S8 Small scale production of functional circuits
Initial skills rating *
September 2012
I have no experience in this area what so ever.
I have no experience in this area what so ever.
Monday 10th October 2011
Today following our tutorial from Dean, I went on to make my own PCB board as I wanted to consolidate what I had learned.
PCB stands for printed circuit board.
The raw PCB board is a composite board made up of a layer of fiberglass and a thin sheet of copper which is coated with a light sensitive film (black in colour). Dean had provided us with a PCB mask which had been designed using computer software and printed onto acetate.
1. Taking the printed mask and removing the protective coating from the PCB, the PCB was placed black side down onto the glass screen of the UV light box with the PCB mask sandwiched in between.
It is a good idea to have some writing on the PCB mask so that you can identify which way round the components will go. The writing should appear in reverse when viewed on the UV glass for the writing to be readable after it has been developed. (It is important to quickly place the PCB board in the light booth once the protective coating has been removed as the UV light in daylight will start breaking down the photosensitive coating.
2. By turning the light box on for approximately 3 minutes and exposing the PCB board to UV light, the photosensitive coating will be left with an impression of the PCB mask. (Depending on the condition and age of the UV tubes, the time taken to expose the mask and get a good image can vary between two and four minutes)
3. The photo resist developer, a Ferric chloride solution, is made up following the manufacturer’s instructions. In this case a bag of crystals were dissolved in 500ml of warm water and would have remained active for about ½ an hour. Ferric Chloride is a strong alkaline solution that dissolves the developed photo sensitive film and exposes the copper beneath.
4 . The board is placed face up into the tray of developer and the solution is agitated until a clear PCB track is exposed. As ferric chloride may cause skin irritation, it best removed from the solution using tongs.
5. The board was rinsed under running water.
6. The PCB board is secured into a frame.
7. PCB board and frame are lowered into the Rota spray for about 1 1/2 minutes at 43 degrees or until the exposed copper has been removed.
Lowering the frame into a second rinsing chamber the board is then washed.
8. Having guillotined the board to size, it is now ready for drilling.
9. Always keep the board track side up to prevent damage to the PCB track whilst drilling..
10.The board is now ready to be assembled! Following the diagram the appropriate components are selected.
11. The components were soldered into place using a soft solder containing a flux core.
13.It is important to note that both the prongs on the components and the track need to be heated by the soldering iron for the solder to make a good joint.
Knowledge/Skills rating ***
February 2011
I realised I had not updated my skills rating since my taught session with Dean. I chose to make my own PCB following the tutorial to help reinforce my learning. I went on to use this to make my electronic spider money box. If i had had more time I would have made a new board to house the thermistor but as it was just one component it was acceptable to have it free from the board. As I used the LEDs for eyes and these had to be contained in a very small space and angled through the casing it was necessary also to have these remote from the PCB board.
I realised I had not updated my skills rating since my taught session with Dean. I chose to make my own PCB following the tutorial to help reinforce my learning. I went on to use this to make my electronic spider money box. If i had had more time I would have made a new board to house the thermistor but as it was just one component it was acceptable to have it free from the board. As I used the LEDs for eyes and these had to be contained in a very small space and angled through the casing it was necessary also to have these remote from the PCB board.
July 2012
Sadly due to circumstance beyond my control I was unable to develop my electronics for my activity board which means I never did get to make any more PCB boards. Therefore I am really glad that I made a very good record of my work. This is something I am very bad at but I must adopt this method of working in the future. I any more experience, I will be able to refer back to this record.
Sadly due to circumstance beyond my control I was unable to develop my electronics for my activity board which means I never did get to make any more PCB boards. Therefore I am really glad that I made a very good record of my work. This is something I am very bad at but I must adopt this method of working in the future. I any more experience, I will be able to refer back to this record.