My first professionally made PCBs

A stack of PCBs ready to be assembled

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.

Top side of the board.

It's a bit of mix of surface mount (SMT) and through the hole components based on what I had to hand in my parts box. The resistors are 0603 SMT, the LEDs are 1206 SMT and the voltage regulator is a LM317 in SOT223 SMT package. Everything else is through the hole.

The support tabs on the encoder needed bending a little bit to make them fit. Also there's no copper around the tabs, it would have been handy to have something to solder them to but not a big deal. I should have double checked my library part.

Top side with the SMT LEDs and resistors soldered on.

 

0603 resistors are pretty small but not hard to solder even if they do end up looking a little bit blobby.

 

Bottom side. LM317 regulator providing 5v for the PIC

A couple of errors... but nothing critical.

Assembled, tested and... Working!

I kept the new one pretty much the same size as the stripboard prototype. If I went for a completely SMT version I could probably reduce it to around half the size, but the encoder and the screw connectors dominate the layout so there's no real need for it to be smaller.

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
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2 thoughts on “My first professionally made PCBs

  1. Pingback: Simple PWM control for LED strip « Catmacey's stuff

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