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Soldering for beginners?
01-13-2014, 06:38 AM (This post was last modified: 01-13-2014 06:42 AM by Garth Wilson.)
Post: #7
RE: Soldering for beginners?
Dave has a lot of great video blogs, but I was surprised about how many minor to moderate (no major) disagreements I had with him on things about soldering. The things below are mostly copy-and-pasted from posts of mine on another forum and do not all directly address things in the EEV Blogs.

One thing that has been emphasized for the beginner and I will emphasize it again from a slightly different standpoint is that the soldering iron must be used to heat up the parts you're soldering, not to apply the solder. It's not just about the flux, either. The two parts you're soldering, whether that's a pad and a pin, or an eyelet and a wire, or whatever two parts, must be above the melting temperature of the solder. You cannot just drip a drop of solder onto cold parts as if it were glue. That's not how it works.

I'd say use higher temperature. Sometimes you can actually do less damage with a higher temperature. Temperature-controlled ones often can't do the jobs as well unless you can turn the temperature up higher than Dave was talking about. It was a surprise to our production people when I showed them that soldering a plastic switch years ago resulted in less melting and damage if they would use a hotter soldering iron so as to be able to complete the job so quickly there wasn't time for the heat to reach the plastic before everything was cooling again. Dave could do both a faster and a better job with a hotter iron. A hotter iron transfers heat better so you tend to use less mechanical force of the type that made the PCB foil come loose toward the end of his #186 video (the link should have been anyway.

Don't worry about damaging semiconductors with the heat from the soldering iron. Especially if you're only soldering one pin (or two or three) at a time, you definitely won't get the die very hot. I've seen power transistors actually operating with the die at over 350°C, which is about 165°C (or 300°F) above the melting point of the solder. (I don't recommend operating them that hot, as they won't last that way, but they were not destroyed.)

Yes on the chisel tip. You can use it for soldering fine-pitch ICs too. More on that in a minute.

My solder sucker is almost exactly like the one he shows. I bought it about 35 years ago! Solder suckers and solder wick both have their place. I've used high-priced electric solder suckers at work and they have always been a frustration of getting clogged and so on. The hand-operated one is in most cases just as good. Another way to remove excess solder sometimes is to hold the board upside down and let the excess run off onto the soldering-iron tip. More on that in a minute to, in the context of leaded SMT ICs.

Don't worry about the lead. I grew up drinking water out of pure-lead pipes (not just soldered with lead). It was in another country and I went to an American boarding school because our American parents wanted to make sure we would be able to step into American schools when coming home, and all the water pipes at the school were lead, not PVC, nor copper, nor gavanized. Lead. A very large percentage of the students went on to become doctors and engineers, so I'd have to say the lead definitely did not damage our brains any. (I still don't recommend putting the solder in your mouth though.)

There is no need to remove rosin flux if it's just the stuff that comes in the solder. It is not corrosive like water-soluble flux is, and it does not add conductance between pads like water-soluble flux does. Removing it would be mainly for looks. With the rosin flux that's in the core of solders used to solder by hand, there is no need to remove it, unless, I understand, you're going into space and go through a particular layer of the atmosphere that turns the flux corrosive-- or something like that. I'm not concerned with that, myself. I have stuff I soldered with rosin-core solder several decades ago, and it definitely has not caused any corrosion at all, or caused any other problems of any kind. For our products at work, there is some final manual assembly to do, partly for parts that are not sealed and washable so they can't be put on at the same time with everything else to be soldered by machine and then bathed in any kind of cleaner.

The thing about soldering the fine-pitch parts is that it is helpful to spread extra flux on that is liquid in its cool state, or, if not liquid, at least soft like toothpaste or Vaseline. That stuff is really gooey and sticky, and, if you left it, would get on your hands, clothes, papers, tools, workbench surface, and everything else, and it does not wash off with just soap and water. The mess it not tolerable, so cleaning it off is not optional.

Our experience with no-clean fluxes has been that they don't work as well.

Our experience with water-soluble fluxes has been a disaster. They are corrosive if you don't clean them off. But just as bad for our company's sensitive analog circuits, water-soluble fluxes penetrate the pores in the PC board where it's not masked, and they produce conductive paths, even if the board appears to be clean. And further, those conductive paths don't act like a quiet resistor, but make a noise like frying bacon in the audio signals we deal with. I always specify in PC-board manufacturing instructions that the holes in my soldermask files must not be opened up any bigger, and that any pair of pads that are .010" apart or more absolutely must have soldermask running between them (unless they're connected already anyway). This is more of a flux mask than a solder mask. The first time I encountered the problem years ago, we had just changed assembly houses for a particular board--a rather simple one with no soldermask--and the new assembly house was using water-soluble flux because of the EPA making life difficult for them. A technician who was testing the product before shipping to customers ran into a problem right away and couldn't figure it out. He asked me for help. It didn't make sense. I had him remove various components from a net until there was nothing at all left on it, and still there was maybe 50K between that trace and another. I told him, "Then there's only one possibility left. Take your solvent and really scrub that thing. When you think you have it super clean, do it again." That fixed it.

Every few years after that, someone in assembly would bring in some flux to make it easier to solder wires by hand, and we would get the frying-bacon sound again, and then we would have to find out who did it and explain why they can't do that and make sure we get all of it out of the plant.

As Dave showed, soldering SOJ's and SOIC's by hand does not require soldering one lead at a time. The way I've done it is this: start out by tacking two opposite corners just to hold the part in place as you start the real soldering at a third corner. You just flood the entire side with solder, using a tip that covers two or three leads at once, leaving lots of bridges. When you're done with both (or all four) sides doing that, then hold it vertically and go from top to bottom of each side again with the iron, and all the excess solder comes off on the iron, leaving an even amount of solder on every pin, just right. It's amazing how easy it is! It's helpful, but not imperative, to use extra flux. If you do use extra flux, then you have to wash the whole gooey mess off.

I've also heard of using solderwick to actually apply the solder to an FPGA with 0.5mm lead spacing, rather than to remove the excess. Beautiful! (Lots of HP-41 links at the bottom of the links page, )
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Messages In This Thread
RE: Soldering for beginners? - Dave Hicks - 01-13-2014, 12:35 AM
RE: Soldering for beginners? - htom trites - 01-13-2014, 01:03 AM
RE: Soldering for beginners? - Garth Wilson - 01-13-2014 06:38 AM

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