Solder, flux, and conductivity

[343 Salty Beans]

There's something that's always bothered me when I solder, and I've always wanted to ask the question, but never enough to actually ask it.

I use solder with rosin core, and when I solder, I often notice the clear flux flows a lot further out than the solder does. sometimes, it connects two pads or traces, so I scratch it off. I'd assume that the flux is conductive, because the solder flows onto it, and solid contact needs to be made...

but is it? It could save me a lot of squinting at boards in bad light to find those bridges.

[Meanderthal]

 I don't think it is. I stuck the probes of my meter into a tin of paste flux, (I had the same concern at one point) got no continuity. I think it's just an acid that helps clean the contacts or something. And I know it's necessary, because I tried solid core solder, and no flux once. Don't waste your time- it was almost impossible to get it to stick to anything at all!

[343 Salty Beans]

thanks meanderthal. I may try isolating a bit of the flux and measuring it's continuity. You're a good chap  us bassists have to stick together, lest we be overrun by a mob of metal guitarists with scooped mids.

I didn't say that.

[KerryF]

Flux isnt conductive.  Sometimes when you solder it starts to splash all over the board and getts pretty annoying.  But I usually just use a little sharp thing to scrape away the extra flux.  Doesnt hurt anything though.

[John Lyons]

This came up in another post a while back. It isn't conductive per se but doesn't it absorb water...or isn't there some downfall to having a lot of flux bridging pads...?
Search for Paul Marrosy and flux. He had a problem with it, once it was cleaned it off the problem was gone.

John

[RedHouse]

Used flux is hydroscopic (absorbs moisture from the air) and can lead to bridging conductivity between pads and traces, at the least adding stray capacitance.

This is why commercial boards are thoroughly cleaned of all excess and used flux, boards can are often rejected in the QC phase just for flux residue being present.

[Meanderthal]

 Ahh, good to know! Thanks for the info! That might explain a couple things...

[Peter Snowberg]

See this thread too:
http://www.diystompboxes.com/smfforum/index.php?topic=35278.0

Flux can easily interfere with high impedance circuits. I've "fixed" a lot of devices with flux cleaner.

[John Lyons]

I've been cleaning my boards of flux since I read that thread a while ago. I usually use rubbing alcohol and a toothbrush. What would you guys reccommend for a cleaner of something  sourced from household items?

JOhn

[alderbody]

I usually have a piece of "kitchen paper" by my side when soldering.
I clean the points right after the solder solidifies, while the flux is still fluid.
It gets absorbed by the paper much easier when in fluid condition.

Of course after all soldering is done i use a toothbrush with alcohol.

[343 Salty Beans]

WOW.



glad I've cleaned it off for a long while now. It just gets all over the place, and my dorm isn't too well lit...it makes for tough, blindness-inducing fun. 

thanks to all for the thorough replies.

[John Lyons]

Must haves:
Jewlers loupe
Adjustable Desk lamp
Magnifing/reading glasses (for soldering and those tiny schematic values.)


John

[Meanderthal]

 hehe- been squinting at those tant caps again?

Sorry-way OT...