Example

Plot

The picture shows a plot of a PCB for use with a PIC16F84 microcontroller. The actual quality depends on the capabilities of the plotter which is very high when a fine tip pen is used. Hewlet Packard's plotter specification quotes a minimum pen movement of 0.001inch.

This board is for using a PIC16F84 with an RS232 interface and buffered input/output. It was my first attempt at producing a double sided PCB, not a total success. The alignment of either side requires more patience than I have. This board was etched one side at a time and any vias were drilled so they could be used as an alignment aid for plotting the second side. It still requires very careful positioning though.

As there are no plated through-holes, connections from one side to the other are made with wire I thought
'close enough' would suffice. Maybe not a good idea. Also a number of surface mounted parts are used. This is a good idea as drilling small diameter holes (lots of them) is not to be recommended. The surface mount 1206 size are large enough to handle and solder, it is possible to use the smaller part but it becomes tricky, lots of resistors end up being lost as they 'ping' out off the tweezers.

This design, as far as the track/pad layout, does NOT follow the rules for good design as given in the Protel Easytrax documentation. For instance, 'tracks should not pass through pads' to name but one no-no and 90 degree changes of direction are not recommended.

I have come across other examples on the internet that have very narrow tracks. Myself I would not recommend this form of design unless there is a good reason to have narrow tracks. Two reasons, fine track widths are more likely to be open-circuit and secondly the more copper being removed from the board the longer it takes to etch. Also the greater chance of the etchant eating into the side of the track. Why make things difficult if its not neccessary ?

My designs try to leave as much copper on the finished board as possible, this also allows additional tracking if any modifications are required. The grid of tracks in the top right corner are for adding any components, use 24 awg insulated wire for reworking a PCB.



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