Practical PIC Projects


How I make my prototype PCBs

How I do it

Please note.  This page refers to the prototype PCBs that feature on the project pages.  The PCB's sold from the on-line store are professionally manufactured.

I occasionally get emails from people asking how I make the PCBs that feature elsewhere on the site.  For the benefit of those people and anyone else who wants to know, this is the low down on how I do it.  I have to tell you now though it's not very hi-tech.

I use laser artwork film and a HP LaserJet 1320 printer (better printers don't seem to make a difference - I've printed artwork on very expensive printers and the quality is no different). I've also used clear OHP transparency film with fairly good results. 

I always use pre-coated positive photo resist boards.  My experience suggests it needs to be kept in the dark, keep it cool and don't have it sitting around for months before you use it. I usually buy the board as I need it.  I use both FR4 and economy CEM/1 laminate.  The cheap stuff is easy on drill bits and well...cheaper so it's good for prototypes.

Don't try and cut the board down to the size of the artwork, I like to have at least 10-15mm oversize all round.  You can trim the board to size once it's been etched and drilled.

The artwork needs to be printed so the toner is facing the copper, in other words you don't want the thickness of the artwork film between the toner and the copper otherwise the light blurs the edges of fine traces.  Depending on you PCB CAD program you may need to mirror the artwork to do this.  Also, make sure you put some text somewhere on the artwork, then when you get it printed onto the film, you can easily see which way round it needs to go.

I also use ground planes on my PCB layouts for the simple reason that it reduces the amount of copper to be etched away and therefore my etching solution lasts longer:-) 

The UV light box is one of the few 'proper' pieces of equipment I use.  This is something I would suggest you really need to buy rather than try and build yourself.  I get good results using an exposure time of 2m40s 

The developer lives in a plastic food container at room temperature, stored with the lid on and depending on how many boards go through, it can last for months.  I mix it slightly on the weak side so it doesn't develop too fast, usually goes in about 30-45 seconds.  I find gently rubbing the surface of the board helps lift the photo resist.  When I mix a new batch I always try a small scrap of board to make sure the concentration is about right.

Always rinse the board in cold water, don't transfer straight from developer to etching solution or vice versa.

The etchant lives in another plastic food container.  I took a couple of corks from wine bottles, cut them in half and glued them to the bottom. This stands in a plastic processing tray which I fill with boiling water just before I start the etch to raise the temperature of the etching solution (ferric chloride).

Unless you're etching a lot of boards regularly you really don't need anything more than this.  It also has the advantage that you don't need to mix up large quantities of etching solution; I use a 1litre food container with about 300mL of etching solution in it. This easily handles a 100mm x 80mm board and I can just squeeze in a 100mm x 160mm board.

I normally dump the PCB in the etching solution and let it sit for a minute before taking it out and inspecting it - the exposed copper areas should have gone a matt pinkish colour, if any areas are still shiny I rinse the board, dump it back in the developer for 10 seconds and repeat.

Once I'm happy all the exposed copper is starting to etch away I agitate the board in the solution by hand (wear a glove obviously).  With fresh etching solution at a reasonable temperature (35oC-45oC) the boards are done in about 10-12 minutes, if it gets to 20 minutes something isn't right and I will usually give up on it.

I have a small PCB drill and various drill bits that I buy from suppliers on e-Bay. The sizes I use a lot are .75mm, 0.85mm, 0.95mm, 1.05mm and I just buy these in  boxes of ten for about 10GBP.  I also have sizes from 1mm up to 3.15mm which covers everything you are likely to need.  The hardest thing is lining the damn drill bit up with the PCB but that's an age / eyesight thing:-)

There is a bit of an art to getting it right and occasionally I seem to do everything the same and the finish is lousy, but generally results are good and I can go from artwork to drilled PCB in under 45 minutes.  

Double sided boards

Double sided boards can also be done, the trick is to get the top and bottom artwork aligned very accurately to start with.  The second problem when using a single sided light box is keeping it all aligned when you flip the board over to expose the other side.  The way I do it is as follows:

  1. make sure your board is over size because you will need to stick one edge to the artwork. 
  2. align the top and bottom artwork films, then tape one edge so it forms a hinge.
    When you do this you want 6-7cm between the actual artwork image and the hinge so that when you insert the board in between the two layers of film it doesn't misalign them to much.
  3. now tape the one edge of the board to the bottom artwork film so it can't move.
  4. everything should now be fixed together and will stay aligned so you can expose one side, then flip the whole lot over and do the other side.

The trick to this is making sure the two films are perfectly aligned when you tape them together and not having the hinge too close to the artwork image.

Here's an example of a board I made using this method.  Double Sided PCB

Things to know

For reference I buy most of my stuff from Rapid Electronics. Part numbers are:

  • Artwork film   39-0774
  • Photo etch PCB  34-0160 or 34-0105
  • UV light box 34-0700 (this is similar to the one I use, mine is actually 25 years old now)
  • Developer  34-0790
  • Ferric Chloride etchant   34-0785 
  • PCB Flux Spray SK10 87-0715 
    (this stuff is really good, it works as a flux for soldering, left to dry it provides a protective coating for the exposed copper and will dissolve and lift the photo resist - give the board a quick spray and then wipe over with a cloth)
  • Drill stand 85-8208 (you are going to need a precision drill stand of some kind, tungsten carbide drill bits snap easily and drilling by hand you will break many of them)
  • Drill 85-0350 (also sold by RS Components part # 546-1494)

Drill bits I get from a company on e-Bay called Gloster Tooling, good selection, fast delivery, look under Tungsten Carbide Micro Drills.

The developer and ferric chloride etchant are not very people friendly chemicals so avoid contact with skin, wear eye protection etc. and read the safety information at least once before you use the stuff - it's really hard to read it when the stuff is already in your eyes!

If the ferric chloride gets on to your skin it stains it brown, it will ruin your stainless steel sink and stain clothing brown, even making holes in them given enough time.  Don't lean over the etching solution or breath in the fumes rising from it, it's bad for your lungs.  Don't say I didn't warn you.

Tungsten carbide drill bits, especially the sub 1.5mm diameter ones, will snap with the slightest lateral loading so drilling by hand won't work.  Even using a drill press you need to make sure you hold the PCB firmly and don't move it while drilling.  Sooner or later you're going to snap a bit so I always buy the ones I use a lot in a box of 10. 

Since drill bits snap, you should wear some eye protection.




Fig .2

Fig. 3

Fig. 4

Fig. 5

Fig. 6

Fig 1. Artwork, printed on film using an HP LaserJet 1320n

Fig 2. UV light box, single sided, very simple, not cheap though.  Exposure timing is done with a kitchen timer and I normally give it 2m40s

Fig 3. Close up of my etching container.  Feet are made from a synthetic wine bottle cork cut into four and glued to the corners of the container.  This allows the water bath to circulate underneath

Fig 4. This photo shows the developer (1), a photographic processing tray (2) which I fill with boiling water a couple of minutes before I start the etch. The ferric chloride etchant in another food container (3).  Not forgetting the glove (4) since I agitate the PCB it in the etchant by hand.

Fig 5. PCB drill, drill press, selection of tungsten carbide drill bits (from e-Bay)

Fig 6. All being well you should finish up with something like this.