Flux Damage

jkeny

Banned
2007-02-06 12:43 am
Dublin
I know you should always clean off flux after soldering but I've been lax in this practice up to now! (I didn't realise how corrosive this stuff was)

But I just had a Set Top Box that stop communicating with a PC - when I opened it up I saw the problem.

About a year ago I had soldered some small OsCon caps onto smd caps on the board. Now smd caps with Oscons attached were lifted off the board - obviously I had not cleaned off the flux and it had eaten away at the glue holding the solder pad onto the board.

This is the first time I've experienced this - I didn't use too much flux or heat & the joints were solid & shiny when I made them - just like they should be. The pcb is probably not the most robust but still!

Has anybody experienced this before?

I'm worried about all my other soldering which I'm going to now try & clean up with alcohol - is ordinary spirits Ok for this?
 
jkeny said;

"I'm worried about all my other soldering which I'm going to now try & clean up with alcohol - is ordinary spirits Ok for this? "


Isopropyl Alcohol and Q Tips are fine for cleaning up flux. I don't know what you mean by "ordinary spirits". If you mean alcohol then its OK.

Are you sure you used non acid flux for your previous repairs and mods?Regular electronic grade flux should not mess up the PC lands like you explained, never happened to me in 30 plus years of fooling around with electronics.
 

jkeny

Banned
2007-02-06 12:43 am
Dublin
Oops, I didn't know that there were different types of flux - I got a jar of the stuff - that might be the problem, oh **** I'll go and check! You know what they say - "a little bit of knowledge is a dangerous thing" QED!


Edit: Here's a link to what I have http://www.fernox.com/?cccpage=powerflow_flux&sub=10
and it says the PH < 2 - Oh crap! and it's for pipe soldering -I certainly will have to clean all past soldering

Yes I meant ordinary alcohol!
 
Unless you specifically ordered rosin flux from an electronic supply house, you almost certainly ended up with acid flux for copper plumbing work. Disaster! The stuff is corrosive forever- I don't know that any amount of cleaning will truly take care of it. It's usually zinc chloride based, though I see now your's isn't, and I'd clean first with hot water, soap and a brush, followed by alcohol. Both sides of the board, and replace any non-washable parts like unsealed trim pots.
 
jkeny said;
Thanks guys,
This could be a disaster - I've been using the stuff for a year - I thought flux was flux, Doh!

Let my stupidity be a warning to others.

No, not stupidity. Lack of knowledge maybe. We are here to help you along in your quest for good sound.

Stupidity is knowingly using acid flux on electronics, BIG difference. A nice repair tip for you would be to replace all the acidified lands with 26 gauge wire and re-make the circuits. If you have lands that are lifting up from the flux then remove them all and re-lay with the wire.

Don't beat yourself up too much, we all make mistakes. If not then you must not be doing anything,heh,heh.....
 

jkeny

Banned
2007-02-06 12:43 am
Dublin
Yeh, I'll look over my past work & see what's what!

(I don't want violins playing in the background) but I also blew some lovely speakers 2 weeks ago - vintage Rogers LS3/5As ($1500 or so on eBay) - I'm really beginning to think I'm losing it - it's not like I'm a complete noob to this - have been playing around for a number of years now!

Bad karma, I guess
 
Before cleaning the acid stuff off the PCB, I would try neutralizing it. Try natrium bicarbonate diluted in water, use a toothbrush and apply until you see no more residuals. Then clean it off with water or alcohol. Finally dry with hairdryer and check visually using a magnifier lens.
Ordinary electrolytic capacitors are sometimes leaking and eat up the PCB tracks beneath them, the cleaning procedure is the same.
 

jkeny

Banned
2007-02-06 12:43 am
Dublin
Thanks oshifis,
I was thinking along these lines myself - thought I'd use Sodium Bicarbonate or some other household alkaline.

Good news is I took off the SMD caps from the board & the underlying traces & pads seem OK & test OK with DM. So only the cap itself was disintegrating - replaced with OsCons after cleaning! It's good to go!
 
A ph of 2? What is driving that?

Halides are introduced into flux to activate it. Chlorine, Bromine, Flourine, and Iodine in various compounds.

Zinc chloride converts to hydrochloric acid during the soldering process...that's why the zinc chloride...duh..

Is sounds like the manu reasoned that "zinc chloride" was the bad bad thing to keep out... for sales reasons...so they must have bypassed the middle man and just dropped hydrochloric acid into the mix...


Hey, it doesn't have zinc chloride innit, now does it??:D

Cheers, John