I thought I’d have a go at getting my PWM controller PCB made professionally.
There are quite a few options out there these days, most seem to be based in HK or China. I used Seeedstudio’s prototype PCB service; 20 Dollars plus shipping for 10 copies of a 5cm by 5cm double sided board, how’s about that for a bargain! If you only really need a single board then I guess it could seem expensive, especially if you make a mistake and have to scrap them. But for hassle free PCBs I think 20 Dollars is more than a fair trade against the time it would take to make them myself using toner transfer. In fact when I compare it to the amount of hassle it takes to make a double sided board at home with toner transfer I don’t know why I didn’t try this before.
There are restrictions to getting super cheap prices. The board size, thickness and silkscreen options are limited unless you pay more, but they fit what I need. What you get is a double sided board with double sided solder mask and silkscreen plus a minimum trace/space size of 6mil. 6mil is pretty fine detail and far beyond what I can reliably do using toner transfer where my limit was around 12mil. Five of the boards are electrically tested to ensure they have been built correctly. That ensures that the PCB doesn’t have any shorts or open circuits and faithfully represents the design you submitted. It doesn’t ensure that your design is going to work… That’s up to you!
The down side of course is that it’s not immediate. You have to plan ahead and send them off to be manufactured, then assuming your design is suitable you’ll get them back in a couple of weeks. I sent my order off on the 18th of Nov and got the boards back last Thursday (2nd Dec) so that’s… Wow! 14 days! Not bad!
Of course the nice thing with toner transfer is that if you’re on a roll and need a circuit board right now and have a few spare hours then you can get results fast. But these days with a two year old child and a busy job I find it’s rare to get the time anyway, at least not at a time of day when it’d be convenient to be messing about with chemicals or drilling the board with a noisy Dremel.
Seeedstudio provide a DRU (Design Rule Set) for Eagle CAD so you can check that your board meets the spacing and sizing requirements. They also provide a CAM routine that separates the layers out into the required Gerber files. Its sounds like tricky thing to do but in fact it’s fairly simple. Gerber files are in industry standard format and essentially a text file. In our case we need a collection of files, one for the drill locations and sizes, 1 each for the copper top and bottom, 1 each for the solder mask top and bottom and 1 each for the silkscreen.
It’s important to check that your board passes the DRC in Eagle. This checks the board for placement problems that don’t meet rule set and will highlight issues that are sometimes hard to spot such as components that are too close together or traces or pads that are too small. It’s also important that you make sure your component library is accurate. The DRC checks things based on the information provided in your component definitions. If you use the libraries that come with Eagle you’ll probably be fine, but if you have modified them or drawn your own you’ll have to extra careful that all the various layers are correct, especially the solder mask that you normally don’t care about when doing toner transfer.
Another important thing is to make sure that your silk screens work. By default Eagle places the component names (Layers 25 tNames and 26 bNames) right next to the component. In most cases this is not the best location, it’ll be underneath another component or over a pad. So you’ll need to “smash” the component to be able to move the name independently from the component. That way you can move, rotate or scale the name to a better place… Or just delete it if it is really unnecessary. At this point it’s handy to add some extra labels to identify the design or point out other useful features such as power ground or test points.
The last thing is to make sure you have a clear outline of the board in your dimension layer as this will be used to cut the board out. And in Seeed’s case you need to make sure that the board dimensions are within the limits for the service.
So once you’ve got all the layers tided double check and send them away!
Anyway here’s mine.
So there you go. Not perfect as you can see, I’ll have a few things to correct for next time, but all in all a great success, I’m already lining up my next order with a re-working of my lighthouse circuit.
Finally, I’ve got 9 spare boards so if anyone reading this would like a bare board to build the circuit for themselves I’ll be happy to send you one for 5 Euro including shipping.
The parts list is as follows;
Part Desc Package ---------------------------------------- C1 100nF E2,5-5 C2 1uF E2,5-5 FET 2n7000 TO92-SPLAYED ICSP ICSP_HEADER 1X06 LED Connector AK500/2 LED1 LED 1206 SMT LED2 LED 1206 SMT PIC PIC12f68329P DIL8 PWR Connector AK500/2 R1 50R R0603 SMT R2 1K R0603 SMT R3 1K R0603 SMT R4 10K R0603 SMT R5 330R R0603 SMT R6 1K R0603 SMT SW1 ROTARY-ENCODER Sure Electronics U$2 LM317M SOT223