OBSERVATIONS FROM SCOTLAND                            28 May 2008                                GM1SXX

Copper Island Construction.

Some of us like to dabble, to build various circuits and prototypes. In general, it's not cost effective to make a PCB for a 'one-off' so alternative construction methods have to be sought.  Depending on the type and complexity of the circuit, the common methods include VERO-board, 'ded-bug', various types of prototyping boards, solder-less breadboard or my favourite.. copper island, AKA 'Manhattan construction' method.

'Copper Island' construction is a simple idea for producing neat tidy prototypes. You simply use single-sided PCB as a ground-plane and glue on 5 or 6mm diameter disks of material punched out of single-sided SRBP board as anchor points for the components. The disks are  generally cyano-glued to a sheet of single sided PCB in the appropriate places and tinned to provide insulated fixings for the circuit components.  It's a particularly good system for beginners because it's easy to lay out circuits to mimic the circuit diagram although experienced constructors will tend to save space by cramming more parts onto a given area of PCB.

The punch set shown here was obtained inexpensively from EBay and was modified by grinding off the pointed ends of the cutters in order to produce perfectly round disks of PCB material as shown.

The Copper Island method of prototyping can be used from DC to at least 23Cms if due care is taken over layout.  This make it very attractive to the home constructor looking to build moderately complex prototypes. It's even possible to use the larger SMD components with copper island. In fact, I use mainly SMD in my prototypes.  Should you need to fit an SMD decoupling cap, it can simply be leaned against a pad at a forty-five degree angle and soldered to both pad and groundplane. By placing adjacent pads at a suitable distance apart, resistors and capacitors can simply straddle adjacent pads. 

Punch before modification	and after the 'pip' was ground off.

Above you can see the punch parts with it's pointed 'pip' and after the pip was ground off. The material appears to be carbon-steel.  I used a Dremel machine fitted with a carborundum cutting disk which made short work of it. After removing the pip as shown above, I dressed the surface to an even finish.

The punch came with a variety of punches and dies including 4, 4.5, 5, 5.5 and 6mm, all of which could be used to made copper island pads.  5MM diameter is about the optimum size IMHO.

To make the pads, I used SRBP single-sized PCB and the punch gives a nice rounded-over edge to the pads. Don't be tempted to use Fibreglass PCB material with this punch. Fibreglass will damage the punch and die in very short order because of it's very abrasive nature.

Using Copper-Island pads

Small SMD components such as MMIC's can be fitted to a single copper pad after a Dremel and cut off disk are used to cut a 'cross' shape into a standard pad so the device can be placed on it and soldered.  Should you have access to a hand punch with different sized heads, a larger than standard pad can be made for short leaded parts such as ga-asfets and MMICs.  If you do use this mounting method, make sure your ground leads are as short as practical.  One other method of mounting MMICs is to bend both ground leads carefully downwards, solder to a pre-tinned spot on your pcb, gently bend input and output leads upwards and slide a pair of cyano-coated copper island pads under the input and output leads using tweezers. This method results in the lowest stray capacitance. 

 Be inventive! Who knows, perhaps YOU could come up with something even better than copper island.

73 AL.
GM1SXX