At 05:41 PM 9/29/2004, Phil wrote:
>One thing that hasn't been mentioned in the list of problems to crack
>is alignment for double sided resist application. I know that if you
>take a piece of paper, print on it and then print the same thing on
>the same side you will see some "mis-registration". I'd guess its in
>the 10-20 mil range on my copier though I'm sure it varies with each
>printer/copier as well as the age of the transport mechanism.
I've previously mentioned (many times) the simple technique we've been
using for more than 20 years:
Take a scrap of copper clad PCB material and make an L shaped piece with 3"
X 4" long legs about 3/4" wide. In other words, shaped like a carpenter's
square.
Tape one of the pieces of artwork to both arms. Flip the whole thing over
and very carefully line up the other piece of artwork. Tape one edge only
- to the longer arm. The tape is your hinge.
I like to leave about 1/4" of border around all sides of the PCB. Be sure
to place the artwork such that you leave at least some border - don't try
to position the edges of the finished board right at the edge of the L
shaped holder.
Tuck your board into the pocket formed by the artwork and holder. Process
as normal. Be sure to feed one edge of the "L" first.
The reason this works so well is that the "L" is exactly the same thickness
as the PCB material. Because the "L" is tucked right up to the PCB, it
doesn't slip or move when it goes under the rollers.
I've used this technique for aligning the transparencies used for making
boards with the photo process since the mid '70s. It also works just fine
when laminating directly onto the board. I routinely get boards with
registration errors barely or not visible to the naked eye.
dwayne
--
Dwayne Reid <
dwayner@...>
Trinity Electronics Systems Ltd Edmonton, AB, CANADA
(780) 489-3199 voice (780) 487-6397 fax
Celebrating 20 years of Engineering Innovation (1984 - 2004)
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