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PCBs correct first time?

Discussion in 'Electronic Design' started by Leon Heller, Nov 25, 2003.

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  1. maxfoo

    maxfoo Guest

    If it works, it means the concept works, so now it can be done on a
    pcb.


    Remove "Your_lips_from_my_dick" if replying by email.
     
  2. Not when the products are already made, and even worse
    after they have been shipped.

    There a tradeoff between levels of checking and getting on
    with a prototype. Like you say, 'generally I choose to'. It's
    exactly there where it happens. Even when it's ready for
    production, mistakes are made. Cars are called back, Hubbles
    need to be fixed, people get faulty pacemakers installed...

    It's not simply lack of 'old-fashioned notion' that brings
    in the errors.
     
  3. budgie

    budgie Guest

    Maybe not. the law of diminishing returns applies here also but, as
    others have testified, lack of commitment to root out the problems at
    that stage almost guarantees that some will remain.
     
  4. Russell Shaw

    Russell Shaw Guest

    I) Unimaginative

    J) Overly conservative

    K) 1 week committee signoff process for every little thing

    L) Rather work for McDonalds
     
  5. I read in sci.electronics.design that Greg Neff <>
    EE PCB PERFORMANCE
    RTF = ------- + ------ + ----------- - EMC COMPLIANCE
    LOADED SIZE SAFETY
     
  6. I read in sci.electronics.design that John Larkin <[email protected]
    techTHISnologyPLEASE.com> wrote (in <[email protected]
    4ax.com>) about 'PCBs correct first time?', on Thu, 27 Nov 2003:

    I feel that pre-emptive 'generic' decisions are misguided. I consider
    each project on its own merits, and sometimes go for 'first time' and
    sometimes for 'cut and try'.
    It may have been a mite difficult to test the whole thing without a
    crew. Going to orbit probably wasn't such a big deal in itself, because
    the launch and immediate post-launch phases are very hazardous, and de-
    orbiting is the only way to test re-entry anyway. Of course, all the
    bits were extensively tested.
     
  7. Minutes for each of many millions of users having to re-boot several
    times a week.
     
  8. Since (when you add it up) entire lives are being wasted with this
    sort of thing, manslaughter charges might be in order.

    Best regards,
    Spehro Pefhany
     
  9. Greg Neff

    Greg Neff Guest

    On Thu, 27 Nov 2003 16:38:12 -0800, John Larkin

    (snip)(snip)

    We are in 100% agreement on this, except that the effort to get it
    right the first time is not minimal for everyone. The procedures and
    cross-checks take resources including tools and time. An expectation
    of done right the first time can only be applied in proper conditions.
    For example, our company is small enough that we can't yet afford a
    decent PCB signal integrity simulator. We still do high speed digital
    design, but we do get bit from time to time by signal integrity
    problems on PCBs. If we had all of the simulation tools then we would
    have fewer problems of this nature. We don't have the tools, and the
    time it would take to manually evaluate 1,000 nets on a layout would
    cost far more than a second spin. For now, we live with some bad
    boards.

    Also, it's very hard to eliminate all human error. I'm not talking
    about poor design practice, I'm talking about a typo in a footprint
    designation. This isn't bad engineering, it's a simple keying error.
    It happens, and it takes a rigorous set of cross-checks to catch
    these. Most of the time the typos get caught, sometimes they don't.



    ================================

    Greg Neff
    VP Engineering
    *Microsym* Computers Inc.
     
  10. Exactly!

    ;)
     
  11. I read in sci.electronics.design that Spehro Pefhany <[email protected]
    The only man's laughter involved is BG's - all the way to several dozen
    banks. (;-)
     
  12. John Larkin

    John Larkin Guest

    So, you equate sloppy work and lots of stupid mistakes with
    imagination, liberalism, speed, and something somehow related to fast
    foods? Why am I not surprised?

    Me and my guys design things nobody else, including big companies with
    their own engineering staffs, wants to take on. We build beautiful
    boards and boxes that do exactly what they were expected to do, and we
    get most of them right the first time because we enjoy being that
    good; it's the game we play, and the pay's pretty good too. If you
    prefer to hack and fiddle, go for it.
    OK, don't send me your resume. Just be aware that McDonalds has some
    pretty demanding quality standards for their employees, too.

    John
     
  13. John Larkin

    John Larkin Guest

    Bill is the richest person on the planet, and it's been said that if
    he had to pay a penny for every time Windows crashes, he'd be broke.

    John
     
  14. Mike Page

    Mike Page Guest

    It's necessary to distinguish technology from implementation. For those
    at the bleeding edge of technology, errors will more often caused by the
    technology than the implementation. For beginners, unfamiliarity with
    their tools and best practice can be the biggest source of errors (we
    all start somewhere).

    Looking back to where I was a decade a go has taught me to be patient
    with beginners. I find it harder with those who refuse to make progress.
    There is a cost, to someone, somewhere, ultimately you !
     
  15. EEng

    EEng Guest

    Ack Sphero, I agree with you AND disagree about certain things...a
    tough call ya know? The board houses I do business with have seen me
    on their door every week or two for the last 24 years. When I tell
    them I want a proof board or two (finished design with exacting
    measurements and specs), I get them on my time schedule in advance of
    the production runs and included in the lot run charges for later
    production of that product because they know that I'm going to come to
    them for those production runs. I guess its a matter of good business
    on their part to give me what I want, absorb some one time costs in
    order to get the larger long term orders from me. Perhaps I've been
    getting my way for so long I've forgotten that many companies only go
    to a board house once or twice a year. Since I design for many
    different companies, I'm at those board houses on a regular basis.

    I suppose in general it would in fact make better monetary sense to
    have a board slopped together but that's what I accomplish with
    breadboarding. Before it comes up again, there are many SMT
    protodevelopment boards available that we'll use and unless its very
    high speed RF, even a Rat Shack copper clad perf board is generally
    good enough. The proof is in the pudding, but I get your drift.
     
  16. EEng

    EEng Guest

    Yes, but what assurance do you have that you have laid out your PCB
    correctly? That's what we've been talking about in this
    thread....proving your PCB Layout.
     
  17. Brian

    Brian Guest

    Again, unless I have bread boarded the design and/ or already know every IC
    on it thoroughly, I just can't expect it to come out right try one. And I do
    too much varied stuff to know it all.

    I generally draw out a design, lay out a board, then build it. This is the
    first time it will run. This is where I shake out everything. I don't
    simulate, been burned there already. Code development changes, performance
    changes, component tolerances, noise, all may require something on the board
    to change. The a second run is usually right, until the standards guys get a
    hold of it. Since this is such a convoluted process, who knows what's next.
    After passing that, it may go to offshore testing! Not to mention marketing.
    With the designs I do, you WILL get burned, I just turned it into a tool as
    best I could.

    Perhaps some designs lend themselves to one proto perfection, I just never
    get them on my desk. Most resemble R&D.
     
  18. Brian

    Brian Guest

    I design for a contract manufacturer, do alot of medical equipment.

    Getting a couple pcb protos is cheap. There are no separate plotting costs.
    Building it does add costs, I have to either place parts myslef or have an
    assembler do it. But they then run thru wave or oven, so at least I don't
    have to solder each part. I don't have to release any info as its still in
    engineering. Only archive it if changes are made, only go thru releases when
    ready for production. Just got 2 four layer protos, 8 by 8.5 inches, was
    $116 at my door. Could be 2 hours to build, add $60 shop costs. At $176 to
    do it, if I save 20 cents on a change, the first 1000 pcs gives the whole
    cost back. Add to that the assurance that it IS right on a second proto,
    then also in production, and its a no brainer. Ever been thru rework on a
    large build? THATS REAL MONEY!

    Don't you ever build designs first? You release designs right into
    production without testing? Seems what I read here, people are saying they
    do.
     
  19. Brian

    Brian Guest

    I have no doubt it can be done, just in my area, its not worth it for
    several reasons, usually the biggest being money. You guys charged them a
    FORTUNE I'd bet. Did you burn any proto boards? Did you build/ test circuits
    during design or was it all simulated?
     
  20. Brian

    Brian Guest

    Gosh, I'd never go work there. They'd make me fix the fryer!
     
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