After the photoresist has been exposed with the pattern
there is no maximum time limit before it must be developed,
provided of course it is not exposed to more light during
this time.
Its probably not a good idea to develop boards by dipping
into a tank of developer solution. The unexposed resist
(negative dry film type) needs lots of mechanical action to
properly remove ∗ALL∗ of it from the copper. I tried this
once with a bubble agitated sodium carbonate tank and found
I always had to go over it with a brush afterwards to remove
those stubborn bits of unexposed resists . If the resist has
been on there a while (> 2 months) then its even more
important to use some form of mechanical action. All
commercial developing systems do it with high pressure spraying.
Normally people would expose one side, then expose the
other, then peel off the protective mylar film form both
sides and start developing in a tray prepared with 10g/L
sodium carbonate at 30 ~ 35°C.
Adam
Mark Farnell wrote:
> Is it necessary to expose both sides of a photosensitive PCB
> simutaneously, so that I can dip the entire board into a sodium
> carbonate tank?
>
> Otherwise if I expose one side first, I have to develop it
> immediately, otherwise it will be overexposed. However it would not
> be nice when I have to dip the entire board (include the opposite
> side which is covered by tape and not yet exposed) into the
> developing solution. Also, it would be messy if I spray the
> developing solution onto the exposed side because the developing
> solution will still seep onto the unexposed side!
>
> Mark
>
>
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