OBSERVATIONS FROM SCOTLAND 2008_08_24 GM1SXX
Copper Island prototyping revisited
I've talked before about the 'copper island' method of prototyping before, but this time, I'd like to show how newcomers to the method can get started. Copper Island is a simple and tidy means of producing low-cost prototype circuits that will happily work into the UHF range is constructed using good RF practices. In short the system relies on using a piece of single sided PCB as a ground-plane, onto which are stuck small 'islands' of insulating material between which the components are fitted. It allows very tidy prototype circuits to be built and has the advantage for the novice that circuits can be laid out exactly as the schematic, making life simpler for them. Of course sometimes you might want to lay things out differently, for example to minimise lead lengths on RF circuits but 'copper island' can accomodate both types of layout easily. You only need a stock of PCB material, components and the all important 'copper islands' to get started.
Why is it called 'copper island'? I think it's probably named after an area in Michigan, USA where an artificial island was created. Perhaps http://en.wikipedia.org/wiki/Copper_Island
At first, I bought a copper island kit (shown below) but since these are no longer manufactured, I sought an alternative method of 'rolling my own'.
In the box shown above, the commercially made pads are the blue disks of PCB material while my DIY 'copper islands' are the yellow coloured ones at the top right. The ideal diameter for copper island pads is 5mm. I tried other sizes, both smaller and larger but 5 or 5,5 mm seems to be the optimum diameter. My punch is 5.5mm diameter.
Incidentally, the pads need not be round...... square works too! It's just not quite so easy IMHO to do.
How to make your own 'copper island' pads.
Any means you can think of to punch out 5-6mm circles of PCB should do but I found that for me, the tool shown below was ideal. It was bought from a US EBay seller and it's a cantilever action punch with a set of different sized dies.
This is the sort of punch you need to punch holes in PCB.
Never try to cut Fibreglass PCB with these hand punches. Fibreglass will ruin them in very short order. Use instead SRBP (Synthetic Resin Bonded Paper) PCB material which is far softer and kinder to the cutting surfaces. SRBP PCB is still available from a number of suppliers including Maplin. It's basically many layers of paper wetted with resin and compressed down to form a PCB substrate. The stuff Maplin sells has the letter 'Kb' stamped on the back. Incidentally, watch what they charge for it. I was charged for double sided fibreglass board by Maplin staff in their St. Enoch Square shop in Glasgow. SRBP is considerably cheaper stuff than fibreglass board! I would have complained, but I only discovered their 'error' when I got home to Paisley.
I had to modify the actual punch and die because as supplied. the punch part has a conical 'pip' intended to stop the material moving while you punch a hole in it. Since the pip effectively destroys the punched out disk... the part we want to keep, I modified it by cutting off the pip using a Dremel tool and carbide cut-off disk, then carefully filing the punch flat. This produces a beautiful flat disk with rounded over edges.
I uses building-grade Cyano adhesive to bond the pads to the PCB substrate. I believe the make of adhesive I use is called Siroflex but I can't be certain.... the labels fell off years ago!
Photos of the punch before and after modification
In the photo above, you can see what's needed. The sharp locating pip has been ground away to leave a flat contact surface.
Here's an example of a simple little circuit module built using the copper island method. It's quite neat and tidy and the circuit is pretty much laid out just like the schematic. The little ally box came from Maplin. Everything else is from my junkbox. The circuit is a simple dual-gate FET mixer stage using a BF981.
If you have never tried the Copper Island method of construction, please try it. It's perfect for QRP circuits and for general electronic prototyping.
73 AL.
GM1SXX
