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Old 13th Jun 2019, 10:52 am   #9
David G4EBT
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Join Date: Feb 2003
Location: Cottingham, East Yorkshire, UK.
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Default Re: PCB Layout Diagrams in Service Manuals?

The original query was 'what do manufacturers use?'

I can't answer that, but I would say that what CAD is used professionally, and the level of skill called for, goes far beyond the needs of hobbyists, unless for example, they wish to get PCBs professionally made by sending Gerber files to a PCB maker. (The picture in the first post was of of course a component overlay rather than a PCB track layout).

I've designed and made my own PCBs for countless home-brew projects over the years and have never found any of the programs generally used by hobbyists for DIY production techniques to be at all helpful. The programs are geared to professional production techniques and examples of artwork produced by hobbyists that I've seen are a recipe for failure when it comes to etching and drilling. The main reason I say that is that invariably the tracks are too thin, inconsistent in width and the pads are needlessly small, leaving little copper on the PCB, risking undercutting when etching, damage to the pad when drilling, and lifting of the track when soldering. It may of course be that the designer isn't especially adept at using the CAD package to take account of amateur production techniques.

The first pic below is example of a small section of a PCB that was published in a magazine some months ago for a SW receiver, which I think was produced using Express PCB. In the top picture the track thicknesses are inconsistent and the component pads needlessly small, especially for the two transistors. At one point there is a hole at a right angled corner with no 'pad' to reinforce the track. The lower picture is how the artwork could, and should have been produced to ensure that it could be etched, drilled and soldered with minimal risk of failure. That's especially important when - as is sometimes the case, the hobbyist is making do with a standard pillar drill to drill the PCB, or even trying top use as Dremel type drill freehand.

When etched, the pads on the original design would have been further weakened by 'undercutting' in the etching process. Etchant doesn't just etch downwards, but sideways too, so as etching progresses the area of copper that has the longest duration of etching is just below the etch resist, as shown in the second pic, making the tracks and pads even more fragile.

I've not set my face against PCB CAD programs, which do marvellous things such as multi-layer boards, auto-routing and so forth, and I dare sat that for those experienced in using such programs will echo my sentiments that the design in pic 1 below is not a good example, but it's typical of many that I've seen.

I design and produce maybe ten PCBs a year for my home-brew projects. That involves drawing the circuit, the component overlay and the PCB artwork for the mask. I also clean up indistinct circuits for radio restorations, design front panels, and routing patterns for radio back panels, along with occasional sketches connected with radio restorations. For all of those applications I just use 'Paint' which comes free with Windows (till MS swing the axe and kill it, which is their avowed intent).

Some PCB designs can be further adapted using 'Paint' or something similar to leave as much copper on the board as possible, which speeds up the etching process, and makes the drilling of holes less critical should the drill not be quite on target. In the third pic below, the two PCBs look quite different, but they're the same basic layout. In the picture on the right, the PCB could be created by using sticky backed plastic (eg: white Fablon) applied to the PCB, the paper design stuck onto the Fablon, and the waste areas cut away with a modelling knife.

Often, makers' data is scruffy and indistinct, and I use 'Paint' to clean up or re-create the circuit and other diagrams. Pic 4 is a section of a Unitra 'Figaro Special' circuit, and pic 5 shows it after I'd re-created the circuit to clean it up.

I hope that's of interest and use.

I'll attach a few more pics in another post.
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Name:	Figaro Special circuit clip cleaned up.jpg
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