Sometimes I can't remember what I had for lunch today. Thankfully, most of the time I remember to put on my pants.
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Amp techs, what's on your bench?
- Thread starter two fingers
- Start date
I snagged a handful of old boards that were being thrown out today. I'll be doing some practicing soldering and unsoldering joints for a while. I need to laern what works for me as far as solder itself, but you guys are right. The lead free stuff SUCKS!!! Oy! It defies the laws of physics! I get it to the flow point and it literally runs around the leg of whatever I am soldering and UP the soldering iron. Like..... it "drips" UP. On what planet is that OK?
And, guys, put on some pants, will ya?
And, guys, put on some pants, will ya?
If it flows around the lead then you didn't heat the lead enough, careful with solder pads they need less heat and overheating them can cause them to lift.
The little features on the circuit board -- donut shapes around leads and rectangular shapes under surface mount terminals -- are called "pads." On a well designed board, they are shaped and sized to provide just the right surface to pick up enough heat, let the solder flow, and form a nice joint.
If you see green paint on the board, that's an epoxy "solder mask" that solder won't stick to. That stuff is absent on the pads, making boards easier to solder.
Good move to grab a board to practice on. The key is to watch the metal change state and get the smooth move of sliding in the the solder sucker and hitting the mark. Hunt around to find a double sided non through plated board to practice on. It'll teach delicacy.
On a board lacking plated through holes too much heat lifts traces. It is a touch thing that takes some practice to get past. Better to mess up a skank board than one you'll get crap for tearing up.
On a board lacking plated through holes too much heat lifts traces. It is a touch thing that takes some practice to get past. Better to mess up a skank board than one you'll get crap for tearing up.
Ah! Thanks. My instructors had not called them "pads". But I know exactly what you are talking about now. So, are you guys saying that soldering will not be the devil if I heat up the pad itself enough? If I am getting this all straight, many of you are suggesting that I heat up both the component leg and the pad (with perhaps a little more heat on the leg), and then bring the solder in from the other side and let it flow around from there?
Too much heat is a killer. When desoldering, it is better to clip the component leaving the leads and remove them separately. With the component present, it can act as a heat sink requiring you to apply more heat to remove it. This is especially useful when desoldering dual inline integrated circuits.
Some techs will leave the leads of resistors or capacitors in place and wrap the lead of the new component around the old one and solder the two together. It saved them time to do it this way and time is money. In some cases they do this because other heat sensitive components tie into the same place. If too much heat is applied, multiple components can be damaged. In a delicate situation, sometimes this has to be done. I hate to see this when it doesn't have to be done.
Some techs will leave the leads of resistors or capacitors in place and wrap the lead of the new component around the old one and solder the two together. It saved them time to do it this way and time is money. In some cases they do this because other heat sensitive components tie into the same place. If too much heat is applied, multiple components can be damaged. In a delicate situation, sometimes this has to be done. I hate to see this when it doesn't have to be done.
My typical technique is to have a chisel point soldering tip, which I gently press against both the component lead and the pad at the same time. With small parts, they heat up pretty quickly, then I jab the solder into the spot where all three -- lead, pad and soldering tip -- come together.
I find that component removal -- desoldering etc. -- is where board damage is most likely to occur. So it makes sense to learn some different desoldering techniques, and have a reasonable array of tools for the purpose.
And a problem for amp techs is that a lot of music gear uses single sided circuit boards to save money, making those boards less reliable and harder to repair. In fact, a pad may already be lifted off the board before you put it on your workbench due to vibration, poor soldering in the first place, or a bad connection causing localized heating. You will do your best to avoid damaging boards, but will end up having to deal with a lifted pad or trace once in a while.
When I suspect that a board is delicate, and want to remove a part, I will sometimes sacrifice the part to save the board by cutting off all of the leads so I can pull them out one by one with tweezers.
That reminds me, another tool for your bench: A little vise. I have one that just clamps to the edge of the bench, so I can get at both sides of the board at once.
I find that component removal -- desoldering etc. -- is where board damage is most likely to occur. So it makes sense to learn some different desoldering techniques, and have a reasonable array of tools for the purpose.
And a problem for amp techs is that a lot of music gear uses single sided circuit boards to save money, making those boards less reliable and harder to repair. In fact, a pad may already be lifted off the board before you put it on your workbench due to vibration, poor soldering in the first place, or a bad connection causing localized heating. You will do your best to avoid damaging boards, but will end up having to deal with a lifted pad or trace once in a while.
When I suspect that a board is delicate, and want to remove a part, I will sometimes sacrifice the part to save the board by cutting off all of the leads so I can pull them out one by one with tweezers.
That reminds me, another tool for your bench: A little vise. I have one that just clamps to the edge of the bench, so I can get at both sides of the board at once.
When you put an amp on a bench, it is best not to put any weight on the power tubes. Here is an amp cradle that I built. It tilts and elevates the chassis and can accommodate chassis of different widths and depths. It disassembles with a screwdriver so I can take it on the road. There's a '67 Fender Vibro-Champ in this one. There are some plans for a similar one here.
Its one of those things that takes practice. Basically, start by heating the biggest lump of metal first, which is usually the component lead. Then change the angle of the bit to heat that and the pad, then add the solder.
Three key rules:
1. Keep it clean, or clean it before you solder it
2. Heat the stuff you're joining, not the solder
3. A good mechanical joint is essential for a good electrical joint
I'd reccomend always using some "no clean" flux. While modern solders have raisin cores, using extra flux makes soldering a lot easier. If there is need to use some stronger stuff then make sure you clean all the excess and residue after soldering.
Also, use the correct tip size for the job, beginners tend to use small tips that won't have enough contactsurface with the pad and the component. For most jobs I prefer chisel tips. When doing SMD work a magnifier is your best friend. It may feel weird at first but it is the only way to guarantee good solder joints. You have analog controll over your hands, just need to get better feedback : )
Don't buy the cheapest solder, especially when dealing with lead free stuff.
Also, use the correct tip size for the job, beginners tend to use small tips that won't have enough contactsurface with the pad and the component. For most jobs I prefer chisel tips. When doing SMD work a magnifier is your best friend. It may feel weird at first but it is the only way to guarantee good solder joints. You have analog controll over your hands, just need to get better feedback : )
Don't buy the cheapest solder, especially when dealing with lead free stuff.
Component leads usually come oxidized. If you look at NOS carbon composition leads for example, you see a gray coating. I clean these leads with a Mr. Clean Magic Eraser and wipe away the residue with a solvent before I solder. Flux is supposed to help clean these surfaces and what I do isn't necessary but I figure that everything helps. I think that it looks better on the board after it is cleaned.
Here is an example of how the eraser cleans. The top resistor is how it comes out of the package, the bottom one has the leads cleaned, the residue is on the sponge. Cleaning leaves a powder on the lead, I either wipe it away or use some alcohol before soldering.
Here is an example of how the eraser cleans. The top resistor is how it comes out of the package, the bottom one has the leads cleaned, the residue is on the sponge. Cleaning leaves a powder on the lead, I either wipe it away or use some alcohol before soldering.
The cradle is actually pretty handy to have.
For building turret and eyelet boards I use a low profile machinists vise, like the one below, with rubber jaw liners in place to protect the board. It can fit in the cradle but I usually just use it on a desk.
