Printing the grid and other geometrical drawing , I pinpointed the problem. There is nothing on the vertical direction. The horizontal direction has a non linear increasing offset on the edges.
I solved the problem by printing the top layer (in mirror as always) rotated by 180°.
Putting the two sheet face to face with one of them rotated to get the correct orientation puts the same default on the same side. There is still a slight misalignment but less than 100µ. This is no more a problem with 800µ via.
There was also a scaling default, vertical direction is 0.2% longer, horizontal direction is 1.05% wider. This can be easily corrected by the software I use.
Thank you for your suggestion.
--- On Sat, 7/5/08, Bertho Boman <boman01@...> wrote:
From: Bertho Boman <boman01@...>
Subject: RE:
[Homebrew_PCBs] double sided PCB, accuracy - 2nd part
To: Homebrew_PCBs@yahoogroups.com
Date: Saturday, July 5, 2008, 9:58 AM
Try printing a grid, for example 10 x 10mm, across the page and measure it
to see what is actually happening. If there is a linear error in one
direction you can sometimes compensate for it in software depending on the
software used.
Is the error symmetric? If the artwork is run in the center of the printer
will it be acceptable?
If you are using a laser printer, I would put some marks on the film before
printing and check their dimensions afterwards. The heat of the fuser can
really put a lot of stress on the media.
Bertho
============ ========= ========= ========= ===
From: Michel Baguet Sent: Saturday, July 05, 2008 02:15
I made prints on 76µ (3mil) polyester drawing paper, I bought them 20 years
ago to make PCB, using a pen plotter and UV exposure. This paper is very
stable with temperature and moist.
Placing one sheet on top of the other (not face to face) give a perfect
alignment.
It is not possible to get a good alignment when putting sheet face to face
...
Some via are misaligned by up to 30 mil.
There is only one explanation, the optic inside the printer is not perfect.
Has anyone of you already faced this problem?
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