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Electronics for schools and hobbyists: The Basics

Making printed circuit boards... And notes on PCB CAD software


Here is just a 'sketch' of a process for the use of hobbyists and schools...


This covers doing a single sided PCB. You can use the same techniques to do double sided boards, but 'through plating' is tricky... provide connections between the two sides with holes into which you will solder short wires, or buy the little pins made for the purpose (called 'vias'). Some signals will, of course, be carried through the board on a pin of a component.

For a double sided board, you will "prick" just one side, drill the holes, and then apply the etch resist.

Basic idea: You start with a substrate board of some kind... various materials with various pros/cons (price, strength, etc) are available... which is covered with a layer of copper on one or both sides. Covered across the whole side. You then somehow (details below) eat away all of the copper which is where you don't want it, leaving just the copper where you do want it, the "traces", or "tracks".

At 8/11, one supplier of the "raw materials" was...

http://stores.ebay.com/PCB-Laminates-Copper-Clad

(I haven't been a customer, but from the store's history, I wouldn't hesitate to order from them, myself.)

In the UK, 10/11, I bought some entirely satisfactory copper clad board from RapidOnline.com. It is made of SRBP, a paper-based material, which while not as robust as the "usual" fiberglass board is much easier on your (expensive) drill bits, doesn't leave your work area covered in powdered glass, and is less expensive. I feel like an idiot, not being able to tell you where to find board in the States... you shouldn't have to go to eBay.. although, personally, I don't mind using eBay... but my (limited) researches only turn up fiberglass board.

- - - - - - -

Speaking of "Haven't been a customer", I haven't tried his techniques, but I've seen an interesting .pdf which you can download. It speaks of preparing your board directly from laser printer output! There is some overlap between what he has for you, and what follows. Maybe scan what follows, and then visit the other option? The "gem" in his is how he gets the board to the "ready for etching" stage.



Enjoy!

Check your board very, very carefully before adding any components. Measure the resistance between things that should carry voltages, things that should be zero volts. (Should be zero ohms!) Measure the resistance between distant parts of any Vcc line(s), and between traces which should have zero volts. (Any two points on any segment of any rail should have "no" resistance between them.)

What are you looking for? During the fabrication process, tiny scratches of the etch resist can lead to breaks in traces. Hold the PCB up to a bright light, and you may see it shine though where there is a scratch breaking a track. It is also easy during the fabrication to accidentally create joins between tracks when a line gets just a little too wide somewhere.


Alternatively...

Oh... girl scout cookies.

Once upon a time, this page had the following...

Alternatively, use BatchPCB.com If you can supply a Gerber file, the nice people at BatchPCB.com, connected with Sparkfun will make a PCB for you, and make it available to others too, if you wish. Remember: Fast / Cheap / Good: You cannot have all three. I believe BatchPCB concentrate on the "cheap" and the "good" for you. (There is advice on their site about the Gerber file thing... and see below, re- PCB CAD packages.)

Well, time rolls on, and things change. BatchPCB is no more. I haven't researched it very deeply, but I believe you can get similar services today (7/14) from OSHPark.com/. Again, not tested by me, but looks good: a site with a guide for KiCad users for getting PCBs made by OSHPark.


Computer aided PCB CAD. (Schematic and PCB artwork design software)

I've used a number of PCB CAD tools over the years. Of late (10/11), I've become very enthusiastic about the free, multi-platform KiCad, and have started a tutorial guide to using KiCad. I also have a separate page just about PCB CAD software. Even if you prepare your PCBs "by hand", the PCB CAD software offers two huge benefits:

What do I mean, "discipline"? With PCB CAD, you draw a schematic first. And you keep it up do date, as you discover the "little things" that you always discover along the way of any project.

Then you tell the PCB CAD software to apply the circuit schematic to a board layout. And in any decent package, there are "design checking rules"... do any traces touch? Are they too close? Are any pins missing connections they should have?

Trust me... it is a lot easier to fix these things on a computer screen than with little wires on the back of a PCB!



Assembly

The next step is soldering, of course. The magazine Everyday With Practical Electronics provides an excellent tutorial on soldering (which has been online "forever"!). There's also good information on the Arduino Playground.



'Photographic' preparation of PCBs

In a moment, I'll turn to "proper" photographic board production. First, I will remind you that near the top of the page I mentioned that some people take PCB designs out of computers and put them on boards by using a laser printer. The essence of this approach: Print the design, literally iron it onto the board, "tear" away the paper, and then etch that!

Turning to the "proper" photographic technique: I've only done this once, so you can find more expert advisors, but for what it's worth:

In addition to the usual bits and pieces, you need:

What you do...

(None of this, by the way, needs to be done in a photographic darkroom. Do minimize the exposure of the photosensitive materials to bright light, of course, though.)

Put the positive image of the tracks against the prepared board. The image should have black where you want copper at the end of the day. The 'black' needs to be opaque to UV light.. some photocopiers and laser printers leave you with a pretty 'thin' 'black'. There are service bureaus which will prepare gorgeous artwork for you from CAD files on floppy disc, though the time I did this, the combination of my software and service bureau meant that there were no drilling guide holes in the pad centers. Be sure you put the artwork on the board the right way 'round!

Now shine ultraviolet light on the board, through the artwork. Some people claim satisfactory results with sunlight... but I fear that approach must require a pretty good knack. Care: The UV bulbs made for the purpose emit light which is not good for you. Professionals use a purpose built device called a lightbox.

Immerse the board in the developer. This stage is rather like the ordinary etching stage. You can see the progress of the process, at least with the materials I used.

Wash... with care.. the etch resist material is delicate at this stage.

Proceed with normal etching and PCB fabrication.





Making circuits without a PCB

Consider stripboard ('Veroboard') or wirewrap as alternative. (Latter for low power digital.)


Scraps, to be polished another time....

And now: an 'unpolished' alternative re- explanation of much of the above. Someone wanted to know how to create PCBs from PCB designs out of magazines or books.

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Many magazines offer a PCB service, which always seems like good value to me. They will sell you pre-made boards for things described in the magazine. Not only are the boards made to a good standard, but there's a chance that any errors which crept into the magazine are not present in the boards.

Beware photocopying the magazine artwork onto clear acetate and then proceeding with a photographic approach. The copiers sometimes distort the image. How much? How much is too much? All fine points you'll have to resolve for local circumstance. The worst problems will be with DIL socket footprints. Maybe use a piece of graph paper to locate the pinpricks which will determine where the holes get drilled. There are also special drafting acetates which are less prone to distortion. Are the worth it? Not sure.

I've heard that the magazine artwork can be used directly for photographic production of PCBs. You just spray the artwork with WD-40 to make the paper transparent. Obviously, this depends on the magazine printing nothing on the reverse side. I also wonder about traces of the oil interfering with the etching process.

I heard of something called 'PNP Blue PCB Transfer'. I asked for a sample, even sent s.a.e., but they declined... I can't tell you if it works well, as I haven't tried it. I believe you do a laser printer or photocopy copy (both subject to the distortion problems mentioned above) of your artwork onto this Blue Transfer stuff. (And I cannot promise it will go through your printer or copier without incident!!) You then iron the result onto a bare copper clad board. Peel the sheet from the board. The 'carbon' which stuck to the toner transfers to the board, and is the etch resist for the board's etching. This product was mentioned in Everyday With Practical Electronics. Supplied by Verkonix, 193 Green Lanes, Sutton Coldfield, West Midlands, B73 5LX, UK. Cheques to 'Verkonix Ltd', no VAT. At 6/99, 2 sheets, 11" x 8.5" including UK postage: £6.00.

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If you have access to a flatbed plotter, I believe you can buy plotter pens with etch resistant ink.



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