Rex
As an ex-vendor of a medium-to-high level CAD system (which has a
freeware version limited by the number of pads, but otherwise fully
functional), I can understand your frustration. However, I agree that
most designers have little idea of the notion of concurrent engineering.
To be really effective, a PCB designer (PCBD) should spend at least a
few weeks for a bilateral exchange of information with:
1. the electronics design engineer (so that PCBD receives from him ALL
the essential electrical constraints needed to ensure a successful
design - the CAD system does not KNOW that the engineer needs a given
characteristic impedance, a maximum/minimum track/spacing length/width etc.)
2. the PCB manufacturer (so that the design is as easy as possible to
manufacture and therefore lowest cost, while having )
3. the assembler (so that PCBD knows the constraints of the assembly
machines to avoid having to post-assemble)
4. the solderer (so that PCBD can specify the most solderable surface
finish and that unnecessary traps are avoided, requiring superfluous
retouching)
5. the cleaner (so that PCBD can avoid impossible-to-clean designs
caused, for example, by large components shadowing smaller ones in the
cleaning machine or the use of incompatible components)
6. the inspector (so that PCBD can ensure the design is as easy to
inspect as possible and is compatible with any optical inspection
device, also minimal retouches)
7. the tester (so that PCBD can ensure the design is compatible with any
automatic tester and that test points are correctly positioned, also if
an ad hoc testing jig is needed)
8. above all, the purchasing manager (so that the PCBD can specify the
most suitable components to satisfy all the optimum requirements of 1.
to 7. above; how many times have I seen the buyer purchase components
that, e.g., cannot be cleaned, because he is given an incomplete spec.?)
IMHO, before PCBD starts on a new layout, he should call a round-table
meeting with 1. to 8. above to thrash out any special requirements. Only
this way, can he ensure that the final product is as economical as
possible, remembering that every single manual operation (e.g., retouch,
adding a component etc.) may dramatically increase the cost of the
finished article. Also, he should be able to contact any of them at any
time if a question arises.
This is called concurrent engineering and is an essential part of using
a CAD system, no matter the degree of its sophistication. I have seen
some very clever and sophisticated designs done with the free version of
the CAD system I sold, albeit very small modules to remain in the number
of limited pads, e.g. flexible interconnects with a specific Zo. I have
also seen some atrocious designs made with the most expensive version of
the same CAD software. It is not the cost of a CAD system that is
limiting, it is the knowledge and experience of what is between the ears
of the guy driving it, IMHO.
Brian
On 22/12/2011 13:59, Rex Waygood wrote:
> A follow on from
> QFP centre slug over signal vias
>
> There are some interesting comments in the QFP thread which are to do
> with PCB design and they have caused me to pull out my current soap box.
>
> I would like to be a bit extreme and say there should be a tax of a few
> thousand pounds or dollars imposed upon those that give away free CAD
> packages. The money raised should be provided to vendors who sell real
> CAD packages to subsidise PCB layout training in order to allow cost
> effective and reliable pcb design, assembly design, rework and design
> for test to be taught properly.
>
> Why is it that an electronics engineer will design a circuit and then
> feel that he is competent to lay out the circuit using a free CAD
> package? The fact that the CAD package was free meant that management
> were not involved and the consequences of a PCB being laid out by
> someone with little or no knowledge of the pcb industry or even the
> assembly industry were not considered.
>
> The list of stupid things we see is very long, it results in pcbs and
> assemblies being more expensive to procure, less reliable to
> manufacture, difficult to make, impossible to test, slower to get into
> production and just downright rubbish. The free CAD package cannot
> provide intelligent data means that a reverse engineering process is
> required to attempt to undo some of the stupidities we see. Words like
> DRC and libraries are an unknown for many using these packages.
>
> Also I'd rather tell a six year old that Fred, their pet turkey, is
> required as a sacrifice for thanks giving day than explain to a young
> circuit designer with a free CAD package that he is delving into areas
> that he should stay out of and that his layout is very bad. That doesn't
> mean I don't do it but Fred's demise is easier.
>
> I could go on but mince pies are calling
> Happy winter solstice
> Rex
>
>
>
>
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