Printed Circuit Board Fabrication

This was the week guys! I finally got to learn the whole printed circuit board fabrication process. Of course I had some ups and downs trying to get here, scheduling wise, but I did it nonetheless. Today I met with my on-site mentor Dr. LaBelle to discuss the process. From this meeting, I learned that there is actually two ways to create a circuit board: the old fashioned way and the new way. In his lab, he does both. But he likes to start off newbies, like myself, with the old way to get a better understanding of it all.

Now what is the old fashioned way and the new way? The old fashioned way just means a circuit board is created chemically, while the new way is done by a machining. Since I didn't do the machining fabrication, I know very little about that process. Dr. LaBelle did tell me, though, that a machine strips off the copper for the circuit board; and that this process is standardly used now a days due the process being faster and able to produce fine details onto the circuit board.

So now onto the chemical fabrication process. I will tell you ahead of time that these steps came from Dr. LaBelle's lab. Just like the screen printing process, he puts these directions and these pictures in his lab so his students know what the process is when they do it. This isn't what the circuit board for the pressure sensor will look like, it will look like the design I put in a previous blog. All credit goes to Dr. LaBelle's lab for these pictures and steps! He graciously gave these to me for my update during our meeting so I could have a visual aspect to this blog. Since I couldn't take pictures while I watched the demonstration (I left my phone in my backpack).


STEP 1
Place mask on top of pre-sensitized board after blacking type is removed and place into light box

* Setup etchant tank. For a 6' x6'' board, make 437.5 gm of sodium persulphate to 1.75 L ddH20 (warning pH 1.0). Stir well for 15 min. Fill etchant tank, place bubbler on and heater unit (next to bubbler) and set at 6.0 for1/2 hr and turn down to 4.75 which yields 40 C


STEP 2

Remove mask after 2 min UV exposure

* If using UV light box. Set time to 120 sec. Place PCB onto glass, cover with artwork, turn VAC on and leave on (VERY IMPROTANT) during exposure!! Note: board will not change color at this step.

STEP 3

Remove exposed photoresist with sodium hydroxide and scrubbing for 1-2 min.
Wash board with water to stop developer.

 * While developing, add 40ml of sodium hydroxide developer solution to 360 ml ddeH20 (warning pH 14.0). And pour onto board in plastic tub (glovers needed for developing an etching steps). Gently scrub the board using sponge brush for 1.5-2min to remove the exposed photoresist so that the design is left in green photoresist surrounded by copper. Rinse the board using water to stop developing.

STEP 4
Etch board in ammonium persulphate for 10 min to remove exposed copper

 *The final removal of the copper is done during agitated etching in an sodium persulphate solution for up to 15 min (can take 30 min sometimes). As soon as all the copper on the exposed area is removed, remove board and rinse in water to stop etching. The board will be a greenish yellow with the design in photoresist.

STEP 5

Wash board with warm tap water for  > 30 sec to stop etchant and immediately engrave numbers

*Individual electrodes (or strips) will be cut out form the PCB with a slow speed, fine tooth band saw. The final photoresist can be removed with acetone rinse to expose the copper for electroplating. Otherwise store with photoresist left on

So there it is, the fabrication process of circuit boards. Again, I'd like to thank Dr. LaBelle for allowing me to use these pictures and directions. It took him and his lab a long time to get the fabrication process correct for the printed circuit boards (years he said). If you guys have questions, comment in the comment section below. Until next time!



- Tina Smith