Gareth Griffiths

Home PCB

During the making of my Micromouse Project in my second year of Uni. I felt the need to develop my own Home PCB Manufacturing process. This venture turned out to be so successful that my tutor asked for a complete guide for other students who wished to make PCB’s in their own time.

Introduction

There are numerous expensive professional methods used to etch PCB’s but it us entirely possible to etch a complex single sided board for as little as £30. However to repeat ably etch many boards this process will cost in the region of £70

Requirements list

to make just a few single sided boards it is possible to buy a kit from maplins for £10 (N64BX) and photopaper (Cannon GP105 inkjet paper) and use a laser jet printer available to you .

To make more than 5 boards then you will need to spend about £70

	Part	Bought From	RS Stock Numer	Cost
	Ferric chloride hexahydrate crystal,2kg	RS	551-277	£17.19
	Medium size Suregrip(TM) gloves,1 pair	RS	861-631	£2.57
	FFP1 9300 unvalved disposable respirator	RS	286-7192	£1.05
	Visitor spec eye shield	RS	699-997	£1.75
	Printer – HP Laser Jet 2100	Ebay	-	£30
	Double/Single Sided Copper Board	Maplin	-	£2-£4
	Photo Paper – Canon GP-105 A4 Inkjet	Staples	-	~£10
	Alcohol + Wirewool	B&Q	-	~£5
	Clothes Iron	Sainsburies	-	~£4

Notes

• The minimum pad size is about 0.6mm, this is not because of the etch process but because it is difficult to drill the small pads, sometimes causing them to lift.
• The HP Laserjet 2100(off ebay) is recommended because it is not as efficient as modern printers. It applies more ink therefore giving a more resilient etch resist on the board.
• The more etchant is used the more it becomes saturated, it may be possible to perform electrolysis on the solution to reclaim the ferric chloride though I have only had limited success with this. It’s easier to just get rid of spent solution and make a new batch.
• I’ve made about 30 boards with the same solution, though the time taken to etch a board rises from about 10 minutes in ferric to 40.
• When designing your board I would treat double sided boards as single sided boards with sky wires, that is, it’s easier to make a through hole via in some open space on the board rather than trying to connect a component on both sides. This is for two reasons. One: if your double sided board is out of line then the only things that will be out of line are the through hole vias, so just bend some extra wire on the end that doesn’t line up and solder in place. Two: Soldering through hole vias are just easier than trying to solder an IC or a DIL socket on both sides and more reliable.

Method

If you can, cut the board with about 1cm excess on either side, this just makes it easier to move around when you have the iron on the board as it does get really hot. When I started etching board I didn’t have access to a guillotine so I used a pair of garden shears, which did the trick, though to do with any sort of decent accuracy you need two people! Tin snips might work or a dremel with the small circular saw blades.

• For single sided – once you have designed your board make sure only the pads, vias and tracks are showing. Select print and print in solid black (2 tick boxes in eagle).
• Take the photo paper and feed it into the top tray of the printer. Laser jets become jammed from photo paper easily so by doing this the printer has to pull the paper through less rollers. Print your design onto the photo paper.
• Double sided – print one side of the board then when you turn to the next layer mirror it (usually the top layer). You can run the same piece of paper through the printer once but after that the paper starts to warp making it harder to place accurately on the board.
• After printing both layers cut them out with about 5cm of excess paper either side of the boarder of your design.
• Put the two sides together (photo facing in) and line them up by sight (I find a patio window is one of the best ways but a desk lamp works well too), then tape them together using a thin tape like parcel tape or sellotape, leaving one side untapped making an envelope that you can insert a double sided board in later.
• Clean the board with wire wool and alcohol until you can almost see a reflection in the board. This is a very important step, if the board is even the slightest bit dirty, the ferric chloride may get under the toner and etch out the copper from under neath it. Cleaning the board also speeds up the etching process. I usually take about 10 minutes doing this part, cleaning the board once, drying it and then cleaning it once again.

Once your satisfied that the board is completely clean (don’t get any fingerprints on it) leave the board to dry or gently wipe with a kitchen towel until dry.

• For single sided boards place the photo paper face down on the board roughly in the middle.
• For double sided insert the board in the envelope style cutout made earlier. If this had been taped up well the board should just fall in and it should stay lined up on either side, unfortunately the only way to tell is etch the board. The largest I’ve ever been out is about 3mm.
• Heat the clothes iron to its highest temperature. I would put something underneath the board too, in the picture below we used cardboard from a box of beer, though this wasn’t anywhere near good enough and the table in the picture below got pretty badly burnt! Also I wouldn’t count on using that clothes iron for clothes afterward.
• Iron on the design for 20 minutes applying heavy pressure, making circular motions over the tracks with the tip of the iron for a couple of minutes, then leaving the iron resting on the board for a few more minutes and repeat. After a while if you lift the iron off you may see a light outline of the ink through the paper or the paper slightly browning. At this point the ink has come away from the paper and adhered to the copper.

• Once you think you’ve finished ironing on the print, quickly remove the iron and dump the board in a tub of cold water.
• Leave to stand for 20 minutes then peel the paper off very gently. If there is a considerable amount of ink on the paper that you peel off then the process has failed and you’ll have to clean the board again and try another transfer.

• use a toothbrush to remove the finer pieces of paper left on the board until no paper is left, sometimes I find using a sharp knife helps getting the paper out of via holes. Be careful as to not remove the black ink. Errors can be touched up with a black permanent marker.
• Check the board for errors, rather than etching it and wasting a board and your time.
• Now mix the ferric chloride as per instructions on the container.
• Mix in a disposable bucket (rather than the kitchen sink like I did! It stains just about anything)
• Apply safety gear. Ferric Chloride is an irritant and in some cases can stain the skin yellow, rinse immediately if it does contact your skin.
• Swill the board in the solution checking every couple of minutes to see how much copper has been removed. Swill until only black tracks remain. If you so wish you can rinse the board in water then check to see if etching is done and then re-immerse in ferric chloride.

• This takes between 10 and 40 minutes depending on how diluted the solution is. try to use as little solution as possible (like in the picture).  If the solution is starting to take a long time to etch, just make up a new batch of etch-ant (make sure to get rid of the spent solution according to your local laws).
• Once etched rinse the board in water.
• Dry the board and rub off the black ink with wire woll leaving the copper tracks behind.
• Drill the board. I’ve always had access to a proper PCB drill press and drill bit in my University (UWE), but if you have a dremel or something similar that can go to a very high rpm and some tungsten carbide drill bits then you can use that. Though a drill press would make it a lot easier for yourself and the drill bits are very delicate.

Here is an (not yet etched) example board with the line widths next to them.

Here is a Double-sided board being etched in an old fish tank.

I wouldn’t count on this working perfectly the first time around (Practice makes perfect) but this is the most successful technique for me.

Good Luck!