Homebrew PCBs

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

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\ufffdC.

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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> http://groups.yahoo.com/group/Homebrew_PCBs
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i always exposed the one, turned upside down, exposed other side.
i made a "pocket" of the film with a strip of pcb at the edge.
then developed/etched simultaneously.
didn't do much doublesided bards......

st





On Mon, 07 Jul 2003 09:10:21 -0000, Mark Farnell <farnell_mark@...> 
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
>
>
>
> Be sure to visit the group home and check for new Bookmarks and files:
> http://groups.yahoo.com/group/Homebrew_PCBs
>
> To unsubscribe from this group, send an email to:
> Homebrew_PCBs-unsubscribe@yahoogroups.com
>
>
>
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
>
>
>