Week 8

Title of Activity : Etching process

Objective : To develop the circuit on the PCB board

Content/ Procedure :

1)  
Firstly, one goal was to keep the circuit single sided so I etched using single sided PCB board. This will allow I to gain some experience before moving on to double-sided.

2)  

Here was a list of materials I need to produce a single-sided board.
Materials: A dedicated CAD program or simple art package, an inkjet or laser printer, compatible transparency film sheets, a UV exposure box, pre-sensitized copper clad board, optional: tin-plating crystals

For developing the board:

Materials: Sodium Hydroxide (Caustic Soda crystals), water, cold, a pair of plastic tweezers (for getting the the board out of the chemicals without using your fingers)

For etching the board:

Materials: Ferric chloride (crystals or ready made solution), water – hot, but not boiling, a small tray, slightly bigger than PCB is ideal

For drilling:
Materials: Ideally, a bench-mounted vertical drilling machine of some sort, a drill bit of 0.75mm diameter for most holes (0.9mm for pin headers etc.)
 
 3)

I printed the bottom side layer on a piece of paper from a high quality magazine. I used one actual page from the magazine, the thicker and shinier the magazine paper the better, but I do not use the cover. I used a laser printer, not an inkjet. If the printer uses ink cartridges and not toner cartridges, it will not work.

4)

I drenched PCB layout with sunflower-seed oil. I removed superfluous oil carefully with tissue paper. The sunflower-seed oil is used to make the white part of the layout paper transparent for light.

                                   Drench layout with oil                            Greasy layout

PCB UV Exposure

I removed the protective plastic layer and peeled back from the photosensitive PCB. I placed on the toner side of the greased layout into the copper of the PCB. I carefully captured air-bubbles that gently pressed away from underneath the layout. The PCB with the layout is now covered with an appropriate sized windowpane and I placed it on a piece of plain polished tile or marble. The tile or marble absorbs the heat coming from the UV bulb, which is significant. Three to four minutes 300W bulb UV exposure from a distance of 30-40 cm will do the photo process. I removed the PCB when all procedures were finished.

 

  Place layout with toner side on copper of the PCB

 

   Cover PCB and layout with window-pane

 Exposure

 
5)

I developed the PCB with a 1% solution of sodium hydroxide NaOH. I did this solvent by adding 10 gram of sodium hydroxide pellets to 1 liter of water and mix it until everything was dissolved. I used a brush to speed up the developing and clean the PCB during the process if the PCB was still greasy due to the applied sunflower-seed oil. The developing process takes about 1 minute. The traces should become clear and the exposed photosensitive layer has dissolved.

6)  

I developed PCB with etched in a solution of ammonium persulfate, I added 1 liter of water and mix it until everything is dissolved. I dissolved ammonium peroxydisulfate into water. I heated it which is air-bubble circulated etching fluid tank available. At higher temperatures the etching performance decreases. The etching process is an exothermic reaction, it generates heat. Then, I cooled the etching tray. I minimize the amount of copper to etch by creating copper area in my PCB layout as much as possible. When the ammonium peroxydisulfate was dissolved it is a clear liquid. 

 

Rock the etching tray

 

The epoxy of the PCB becomes visible

 Finished

 7)  

 

I drilled all the holes for the through-hole parts using the correct size PCB drill bit and rotary tool. I drilled     large mounting holes with a normal drill. PCB drill bits are carbide and made to drill through fiber glass that would quickly dull standard bits. There are  a few very common sizes of bits and these are often sold in packs. I used  0.0260″ for IC holes and 0.0310″ for resistors and caps.
      

Result and analysis : 

PCB board before developed

PCB board after developed

PCB board after etching

 UV box for exposure

 Conclusions :  

In this week, I just study how to etch the circuit on the PCB board in the PCB lab using its materials to produce the completed circuit. Then, I know how to develop it with the supervision of technicians there. They gave me advise and guideline on how to build the printed circuit using the correct techniques. I hope with this knowledge, can help me in future when I work later.