TECHNET Archives

December 2011

TechNet@IPC.ORG

Options: Use Monospaced Font
Show Text Part by Default
Show All Mail Headers

Message: [<< First] [< Prev] [Next >] [Last >>]
Topic: [<< First] [< Prev] [Next >] [Last >>]
Author: [<< First] [< Prev] [Next >] [Last >>]

Print Reply
Subject:
From:
Brian Ellis <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Brian Ellis <[log in to unmask]>
Date:
Thu, 22 Dec 2011 17:00:15 +0200
Content-Type:
text/plain
Parts/Attachments:
text/plain (126 lines)
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
>
>
>
>
> ______________________________________________________________________
> This email has been scanned by the Symantec Email Security.cloud service.
> For more information please contact helpdesk at x2960 or [log in to unmask]
> ______________________________________________________________________
>
> ---------------------------------------------------
> Technet Mail List provided as a service by IPC using LISTSERV 16.0
> To unsubscribe, send a message to [log in to unmask] with following text in
> the BODY (NOT the subject field): SIGNOFF Technet
> To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL)
> To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
> Search the archives of previous posts at: http://listserv.ipc.org/archives
> For additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
> -----------------------------------------------------
>

______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
For more information please contact helpdesk at x2960 or [log in to unmask] 
______________________________________________________________________

---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 16.0
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL)
To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
Search the archives of previous posts at: http://listserv.ipc.org/archives
For additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
-----------------------------------------------------

ATOM RSS1 RSS2