Etching heater

Etching with Ferric Chloride is a messy business. So the quicker you can get it over with the better - and for a few reasons. One way to decrease the time taken to etch is agitation: basically stir the mixture or dunk the board in and out of the etchant.

The problem with this, of course, is more opportunity for spillage. And with ferric chloride being such a nasty staining solution, you don't want it splashing around the place.

Another way to speed up etching is using heat. Ferric Chloride works best at about 50 degrees. But sitting the solution in a bath of hot water only increases it's temperature by a few degrees at best. So we tried one of these things - it's called an etching heater, but really it's just a fancy aquarium heater!

It's like a super-duper tropical aquarium heater in a sealed glass case- complete with temperature control on the top, so you can set the thermostat to anywhere between 40 and 60 degrees: perfect for ferric chloride etching! Just search ebay for "etching heater". This one cost less than �15 including delivery to the UK and took about 8 days to arrive.

We put about a litre of ferric chloride solution (made up quite strong, with a full 500g packet of crystal dissolved into about 1L of warm water) into a sweetie jar. This should allow us to etch rather larger boards if we need to. Just stand the heater in the solution, switch on and back away. After about five minutes, the entire thing is up to perfect etching temperature.

(heating the solution is easy - plop in the heater and switch on!)

A relatively small board can now be etched in about two-to-three minutes, rather than the 15-20 minutes it has been taking recently, when etching "cold" (as the winter nights draw in, it does get colder in the nerd cupboard, so ambient temperature is about 16-20 degrees).

The great thing about etching quickly is that because the board is in the solution for a lot less time, the chance of under-cutting is much less (under-cutting is where the etchant eats away at the copper under the toner-transfer mask because the board is left for too long in the solution). By etching hot and quickly, we get really sharp, clear etching, even with thin traces. 

In the photo above, we've managed to get traces down to 0.2mm and they've etched perfectly. When etching "cold" we would rarely go below 0.38mm trace size to avoid over-etching the tiny thin traces.

Here's the board cleaned up, with a micro sd card connector soldered in place, ready for populating. In short, 

BuildBrighton PCB making workshop

Yesterday (Saturday) was BuildBrighton's PCB making workshop, as part of the Brighton Digital Festival.
From a worryingly quiet start, we ended up with six people taking part in yet another successful practical workshop - 100% success rate!

Over six hours, we introduced the attendees to schematic drawing using ExpressPCB (it's much simpler and easier to get going with than Eagle for anyone new to electronics/PCB layout) and their PCB layout software. A few people had brought along projects that they were working on and we helped them create PCBs for their own creations, while everyone else set about recreating the famous BuildBrighton Drawdio  kit.

(all the tools needed for making your own PCBs, including ExpressPCB software, press-n-peel blue paper, ferric chloride, a sanding block and a heavy duty laminator!)i

Sadly, the workshop was such as success and everyone was having such a lovely time that we forgot to take any more photos! But, for reference, for anyone who attended and would like to know more:

The first step was to create/draw your schematic (the bit with the little squiggles and symbols for electronic components). The most important thing to remember here is to give every component on the drawing a unique Part ID (the name can be anything, it's that part id that's referenced in the PCB layout software)

Then we drew our actual PCB layout using ExpressPCB.
File -> Link schematic to import the list of part IDs used in our circuit. A lot of people found it easier to drop symbols for all components used onto the screen before starting the layout process (menu Component -> Component Manager). Make sure that all components are drawn on the top (red) layer!
The most important thing to remember here is no crossing the lines!
In a few instances, some people ended a trace with a round pad, allowed another trace to pass "through" and started the trace again the other side, with another pad

Where a trace is continued after allowing another to "pass through" we tend to draw a connecting line on the silkscreen (yellow) layer, to act as a reminder when assembling the final board.

Once the PCB layout was complete, it was time to get on with the toner transfer.
For our workshop, we used Press-n-Peel (blue)

Toner transfer paper tends to be quite expensive, so rather than just print straight onto the blue sheet, we printed our PCB layout onto plain paper first (using a laser printer - inkjet just won't work for this!). Then cut out a piece of p-n-p blue just a bit larger, stuck it over the printed image with regular tape (shiny side down, powdery side up) and re-printed the image. This gets the PCB image onto the smallest sized bit of press-n-peel, meaning you've got plenty more left for another go!

With the image on the press-n-peel, we cleaned up some copper clad board (available from various online suppliers - eBay sometimes is a cheap source) using a fine-grit sanding block.
Sanding the board not only cleans it up (it needs to be bright and shiny and all traces of oxidation removed) it also provides a slight "key" for the toner image to stick to when transferred.

Tape the image (face down) onto the shiny copper board using paper-based masking tape, preferably cut to fit into a corner of your copper board (so it takes less cutting later). It's important not to use sellotape or similar plastic backed tape, as this will melt during the transfer process.

We used a heavy-duty laminator, but you could also use a regular household iron.
After three passes through the laminator, the image is transferred onto the copper board. Douse in cold water (carry the board by its edges, it gets very hot!) and carefully peel off the backing.

When done correctly, there should be no black traces left on the backing sheet. Check all traces carefully on the copper board. Where necessary, touch up any missing detail with a fine-tipped permanent (black) pen.
When happy with the transferred image, it's time to actually do some etching!

Ferric Chloride (FeCl) is messy stuff. Make sure you're wearing your old clothes and get ready to clean up any spillage immediately (it stains!). We made up a small batch using hot water and about a quarter of a pack of crystals. Etching in warm solution is quicker than in cold, although the end result(s) are the same.

The Ferric Chloride solution should be a dark brown in colour. If it's pale yellow, you need to add more crystals. If it's an orange-y colour, it will probably work but will take a long time. If you're re-using old solution (that's already had a few boards etched) and it's a dark green-y colour, it's getting a bit old and you should consider refreshing it. A dark brown (which is a golden yellow colour at the edges) is the perfect strength mix.

Submerge the board and either tip the container slightly to wash the mixture over the board (large boards in a small, shallow contianer) or dip the boards in and out of the mixture (smaller boards, suspended in a tall container on bits of wire). It will take 10-15 minutes for the board to etch completely.

The copper board etches in a couple of stages and if you keep checking it regularly, you'll see:
Firstly, the board goes a very vibrant pink.
Then the edges of the board (where the copper is exposed) start to look a little bit green.
Finally, the edges of the board turn a beige colour (the natural colour of the board the copper was stuck to) and the etching continues, usually from the edges, towards the centre of the board)

When no trace of copper remains (double-check for little bits of pink between the black traces on the board) your PCB is fully etched. Congratulations!

Some people prefer to drill then clean their boards - we did it the other way around.
You can use nail-varnish remover or similar acetone-based cleaner, or simply scrub with a fine-grit sanding block until all traces of the black toner are removed and you're left with a shiny new PCB.

During our workshop, everyone successfully made their PCB, etched and drilled to a finished standard! A few brave souls even populated their boards with the Drawdio components provided - and they worked!!

All  in all, another successful BuildBrighton workshop and a great day making stuff!

MIDI bass frets

There's something not quite right with our laser printer.
It seems to be printing bitmaps at about 95% of full size.

We made up a couple of frets for our MIDI bass and allowed a generous border around each piece (so it can be cut/sanded/filed to an exact fit after being mounted onto the guitar neck)

The only thing is, that even allowing for this relatively large border around each piece, they are only just the right size to go on the fingerboard.

Here are some surface-mount resistors connected onto each section of fingerboard. These boards will be mounted face down onto the neck. The pads on the edges of each board will be connected by strips of copper tape, running under one, over the top of the  (plastic, non-conductive) fret between the two, and joining the pads on the next section of fingerboard. By doing this, we can create a resistor ladder for each string along the length of the guitar neck.

BuildBrighton midi workshop

Over at BuildBrighton, we're working on putting together a make-your-own-MIDI-instrument workshop to teach people the core basics of MIDI messaging and how to send and receive MIDI commands. As part of the workshop, we'll be providing all attendees with an Arduino shield with some buttons, LEDs, volume/pitch bend pot and more.

As the workshop is just a few weeks away (on Saturday 23rd June) we've got some boards to make up!

Which means the nerd session or two is going to be taken up etching and drilling PCBs.

Using a mixture of press-n-peel blue and the cheap Chinese alternative, we've managed to toner transfer about 20 boards.

After a marathon etching session (about three hours!) here are no less than sixteen boards (the final three boards were still etching when this photo was taken)

All we need now are some spanky cool looking stickers (for the component side) from Robot Steve then we can drill and populate the boards next Thursday night.

Speed up etching times

Like many people who post on the internet, I've used online guides for etching my own PCBs. I use press-n-peel blue and a laminator (a big chunky metal thing built by Alphatec which is just perfect) to create toner-transfer etch masks. Like most other people, I put my ferric chloride into a shallow, flat container and etch by gently rocking it from side to side, so that the etchant "washes over" the PCB:



The other day, after making up three failed Invisible Instrument PCBs and putting all my messy PCB making equipment away I decided to quickly throw a board together to try out a new idea. Instead of pouring the ferric chloride into a shallow tub, I suspended the board on a piece of wire and just dunked it in and out of the etchant (I always replace my ferric chloride into a large coffee jar - the batch I have at the minute has been reused regularly for about 12 months and is still going strong!)



The peculiar thing was the board etched in no time!
Normally I heat up the etchant by placing the shallow tub into a larger container filled with hot water. This time, I etched "cold" but inbetween dunking, lifted the board completely clear of the etchant. It's well known that agitating a copper board in ferric chloride speeds up etching (and that heating the etchant gently also reduces etching times). What I hadn't realised until now was that exposing the board to the air during etching also seems to improve etching times too.



In fact, I noticed that the board etched from the top, down. i.e. the parts of the board that were out of the ferric chloride for longer actually etched quicker. While this seems counter-intuitive, maybe some chemistry genius will explain how oxidisation (or something) improves etching time.......

Anyway, it works for me. And from now on, my ferric chloride will stay in it's large coffee jar - my brown-stained plastic tubs have been junked and if anyone asks, I'll tell them I'm a dunker, not a rocker.