On 13/11/2012 15:59, Nick wrote:
Very pretty indeed, as always!
Nice PCBs - how are you doing those? (I know you use Eagle :)
Nick
Nick
Manufacturing I assume?
Eagle to laser film using my trusty HPLJ4 printer that's some 30+ years
old.
Photo etch pre-coated FR4 PCB (normally cut from 160 x 100mm from Rapid,
DS or SS as appropraite). For DS boards I print both the board sides on
film, the top is mirror image so the toner will be in contact with the
board, I make an envelope out of the two films just using staples to pin
the film together and hold the PCB in place.
Onto UV box: SS boards just one exposure, DS boards are flipped over
carefully for a second exposure as I only have a single sided UV box.
(occasionally, pull it all apart, remembering this time to remove the
black plastic film from the PCB and start again!)
Develop, etch, drill and clean. The etch tank is heated and has a
bubbler for agitation.
I'm using clear etchant not ferric chloride after an accident that did
not please SHMBO (let's say I had to buy some oxalic acid to clear up
the mess).
To drill I have a cheap pillar drill from Screwfix and can drill down to
0.6mm with TC bits with care, although my normal drill size for
components is 0.8mm.
With care, I can get DS boards to line up to a small fraction of a mm so
rarely have problems with side to side alignment. But then I'm not
doing using very high component densities or narrow/close spaced tracks.
I bought some very small copper rivets from Mega for via connections,
these I push fit and solder. Mega sell a special rivet punch but it
frightfully expensive. Otherwise I use offcuts of wire from trimmed
resistor leads etc. On the DS board I often use pair of vias especially
when linking ground planes or wide power tracks. This means I'm putting
a U shape of wire through from the board top and folding the leads under
the board before soldering both sides. This gives a neat appearance.
I have used the chemical tinning stuff but don't feel the finish is
worth the cost.
Lastly I'll spray the completed board with a clear lacquer if its going
somewhere like the greenhouse or other outdoor application.
I suppose I could put a web page on the technique but its nothing
special. It is a more expensive route than transfering the LJ toner to
the PCB but I've found it gives better, sharper results and to do DS
boards would be more tricky to get side to side alignment (I have done
it by drilling the through the PCB with a small TC bit to create
alignment marks).
Did I answer your question or miss what you wanted?
Grahame
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