PCB Design

[krishtriram]

Dear All,

Can anyone guide me how to design a PCB from an Schematic (without any software)

Regards

 

[Klaus]

I've done that for a few years before they wrote software to do it

You have to make a few decisions, depending on the complexity of the circuit:

1. single or double sided board. For home etching a single sided board is much easier, you could even paint on the tracks with an etch resistant pen but I recommend that only for very basic boards.
Anyway, I did all my boards by the artwork and photograph method.

2.You have to arrange your parts on a scale drawing, I used 2:1, with a .1" grid underlay and mylar film for the artwork.
The board outline was layed out then parts were shuffled about, keeping in mind they are 4 times the size (area) if you're doing 2:1 artworks (templates help there).

3.Decide where the majority of the connections go, where the board edge connections are, where there are physical restraints from mounting holes, location of switches, LED's, displays etc. etc. Once you have figured out a layout which involves the least crossed tracks and short distances between the majority of connections the actual laying of the track begins. You can use a blue pencil on the mylar film to trace tracks, etc. for trials as the blue can be filtered out in the photograph.

I used the stick on 'Bishop' pads and tapes to create an artwork which then got photographically reduced to 1:1 size and was etched by a commercial operator. They also drilled the boards but I drilled the ones for my own projects to save money - its a tedious job and one needs a good quality drilling machine and sharp eyes

Simple boards had wire links where crossing tracks were unavoidable, double sided boards had through links and, later, through hole plating.

Start laying tracks by routing the power connections, then the majority tracks, last the minority (major means many parallel, like a data 'bus', minor means individual logic interconnections).
There's no hard and fast rule to this, use whatever order gets the best result - I've been known to redo a complete board when it started to resemble an intangible mess and I ran out of room for all the tracks.

You can practise on graph paper with pencil, just draw the board & components to size, probably a good idea to get a feeling of how many tracks you can squeeze between components and the relative sizes of them.
Hint: try not to lay too fine a track size first, not advisable for home etching either.
It is an art that is learned easily enough by doing if one has a talent for it, reading or writing about it is an entirely different matter.
Start with something simple, single sided, no IC's and work up from there.

Good luck,
Klaus

P.S. I've never done a computer assisted layout yet, believe its a heck of a lot easier with the right software :wink: