[sdiy] solder questions

[Paul Higgins]

Responding to lots of comments posted:

> I agree with you Harry, I do it ~exactly~ the same way. (After trying 
> all the fancy alternatives I'm sold on
> good old number 44)

That's been my experience, except that I really haven't given the 
reformulated stuff a fair shot--old habits die hard, I guess.  I have 
some newfangled solder around but just kinda keep going back to the big 
roll of "44".  63/37, of course.

> I generally don't use anything but Kester '44'. It may be old school, 
> but it's not low-tech. That, a 700° tip, and a wet sponge will get me 
> through just about any job...

Wow...700 F...that's hot!  I use an XYTronic temp-controlled iron set 
from about 605-625 F.  I rarely if ever go over 625.

> Did I mention that Kester 331 is corrosive?

Got the message!  : )

Maybe a good way to think about the 331 stuff is that it's like a 
plumbers' acid core solder that will get you a really good bite into 
the metal, but the price you pay is that it _must_ be cleaned 
immediately.  It took me a little while to get my head around that 
concept, because since I was a kid, everyone has always warned "don't 
use acid core for electronics work!".  I'll admit it's nice that it 
cleans up with DI water instead of flammable or carcinogenic solvents 
(see below).

> Kester 44 requires a much stronger solvent (generally some sort of 
> alcohol at the very least, TriClor at the worst), and even then, it 
> takes a good amount of work to get a truely clean board.

Yikes...stay away from trichloroethane, everybody!  That's speaking as 
someone who's spent way too much time in organic/bio chem labs (my 
academic background).  Really bad news.  I find any common ketone works 
quite well (methyl ethyl ketone is probably the most ideal; acetone 
works great but is very low-boiling and volatile).  Just don't light up 
a smoke while you're stripping the board!!  MEK oughta strip any amount 
of flux clean.  I use MEK in a little glass jar to clean up old guitar 
amp jacks, etc. caked with rosin.  That and a natural-bristle wood 
"toothbrush" from a spraygun cleaning kit works wonders.  I just 
collect the waste solvent in an empty metal paint can and take it to 
the hazardous waste people when it's near full.  (Do them and the 
environment a favor--write what is in the can on a piece of masking 
tape; make sure you document "trace Pb, Sn, Ag" or whatever other 
exotic metals are in your solder).

> Never use Kester 331 on a board that already has Kester 44, or any 
> other rosin flux, on it.  This make a disastrous mixture that is 
> almost impossible to clean up.  Never use Kester 331 anywhere where 
> you cannot clean.

Well, speaking of chemistry, I can make a guess as to what is 
happening.  If the organic core stuff is indeed an organic acid 
(citric, pyruvic?) and you mix it with the rosin stuff, you're probably 
getting a nasty polymerization/esterification reaction.  It explains 
the gummy, impossible-to-clean nature of the residue I've heard 
described.  Now for the bad news...when we got that kind of crap all 
over our lab glassware, we had to use a mixture of concentrated 
sulfuric and nitric acids to get it off.  Not a good option with PC 
boards.  : )

> Also, stay away from paste flux.  I have found (in general), that 
> stuff is pretty much only good for making a mess.  If you want extra 
> flux, buy a bottle of either Kester 44 or 331, depending on what you 
> are doing (Did I mention that Kester 331 is corrosive?).

I've gotten OK results from the paste stuff, but you're right, it makes 
a real mess which often you have to clean up with MEK; it leaves a 
nasty oil coating all over the place.  Yuk.  I've used it to solder the 
huge 10 AWG buss used for the main star ground in tube amps.  I think 
I'll try the liquid stuff next time.

> Leaving Kester 44 alone is a lot better than doing a half ass job of 
> cleaning it.  I have stuff around here that is 30+ years old that was 
> assembled with Kester 44 and never cleaned...still works just fine.

My experience is the same.  I've had some goofy old Paia kits from my 
youth (remember the "Phlanger" BBD kit, Harry?) that were covered with 
"44" rosin and still worked fine after 20 years.

And for any newbies out there, feel free to profit from my failures--as 
they say, sometimes the hard way is the easiest to learn.  Trust me, 
you do NOT want to clean a PC board half-assed.  Especially not a DIY 
board with all sorts of open-holed pads for attaching wires, etc.  
You'll have streams of diluted rosin and solvent coming through, 
leaving leakage traces all over the board.  Even more fun, the safer 
solvents like MEK will often trash plastic parts on the board.  (I 
remember those polystyrene caps used for VCFs being especially 
susceptible).

> OK so I'm old school...

Well, old school is good...

> HAH... read the fine print. It is still available in both 60-40 AND 
> 63-37
> the 60-40 is cheaper, guess what I use....

...but I'm not _that_ old school!  I bought a big roll of 63/37 a 
couple years ago, and still have a large amount left.  I have to say 
that I do like 63/37 somewhat better, though I never had problems with 
cold solder joints even with the 60/40 stuff.  But I like the way it 
solidifies better, without that intermediate state.  I guess it's a 
confidence thing.

> Kester 44 flakes right off soldermask with a little push.   While you 
> troubleshoot...
> just flick it off a little at a time. By the time you are ready to 
> run, its all clean !!!

Yep, that's what I do as well, thanks to Harry mentioning it on the 
list.  Otherwise, I'd still be ruining DIY boards by trying to clean 
them with solvents.  And for the most part I don't clean boards at all, 
unless they've got bad coatings of the stuff from repeated mods and 
repairs.  I use a little awl-like PC board tool to scratch it off.  
About the only time I use MEK is to clean up totally disgusting 1/4" 
jacks from 40-year-old tube amps caked with rosin from years of 
repairs.  Believe it or not, I've even salvaged a few pots this way, by 
immersing them in MEK for a couple minutes.  Just make sure you re-lube 
them with that silicone stuff afterwards; the MEK does a real number on 
whatever lubricant is in there, not surprisingly.  Oh, and do yourself 
a favor and don't solder the pot right away (or light up a smoke!).  
This probably isn't recommended practice, but it worked for me OK even 
with those plastic-shaft pots.

-PRH