care of by pumping the sucker a few times after desoldering a joint. after every job take 5 min to diassemble and clean it out and relube it every other time. i have never had it suck out a lead port. if you are decent with your thumb, then a mechanical sucker will do fine.

i don't like the bulb. looks like it would be a pain to clean out. and it would be HEAVIER action than the mechanical sucker- a button press vs. squeezing a bulb... the button iq quicker and lighter than squeezing the bulb.

desoldering irons would be nice if they were cheaper... sounds like a waste of money to me

ps, helps if you use silver bearing solder. melts faster and helps desoldering (softens solder to the point where you don't have to worry about sucking out lead ports. costs a little more but is totally worth it.

[ratdude747]

Re: The Recapping FAQ

oh, and beyond the solder and sucker, i use a xytronic 30w grounded temp-controlled corded iron with small chisel tip. on max temp, with the addition of some silver solder, seems to melt joints really well (maybe it is capable of more than 30w... same model that the irons at my high school's robotics team uses for custom circuit boards)

for iron accessories i use a weighted tin can for iron holder (works great as long as you keep the cord on the table) and a yellow wetted sponge from a multipack from the supermarket. cheap and effective.

i use a tiny set of diagonal springed pliers to cut leads. keep it lubed with wd40 and it does really well.

on my choice of tools from the this post and the one before:

[ratdude747]

Re: The Recapping FAQ

my tools:



notice the temp control knob on the iron. off-screen, the iron has a grounding prong. because of that i like to think of it as a soldering station in corded iron form. am i even close to right?

i probably need an actual stand not a weighted tin can, but i already have the sponge:

[ratdude747]

Re: The Recapping FAQ

i have a different solder sucker now. that other one died when the threads in the tip stripped and shot the tip across the room. i now have a:



it is all-aluminum, compact, and esd safe. all i hd to do is wd40 the piston and sand down some sharp edges. works great.

[Sigmo]

Re: The Recapping FAQ

I agree with a lot of that. I've been an electronics tech and designer since the mid 1970s, and I have de-soldered and re-soldered thousands if not hundreds of thousands of devices.

I greatly prefer using a good solder sucker over any other means of removing old solder. You need a good solder sucker and you need to clean it fairly frequently to keep it from barfing out bits of solder. Lubrication is paramount. I prefer Teflon-bearing silicone grease (they used to provide this with RF connectors).

When the sucker wears out, toss it. They're cheap!

Very very occasionally, solder braid can be useful, but generally, it's a waste of time and leads to damage.

The keys to soldering and desoldering are rooted in an understanding of thermodynamics and heat-transfer. If you understand (and have a good gut feel for) Ohm's law, then you understand heat-transfer, too.

The main thing that damages circuit boards is heat coupled with pressure. Read that again. Heat coupled with pressure.

Heat alone (as long as you use a temperature controlled iron) rarely damages a circuit board. Pressure alone rarely damages a board. But if you heat a trace AND apply force to it at the same time, that's a recipe for damage. The adhesive that holds the traces in place melts when you get it hot. So if you heat it, do NOT apply force to it at the same time.

This is where most inexperienced workers get into trouble. They heat up a connection, but not enough to melt the solder completely. So they yank on the component or push on it with the tip of the iron and there you go: The adhesive is melted and now you've pulled or pushed the trace out of place or ripped a plate-through out of the board.

Normally, the best course is to cut all of the legs off of a device before trying to unsolder them. That way, you can heat and remove them one at a time. You can feel the lead "free up" when the solder is melted, and you can just pull it out with hemostats, needle noses, or tweezers. So for ICs, I just cut off all of the legs (as close to the body of the IC as possible) and then toss the IC body. Then I remove each leg, one at a time very easily, and without damaging the board. Remember: It's the BOARD you're trying to save. The IC is already assumed to be dead or you wouldn't be replacing it!

But for these caps and some other parts, you cannot cut their legs free of the body before unsoldering. This leads to problems, of course.

Fortunately, we're dealing with only two leads per cap.

So you can heat one side and bend the cap away from that heated lead with a small amount of pressure. When the solder melts, the cap will shift. Then you go to the other lead and push the other way on the cap. Again, when the solder melts, the cap will shift.

Be careful, go slow, wait for the solder to melt and don't use excessive pressure!

Always apply fresh solder with flux to both connections before starting. You have to "prime" the connections with fresh flux AND more solder. That solder forms a large area bridge between your soldering iron's tip and the board and lead. This is the heat-transfer part of things.

Imagine a clean soldering iron tip with no solder on it. You want to melt a solder joint where a component lead comes through a plated hole on a board.

You touch that dry soldering iron tip to that joint, and it touches in a couple of points. Think about that. It touches in a couple of points.

By definition, a point has zero surface area. How much heat can pass through a point? None!

You need to increase the surface area between the soldering iron tip and the area you're trying to heat so that heat can pass from the tip to the joint.

That's where some fresh solder comes into play. It forms a nice "blob" of liquid solder (which is a good conductor of heat) which increases the area through which heat can transfer. In effect, it reduces the "resistance" to the flow of heat just as a larger joint decreases electrical resistance.

And the fresh flux helps clean off the joint and the soldering iron tip. You MUST have a clean joint and tip for good heat transfer. That burned up crud on the tip is a great insulator. NOT what you want.

This is another reason to use a temperature controlled soldering iron. When you overheat solder and flux, it burns. It oxidizes and that oxide is a bad conductor of heat and prevents you from tinning the tip. You must have a clean, shiny, tinned tip to get good heat transfer.

Everything must be clean, shiny, and coated with fresh liquid solder for things to work well.

The wet sponge is your friend. Wipe and tin the tip over and over.

And while we're at it, you have to get the joint completely hot. If you're soldering on a large area of foil on a PC board, you will have a challenge. And unfortunately, a lot of these motherboards use very large areas of foil on both sides of the board where the very caps that are most likely to fail are located.

Use the largest soldering iron tip you can effectively get in there. Large tips hold more heat (think of it as thermal capacitance). They also transfer that heat faster and more effectively because their large cross section has lower thermal resistance. You have to get the heat into the joint!

If, as with the Soyo boards I've been working on, they have a huge area of foil on both sides of the board for these CPU power supply caps, it's virtually impossible to get both sides of the board hot enough to let you clean the holes out.

I put one 60 Watt temp controlled iron in a vise and a smaller 40 Watt temp controlled iron in my hand. I just carefully arrange things so that the board can be leaned up against the tip of the iron that's in the vise while I use the hand iron and solder sucker on the other side of the board. I can suck out those holes almost instantly. It's a hassle, but it works great with zero damage to the board.

If you have someone who can help you, it'll be even faster. Have them hold the board up, standing on one edge. They put one iron's tip on the back side of the hole in question and you use the other iron and the sucker on the other side.

Again, as counterintuitive as it might sound, put a bit of fresh solder on the hole. You need to have the hole full of fresh solder so you can get the heat to transfer it properly. The sucker can suck it all out in one shot.

On the subject of suckers:

A lot of the problems people have with solder suckers stems from their failure to envision and understand what it takes to vacuum solder out of a hole or joint.

You obviously want to have the greatest suction and flow rate of air possible right at the proper instant.

To that end, you want to position the tip of the iron and that of the sucker just right. You want to mostly seal off the area, but leave a bit of space for air to rush in so that the sucker's piston can develop some velocity. If you seal things off too well, you actually get a weaker "suck". If you leave too much space, then the air doesn't go where you want it to go, and the solder is not lifted.

Again, a GOOD solder sucker makes a big difference. It's got to get down on it! Blam! Clean, lubed, a good spring.... Yeah, baby!

It takes practice, but believe me, it can work fantastically.

Get in the habit of holding the sucker over a trash can every time you push the plunger down to reset it. That way, the bits of solder don't get everywhere. Lead is toxic. Be careful. Don't eat or smoke while doing this kind of work, and wash your hands when you're done. And be very careful of those nasty wet sponges. They'll be LOADED with lead-oxide in water. Very nasty indeed!

Wash up when you're done.

Clean the component side of the board very well and inspect it under magnification before putting the new parts in place. You do NOT want any hair-like threads of solder bridging things under the new parts where you'll never find them. Take the time now because it'll be a pain to try to find the problem later.

When you solder new parts in place, avoid heating them for too long.

Use a good, clean, temp controlled iron with a large enough tip to get the job done fast and clean. Remember the heat transfer thoughts. You've got to have melted solder between the tip and the joint to get heat into the joint. So position your rosin-cored solder right there at the intersection of the tip and the joint. All three come together in one small area.

And imagine pushing the flux-core of the solder into the joint, and even into the plated through hole as you start. That way, a burst of fresh flux floods into the plate-through, around the component lead just as you start. That fresh flux will flow into the joint and down through to the other side of the board under the component and will encourage the solder to "wick" into the annulus between the lead and the hole. Capillary forces will draw the solder in, and it'll make a good joint if there's nice, fresh flux in there.

When you get good at it, you can make the solder joints quickly and cleanly with very little possibility of any heat damage to the parts or the board.

I'm sure I'm forgetting something!

As has been said: Practice up on some junk boards. Play with it all and get comfortable with your equipment, your solder, and the whole mental image of heat transfer. Think about the masses of the things involved (and their heat-storage capacities). Think about the surface areas of things like the foils on the board and imagine how those larger areas pull the heat away from the joint, inhibiting your ability to heat them properly.

[rxtxau4]

Re: The Recapping FAQ

I have been in electronics for over 40 years and the best way I found to clean out holes after removing a part is to use compressed air set at about 10 to 15 pounds. USE ONLY A LOW AIR PREASURE!!! THIS MUST BE DONE CAREFULLY!!. I hold the board vertically in a vice by putting some padding one the edge so I do not damage the board. I put a cut down box about a foot in back of the board. Wearing a glove on the hand with the soldering iron I heat the hole while at the same time I hold a blowgun one the other side of the hole. As soon as the solder is melted I press the button on the blowgun and quickly remove the iron. This blows all the solder out. The box collects the solder splatter and the glove protects my hand. CAUTION SHOULD BE USED AND SAFTEY GLASSES SHOULD BE WORN!!.

A safer way is to get a blower used by watch repairers. There are some that are just a plastic squeeze bulb but the better ones have a plastic body with a piston in them. They are about 50mm in diameter (2 inches) with a thin metal tube coming out the end. Really old ones were all metal & show up from time to time on eBay.

The military actualy had them in the soldering kits when I was in & used to blow dust out dry off solvent etc.

A great little item. You would be surprised at the nice jet of air they put out & it is nicely directed.

[s6@riversunhk.com]

Re: The Recapping FAQ

have rubycon capacitor stk , support small qty, 16ZHL ect. have any rfq can contact me !