I found that to get anything close to 8mil (0.2mm) features, you need a
much better collimated light than an array of fluorescent 'BL' tubes.
Try a 250W clear mercury vapor HID. With correct setup your limitation
should the capabilities of the inkjet printer/transparency film. My
Epson Stylus with Epson dye black ink and Epson transparency, you can
achieve 8mils quite reliably. My Cannon i550 with HP, Kodak or Epson
transparency film, and using pigment black ink, the reliable minimum
trace/space width is more like 10mil (0.25mm). Also, the Epson prints
are so dark, that a 3:1 exposure ratio variation does almost no harm.
I have not tried IBM transparencies. The HP transparency seem to work
best with pigment ink. Inkjet transparencies in the office are becoming
increasingly rare because these days people prefer to use digital
projectors for presentations.
With currently technology, the limitation is in the inkjet printer, and
how precisely it can place drops of ink. The DPI claims are absolutely
meaningless for PCB artwork if the drops can wonder off a few thousands
of an inch. Look at your transparency prints under a microscope and you
will see what I mean. There are no market expectations to encourage
inkjet manufactures to build printers with more precisely placed drops.
This is a shame because the potential is there.
Adam
Stuart Wallace wrote:
> Leon Heller wrote:
>
>
>>What are you printing the transparencies on?
>>
>>
>
> I'm using a Canon i560 to print on IBM inkjet transparencies. I've tried
> a few different types of easily-available transparencies (the sort of
> stuff that places like PC World stock) and haven't noticed much of a
> difference between the types. I've made a number of test boards
> containing designs with 8/8 rules -- in each case the results haven't
> been nearly good enough to be usable. Something is definitely badly
> wrong with my process! I struggle to fully develop the boards without
> mechanical assistance (generally rubbing at the boards with cotton buds)
> -- this invariably leaves contaminants on the board, which in turn
> causes etching problems. Etching is in any case very uneven. This seems
> to point to either bad artwork or insufficient exposure.
>
> I expose the boards (6" x 4" DS FR4 stock) about two inches above two
> 15W UV tubes for three minutes. I'm extremely nervous about
> over-exposure: perhaps too nervous!
>
> I'd love to be able to make 8/8 double-sided boards at home; the reduced
> turnaround time would really help some projects. I suspect, however,
> that DIY PTH may be beyond my abilities. I'm getting ready to send
> artwork over to Olimex in order to get some proto boards made up, but I
> have my doubts: my requirements seem to be at the absolute limits of
> what they offer -- 8/8, lots of fine-pitch high pin count SMDs, and so
> forth -- so I'm not sure whether the results will be any good. Still, it
> doesn't cost much to find out!
>
>
> Stuart
>
>
>
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>
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