Joseph,
I for one stay away from using footprints provided by the CAD vendor, CAD vendors are in the business to sell CAD software not footprint libraries, but that's just my personal opinion. I too was thrown to the wolves and forced to learn about designing PCB's in a crunch. From first hand I can tell you that there is no good time to start learning, and experience is the best teacher. Learning PCB design will also make you more marketable, and a better Design Engineer. If you have access to some of the IPC doc's that's a great place to start. I would also suggest you take a look at the book Karl suggested Printed Circuits Handbook it is worth its weight in gold. Also check with your CAD vendor most have forums that you can get on that have a knowledge base that is usually better then their customer support, and much faster.
Tom Hausherr wrote an article in PCDmag about the future of CAD libraries, this article will not give you all the answers but may clear up some questions. http://pcdandm.com/pcdmag/mag/current_issue.shtml
What type of design is this Analog, Digital, or both? There is a lot to designing a PCB then throwing a bunch of parts down, connecting the parts, and sending it to the contract manufacture to be manufactured. If you need help use the Designers forum as a sounding board, that's what it is here for.
Good luck in your first design and welcome to the PCB designers world :)
Ted
-----Original Message-----
From: DesignerCouncil [mailto:[log in to unmask]]On Behalf Of
Joseph Matthews
Sent: Tuesday, February 08, 2005 12:58 AM
To: [log in to unmask]
Subject: Re: [DC] Designing PCB footprints
Dear Mario, Everyone;
Thanks for the feedback everyone. Thanks Mario. Understood, it'd be impractical for me to think I could learn all of the nuiances of PCB design and in being perfectly candid, I'm not about to -- there are too many seasoned people out there...it makes no sense for me to embark down that road at this stage in my carrer -- irrespective of how lucrative it might be ;) (trust me, hardware engineers aren't paid *that* much).
No less, for simple, one or two day prototypes I need to be able to layout my own boards. It's not practical to outsource hardware test boards (Processor/Controller boards, FPGAs, CPLDs, etc -- literally 20-30 components, a few pull ups, bypass caps, etc., and usually one or two real "interface" devices -- i.e. a header or two, comm. connector (RS-232, I2C), power, etc.)
The unfortunate thing is that I've gone down this road before and to-date I've been able to get away with literally giving a schematic over to the baord house and for pennies (ok, maybe not pennies, but cheap) they've gone ahead and taken my schematic and a little chicken-scratch and put out a board for me. Well, things are getting a bit more complicated that that and our proto shop has had to change...long story short, I need to be able to turn out something like a decent set of gerbers and though I fancy myself pretty good at interpreting standards and information, thought who better to ask than the experts (I too am aware of just how little I know sometimes, beleive me).
So I'm hoping that people have some tips, some basics, some fundamentals that'll help me get started in making something farily reliable. I checked with the board house and they are fine about specifying certain design constraints, and as you'd expect, the datasheet gives you some more to go with. The problem is that all the informaiton I can get from the fabricator is not going to be enough to spare me the inevitable reject and I'm sure (though you may hat e to admit it) you've seen years of mistakes that I'm hoping to avoid. Any wisdom, insights, thoughts, prayers, would be appreciated :)
Sincerely,
Joe
Mario Irigoyen <[log in to unmask]> wrote:
Hi all,
Well, here we go. I guess that's why there are professional PCB
designers who design circuit boards and there are hardware engineers who
design circuits. I certainly wouldn't try to grasp (or even attempt to
learn) all the caveats of hardware design so I certainly wouldn't expect
an engineer to do the same for PCB design. Us PCB guys understand the
processes, guidelines, rules ... because we deal with them every day. I
feel for you. You are being asked (forced) to move out of your realm
into uncharted territory for what, to save time, money? The reality is -
neither. Engineers get paid more than PCB designers (if not true please
correct me). So, even if you could design a board in the same time as a
PCB designer the cost is higher. But that won't happen. Then there are
all of the manufacturing, testing, reliability ... issues that you have
to "learn". Wow. The company would be much, much better off from every
aspect to have the board designed by a seasoned professional PCB
designer. Lower cost, certainly much better quality and a lot quicker.
I'm sure you are an excellent engineer so please do not take offense. It
takes years of experience to develop the expertise required to be a good
PCB designer.
Good luck.
Best regards,
Mario Irigoyen
MPC Engineering
[log in to unmask]
[log in to unmask] Message-----
From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of
Joseph Matthews
Sent: Monday, February 07, 2005 5:50 PM
To: [log in to unmask]
Subject: [DC] Designing PCB footprints
Greetings,
As a hardware engineer I have been tasked with laying out my first real
circuitboard in years (first *real* board I guess). It's proved a bear.
With years of experience designing hardware I am totally unprepared for
the leap from the "logical" into the "physical" at this stage in my
career. No less, I am under a crunch (as we all are, right?) and this
being a fairly simple board, I figured it's time I dove in and
learned...Simply stated, I'm stumped. Where can I find a comprehensive,
clearly defined explaination on how to create *quality* PCB footprints
and/or what the terms are used by the Footprint calculator made by PCB
Libraries. I see all of these fields to enter information but I'm not
sure what these mean and how to translate what's on the datasheet to
these fields.
I have read through a few of the IPC standards (some of the 122x stuff)
and still can't say I undertsand much more of what's required. Is there
a more comprehensive standard or something that more clearly deliniates,
"do this...don't do this"...or, "if the pad is this big on the
datasheet, add n%". These standards seem fairly high-level and at times
seem almost circular. No less, they are not totally specific and I'm
not sure where I can get the very specific information. I of course am
aware that there's probably more to it than simply adding a bit here or
a bit there, but assuming I know nothing, can someone offer some
straight-forward advice on how to build up a board. Nothing fancy, just
the basics. I should be smart enough to take it from there.
I hate to inundate people with how-to's but everything I've read,
including a book on the fundamentals of PCB layout seems very high-level
and seem almost afraid to say anything for certain.
Thanks for your help.
Joe
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