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Optimizing for best photomaster quality

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+---
+layout: post
+title: "Optimizing for best photomaster quality"
+date: 2014-02-22 05:48:15 +0400
+comments: true
+categories:
+ - pcb
+ - photoresist
+---
+
+Objective:
+: find the combination of paper, environment and printer configuration resulting in most faithful
+ reproduction of the original image with least amount of defects and highest toner density.
+
+Result:
+: use high-quality transparent film ([Lomond 0707415][0707415] works), verify printer output
+ very rigorously and check which of the "Paper type" settings results in best imprint. No settings
+ appear to affect toner density.
+
+[0707415]: http://online.lomond.sk/en/detail/0707415
+
+<!-- more -->
+
+Tools
+-----
+
+Printer
+: [Brother DCP-7010R](http://www.brother.ru/g3.cfm/s_page/92250/s_level/39720/s_product/DCP7010R), Brother cartridge/toner
+
+Laminator
+: [ROYAL PL-2100](http://www.royalsupplies.com/Laminators/PL-2100-Laminator.html), 120°C roller temperature
+
+Materials
+---------
+
+"MGChemicals" film
+: [MGChemicals 416-T 100µm PET film](http://www.amazon.com/gp/product/B005T8WR6I)
+
+"Lomond" film
+: [Lomond 0707415 125µm PET film][0707415]
+
+Finding correct paper type setting
+----------------------------------
+
+The printer driver handily provides a paper type setting, which includes "Transparencies"
+as an option. I've tried really hard to figure out what exactly does the setting change,
+to no avail. I've read the entire service manual for the printer, but it sadly does not
+mention anything about that.
+
+My guesses, as there aren't as much parameters the printer can control:
+
+ * Toner density (i.e. changing Vbias). This does not appear to be the case.
+ * Fusor temperature. This has been confirmed (see below).
+
+However, after setting "correct" paper type for printing on PET film, i.e. "Transparencies",
+I've noticed some odd distortion. I have decided to repeat the job on plain paper, setting
+the paper type to both "Plain" and "Transparencies". The results are horrifying:
+
+{% fancybox gal-paper-type /images/photomaster/2014-02-22/paper-type.jpeg 700 %}
+
+Have you noticed anything? It's not immediately obvious to naked eye.
+
+{% fancybox gal-paper-type /images/photomaster/2014-02-22/paper-transp-highlight.jpeg %}
+{% fancybox gal-paper-type /images/photomaster/2014-02-22/paper-transp-highlight-2.jpeg %}
+
+That's right. When I select "Transparencies", the printer (or perhaps its driver)
+distorts the image oddly. It appears as if it duplicated some pixel rows and removed
+some others. The picture printed with "Plain" setting is reproduced faithfully.
+
+By the way, on actual transparencies the distortion is identical. You may even notice it now
+in the [previous note][]:
+
+{% fancybox gal-resist /images/photoresist/2014-02-13/try-8-developed.jpeg 300 %}
+
+Do you see how the 0.3 mm line is wider than 0.35 mm line? That's not how millimeters work.
+I initially assumed it was an exposing-related defect (UV reflecting off copper), but no, that
+distortion is present in exact same way on the negative I've used.
+
+[previous note]: /notes/2014-02-16/optimizing-for-best-photoresist-adhesion/
+
+Using quality laser printer film
+--------------------------------
+
+Make sure the transparent film you're using does not deform while in the laser printer
+fusor. For example, this is the imprint on "MGChemicals" film left after a few tries:
+
+{% fancybox gal-mgchem /images/photomaster/2014-02-22/mgchemicals-fail.jpeg 500 %}
+
+ * Picture marked "first" was done on a freshly unpacked sheet.
+ * Picture marked "second" was done immediately after on the same sheet. As it can be seen,
+ the sheet was deformed after first run, and not all toner was well-attached.
+ * Picture marked "sandwich" was done by running the film through the printer together with
+ a sheet of plain paper. Likely, the fusor temperature is not enough to reliably
+ melt the toner in this case. If I set the paper type to "Thicker paper", the imprint
+ is much better, but is still far from perfect.
+
+It is nearly impossible to take a picture of, but if you view the sheet under a sharp angle
+to a light source, it can be seen that it's all "wavy", and, additionally, it has four
+deep depressions from some internal guiding mechanics of the printer.
+
+Running such a distorted sheet through a laminator with roller temperature of 120°C (which is
+less than typical fusor temperature of a laser printer) partially fixes the distortion: the
+sheet still shows the "wavy" pattern, but the depressions from rollers are no longer present.
+
+Printing on such fixed sheet results in somewhat higher quality imprint (fourth on the picture
+above), but it's not as good as first one.
+
+Another way to verify quality of your film is to print the exact same pattern on film and
+on paper:
+
+{% fancybox gal-mgchem /images/photomaster/2014-02-22/mgchemicals-fail-grid.jpeg 500 %}
+
+The film and paper are lying with their toner side adjacent to each other. A highly nonlinear
+distortion can be clearly visible. Of course, it's not possible to print a high-quality
+photomaster on such film.
+
+Not satisfied with this, I bought "Lomond" film. It is still deformed slightly by the printer
+rollers, but that doesn't at all affect the imprint quality. Also, as evident by the grid
+test, it has near zero in-plane deformation even after five runs through printer:
+
+{% fancybox gal-lomond /images/photomaster/2014-02-22/lomond-win.jpeg 400 %}
+{% fancybox gal-lomond /images/photomaster/2014-02-22/lomond-win-grid.jpeg 400 %}
+
+Toner density
+-------------
+
+I have not found toner density to be affected by paper type or DPI settings. Toner conservation
+was (obviously) set to "Off" at all times.
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