Monday 01 April 2013
Below is a photo overview of how we make our own PCB’s using a UV box and developing the boards.
Disclaimer: Wear appropriate safety equipment when handling chemicals and when using UV boxes and lights. Don’t try this at home unless you are confident in your ability to pour chemicals and acids into containers and not get them on yourself !
Step 1: Make a stencil which printed onto transparency film, ideally using a laser printer with the printer set on the darkest settings. Any gaps in the print will appear on your finished PCB so if you have any tracks which didn’t print correctly you can cover them with permanent pen ink on the stencil before exposing the boards to the UV light.
Step 2: Expose the UV sensitive board on the UV box. Depending on the brand of board and strength of the UV lights this can take a few minutes using commercial UV boxes. On our DIY box which was built using an old scanner case it takes 50 seconds to expose the board.
Step 3: The exposed board should be placed straight away into photo developer and this will wash away any exposed photo resist leaving the PCB tracks from your stencil on the copper on the board.
Step 4: Next you must etch the board in acid, we use ferric chloride which is supplied in a dried form which is mixed with water. The acid works much faster if you have access to a bubble etching tank with heater but we find that a small board will etch in around 20 minutes if you place the tray with the board and acid into a container with hot water to warm the acid and then keep rocking the tray to keep everything moving.
Step 5: Once the board has finished etching you need to clean the photo resist covering off, we use alcohol to remove the coating but specialist removal chemicals are available.
Step 6: Drill the board and then it is ready to use.
If you over expose the board as shown in the left board below you will get very thin tracks or breaks on the pcb tracks. The circled areas on the photo show where 0805 resistors are fitted and surface mount mosfets.