Computing stuff tied to the physical world

The magic of copper and solder

When it comes to physically connecting components together, there are many options. You could just twist wires together and make the whole thing self-supporting, but the problem with such connections is that they will eventually fail, because the oxygen in the air (and other even more corrosive gases) will cause the surface to become non-conductive.

Then came soldering and the solder joint, creating a strong yet easy to alter connection between copper, tin, and some other metals – as an alloy which holds everything together.

An old technique was to just wire everything point-to-point using some mounting stubs:

DSC 2864

Effective, but messy, and each new assembly is prone to error.

Here’s another useful solder technique for parts on a 0.1″ grid, using thin wire insulated with kynar, which doesn’t immediately melt away when touched by the soldering iron:

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But the breakthrough came with the Printed Circuit Board (PCB), which is a rigid board with copper “traces” on both sides, and “via’s” – copper-plated holes connecting both sides:

PCB Spectrum

Each hole connects a thin trace on top to another trace on the bottom of the PCB. The result is not only electrically compact, it also creates a robust mechanical construction.

Design tools

And that’s where tools such as EAGLE and KiCAD come in – they not only let you draw a schematic, they also help create a complete PCB design. Here’s a JeeNode v6 as example:


The colour-coding conventions used above make it very easy to interpret this layout:

  • red is copper on the top, component side
  • blue is copper on the bottom side
  • green is copper on both sides, plated through
  • everything else is without copper, and therefore non-conducting

The key trick here is that with two or more layers, electrical connections can be made to cross – something which is impossible in a single layer without creating a short circuit.

Some copper traces are thicker than others, which means they can carry more current.

The whole idea of applications such as EAGLE and KiCAD, is that you end up with a graphical design which matches the circuit design created in the schematic diagram: first you create a diagram, then you create a layout with all the parts placed, and then you have to work out how to “route” the traces to match the design. This routing process can either be done manually, or via nifty software called an autorouter – or it can be a mix of both.

There are several “design check” algorithms to verify all logical and physical parameters.

Once the copper design is done, the software can create Gerber files – an industry standard format which PCB manufacturers use to produce the actual board(s). Other small-scale techniques are also possible: manually etching a copper-clad board chemically at home, or using a precise CNC router to remove some copper mechanically.

As with paper printing, the “printing” of electronic designs is now available to anyone!

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