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PCB Fabrication from CAD to Reality

Have you ever wondered what goes into making a printed circuit board? This post will show you semi how-to/diy fabrication for single or dual layer circuit boards (PCBs). That is board fab using a UV photo sensitive dry film (acid resist) and a copper chloride etchant.

PCB Fab Overview

Steps in fabrication of printed circuit boards:

  1. CAD 
  2. Mask/Pattern
  3. Copper Clad 
  4. prepping a copper clad 
  5. Dry film application
  6. Exposure 
  7. developing 
  8. Etching 
  9. Solder stop
If you want to see a working board I made with this process, check out my post about my capacitive discharge spot welder (CD Spot welder)

Circuit board CAD Design.

The image above is a circuit board CAD screenshot. It's one of my first printed circuit board designs. 

For this particular project it was the first working model or prototype. 

It was probably the third time I had used PCB CAD. 
A lot of the design decisions were also influenced by knowing I was going to etch it myself as well. 

Anything in green extends between the top and the bottom layers or produces copper on both sides when actually manufactured. Anything in red is copper on the top layer anything in blue is copper on the bottom layer. White are outlines of where components go. Which can translate into keeping the copper in those areas but I'll probably go more in depth on pcb cad and layers in a later post. 
If you've used Photoshop the idea of layers is very much the same; but instead of separation for ease of movement or editing or compositing separation often has to do with the entire physical manufacturing process after the design is done.

One last thing on the particular design above; I look at it now and see a lot I would change (the most basic being a power plane on the top layer of the bottom half)

 I was new to the whole process and would have done quite a bit differently if I were to revisit this one. That said it's still a good PCB teaching experience and the board worked.This post is a Work in progress.

The rest of the photos below (where possible) will use the PCB design shown above

Tools and materials needed:

You can do this on a laptop touch pad but you will probably hate it and yourself for least in my experience it is so much faster with an external mouse.

Printing Your Pattern/Mask/Design

Screen printing emulsion transparencies are what you want. There are most of layer absorbed inkjet ink extremely well. 

What you need:
  • An inkjet printer. Pigment-based models do better.
  • Inkjet transparencies 
  • Light box
  • Spray adhesive 
  • Guillotine cutter.

The only trick here is you need to double layer your transparencies. That is print them twice line them up with the light box and adhesive them to the other. The dual layers are required for blocking the UV light. 

Copper Clads

These are to PCBs like a sculptures raw block of marble. Another way to consider it is a blank circuit board.

A copper clad is a layer of fiberglass (usually fr4) with one or two sides covered in copper. The idea is to make a circuit board you eat away or etch the copper not needed leaving only the connections you wish to form between your components.

Circuit board etching is what's considered a subtractive manufacturing process. For reference 3D printing would be an additive process.

Prep Work

What you need to prep a copper clad.
  • Nitrile Gloves
  • Scour pads (green dish pads)
  • Comet Cleaner
  • Isopropyl alcohol.
  • Distilled water
  • Plastic basin

You should wear nitrile gloves while preparing and handling afterwords. 

Any oils on the copper clad will interfere with the adhesion of the acid resist film in the next step.

Basically the point is to get everything off the copper clad except shiny uncontaminated copper.

UV Photo Sensitive Acid Resist Film

The next step is to apply acid resist. There are liquid and film acid resists. I went with the dry film process.

I tried three brands and paid attention to prep for each. In my experience Finding actual Dupont riston is hard but worth it.

What you need: 
  • Plastic basin 
  • Distilled water
  • Tagboard pouch 
  • Laminator 
  • Scissors
  • Nitrile gloves
  • Uv Photosensitive acid resist dry film
  • Red or yellow lights to work under 
I had lifx wifi controlled LEDs in my living room so I simply set them to red when working with the film.

The film is carefully cut to the size of the copper clad and then run through a laminator.

Actually the really shitty part is there is a protective layer on both sides of the blue film. There's quite a bit of effort required to get it bubble free and firmly laminated to the board.

The best trick I found was dropping the prepped copper clad into a tub of distilled water. Then peel off your film squares first protective plastic and float it on the water. With gloved hands lift the copper clad from the bottom of the tub to the floating film. Repeat for side two (if doing double sided boards.

These cheap laminators are all it takes. Use a tag board folder though to avoid maring your film

Sit period. After exposure it's best to place the board in a dark room or envlope and let everything settle down chemically for a little bit.
(not pictured)

Developer Bath

A heated solution of washing soda and water.

 This and a gentle brush makes the magic happen

If your prep work , exposure time, bath temp and time were correct here's what you end up with

All the copper you want to save is protected by acrylic and everything else is ready to be disolves away.

Acid Bath

The photo bellow is after a solder stop layer has been applied. I'm trying to find a photo of the welder board after acid Bath before solder stop but as of yet have been unsucessfull 

Some of the edges look odd for a reason. You might notice the resist on the photo bellow is a different color. It was non name brand and it sucked. So I got used to reinforcing trouble areas with nail polish pre acid Bath. The actual name brand Dupont riston didn't need that step but the board above was the first I etched with it.

Also the black smudges are after a failed attempt at a top coat(see bellow)

Dilling (2 sided pcbs)

If you have a two-sided printed circuit board you often have places where one side needs to connect to the other. In the CAD program this is as simple as placing a via when it comes to the actual fabrication you're going to want to drill press.

Riveting (the holes)

Solder Stop (the black layer)


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