Monday, 18 July 2016

Through hole as surface mount components

We love surface mount components at Nerd Club. Not just because they're tiny (although miniaturising designs to as small an area as possible is quite fun sometimes too) but because they eliminate the need for all that fussy drilling.

Putting a 1mm hole in the centre of a 2mm pad is straight-forward enough. But if you're soldering up a 40-pin DIP and a number of wire-pads for socket connectors then all that drilling can make your eyes go funny! Surface mount components mean far fewer holes, which means more time making cool stuff and less time hunched over a dremel drill.

We've already come up with a number of designs for our electronic board game, using surface mount components. But, going down the open source route, we're also acutely aware that not everyone is as confident at soldering, or has the same degree of practice we have, with soldering tiny little surface mount parts.

Coupled with the extra difficulty when soldering to homebrew boards (there's no solder resist to ensure it only goes where you want it, so bridging tracks is quite easy to do) we thought about how best to make the controller PCBs as simple as possible to solder.

Now it seems like through-hole is obviously the way forward; everyone with a soldering iron has probably soldered through-hole components in the past. But that then means that our PCBs would have a load of components on the top, and a whole load of little spiky bits on the bottom - neither surface would be completely flat (which would be preferable, so you can stick the flat part of the board to be flush with the bottom of the playing surface).

Through-hole components are larger, and therefore easier to solder. So we came up with (yet another) compromise: use through-hole components (for their larger size) but treat them as if they are surface mount components.

So the components go on the "copper side" of the PCB, but have much larger pads and legs, for the homebrew hobbyist to have a go at soldering.

(our "surface mounted" through-hole atmega DIP chip waiting to be soldered in place)

This approach has meant that pretty much all the designs we've spent the last few evenings working on are now redundant. But that's just a casualty of the rapid-reiterative-design-process we're embarking on - not to make the PCBs the "best" or the smallest, or even the cheapest; but to make them the easiest for most people to work with.

(checking the overall height of the board + mcu against 6mm thick mdf playing surface)

(before soldering, we'd snip the legs off, to make the understand completely flat and flush. By turning the entire thing upside-down we can more easily see that it fits within the profile of piece of 6mm thick mdf)

More updates with more designs as they are worked on (and, probably, discarded!)

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