[sdiy] Removing flux from PCBS?

[Kevin Lightner]

>On Wed, 16 Mar 2005 15:19:22 -0500, doof <doof at cox.net> wrote:
>>
>>
>>  From: "Samppa Tolvanen" <samppa.tolvanen at gmail.com>
>>
>>  > Acetone - anyone? I think that my solder is pretty basic 60/40 Rosin
>>  > core and this cleans up the mess, if there is one, pretty nicely..
>>
>>  I'm curious too, anyone?
>>
>In a private message, Ian Fritz made me aware of the asetone
>residues.. althought, I can't see any harm done If the board is
>completely rinsed..... (in a tap water, containing who knows what? :)
>
>But acetone WILL be harmful or melt some (the most?) plastics, so I
>would be careful.
>
>Bye, Samppa
>
>p.s. What does those plastic caps have in the inside? Nuthing?


I use acetone all the time, but just with cotton swabs from a 
dispenser canister.
IF the board has no holes passing through it, I may douse a small 
amount onto the pcb and let it dissolve things with a small pool, 
then spray it off with a spray solvent. But in general, acetone is 
nasty stuff on anything with a petroleum or acyrlic base. It loves 
polystyrene, which many switches, key tops and capacitors are made 
with. MEK is about the same.

Also, some boards have silkscreening, masks or other coatings. Unless 
you plan on wholly stripping away this coating, it's probably best to 
leave the flux there. Small areas with fets or other sensitive nodes 
can be done by hand with a swab and alcohol or a less reactive 
solvent.

As far as rinsing stuff, the only problems I've ever seen are low 
leakage oriented caps or old carbon resistors, usually in the 
megaohms, that absorb the water. Rare, but has happened. I use soft 
water, followed by an air compressor and live in a very dry place 
though. If you use regular water, don't get all of the excess out and 
live in a humid area, all bets are off ;-)
I've heard of people doing a final rinse with distilled or deionized 
water, but I've never tried it myself.
But if water is left on an unprotected tin/lead solder joint, it can 
corrode the connection and leave highly conductive salts. Very common 
to see on units that were flooded and horrid for high impedance 
circuits.
There can also be salts that form at joints of dissimilar metals, 
caused by galvanic actions from the increased moisture. Much worse if 
the unit is powered on while still wet too. ;-)


-- 

Kevin Lightner

Myself: http://www.synthfool.com
Service and sales: http://www.moogmusic.com/service.php
Sales: http://www.cluboftheknobs.com