De-soldering PCB's (tips)

[Hupla]

Hey guys,

Sorry if this has been done before.

Basically I'm currently modding my Cry baby and I'm finding that as i am de-soldering components, putting new ones in, not liking it and then de-soldering again, I am just wrecking the tracks on the PCB near the component and the round metal track that you solder the leg to has come off on a few occasions.

I have even had to solder the resistor in parallel with the inductor right to the legs on the underside because of wrecking the tracks.

So basically I'm wondering if you guys can give me any tips to help prevent this.

Thanks

Colin

[bbmonster]

Flux and desoldering braid for small amounts, works like a charm. Just dabble some flux on the joint, apply braid, heat with iron. Most times the braid will suck everything up and you can pull the part out with no problem. A few occasions you'll have to add a bit more solder, then do the procedure over again. If the joint has lots of solder, use those desolder pumps first, but i tend to dislike them cause they tend to splatter solder over the board.

There's also a tutorial on geofx somewhere. If you don't need the the part, clip the legs from the top, then use the iron below and the rest of the leg will stick to the iron and you can pull it out. Then use the braid to clear up the hole.

[Hupla]

Flux and desoldering braid for small amounts, works like a charm. Just dabble some flux on the joint, apply braid, heat with iron. Most times the braid will suck everything up and you can pull the part out with no problem. A few occasions you'll have to add a bit more solder, then do the procedure over again. If the joint has lots of solder, use those desolder pumps first, but i tend to dislike them cause they tend to splatter solder over the board.

There's also a tutorial on geofx somewhere. If you don't need the the part, clip the legs from the top, then use the iron below and the rest of the leg will stick to the iron and you can pull it out. Then use the braid to clear up the hole.

Yeah i need to get some braid. Whats flux?

Ive been use a solder sucker and it really is annoying. It's only good for big blobs of solder.

I clipped the legs off from the top to get rid of the stock components as I wasn't going to use them, but I've had to do it with other ones as well which is annoying.

[JasonG]

Some guys do well with the solder braid for me it's the el chepo de-soldering iron at radio shack. I change the tips maybe twice a year and save wear and tear on my good iron.

[Mark Hammer]

Whats flux?

Ive been use a solder sucker and it really is annoying. It's only good for big blobs of solder.

Solder suckers are good for big blobs,.  Unfortunately, once the big blob is gone, there is still usually a "web" of solder holding the part in place.

Flux is hard to explain (especially when you don't know much about the chemistry! ), so we'll just say it enhances the flow of solder to the sorts of surfaces it will adhere to.  There is generally a flux core to the solder you/we buy.  The kind we're talking about here comes in liquid form.  You can buy a bottle for about $10 or so, and unless you foolishly spill it like I did, one bottle will likely last the hobbyist for their lifetime.  It can be thinned with methyl hydrate.  Dab a bit on a Q-tip or whatever brand of cotton-tipped swab you use, and smear it on the desolder braid.  This will improve the solder-removing capacity of the braid several fold.

Although it may seem counter-intuitive, putting some solder on the tip of the soldering iron before attempting to melt the initial "big blob" helps a lot.  The liquid solder transfers the heat efficiently.

Finally, excessive use of a solder sucker in close proximity to your soldering iron will tend to impair the quality of the "tin" on the tip and make it look corroded, so don't go overboard.  Personally, I keep a small container of tip tinner on hand to bring the iron tip back to life in those circumstances.

[frokost]

Finally, excessive use of a solder sucker in close proximity to your soldering iron will tend to impair the quality of the "tin" on the tip and make it look corroded, so don't go overboard.  Personally, I keep a small container of tip tinner on hand to bring the iron tip back to life in those circumstances.

At my bench, excessive use of a solder sucker in close proximity to the soldering iron has been a lot worse on the solder sucker. Several of them, in fact  .

[bbmonster]

... Whats flux?

I use the paste form and apply it with a toothpick just because I don't trust myself with a liquid bottle, had many oopsies with drinks and other containers on my desk/bench. I just got the one from a local radio shack (http://www.radioshack.com/product/index.jsp?productId=2049774) at the mall out of convenience, a bit pricey though compared to a good electronics shop.

[Paul Marossy]

If I anticipated doing a lot of tweaking with a few parts, I might temporarily solder in some resistor leads so I can use alligator clips while testing various component values. When I found exactly what I wanted, then I would solder them in. I've done that on occassion.

[frank_p]

Rosin is taken from conifers and is an antioxidant.  When brazing material get in contact with oxygen in the air the metals oxidise on the surface of the « blob » making a skin of oxides.  This skin prevent capillary effect to take place. It is the same effect that is in cause when wetting clothes:  So the alloy can't be sucked between the adjascent pieces of copper.  This sucking effect is done by such effects as cohesion of the fluid molecules and adhesion to an other matters. One example is the way water cling to the side of a glass. By rubbing the surface of molten alloy and putting rosin in it at the same time, it creates a barrier to the oxygen so that the capillary effect of the fluidised metal is intact (not disturbed by oxides) and can take effect for a moment.  With the effect of heat, a part of the brazing material have the ability to migrate in the copper making a very tough bond of alloy.  In some applications like carbide brazing on the steel body of a milling cutting tools, the effect of the capillary action is very important because it produce a fillet between the two pieces to be jointed and thus prevents stress concentration that could initiate cracking.    Contrary to some strong fluxes like borax, conifer rosin will not « eat up » the copper with time.  As funny as it can appear, pure rosin had been used also in the natural medicine field as antioxidant to replace grape seeds powder (Pycnogenol is one of the trademark of such product).  Now please don't drink your bottle of rosin to eradicate free radicals in you as there might be other additives and the methanol (solvent for the rosin) will just make it worse.  So when desoldering (or unbrazing) the capillary effect can allow the pull of molten metal into the copper braid effectively when rosin is present in the process in a similar way that a mildly wet towell will suck a spill more effectively than a completely dry one.

[Paul Marossy]

Rosin is taken from conifers and is an antioxidant.  When brazing material get in contact with oxygen in the air the metals oxidise on the surface of the « blob » making a skin of oxides.  This skin prevent capillary effect to take place. It is the same effect that is in cause when wetting clothes:  So the alloy can't be sucked between the adjascent pieces of copper.  This sucking effect is done by such effects as cohesion of the fluid molecules and adhesion to an other matters. One example is the way water cling to the side of a glass. By rubbing the surface of molten alloy and putting rosin in it at the same time, it creates a barrier to the oxygen so that the capillary effect of the fluidised metal is intact (not disturbed by oxides) and can take effect for a moment.  With the effect of heat, a part of the brazing material have the ability to migrate in the copper making a very tough bond of alloy.  In some applications like carbide brazing on the steel body of a milling cutting tools, the effect of the capillary action is very important because it produce a fillet between the two pieces to be jointed and thus prevents stress concentration that could initiate cracking.    Contrary to some strong fluxes like borax, conifer rosin will not « eat up » the copper with time.  As funny as it can appear, pure rosin had been used also in the natural medicine field as antioxidant to replace grape seeds powder (Pycnogenol is one of the trademark of such product).  Now please don't drink your bottle of rosin to eradicate free radicals in you as there might be other additives and the methanol (solvent for the rosin) will just make it worse.  So when desoldering (or unbrazing) the capillary effect can allow the pull of molten metal into the copper braid effectively when rosin is present in the process in a similar way that a mildly wet towell will suck a spill more effectively than a completely dry one.

Interesting info!

[frank_p]

Interesting info!

Well, I had an internship in a wood machining tool manufacturer when I was in engineering school. They were making router tools (for shapers) and sawblades.  One of my projects was around studying how well a tool would hold its blades, may they be HSS, carbide or diamond and attached with press-screw fixtures, brazing, etc.  So the question was, with a couple of words: what is the maximum of production speed the clients in the wood industry (thus maximum RPM of the cutting tool) can achieve before the tool becomes a public danger.  As stupid as it look, how well a rotating tool is balanced, brittle materials for blades, how well the brazing is done, the design of the "seat" for the blades, the overall geometry, friction with the clamping forces in the fixtures, vibrations from cutting, shocks, type of wood being cutted, "centrifuge" force, etc...  It becomes relatively complex pretty fast.  So I had to dig a bit in that brazing stuff and design some experiments mainly with traction measuring machine and analyse some curves to give some insight to what was happening with the different alternatives.  One thing that surprised me is how large was the pulling force (or should I say stress) brazing could withstand in "pure" sheer. If the brazing was well done, the carbide blade would often break before the joint would break and leave the blade.  Carbide being very hard, rigid but fragile, it's nature is prone to crack by traction stress (thus the fillet and stress concentration importance).  One other variable was how deep the cutting traces in the seat of the blade were from the machining process, so the solder could be "sucked" between the blade and the "finish" marks and so that the capillary effect could be optimal: ie: the amount of solder in the joint was optimal for the amount of retaining force (and mostly, facilitation for the guys who were "welding" the blade).  I wished I remembered more of all the issues.  R&D was fun stuff.  But hey Paul, we are not in a mechanical forum    .  So basically, rosin is an acid (abietic acid) that react with metal oxydes preventing contamination by the oxyde and protecting from further reaction with oxygen.

[darrylportelli]

Hey if I smear a newly etched pcb with solder flux http://www.radioshack.com/product/index.jsp?productId=2049774 (this kind) will the solder attach better to the copper???
Thanks

[Mark Hammer]

Hey if I smear a newly etched pcb with solder flux http://www.radioshack.com/product/index.jsp?productId=2049774 (this kind) will the solder attach better to the copper???
Thanks

Yes.  Whenever I make a new board, I always buff it (after drilling) to a nice shine, and before the shine wears off, smear it with a coat of flux.  I can then either tin it right away, or leave it sealed in a plastic bag for tinning later.

Why tin the whole board?  I like the way it looks.  I also like having the option of adding parts, whether by popping holes or simply tacking things on the back.  Occasionally one might want to tack a couple of wires on the back to add something in parallel.  having every trace solderable everywhere provides a lot of post hoc flexibility.  But that's me.  Don't consider it a necessity on your part to apply solder everywhere.

[MikeH]

Some guys do well with the solder braid for me it's the el chepo de-soldering iron at radio shack. I change the tips maybe twice a year and save wear and tear on my good iron.

+1 over here

[MikeH]

Hey if I smear a newly etched pcb with solder flux http://www.radioshack.com/product/index.jsp?productId=2049774 (this kind) will the solder attach better to the copper???
Thanks

Yes.  Whenever I make a new board, I always buff it (after drilling) to a nice shine, and before the shine wears off, smear it with a coat of flux.  I can then either tin it right away, or leave it sealed in a plastic bag for tinning later.

Why tin the whole board?  I like the way it looks.  I also like having the option of adding parts, whether by popping holes or simply tacking things on the back.  Occasionally one might want to tack a couple of wires on the back to add something in parallel.  having every trace solderable everywhere provides a lot of post hoc flexibility.  But that's me.  Don't consider it a necessity on your part to apply solder everywhere.

Mark- do you just use your soldering iron to tin the whole board?  Is it how I'm imagining it in my mind?

[Mark Hammer]

Yes, as a matter of fact I do.  But as long as we're not talking about something like a board for a microsynth clone or a one-board synth, you'd be pleasantly surprised at how fast it goes.  The flux makes the solder flow extremely well and quickly.  I won't vouch for every case, but something like a TS-9 board can easily go from bare copper to etched to drilled and tinned within an hour.

Once the traces are tinned, I go at the board with a paper towel and some methyl hydrate to remove the excess flux.

Is this any better than using liquid tin?  In terms of coverage, no.  After all, liquid tin immerses the entire board.  On the other hand, I've never seen a liquid-tinned board look at shiny as one of my tinned boards.

[MikeH]

I've looked in to that tinning stuff that uses some sort of salt solution, and you have to heat it up, and yadda, yadda... it seems like a lot of work.  This will be much easier.  I'll try it out.

[Hupla]

Ok so ive just started using a desoldering braid and it really isnt that easy to use. Its not sucking up all the solder that easy. Do I really need extra flux or am I doing somthing wrong?

[Ice-9]

Ok so ive just started using a desoldering braid and it really isnt that easy to use. Its not sucking up all the solder that easy. Do I really need extra flux or am I doing somthing wrong?

I used to have that problem, and i ended up hating de-solderbraid. That is until i found a supply that works so much better than the old stuff i used to get. I now find that the braid is far better than a solder sucker. I do laptop repairs at work, replacing many through hole components and its a breeze. The stuff i buy is from "RS components" i will dig out the order code for it if anyone wants it.

[Cliff Schecht]

I don't think anyone mentioned that flux also has a "wetting" effect that helps reduce the surface tension of the lead/tin when heated. This reduced surface tension helps the solder flow easier (stronger capillary action).

My preferred method of part removal, at least for just about anything mounted on a board, is also solder braid. Just don't buy the cheap stuff! I've had cheap braid that didn't work at all and it's very frustrating.. Surprisingly the Radio Shack brand works quite well.