Homebrew PCBs

DJ Delorie wrote:
> Philip Pemberton <ygroups@...> writes:
>> <http://pcbwiki.philpem.me.uk/tiki-download_wiki_attachment.php?attId=1>
> 
> I do not have permission to use that feature :-(

That would be because I left "View Attachments" set to "Admins Only". It's set 
to "All Users" now, so anyone should be able to see that file.

> For DS boards, what I do is include targets on my artwork.  I print a
> paper copy of the artwork (in the same printer, just not film
> quality), tape it down, and pre-drill the targets, usually 13 mil
> holes.

That's what I was thinking of doing -- cut the board 1" or so oversize on each 
side, then Scotch-tape the artwork to the board, drill through, then flip over 
and align the other side.

I do have a double-sided exp. box, so it's a bit easier. What I've been doing 
is aligning the two layers on an A4-sized light box, then using lengths of 
foam mounting tape (B&Q, a shade under £2 for a 1.5m roll) to hold the masks 
together. This stuff happens to be just about the right thickness to hold a 
PCB between two transparencies, while maintaining near perfect alignment. 
Ordinary double-sided tape seems to be a bit too thin.

Like said, I align the masks, stick it along three edges (leaving one side 
open), leaving a pocket. Insert the PCB blank (with the lightproof film 
removed!) into the pocket, check alignment, then put it in the UV box and 
switch on.

I've just finished etching and drilling my first board, and it looks like it's 
worked just about perfectly. I don't usually get this much success from a 
completely new (to me) process :)

As for making the transparencies, I've been using "Jetstar Premium", in my 
Canon iP4600, with the following settings:
--- Main ---
   - Media type:         Photo Paper Pro II
   - Paper source:       Rear Tray
   - Greyscale Printing: On
   - Print Quality:      Custom [Set ==>]
     - Quality:            1 (Fine)
     - Halftoning:         Auto
   - Color / Intensity: Manual [Set ==>]
     - Brightness:         Dark
     - Intensity:          50 (maximum/Dark)
     - Contrast:           50 (maximum/High)
--- Page Setup ---
   - Page size:         A4, portrait
   - Page layout:       Normal-size printing
--- Effects ---
   Make sure everything on this page is UNchecked.

This works pretty well for me, with very dense black print. Only problem is 
you have to remember to apply these settings every time you print with EAGLE 
(it doesn't preserve print settings AT ALL -- they reset to the driver 
defaults as soon as the print dialog closes). Thankfully the Canon driver 
allows configuration parameters to be saved to (and loaded from) a profile, so 
it's not (too) bad, but you still need to remember to reload the profile 
before hitting Print...

Ink needs to be on the matt side of the film (hold it between thumb and index 
finger -- one side will feel "stickier" than the other -- that's the matt 
side). EAGLE prints what's on screen, so turn off all layers other than the 
ones you want to print (e.g. for the top layer, turn all layers off except 
Top, Pads, Vias, and Dimension). Print the top layer mirrored, and the bottom 
layer non-mirrored (the option for this is in the Print dialog). Check the 
"Black" and "Solid" boxes to force EAGLE to print everything in black, with no 
hatching.

... and that's basically it.

> For my targets, I use four square pads, placed together in a square,
> with about 1 mil between them.  Since I use negative film, this
> results in a 1 mil crosshair inside a square hole in the ink, which is
> really easy to align with those holes.

I've been using the drill holes in the pads for coarse alignment, and the "0 
mil" (translation: print as thin as possible) outline on the Dimension layer 
for fine alignment (if it looks thicker than "just barely visible", it's out 
of line). This gets close enough for the part pitch I've been using.

-- 
Phil.
ygroups@...
http://www.philpem.me.uk/