Hi Russell,
Yes based on the "Flux study" we changed to rosin flux for hand soldering. Please note however that rosin flux is still hygosopic and absorbs moisture that makes it conductive and hence sensitive to humidity. The inter trace impedance is proportional to length of the adjacent traces that the flux makes contact to, the amount of flux residue and the humidity. It is usually in the range of 400k to 1meg, so low in medium impedence designs (< 100k) it is rarely a problem.
Also, if you are not going to clean the flux off the board completely, you are better off not cleaning it at all. If the flux is applied only to the point where the soldering is done the amount of trace that it makes contact to is small so its impedance is realitively high. If you use a brush with flux cleaner it just spreads the flux over a larger area and, although it may look better, the flux contacts more trace area and the impedance will drop noticably. Also please note that use of solder mask on the board really improves the situation since the flux can't come in contact with the etch where there is solder mask.
BTW, if anyone wants to experiment with this, take a clean blank PCB (without solder mask) and meausre the impedance between two adjunct traces (usually >1 meg) Then apply flux to a small area between two adjunct traces and when dry measure the resistance between the traces. Slowly breathe on the board to increase the effective humidity and you will see a noticable decrease in resistance (usually <1meg) . Then take a brush soaked with flux remover and "clean the board" by brushing it around between the two traces. When dry redo the above measurements ( I have seen the impedance go down to 80k with heavy breathing). Finally use the brush with enough flux remover to flush the flux off the board and redo the measurements.
Thanks
Ron
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>What's wrong with rosin flux and not cleaning it? I've been doing that
>for 10 years. Old valve gear works for eons. My stuff is hand-soldered
>leaded components.
>If you need to clean rosin flux off, there's a really good aqeuous
>cleaner i've used, and it makes all the solder and other metals look
>extra shiny too.
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