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[Uploaded Sep08] My Matrix Board Construction

By: Brian Broad

Most of my projects are built on Vero matrix board with lmm holes on a 0.1" pitch. Boards which have been constructed with care are as neat and tidy in appearance as PCBs. As there is no copper on the on the matrix board, components have to be connected with wire. I use single stranded 0.25mm wire wrapping wire, with Kynar heat resistant pvc insulation and strip the insulation with a soldering iron. For reliability it is essential to avoid damaging the thin single strand wire as this can cause it to break, so it is not a good idea to use wire strippers. The wire is available in several different colours so wiring can be colour coded.

Small components are mounted on pairs of 1mm double-sided Vero pins 4, 5 or 6 holes apart. Clearance of 0.2" between adjacent pins and between pins and pins and other components seems to work well. Small plastic mounting pads which spread the lead-out wires of transistors make it easier to fit them neatly. Sockets are best for ICs and remove the need for anti static precautions until the board is completed. It helps when wiring if pin 1 of each IC socket is marked on the wiring side of the board.

A reliable method of wiring is to wrap a bare end once around a pin on the component side then take the wire through a hole, along the wiring side, through another hole adjacent to the next pin to be connected and around the pin. Components with two short pins which go through the board (mainly radial Capacitors) can only be wired on the wiring side of the board. For reliability these are best glued securely to the board, preferably with a removable glue to allow for modifications. IC sockets are easier to wire if glued down first. A little slack I each wire is essential to allow wires to be moved away from other pins whilst soldering them and to avoid pulling the board into a curve! It seems unlikely but it does happen.

A jig consisting of a small piece of board with pins fitted at the pitches used for small components is essential for forming leads before fitting components.

Designing the layout of components is easy. First choose the positions of the mounting holes and drill them. Then identify all connections which go off the board and count them. Fit pins and/or terminal blocks on 0.2" pitch in suitable positions on the board edges for these. Leave a little room for extra connections, it is easy to miss a few.

Divide large circuits into sections. Choose a section to start with and count the components which can be fitted on pairs of pins. Fit rows of pins for these. Place the other components on the board then shift around a little until a tidy layout is achieved. Draw a sketch of the layout, choose a position for each component and mark it on the sketch. Wire up from the circuit and your sketch. I like to do all the power wiring first in appropriate wiring colours.

It is wise to use a continuity tester to check all inter-connections. I check that the correct voltages are present on the IC pins before fitting the ICs. I've not compared the man hours with making a PCB but I'm sure its quicker for making one offs. The PCB wins of course if several identical units are needed.

The single strand wire breaks easily with flexing so it is best to use multistrand wire to connect panel mounted components to the board.

Disadvantages:- It is very difficult at first and slow, even when skill develops. The circuit must be thoroughly checked as mistakes and omissions are easily made. making quantities of identical boards this way is inefficient. Solder joints are more difficult to inspect than on PCBs. The soldering iron needs cleaning more often because of contamination from the hot stripping.

Advantages:- Layout design is easy. Component density is quite high, slightly better than can be achieved with a double sided PCB layout. This is important to me as I always seem to choose a case which is only just or not quite big enough for the project! Stray capacitance is low so high frequency circuitry works well. Wiring errors can be easily corrected. Areas of circuitry can be stripped of completely and rebuilt if necessary so it can be good for development work, As most discrete components are mounted on pins there are lots of monitor points. Colour coded wiring makes it easy to identify pins at supply voltages and ground. When built with care reliability is good. I have equipment built in this way which has been in regular use for 10 years or more. The matrix board is very cheap compared with strip board, DIP board and prototyping cards.

Sources:
Rapid Electronics have matrix board:
34-0585     85 * 127mm          £0.82
34-0595     119 * 455mm        £3.85

Terminal pins:
34-0610     100 single sided     £0.48
34-0620     1000 single sided   £3.70
34-0610     100 double sided   £0.70

Maplin have matrix board, pins, wire and terminal blocks; a few examples:BL83E white 1/0.25 wire wrap wire, silver plated, Kynar insulation, 25 metres £2.13. also available in black and red.

JU37S SRBP 0.1" matrix board, 300 100mm with lmm holes £2.99 and smaller sizes.
FL23A, 1mm double sided pins type 2144, £2.99 for 100.