making-pcb-cliff-shirra-tutorial-september-2018

Making PCBs (Printed Circuit Boards)

Aim:

Create an electronic artwork and transfer the “positive” image onto a copper clad board which can then be etched.

Materials Required:

Copper clad board

Positive Photoresist

UV Exposure Source (or the sun)

(Homemade using an old scanner bed)

Transparency Film

Positive PCB Artwork on transparency film

Copper Etchant

Rock (requires mixing with water) Pre-mixed
Other etchants are available other than ferric chloride.

Positive Developer

Many brands available from different manufactures, both pre-mixed or powder form (to be mixed with water). Combined positive and negative developers are available.

Drill press (or small hand drill [ie Dremel]) and drill bits for drilling holes in the PCB

Containers suitable to hold the developers and etchants- usually small tray made of hard plastic

PPE (personal protective equipment) such as gloves and glasses

Safety data sheets for all chemicals used

Method:

Develop your electronic circuit and then draw it in a suitable cad/software package. I use DesignSpark. It is free and creates a BOM (Bill of materials) for you. Using it in conjunction with Library Loader ensures that pad spacing/layout for pre-created CAD (computer aided design) representations of components are done already.

Once the design has been laid out in your chosen design/drawing package, print it out on a transparency film.

Clean the copper clad board with suitable materials (sometimes even fine sandpaper for badly oxidised copper). Ensure no oils from fingers etc are on the copper surface.

Coat the copper with the positive photoresist to manufacturers specification. If using precoated board peel the protective plastic film off the board.

Place the artwork on the sensitised surface and expose it to UV light for adequate time. There may be some need for experimentation at this stage. The artwork should be pressed firmly against the board surface to avoid light creep under the edges of artwork tracks and pads etc.

Remove the artwork and place board into the developing solution. Leave it in there until all the exposed areas have washed away. Agitation of the tray/container may be necessary. Only be the areas that were protected from the UV light (ie the tracks, pads and text) will remain. Wash residue developer off with water.

Place the board into etchant and gently agitate the tray/container back and forth. The copper will “dissolve” where there is no resist. Time will depend on temperature and strength of solution. Wash residue etchant off board with water.

Drill board where required and solder components onto board and then check the operation of your circuit.

Happy circuit board making!

Remember to adhere to all safety requirements and recommendations for any processes of this type. Dispose of all materials in a safe and environmentally responsible manner.

Conclusion:

Once all the constituent materials have been purchased, the cost is reasonable to make 1 off boards. The etchant, specifically ferric chloride, can be used multiple times before disposal is required. Storage and disposal are possible constraints. If a design needs “tweaking” then artwork can be changed or redrawn and pcb made immediately. Once the artwork has been prepared a board may be made in about 30 minutes, using pre-sensitised copper. This time does not include drilling. Overall cost of the raw materials is relatively cheap.

Future Presentations:

    • Using Designspark
    • Using Library Loader
    • Making your own UV LED exposure unit

Note: Images in this document were taken from the internet. This document has not been prepared for commercial gain. The author does not endorse any manufacturer that has its name on an image. It is accepted that any product specifically mentioned in this document may be used by the Author but is equally accepted other products may be the same, or better.