PCB Design Rule Simplified

The followings are the suggested PCB design rule that one should try to adhere to in order to minimise the cost of fabricating the PCB. This design rule is specifically done for electronicsenthusiasts as well as students who are still not familiar with the fundamentals of PCB design and layouts.

a) Single Sided PCB and PCB material

As far as possible, one should try to layout the PCB to single sided layer as far as possible.It may be quite difficult to rout the PCB but with the use of jumpers, you should be able torout most of the simple circuity into single sided PCB. Of course at times you may need to usedouble sided PCB and multilayer PCB. The use of double sided PCB will increase the price to 1.5 to 2.5 times compared to single sided PCB. Common single sided PCB thickness is 1.6mm, 1 oz cooper clad, CEM-1 or FR-2 materials. As far as possible, try to use FR-2 which is paper phenolic type of PCB material. This is by far among the cheapest PCB that is used in most consumer electronics products today.

b) Panelisation of PCB

The PCB laminates normally comes in standard sizes. One of the common PCB laminates come in dimension of 40 inches X 48 inches. In order to maximise the use of the PCB, you should findout from the manufacturers the standard PCB sizes that they are using. By effective panelisationof the PCB, you can use up to 80%-90% of the PCB laminates. This will reduce the cost of eachPCB. If the layout panelisation is not effective, wastage up to 50% may occurred. Therefore,always check the effective panelisation of PCB before sending for fabrication.

If you are doing the prototyping yourself, this PCB Design Rule applies as well.

c) Size of the PCB

You should try to make use of the smallest area of the PCB as possible taking into considerationthe track width, spacing and other constraints. Always try to minimise the size of PCB duringthe layout of the PCB. The size of the PCB is critical being the fundamental of the PCB DesignRule.

d) Reduce the number of holes and vias

Whether you send the PCB for CNC (computer controlled PCB drilling) or you drill the holes yourself, you should try to reduce the number of holes and vias on the PCB. Since the timeutilised by the machine will determine the price of the PCB, the lesser holes and vias willreduce the cost of the PCB. The rule is to keep it simple and as basic as possible.

e) Reduce the number of types of holes sizes

Try to design with common hole size as much as possible. This is to avoid changing the drill bitsused by the machine. By having many types of hole sizes, the machine will have to change the drill bits and this takes time. The time taken will determine the cost of the PCB. Common drillbits sizes are 0.7mm, 0.8mm, 0.9mm, 1.0mm, 1.2mm, 1.5mm, 2.0mm and 3.0mm.

f) Track Width and track spacing

For your own prototying or even sending out for PCB houses for fabrication of the PCB, it is always advisable not to design the track width and track spacing to the limit of the manufacturercapabilities. For instance, if you need to design 0.3mm track width, try to use 0.5mm. Similarlyif the minimum track spacing needed is 0.3mmm, use 0.5mm instead. This will help to ensure thatthe yield is high during the production of the PCB.This PCB Design Rule is especially critical if you are fabricating the PCB on your own.

g) Silkscreen minimisation

If top overlay silkscreen is required, the PCB Design Rule recommend that you do not need to silkscreen the bottom overlay. It may be difficult to do trouble shooting later on but eliminating this process will save some cost as well.

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