Desoldering: Thin layer of solder left on pads

Yes. What is left is called a tinned copper surface and is perfectly fine. It will help the new solder to coat the copper easily.

No. Once enough solder has been removed to easily remove the original component and insert the new one, you have removed enough solder.

(snip)

That solder has a high melting point that will easily damage many circuit boards, separating the copper from the substrate. Must you use lead free solder? 63% tin, 37% lead solder melts at a much lower temperature. 62% tin, 36% lead, 2% silver melts almost as easily, and gives a fine looking joint.

I've tried 60/40 tin/lead solder and noticed a huge difference between the solder with lead and the stuff without, especially when I was using a 15-watt iron from Radio Shack. That iron could barely melt the lead-free stuff. Most of my solder joints looked like crumpled up tin foil.

The main reason I was using lead-free solder was to make it safer for people/pets, because I'm working at home. I'm not sure if that's a good reason or not. I just wasn't crazy about having lots of little pieces of lead laying around for unsuspecting critters to walk in and track around the house, or the best way to clean the mess up, so I avoided the problem entirely. :)

With that said, I may switch back now, as long as I can keep my work area squeaky clean. What sort of steps to you take to keep everything tidy? Just a decent broom? Or do you even worry about it?

Thanks again for the help.

I do a lot of soldering on the kitchen table and I try to remember to wipe it clean before making a sandwich there, but I don't worry too much about it. The lead in 63 37 solder is pretty well locked up in the alloy as far as absorbing it in the body, compared to lead oxides used in old paint, etc. I think there is very little risk from ingesting an occasional tiny solder ball.

Make sure you have a good quality, activated rosin core solder designed for electrical work. For hand soldering, I have less success with the no clean solder. The flux just doesn't do as good a job at helping the solder wet the board and component leads. Never use plumbing solder paste flux on a circuit board. It leaves a residue that conducts electricity and corrodes metals it contacts.

If the flux and temperature are right, the joints should have a bright shine, especially when eutectic alloys are used. These do not go through a pasty stage (crystals of the excess metal growing in the eutectic liquid before the freezing temperature is reached) but solidify very suddenly.

Here is an interesting document on some flux choices:

noticed a huge difference between

especially when I was using

barely melt the

crumpled up tin

make it safer for

that's a

little

and

around the house, or the best way to clean the mess up, so I

problem entirely. :)

can keep my work

everything

I do a lot of soldering on the kitchen table and I try to remember to wipe it clean before making a sandwich there, but I don't worry too much about it. The lead in 63 37 solder is pretty well locked up in the alloy as far as absorbing it in the body, compared to lead oxides used in old paint, etc. I think there is very little risk from ingesting an occasional tiny solder ball.

Make sure you have a good quality, activated rosin core solder designed for electrical work. For hand soldering, I have less success

with the no clean solder. The flux just doesn't do as good a job at helping the solder wet the board and component leads. Never use plumbing solder paste flux on a circuit board. It leaves a residue that conducts electricity and corrodes metals it contacts.

If the flux and temperature are right, the joints should have a bright

shine, especially when eutectic alloys are used. These do not go through a pasty stage (crystals of the excess metal growing in the eutectic liquid before the freezing temperature is reached) but solidify very suddenly.

Here is an interesting document on some flux choices:

no, only enough to get the new component in, if you're experimenting with different components you can often temporarily mount them on the underside, which can be easier, but through-hole mounting is mechanically stronger and therfore reccomended for permanent replacements.

Bye. Jasen

I'm sure I could get the component to stick if I put it in there, but I was mostly wondering if doing so was "bad practice," or would cause poor connections/dry joints or something. I guess the answer is "no" on both counts. I should have been more straightforward.

I have a suggestion for a thought experiment: If you've removed enough solder that the old component falls out of the hole, what will happen if you try to insert a new component lead into the same hole that the old one has just fallen out of? :-)

Then, part 2: Once the new component is in place, what gets put back into the hole? :-)

Should I leave spoiler space? ;-)

That's as clean as it gets. To get any more solder off of it, you'd have to use sandpaper. The copper is _tinned_, that means "coated with solder". If, after wicking, there are no more big huge lumps, then your wicking job is done.

I apologize if I sound condescending and patronizing here; after all, this is the basics group, and any question is acceptable.

But, I _do_ wonder, being a tech myself, I have to ask, haven't you just tried it and see?

If, in fact, the question was, "am I leaving too much solder?", then the answer is, "If the lead fits, no." :-)

On the other hand, if you're having trouble getting solder out from the inside of the plated-through hole, then the answer could be a solder sucker:

Sorry it took this whole tirade to get to it! Shoulda signed it "Rich the stoner." %-}

Good Luck! Rich

It's not. People have been using 63/37 eutectic solder in their home labs for ever since electronics was discovered, and nobody's reported any ill effects yet.

Just don't leave little pieces of _solder_ (you're not melting down car battery plates, are you?) lying around where pets and children can lick them up off the floor. And even then, the dead epidermis cells and dust mite feces are probably more hazardous. ;-p

Just do your normal, usual, day-to-day, boring, mundane, uninteresting, tedious, dull, dreary, mind-numbing, tiresome, lackluster, unexciting, monotonous, repetitive, wearisome, humdrum, uninspiring housekeeping as usual. Stuff that falls on the floor, even little droplets of solder, is just dirt. Just treat it like ordinary dirt, and you'll be perfectly fine. :-)

You're more than welcome. :-)

Have Fun! Rich

It's not. The whole lead free thing is a hyped up mess.

You need specialist soldering gear to use lead free reliably too. Specifically, maintaing the correct soldering temperature is far more critical.

Graham

Not a problem. Actually, it was one of our better questions. ;-)

But yeah, it's not bad practice. There might be some oxide flakes left over from the old solder, but the new solder and its flux will clean that right up, and the solder will pull itself into the hold by capillary action and any crud will float out and get fluxed away. ;-)

Cheers! Rich