Archive of the former Yahoo!Groups mailing list: Homebrew PCBs

----- Original Message -----
From: "derekhawkins" <derekhawkins@...>
To: <Homebrew_PCBs@yahoogroups.com>
Sent: Wednesday, November 16, 2005 3:18 PM
Subject: [Homebrew_PCBs] Re: A $500.00 "UV" non-trivial exposure box.....


> >For production runs of one or very few, the case for
>>100% of "HOMEBREW PCBs", you'll have to explain as though to a young
>>child the advantages that offset the cost and complexity of photo
>>exposure.
>
> We'll get into the quality of the finished product later. Have you ever
> done a double sided board using TT? If yes then explain the TT process.

The workflow for both the top vs. bottom (or bottom vs. top) are identical.

-- Combine in Photoshop the artwork for top, bottom, and silkscreen. Print
this centered onto ordinary bond paper. Trim and tape a piece of transfer
paper over the artwork, and run it through the printer again, this time
printing onto the just-right sized piece of transfer paper. Separate the
three images.

-- Print the drill guide and legend. Stick it to the board with spray mount
adhesive.

-- Drill and debur the board. There are three unconnected vias in the board
corners for alignment pins.

-- Pierce the alignment vias on the top artwork; place the pins in the
board; place the top artwork over the pins. Visually confirm alignment, and
tape in place. Black toner should occlude all holes.

-- Remove the pins. Tear off a suitable size scrap of bond paper to use as
slip sheet. Fold in half; place the board with top artwork in the crease.
Run it through the laminator.

-- Soak off the transfer paper. Pulsar's paper comes off cleanly in a few
seconds. Dry the board. Examine for alignment errors and incomplete traces.

-- Cut a piece of green sealer paper to size; laminate to the exposed toner.

-- Repeat for the bottom. The sealer prevents the completed top artwork from
sticking to the slip sheet.

-- Etch.

With one success for one try with the alignment pins, I'm ready to try both
sides at once. Pulsar's paper releases completely when wet and makes it
brain dead simple with a clean and deburred board. Slight hole misalignments
are entirely attributable to imprecise manual drilling. Since the drill
guide is printed on the same printer as the transferred artwork, I'm not at
all surprised to not find any systematic errors.

Quality differences? It's difficult to see where the TT process can be
improved.