Primer on Electronics Rework
Rather than reinvent the wheel, there is a comprehensive beginning guide at: http://www.pinwiki.com/wiki/index.php?title=General
The remainder of this section is my subjective opinion. What I've written here is what works for me, but all of it may not work for you. Conspicuously absent are details on using hot-air tools for surface mount work.
The topics listed here are appropriate for through-hole and early surface mount manufacturing.
- 1 Soldering Iron
- 2 Desoldering Tools
- 3 The Solder Itself
- 4 Volt/Ohm Meter, or the VOM
- 5 Other Tools
- 6 Troubleshooting
This is the most important rework tool that you have. Period. It should be of reasonably good quality. Luckily, quality can be had for not too much money.
Here's what I look for:
- Recognizable name brand
- There are a lot of off-brand looking irons, and people have had good luck with them. For my own sanity I stick to brands that I know and trust.
- Adjustable temperature
- That's temperature as in degrees C or F, not an arbitrary numerical scale. You want an temperature controlled iron, not an iron that goes to 11. You'll want one that does at least 700-800 F. You won't routinely solder that high, but if you encounter a beastly old device with metal shielding that's been soldered together, you'll go crazy waiting for it to melt if you can't get enough heat into it.
Is it possible to put a price on sanity? When it comes to desoldering, the answer is YES.
Copper mesh that comes in a small spool. You place it on the original solder, heat it up with the iron, the solder melts and is absorbed into the wick.
- Barely works on parts soldered to a ground plane or any component/feature that is capable of sinking heat
My biased opinion: For all but a few applications, I loathe solder wick. It works well for cleaning up solder pads, or basically any time you need to leave a thin, uniform layer of solder behind. It's also decent at taking down overzealous blobs of solder. Mostly I use solder wick for repairing large, broken traces. Literally, I use it like wire and solder it to the board, because that's what it seems to be best at :)
Desoldering click-pump (Soldapullt or other similar device)
A large pen-shaped tube with a fine tip. Removes solder by drawing it out with vacuum. You click the piston into place, melt the solder, hold the tip over the melted solder, and push a button to release the piston, drawing the molten solder into the tube.
- Solder cooling means it can be difficult to time right
- RSI (Repetitive Stress Injury) inflammatory
My biased opinion: Unlike solder wick, this is an actual desoldering tool. It's inexpensive and works decently. What I don't like is that you have to time it just right to make sure that the solder stays molten enough to be extracted. You can melt the tip of the desoldering pump if you get it too close to your iron. The repetitive click/release can be fatiguing for large jobs. Failing to get the pump in just the right spot mean that you may only partially extract the solder and have to reflow the joint and start over.
What I like to do, assuming you're desoldering a through-hole device, is to prop the board on its side, heat the joint on one side and hold the desoldering pump on the other side. Once you see that the solder has melted all the way through, it will usually come out easily.
Desoldering iron with integrated vacuum bulb
Basically a soldering iron with a hollow tip, and an attached rubber bulb to extract molten solder. Hold down the rubber bulb, heat the part, and release the bulb to remove the solder.
- Single-handed operation
- RSI potential
My biased opinion: These offer better control due to combining the iron & extraction device into a single unit. Solder cooldown isn't an issue since you can apply constant heat during extraction. These are inexpensive and work decently. Like the click-pump, the amount of vacuum that you have to work with is limited, so you can still get a partial extraction and have to reflow and retry. Removing large amounts of solder can be tedious as you're forced to take tiny bites, unless you bring your soldering iron in to keep everything molten. You also have to draw the iron away from your material to squeeze the bulb, lest you blow molten solder all over your project.
Electrically powered pump-based desoldering tool
These can be a handheld gun-like device or a desoldering station with cord-attached tool
- Single-handed operation
- Low RSI potential
- Require regular cleaning and filter replacement
My biased opinion: If you're going to do a lot of rework, buy one. It will change your life. Some of them can be phenomenally expensive, but units like the handheld Hakko 808 are reasonably priced. You'll want to keep a few different tips around, along with a decent supply of filters.
The Solder Itself
There not much to say here, simply:
- Use actual electronics-grade solder. Even the stuff that Radio Shack sells is fine.
- Keep a spool of thin and a spool of thick solder. Use the size most appropriate for the job.
- Avoid mixing lead & lead-free solder.
- Don't use plumbing solder or acid flux solder, ever.
Lead-free is used in modern devices, beginning in the mid-2000s. Chances are if you have something that's lead free, it's almost all surface-mount and the techniques in this document aren't appropriate.
Volt/Ohm Meter, or the VOM
You need a decent, basic meter. Not too cheap, and not too expensive. Any store that sells tools will probably sell decent meters.
- Things to look for
- Auto ranging
- Recognizable brand name
- Diode test
- Things you probably don't need
- Clamp ammeter - You'll rarely need an ammeter, let alone one that is probably intended for residential wiring.
- Capacitance meter - probably won't be very useful as capacitance is only part of what makes a cap good or bad.
- Analog-needle meters - they need to be zeroed in and don't autorange. The advantages of an analog display are of little use for rework.
- Things to outright avoid
- Meters from "Import" tool stores, like Harbor Freight. I have tried them on many occasions under many different circumstances. They are worthless for anything but coarse measurement.
- Must haves:
- A variety of small pliers, including needle nose, curved tip and duck bill
- Small, fine diagonal cutters
- Hobby knives
- Scratch tool
- Wire stripping tool
- Alligator leads
- Maybe haves:
- Needle files
- Large pliers
- Large diagonal cutters
Difficult time removing solder
A few reasons for desoldering difficulty:
- PCB is wicking heat away and preventing solder from melting completely through.
- More heat may be necessary. Turn up the iron, or if you only have a small fixed-wattage iron, you may need something more powerful. Especially true for soldered-on shielding or connections to thick perimeter grounds.
- There may not be enough preexisting solder to get heat into and through the solder joint.
- Add more solder first. Some PCBs have very little solder from the factory (Atari Jaguar is one) and you will have a difficult time creating a solder heat bridge until more has been added to the joint.
- Incomplete melting of joint
- This can be due to insufficient heat or an issue with technique. If the joint hasn't fully melted before extracting the solder, you'll end up with a component that's still attached, but no exposed solder for your desoldering tool to work. Add fresh solder and try again more slowly.