PCB etching instructions

Making PCBs @ LHS

Here's the overall process

<graphviz border='frame' format='svg' >

digraph rfboard{
  rankdir=TD;
  size="14,9!";

  cleaning [label="Copper board cleaning",shape=box,style=dashed];
  photoresist [label="Photo resist coat",shape=box,style=dashed];
  resist_cure [label="Photo resist curing",shape=box,style=dashed];

  breadboard [label="Breadboard",shape=box];
  board_layout [label="Board schematic",shape=box];
  uv_exposure [label="UV exposure",shape=box];   
  develop [label="Develop (Tank A)",shape=box];
  etch [label="Etch (Tank B)",shape=box];
  strip [label="Clean (IPA) ",shape=box];
  drill [label="Drill",shape=box];
  solder [label="Assemble and solder",shape=box];

  breadboard-> board_layout [label="Fritzing"];
  board_layout-> uv_exposure;
  cleaning->photoresist;
  resist_cure -> uv_exposure;
  photoresist->resist_cure;
  uv_exposure->develop;
  develop->etch [label="Spray wash"];
  etch->strip [label="Spray wash"];
  strip->drill [label="Spray wash, dry"];
  drill->solder;

} </graphviz>

Note : see Pcb for other references

Printing Board Schematic

Plain paper works surprisingly well! The printers at the space do a good job.

If you use eagle, you can use the print option (as opposed to exporting an image). Print on normal paper first and check dimensions on some components.

Some people get better (resolution mostly) results with acetate, but this needs to be special laserable acetate. Do not use normal transparency! Melting a sheet onto a fuser is expensive!

If you want to get really upmarket, you could try Mega LaserStar transfer film (for printing with a laser printer of some sort). Hugely expensive, but does take on plenty toner and produces excellent results.

Double Sided Boards

There's a couple of extra steps required for two-sided boards:

• Print both sides out on separate sheets (or cut one sheet in half)
• Align the two sheets and staple them together to retain registration
• Cut them to size so that they are slightly smaller than your photo PCB material.
• Remove the protective film on both sides, place the PCB between the two transparencies leaving a slight overhang, and tape the PCB to the transparency. so it does not move when you flip it during exposure!

UV Exposure

Use the UV Exposure Box to expose a photosensitve board.

Make sure your print is the right way round so that your board isn't back to front when it's etched!

5 minutes with acetate and something like 15 with paper. The uv board should look green with faint lighter green traces where your traces are.

Ensure that there are no creases or folds, and that your paper/film is perfectly flat against the photo board!

Developing

Put the board in the developer (tank A). Developer does not need to be heated to above room temperature to remain effective. Developing should take around 30 seconds to a minute or so - but check on the board to see when it is complete. All of the copper to be removed should be exposed, and only your tracks should remain coloured ( probably green for UV exposure board).

You may wish to give the board a rinse after this stage.

NOTE : the developer in tank A is from Mega Electronics, also sold through Rapid. It works well with photo PCB material from the same source. It does NOT work with Maplin photo material !

Etch

The Cupric Chloride etchant is in tank B

Follow instructions on the notice, but the board is done when all the exposed copper is removed. The balance is removing too much copper and getting breaks in traces vs not enough and some small closely laid traces may have bridges. You are looking for clean edges to your traces - not wobbley "chewed" looking edges.

Stripper

The stripper is in Tank C

The stripper removes the photo-resist left over after etching. Use the stripper for the specified time then scrub the black off and you should have nice copper traces! Use a multimeter to check for bridges.

After this stage, you may want to rinse the PCB in clean water, and then IPA.

Drilling

Some people have found drilling holes works best using the mill. Normal drill press probably not ideal (not immune enough to wandering!).

Test / Assembly

If you're doing a double sided board, you'll need to solder up your vias first (we have no through hole plating facilities). A bit of solid core wire works well for this.

See also

More info on the process, including photos of an SMT breakout board

Project:DIY_PCB_Making

Results people found with materials/compounds

Name	Date	PhotoResist source (Rapid photo resist spray/pre sentesized deluxe board?)	UV exposure stencil used (paper/acetate?)	Exposure time	Develop time	Etch time	Notes
mentar	3/4/2014	Farnell presentesized epoxy glass FR4 board	Plain paper	2	5	12	First run in the new space
Miguel	13/5/2014	white, single sided presentesized board (space stock)	Laserable acetate supplied and printed on by local printshop (£1.50)	3	1.5	8	Professionally printed acetate

Project:DIY_PCB_Making

For those wanting to get training

If you want more traning please add yourself to the list here and there'll be another workshop

Name
Liam Lynch
Rob Kam
Bradley Wood
Ian Lewis (Ianadan)
Jiri Richter
Nathan Spence
Colin Cooper
Matt Camp
Ertion Axha
Chris Roberts
Daniel Garrido
Owen Smith