1.11 PCB Production and 1.22 Electrical safety

Key learning points

PCBs are manufactured using CNC machining or chemical etching
- CNC machining mills away copper using a CNC router and design software
- chemical etching uses UV light, photo-resist, and chemicals to remove copper
  - CNC machining is safer and less wasteful, but slower
  - chemical etching is faster and cheaper, but uses hazardous chemicals
PCB design involves placing components, creating tracks and pads, and using design software
PCB amendment involves updating components, modifying tracks, and repositioning pads
PCBs are used for space-saving, reliable connections, ease of repair, and professional appearance

There are two main ways to manufacture printed circuit boards (PCBs):

Tools required: Computer with PCB design software, CNC router and copper-clad board

Design the circuit using PCB design software
Export the design to the CNC machine.
Secure copper-clad board to the CNC bed.
Run the CNC program to mill away unwanted copper.
Drill component holes, if needed.
Clean the board to remove debris.
- Pros: safer, no chemicals, less waste
- Cons: slower for complex designs

Tools required: UV light box, photo-resist board, developer solution and an etching tank.

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Copy
Photocopy or trace a copy of the circuit onto an acetate sheet to make a mask of the circuit. This is called the PCB Artwork.
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Expose
Place the mask into an ultra-violet light box and set the photo-resist board on top. Close the box and expose for three minutes.
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Develop
Place the board carefully into the developing solution (Sodium Hydroxide) to remove all the film except where the tracks are. Once you can see the copper tracks rinse under water.
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Etch
The chemical (Ferric Chloride) is heated to about 50°C. It will dissolve any unprotected copper leaving a PCB with copper tracks on one side.
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Rinse
Rinse with water.
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Drill
The last stage is drilling the holes for the components. A small PCB drill is used for this purpose.

Design the circuit using PCB design software. Print the design onto a transparency/acetate sheet. This is called the PCB artwork
Prepare the photo-resist board by peeling off the protective film. Place the transparency on the photo-resist board. Expose to UV light in a light box (approx 3 minutes)
Develop the board in Sodium Hydroxide solution (about 10 seconds). Rinse the board with clean water
Place in a heated etching tank of Ferric Chloride (15-45 minutes). This will remove unwanted copper. Remove and rinse when etching is complete.
Drill component holes with a PCB drill
- Pros: faster for multiple boards, cheaper
- Cons: uses harsh chemicals, more environmental concerns

When working with printed circuit boards (PCBs) or , it's crucial to stay safe. Here are the key hazards to watch out for:

short circuits:
- double-check connections before powering on
- use insulated tools to avoid accidental shorts
- keep metal objects (like paperclips) away from live circuits
component damage:
- handle components gently, especially integrated circuits (IC)
- be aware of static electricity
- check polarity of capacitors and diodes before inserting
burns:
- let soldering irons cool completely before storing
- be careful with hot components after extended use
chemical exposure (for pcb etching):
- wear gloves and eye protection
- work in a well-ventilated area
- dispose of chemicals properly

Keep things organised and you'll reduce risks!