Feasibility of diy PCBs?

Hi all,

I'm really fascinated with the reprap project and am keen to give it a go, but I'd like a bit of advice if you experienced builders can share. Some of my questions may seem very basic and obvious but please bear with me, remember everyone had to start somewhere.

I want to tackle the electronics first, specifically building the motherboard and a stepper driver, and connecting up a couple of steppers I got from old printers. The thing is, the pcbs are out of stock and I'm wondering if it's really feasible to build my own.

I've got very basic skills and knowledge, but am treating this as a learning exercise.

I'm new to photoresist etching, but done a bit of research, and am pretty comfortable with the copper trace printing, UV exposing, developing and etching process.
Double sided pcb means I'd have to get it to line up very well, but I've found a technique that will probably work.

I'm willing to get the 0.8, 1.0 and 3.0 mm carbide drills. Don't have a drill press, but hoping that the dremel with steady hands won't break too many drill bits.

Now comes the problem: I've printed the motherboard 1.2 and stepper 2.3 traces out, and there are quite a few vias that are pretty much 0.7mm holes. Let's assume I line the two sides up well enough. From what I read, on professional boards they might use a tiny copper through tube, but I can't see a handmade board having that, so do I just put a dollop of solder in each via hole?

Now I'm also new to smt soldering, but the instructions seem pretty straightforward, follow a preheat profile then spike to correct temp to melt solder and turn off. The problem is, I'm wondering if I would need to mask off all the copper traces except for the component pad portions, to prevent components from swimming up the copper traces. As I understand in professional pcbs, they have a conformal mask covering all areas not to be soldered.

Another potential problem is the fine tracks and clearances of 0.5mm in the design. It looks ok in the 600dpi postscript printout, but I'm wondering if photoresist etching is really that good to capture all that detail accurately.

I guess what I'm asking is, is creating a pcb such as that for the motherboard and stepper driver really something doable even for an experienced hand, much less a newbie? Or do people just farm the pcb manufacturing off to the pros?

The other thing to consider is that I'm in the land where everything is 10 times the price (Australia) so getting the tools/raw materials just for the PCB alone is exorbitant, but I'm willing to give it a go if feasible, for an educational experience, the satisfaction of doing something myself, and potentially the flexibility to create other boards in the future.

But it won't come cheap; just as a comparison, a piece of double sided positive photoresist board to make the motherboard and stepper board will already cost AU$8 = US$7. And that's before developer, etcher, drill bits, UV lamps. I cried when I saw Makerbot selling them for US$2 each (but they are out of stock and probably won't do another run anytime soon.)

As an aside, sourcing all the smt components and connectors would cost AU$50+ = US$43 for each board. Yup, each. Just components, IC and connectors, no board, no solder, no postage.

I guess an alternative would be to redesign the board for single layer, using through hole components like someone else is doing, but some components can't be found in a bigger form, and I also don't know enough to avoid design problems with EMF interference, etc.

Another alternative is to farm it out to a pro shop, but I don't see them doing anything for less than 3 figures.

Anyway, am I barking up the wrong tree or barking mad? Any advice and thoughts welcome, thanks in advance!

Andrew

Edited 2 time(s). Last edit at 09/11/2009 12:47PM by acediac.

Hey Andrew,
If you're going to build your own V1.2 mobo, it is certainly possible, just use a 0.8 or 0.9mm drill bit, available from Jaycar, and use a piece of wire soldered from both sides of the board to get your vias ok.

Clearances can be a problem, though you could try using Press n Peel, available from Jaycar, a friend of mine managed to get own to 5mil track and space with that stuff, so photo-resist should be just the same.

Get yourself a Dremel drill press, which you should get from your local hardware shop, and also get a 3 jaw chuck for the Dremel too, that will let you drill a lot easier, but don't forget to buy a punch before you drill the holes where you want otherwise you may end up with a few holes not where you want them.

For the V1.2 driver board, I reckon you should go for that instead of the V2.3, both do the same thing, but the 1.2 board uses through hole technology, which will give you important experience with making boards. The v1.2 boards are easily adaptable for single layer, providing you use wire jumpers.

For the vias, I drill a tiny hole, put a thin bit of wire (usually resistor trimmings) through the hole then solder both sides. A bit ugly, but solder has too much surface tension to flow through the hole. I'd consider trying the laser printer + photo paper method. There are loads of instuctions online on how to go about this, basically you laser print the design onto photo paper, then iron onto the board, then soak off the paper. I managed to transfer a layout for the drv8811 (0.65mm between pin centres!) without problem, though I forgot about it and left it in etchant for too long. I wouldn't try the uv method, its more difficult, and more expensive (you can keep trying with the laser printer method for only the cost of a bit of ink and paper vs a whole board)

Hurro acediac

Sounds like you are planning on having some fun.

Take a quick look at my blog I wrote up how to make reasonable single sided PCB's cheap at home.

[aka47.adsl24.co.uk]

This uses the Toner transfer method so works with any reasonable Laser printer and is as cheap as it gets.

I covered how to line up on both sides of the board. Although I was discusing lining up the ident layer with the copper on the lower side. you can use a similar technique to do the same on the top for double sided.

Getting the right paper is key, but very much doable.

Hope this helps.

On vias, professionally these are through hole tinned. For an at home method as already suggested above put some tinned wire links through and solder both sides.

On through hole components, solder these both sides of the board as the leads are quite often vias as well.

On surface mount components, if you are worried about these and redesigning a board layout make up some single sided adapter boards. these usually have pads for surface mount (can be done manually with care using a 1mm soldering iron bit) with the pads connected back to through hole pins that can be pluged into sockets or soldered (see note above on through hole) onto the main board. As these are single sided they are cheap to make and lend themselves well to the techniques described at the link above.

Hope this helps

Cheers

aka47

---

Necessity hopefully becomes the absentee parent of successfully invented children.

Thanks for the great suggestions, guys! I'm encouraged to give it a go now!

Surely is is cheaper and much easier to buy them from MakerBot as they now ship them ready assembled.

---

[www.hydraraptor.blogspot.com]

Oh no, they don't do they? I wish I'd waited now! I had no idea that was in the offing.

Still, my (hand) soldering is getting pretty good!

Hazel

The pound v the dollar returning to something sensible sure does help too.

---

Necessity hopefully becomes the absentee parent of successfully invented children.

Hazel, yes I felt for you when they announced it. [store.makerbot.com]

---

[www.hydraraptor.blogspot.com]

reusable etchant: [members.optusnet.com.au]

Just finished reading this.

Most excellent.

When I get a workshop built I will have a play with this. Probably in a to be built bubble etch tank. I think I would prefer this technique to ferric chloride.

I like the idea of making more as you go, you can give some away to a friend then.

cheers

aka47

---

Necessity hopefully becomes the absentee parent of successfully invented children.