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[[Category:Equipment]]
[[Category:Equipment]]
[[File:PCB_Photoexposure_Jig.jpg|500px|right]]
When the 10mil isolation paths offered by CNC Milling are insufficient, photolithography becomes the PCB fabrication method of choice.
When the 10mil isolation paths offered by CNC Milling are insufficient, photolithography becomes the PCB fabrication method of choice.


The process is simple, consisting of:
=PCB Design=
1) Dry film photoresist, laminated onto copper clad board by laminator.
Recommend gEDA. Project template with CNC Mill and gerber export scripts available on [https://github.com/mirage335/gEDA_Template github].
2) UV exposure. Can be done by low-power UV laser strapped to CNC mill or high-resolution inkjet printed transparencies and various random light sources (eg. sunlight, CFLs, etc).
 
3) Development. Strong basic solution (sodium carbonate for negative resists, sodium hydroxide + sodium silicate for positive resists) chemically removes exposed resist.
=Process=
4) Etching. Acid solution removes exposed copper.
Simple, consisting of:
5) Striping. Sodium hydroxide completely removes photoresist residue. Probably unnecessary and/or excessive.
# Photosensitive copper clad board. If not already available, more can be made by laminating dry film photoresist to bare copper clad board.
6) Solder mask. Optional. Repeat steps 1-3 and bake in oven at 220F for 10 minutes. Alternatively, laser cut a negative solder mask from blue tape, and apply high-temperature spraypaint.
# Via/hole drilling, outline milling, etc. Best done automatically on CNC mill.
7) Via/hole drilling, punching, etc. Easy to do with the thin variety of copper clad board. Alternatively, can be done automatically on CNC mill. If using printed transparency photomask, CNC milling should be done first to ease alignment.
# Photomask. Printed on transparencies at high-resolution. Some laser printers may require double layer photomasks. Alternatively, <445nm lasers may be able to selectively expose the photoresist.
# UV exposure. Sunlight or high-brightness CFL bulbs can expose the photoresist in ~30 minutes.
# Development. Use a foam brush with the appropriate developer solution from the chemicals shelf.
# Etching. Copper etchant acid solution removes exposed copper.
# Striping. Sodium hydroxide completely removes photoresist. May need additional UV exposure.
# Solder mask. Optional. Laminate two dry film photoresist sheets onto the PCB, apply photomask, expose, and develop. Alternatively, laser cut a negative solder mask from blue tape, and apply high-temperature spraypaint.
 
=Assembly=
For large boards with hundreds of components, reflow can be quicker than manual soldering.
 
# Laser cut solder paste stencil from blue tape. Apply stencil to PCB.
# Add smooth, paper thin layer of solder paste with a razor.
# Remove stencil.
# Place components on the appropriate pads.
# Carefully melt the solder with the hot-air reflow tool. Hold the hot-air tool close to the components at 400C and maximum airflow, watch carefully, and progressively move the tool across the board as solder melts.
 
=Resources=
HacDC has the requisite resources:
* Laser printer.
* Transparencies.
* Photosensitive copper clad board.
* Dry film photoresist.
* Various photodeveloper chemicals.
* Copper dissolving etchant.
* CNC Mill.
 
=Demo=
Chemically developed and etched PCB. Photomask remaining.
[[File:DevelopedEtched.jpg|500px]]


For surface mount projects, solder paste stencils are the easiest assembly technique, and can be made from blue tape on HacDC's laser cutter.
Photomask stripped, bare copper PCB electrically tested.
[[File:DevelopedEtchedStrippedTested.jpg|500px]]


HacDC has all the required materials. The chemical process has been thoroughly tested, and a multilayer photomask has produced slightly better than 10 mil resolution. A more capable photomask printer is strongly expected to enable 'professional' 6 mil or better resolution.
Aligned reverse side.
[[File:DevelopedEtchedStrippedTested_Reverse.jpg|500px]]


=Reference=
=Reference=
http://www.instructables.com/id/Killer-PCBs/
http://www.instructables.com/id/Killer-PCBs/
http://www.mgchemicals.com/downloads/pdf/negativePrototyping.pdf
http://www.mgchemicals.com/downloads/pdf/negativePrototyping.pdf

Revision as of 20:47, 27 January 2014

PCB Photoexposure Jig.jpg

When the 10mil isolation paths offered by CNC Milling are insufficient, photolithography becomes the PCB fabrication method of choice.

PCB Design

Recommend gEDA. Project template with CNC Mill and gerber export scripts available on github.

Process

Simple, consisting of:

  1. Photosensitive copper clad board. If not already available, more can be made by laminating dry film photoresist to bare copper clad board.
  2. Via/hole drilling, outline milling, etc. Best done automatically on CNC mill.
  3. Photomask. Printed on transparencies at high-resolution. Some laser printers may require double layer photomasks. Alternatively, <445nm lasers may be able to selectively expose the photoresist.
  4. UV exposure. Sunlight or high-brightness CFL bulbs can expose the photoresist in ~30 minutes.
  5. Development. Use a foam brush with the appropriate developer solution from the chemicals shelf.
  6. Etching. Copper etchant acid solution removes exposed copper.
  7. Striping. Sodium hydroxide completely removes photoresist. May need additional UV exposure.
  8. Solder mask. Optional. Laminate two dry film photoresist sheets onto the PCB, apply photomask, expose, and develop. Alternatively, laser cut a negative solder mask from blue tape, and apply high-temperature spraypaint.

Assembly

For large boards with hundreds of components, reflow can be quicker than manual soldering.

  1. Laser cut solder paste stencil from blue tape. Apply stencil to PCB.
  2. Add smooth, paper thin layer of solder paste with a razor.
  3. Remove stencil.
  4. Place components on the appropriate pads.
  5. Carefully melt the solder with the hot-air reflow tool. Hold the hot-air tool close to the components at 400C and maximum airflow, watch carefully, and progressively move the tool across the board as solder melts.

Resources

HacDC has the requisite resources:

  • Laser printer.
  • Transparencies.
  • Photosensitive copper clad board.
  • Dry film photoresist.
  • Various photodeveloper chemicals.
  • Copper dissolving etchant.
  • CNC Mill.

Demo

Chemically developed and etched PCB. Photomask remaining. DevelopedEtched.jpg

Photomask stripped, bare copper PCB electrically tested. DevelopedEtchedStrippedTested.jpg

Aligned reverse side. DevelopedEtchedStrippedTested Reverse.jpg

Reference

http://www.instructables.com/id/Killer-PCBs/ http://www.mgchemicals.com/downloads/pdf/negativePrototyping.pdf

Subcategories

This category has only the following subcategory.

P

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