Homebrew PCBs

This sort of thing was done for a long time to make plates for fabricating
integrated circuits for quite a while. (ICs use a photosensitive resist spun
onto the wafers.)  Optics had to be precise to set the exact reduction and
be accurate across the field.  However, the area exposed was generally quite
small, less than 0.5 inches on a side.  The images were stepped and repeated
across the plate to the size of the wafer.  The exposures to make the wafers
were done with contact printing.  However, defects were created when the
plate touch the wafer causing bad die and yield loss.  Later a collimated
light beam as use through a plate to make non-contact printing.  Now instead
of full wafer exposure plates, the images are in a relative small plate
(reticle) with a few to several die in a cluster.  These images are made in
redundant groups with the most perfect (defect free) version is selected for
production use.  The cluster is projected and stepped across the wafer to in
consecutive exposures - a   bit slower, but better final yields.

 

The idea of doing a reduction, 2:1 or 10:1 as we did back in the day is
possible, but would require very good optics with a wide undistorted
projection field - bigger than your biggest board.  That would present a
challenge that grew exponentially with board size.

 

From: Homebrew_PCBs@yahoogroups.com [mailto:Homebrew_PCBs@yahoogroups.com] 
Sent: Saturday, February 18, 2017 10:28 PM
To: Homebrew_PCBs@yahoogroups.com
Subject: [Homebrew_PCBs] reducing mask image with lens [1 Attachment]

 

  

The conventional method of using photoresist is to install a mask on top the
photoresist.  I'm considering using a two-to-one reducing lens and placing
the mask above the reducing lens.  Since the mask image would be reduced to
half size when it hits the copper clad, the fine detail requirements of the
mask and printer are reduced. For example a 5 mil trance on the PCB would be
printed as a 10 mil trace on the mask (printer transparency).  Is a reducing
lens possible?  Are there any tradeoffs with a reducing method?

 

A setup for a reducing lens -
http://archive.cnx.org/resources/fb001372e360c7bddb6939364bfb77a57420e7dd/5.
15.png