ASM-1 problems/solder flux

[Tony Clark]

> You guys must be using water soluble flux solder.  The flux left by
> rosin core solder should not have to be cleaned, even though I suppose 
> it is a good idea.

   A lot of people on this list use the "organic"-based flux solder.  
Using the term water-soluable really doesn't mean much when you are 
concerned with the properties of the flux itself.
   Organic based flux is a corrosive flux.  Not only does it seem to 
conduct, but it will also oxidize and eat away at your solder joints.  
This tends to cause various wild things to happen.
   My company had gotten some organic solder that was mislabled as rosin 
core solder.  The flux proceeded to seriously mess up the operation of 
the circuit boards until we got wise and washed them all in plain tap 
water.  Problem cured.
   We also had purchased some flux in which to assemble cables with and 
if the workers didn't wash the flux off afterwards, it would oxidize the 
solder joints and cause the effective resistance of the cable to go WAY 
up!
 
> The point is emphasized when you look at the solder side of a 20-year
> old
> PCB that is still working perfectly and notice the layer of brown crud
> that covers it.  I assume that this is rosin core flux...could someone
> please correct me if I'm wrong?

   Yes, brown crud = rosin core flux.

   I personally have never had any bad experiences using rosin core 
solder.  I did my ASM-1 board with it, no problems.  I've done all of my 
project boards with it, no problems.  Before our business got our wave 
soldering machine, all boards were soldered with rosin core solder.  15+ 
years of manufacturing high gain circuits with rosin core solder should 
have some validation for its usefulness.
   Granted, rosin core flux residue makes a board "look" bad.  Of course 
depending on how well you can solder can also determine how much flux you 
actually "leave" on the board.
   A good rule of thumb is to use as little solder as absolutely 
necessary to produce a good solid soldered joint.  A good joint will look 
like this:
           | |
__________/~~~\___________
__________     ___________
          \___/
           | |

   Like a nice little cone (preferrably concaved) on both sides.  If it 
looks like a round blob, that's too much.  Or if you can still see the 
thru-hole, it's not enough.
   When soldering, clean the tip of the iron VERY frequently.  This will 
remove quite a bit of the flux that comes out of the solder.  If you 
don't, then it tends to build up on the tip of the iron and _blacken_, 
leaving those dark amber pools around your solder joints (that is, if 
you are using rosin flux).  I normally don't do more than 4 to 6 joints 
between cleanings.
   BTW, I don't know what kind of soldering irons people use, but if 
yours doesn't come with a sponge and holder, you can use a household 
cellulose sponge wetted with water to clean the tip of your iron.
   Also, I use 0.020" thick solder wire, as opposed to more standard 
0.041".  The finer wire allows me to control the solder flow really well, 
minimizing the amount of solder I use as well as the amount of flux that 
gets put on the circuit board.
   Well that's it for my tips and tricks for dealing with rosin core 
solder.  :)

   Tony

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I can't drive (my Moog) 55!         |     The E-Music DIY Archive
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Tony Clark -- clark at andrews.edu     | aupe.phys.andrews.edu/diy_archive
http://aupe.phys.andrews.edu/~clark |     Contributions welcomed!
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