Tuesday, 14 May 2013

Artwork for screen printing PCBs

Since we got back from Berlin (after a two-day drive on each leg of the journey, and a total of 1,500 miles there and back) we've been giving lots of thought to silkscreen printing for making lots of PCBs.

We've gone back-and-forth with numerous designs, going from A4 panels (so front and back would fit on a single A3 frame) to 160x140 panels (double-sided 200x200mm copper clad board is easier to source than A4 sheets) to eurocard and back to A4.

After about six iterations of the same board design - each time reducing the number of jumpers and vias on our double-sided board, we still couldn't get a design which used as much of the copper board as possible: no matter what the layout, there was always quite a bit of waste on each panel. And then we had an epiphany moment....

We've been concentrating on making a hex-based board for the Dreadball Board Game. And because the miniatures stand on 25mm clear bases, we've been concentrating on making each "cell" on the board at least 30mm - allowing for a 2mm border around each cell, this allows a 28mm push-button surface (miniatures for other games are sometimes provided on 28mm round slotta-style bases). And it's because of these relatively large cells we can't get them to fit nicely on any "standard" sized copper clad board. But here's a thought....

The miniatures in Dreadball are much smaller than standard (read Games Workshop) miniatures. Originally they were designed to be used as-is from out of the box, but a lot of players complained that they fall over easily (because the bases are so ridiculously small)

So Mantic included some clear acrylic bases for the miniatures to stand up in. But the bases provided are pretty lame too - the recess for the rounded player base is too large and the miniature doesn't clip in nicely - it needs to be glued into place. Interestingly, all of the pre-release artwork for the game shows the miniatures painted up minus the clear acrylic bases, which suggests they were just added in as an after-thought.

So already we're thinking of cutting some fresh clear acrylic bases for the miniatures, to make the playing pieces clip in nicely instead of flopping about or needing to be held in with glue.

And then we got to thinking -  if we're going to laser-cut our own bases from 3mm sheet acrylic anyway, why not make them a bit smaller and just reduce the size of each cell in our game board?

And that's exactly what we did.
This time, we're using cell dimensions of 20mm. Allowing for a 1mm border all around (a 2mm gutter between each space on the board) means each hexagon needs to be at least 22mm high.

And by some bizarre coincidence, when we placed a pattern of 8 hexes across and 4 hexes down, reduced to 22mm instead of 30mm, the total PCB layout fits exactly into a 160mm x 100mm rectangle!

This gives us four "blocks" of 8 hexes per module. Which is a nice number for handling with software/firmware - certainly much easier to deal with than 3 columns of 8 which is what we had on our latest design. And the amount of waste around the outside of the module is kept to an absolute minimum. So all in all, we're quite happy with this latest design.

Making a 3x3 grid of these modules gives us a board of 24 hexes across and 12 hexes down - a few over from the 11x23 that make up the widest points of a Dreadball pitch, but sufficient to make a playable surface. Double-sided eurocard-sized copper board is all over the internet, so this design is perfect in terms of ease of manufacture as well as for sourcing the materials. The final board made up from these modules is a decent size too:

Eighteen inches isn't a massive board, but is still a pretty decent size. And when the board is all made up with etched squares and flashing LEDs, the closer proximity of the miniature playing pieces will make for a slightly more chaotic-looking game - just like a real futuristic sports simulation!

We're planning on getting a silkscreen made up with the top design on top and a mirrored copy of the bottom design on the bottom of an A4 sized frame. This will allow us to use the same screen for both sides of the board - we just need to mask off the unused bit and make sure the board is correctly lined up before each print, but that's not a major issue... is it?