[sdiy] Larry's MOTM/diy/AH pages

[harry]

The old solder may form intermetallic compounds... almost all of which have higher
melting points..

Some boards that were "wave soldered" may be a real bitch. One I salvaged recently
had most of the lead depleted from the bath... the compensation was to "turn up the
heat"...

When I used a torch to heat the board for "depopulation"... the fiberglass burst
into
flames before the "solder" melted...

I agree.. add fresh solder !!!

H^) harry

KA4HJH wrote:

> >> The melt temp seems to be lower.  It goes on very easy.  However, being able
> >> to wash is the prime advantage.
> >
> >Probably it just seems lower since the flux is much more
> >agressive.  I guess I'm just too old .... ;^)
>
> I didn't notice much of a difference myself. I certainly didn't notice that
> the alloy was different, which is is the only thing that would change the
> melting point of the solder itself.
>
> This reminds me of something that always bugs me. I've never seen a book on
> electronics/soldering that bothers to mention what a difference some clean
> solder and fresh flux makes. Most books on the "art" spend most of their
> time preaching about "thoroughly heating the joint", which is funny because
> putting some fresh solder (with its flux) on a joint will get everything
> hotter faster the best physical contact you can possibly contrive between
> the tip of the iron, the board, and the part being soldered. Yet this is
> precisely what they always tell you NOT to do! There is a WRONG way to do
> this and it would be easy for a beginner to mess up at first (no sense
> learning any bad habits at the start, either). But done right it will get
> you the best possible joint and reduce the heating time to boot.
>
> Whenever I'm desoldering I always throw a blob of fresh solder on there
> first. Amazing how much faster and easier it all comes off after that. I've
> had really old solder refuse to melt with a 250W gun until I put fresh
> solder on it! This is also useful when working with untinned boards (like
> homemade boards). You'll have a lot fewer questionable-looking joints. Give
> the flux time to clean the copper!
>
> Of course I'm using a Weller WTCP iron (what else?). 45W, thermostatically
> controlled and worth every dime I paid for it (I just replaced the tip for
> the first time). I've working with some mighty big heat sinks using that
> iron and this technique. Stuff that you'd never get with a cheap pencil
> from Radio Shack. And I've never fried a component with heat and I don't
> use a sink (tinning the shield on coax doesn't count--I have a special
> alligator clip that I use just for that).
>
> >    Being a big user of Organic solder myself, I must emphasize that
> >when you use organic core flux (I use Kester 331), you MUST! clean what
> >you solder.  When you solder wires, the flux will wick up the wire,
> >under the insulation, where you cannot get at it, and it will corrode
> >the wires, no doubt about that.  Keeping the two solders straight can be
> >a big pain in the neck.  I sometimes grab the wrong roll.
>
> I just remember that the solder with the red label is the potentially
> dangerous stuff. As long they don't change the color I think I'll be OK...I
> hope.
>
> >And while on
> >the subject.  Never mix rosin and organic flux.  You must completely
> >remove one flux before using the other, otherwise, you end up with a
> >very corrosive MESS!.
>
> Perhaps it would be a good idea to only use the stuff on NEW circuits, not
> repairing old ones? (even if there are no water-damagable components on the
> board?). Not that I've been tempted to try THAT yet.
>
> >I wish I had taken pictures of the results of
> >mixing both fluxes.  The results are extremely dramatic (espesially when
> >you also combine a 300AMP power supply in the mix).
>
> Yeah, I'd love to see that. Wish I had pictures of some of the lightening
> damage I've seen.
>
> --
> Terry Bowman, KA4HJH
> "The Mac Doctor"