Tuesday, April 26, 2011

Tf-spider boards arrive...

Yay, I received the tf-spider boards... I used Laen's service (DorkbotPDX) so I got 3 copies of the design.  All 3 looked visually correct so I did some quick electrical tests (resistance between linked pins and unlinked pins) and I couldn't find any pad that wasn't connected as intended or any unintended connections.  The one mistake I made was that I made the holes too small (but since this doesn't matter for the surface mount parts and I have female connectors that will fit it's not a big deal - I think I made them 0.032 instead of 0.040).  The holes were where they should be (not off center) and very consistently aligned across the board.

Not a great image here but what I wanted to look at was the quality of the mask and the copper layer.  I expected the silkscreen to have lower resolution (but it's still useful even for the tiny letters that indicate the component values - this makes it much easier to assemble).  The copper layer is better than I expected with extremely uniform line width and uniform spacing between traces.  This is nice to see since the backplane (which isn't here yet) is going to push the production process much more than this board.

Here you get to see dust and fibers (I was handling the board a lot) but what's interesting is that you can see the way the mask and the silk screen is handled by the vias - no problems at all... Overall the productions quality is much better than I expected.

Here is the Xlinix coolrunner II cpld soldered on the board.  One thing I'm always afraid of is how the pads accept solder (it can vary quite a lot and is a very unhappy thing if the solder doesn't wet correctly).  These boards were very happy with the solder I used (classic 67/33 mixture).  There aren't enough components here to justify breaking out the solder paste so I just hand solved.  (Ignore the residual flux because I didn't clean the board after soldering here... also ignore the fact that my soldering skills are not as perfect as they should be and I put too much solder on some pads).  There were no problems on the surface mount pads and the through the hole components had nice flow even thought the holes were smaller than they should have been.

If you look at the design there are clear block of elements that make it easier to assemble a few components and the test for function (for example the resistor + led combo on the cpldVccio power lines -> assemble then test with a couple of AA batteries).  Then the slightly more complicated ldo/resistor/cap/led combos - do the 3v3 first and after testing do the 1v8 because it uses the 3v3 output as the input source - directly connect the 1v8 enable from the msp430 socket).  Then the filter caps and the cpld and then all the female connectors. 

I'm still working on the msp430 controller code (time is at a premium when the weather is nice) but I'll post it when it's done.