How do you design these days?
in [Design]
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From: Spehro Pefhany on 3 Jan 2010 17:02 On Sun, 03 Jan 2010 14:15:52 -0600, the renowned krw <krw(a)att.bizzzzzzzzzzz> wrote: >On Sun, 03 Jan 2010 10:08:15 -0800, John Larkin ><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: > >>On Fri, 01 Jan 2010 19:19:42 -0600, krw <krw(a)att.bizzzzzzzzzzz> wrote: >> >>>On Fri, 01 Jan 2010 17:40:54 -0500, ehsjr <ehsjr(a)nospamverizon.net> >>>wrote: >>> > ><snip> > >>>>You've got a steadier hand than I'll ever have. >>>>I have to do it with a Dremel mounted in a drill press >>>>adapter, and slide the board against guides clamped to >>>>the bed. Even then ... :-( >>> >>>Sounds like you need a small milling machine. >> >>We had one of those PCB mills, on indefinite loan from a customer who >>wasn't using it. It was such a hassle that we wound up not using it >>too. > >Gotta be better than fence clamped to a drill press. With the spindle Morse taper Loctited in so that the side forces don't loosen it up! >>I can do the modest stuff with a knife and some kapton tape. After >>that, it's easiest to just lay out a board and have a pcb house make a >>few. > >You mean copper-clad kapton tape? We use kapton tape as an insulator. >>Teflon board material is a lot easier to x-acto than FR4. You can get >>it on ebay. > >Maybe I'll try it, but I don't do much prototyping. We have a >prototyping machine but bringing it up has always been on the "to do" >list. Best regards, Spehro Pefhany -- "it's the network..." "The Journey is the reward" speff(a)interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com
From: John Larkin on 3 Jan 2010 19:49 On Sun, 03 Jan 2010 14:15:52 -0600, krw <krw(a)att.bizzzzzzzzzzz> wrote: >On Sun, 03 Jan 2010 10:08:15 -0800, John Larkin ><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: > >>On Fri, 01 Jan 2010 19:19:42 -0600, krw <krw(a)att.bizzzzzzzzzzz> wrote: >> >>>On Fri, 01 Jan 2010 17:40:54 -0500, ehsjr <ehsjr(a)nospamverizon.net> >>>wrote: >>> > ><snip> > >>>>You've got a steadier hand than I'll ever have. >>>>I have to do it with a Dremel mounted in a drill press >>>>adapter, and slide the board against guides clamped to >>>>the bed. Even then ... :-( >>> >>>Sounds like you need a small milling machine. >> >>We had one of those PCB mills, on indefinite loan from a customer who >>wasn't using it. It was such a hassle that we wound up not using it >>too. > >Gotta be better than fence clamped to a drill press. > >>I can do the modest stuff with a knife and some kapton tape. After >>that, it's easiest to just lay out a board and have a pcb house make a >>few. > >You mean copper-clad kapton tape? No, just bits stuck to the copperclad and cut into patterns, as local insulators. But I guess you could do multilayer breadboards with layers of kapton tape and copper foil tape. Stained-glass folks sell copper tape. You could make pretty good transmission lines! John
From: John Larkin on 3 Jan 2010 19:54 On Sun, 03 Jan 2010 14:20:24 -0600, krw <krw(a)att.bizzzzzzzzzzz> wrote: >On Sun, 03 Jan 2010 10:19:37 -0800, John Larkin ><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: > >>On Sun, 3 Jan 2010 07:37:19 -0800 (PST), MooseFET <kensmith(a)rahul.net> >>wrote: >> >>>On Jan 2, 7:58�pm, krw <k...(a)att.bizzzzzzzzzzz> wrote: >>>> On Sat, 02 Jan 2010 20:45:11 -0700, Jim Thompson >>>> >>>> >>>> >>>> <To-Email-Use-The-Envelope-I...(a)My-Web-Site.com/Snicker> wrote: >>>> >On Sat, 02 Jan 2010 21:36:09 -0600, krw <k...(a)att.bizzzzzzzzzzz> wrote: >>>> >>>> >>On Sat, 02 Jan 2010 17:03:43 -0800, John Larkin >>>> >><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: >>>> >>>> >>>On Thu, 31 Dec 2009 09:41:54 -0800, "Joel Koltner" >>>> >>><zapwireDASHgro...(a)yahoo.com> wrote: >>>> >>>> >>>>"John Larkin" <jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote in message >>>> >>>>news:7glpj5l1a7i5nm45bsp5gfhc016e3kjgo8(a)4ax.com... >>>> >>>>> On Thu, 31 Dec 2009 09:10:22 -0700, Don Lancaster <d...(a)tinaja.com> >>>> >>>>>>It is NEVER right the first time. >>>> >>>>> We sell about 80% of our rev A boards, with no prototypes. Assuming >>>> >>>>> the first unit won't work is self-fulfilling, and a good way to make >>>> >>>>> sure the third iteration won't work either. >>>> >>>> >>>>I agree with your philosophy John... but you do allow yourself a non-zero >>>> >>>>number of blue wires or a couple of tack-soldered components or something on >>>> >>>>those saleable rev. A boards too though, right? >>>> >>>> >>>Sure, that happens. But it's supposed to be embarassing. >>>> >>>> >>>We make blue boards and I think we should use red wires. But >>>> >>>production insists on blue. >>>> >>>> >>I know one company that does use red wires, so oops's stand out like >>>> >>the sore thumb they are. � >>>> >>>> >Isn't "blue wire" sort of a historic standard ?:-) >>>> >>>> In IBM they were known as "yellow wires", not matter what color. �The >>>> original Teflon WireWrap wires were yellow and the name was kept. �I >>>> don't even remember what color we use now. >>> >>>I tend to spec the part number with a -(any) on the end for color. >>>Batch to batch from production will have different colors. The >>>number of jumpers has dropped to maybe one or two at the most. The >>>most common has always been the missed connection in the layout >>>or schematic. If you call a power supply "+24V" in one place and >>>"+24" in another, they are (no surprise) not connected. I now make >>>it a rule to always check my supply naming as the last check before >>>layout. >> >>It helps to print out a net list and read it. If you see VREF and >>REFV, investigate! >> >>One mistake we used to make too often was swapping V+ and V- on >>opamps. Engineers tend to flip an opamp to make the feedback path look >>nice (different for inverting/noninverting) and that moves the power >>pins too. We check that really hard now. > >We've done that too. The boss caught it last time. In that case the >layout guy screwed up the library. I also made him add an alternative >view for all op-amps so I can show them either way and still have the >power pins in the right place. It was a lot cheaper than a board spin >(with no other information gained). > >>We *almost* made some boards that had the BGA pitch wrong, due to some >>metric/inch rounding error that got us 3/4 of a ball wrong across the >>whole chip. Caught that by accident before it got out. > >That's something I'd never find. > >>I'm always a little anxious until the first successful powerup, and >>then until the uP runs code, and then until the FPGA configures, and >>then... > >You're done, aren't you? ;-) > >>On a recent board, there came a point when Linux was talking through >>PCI Express to our FPGA, and everybody cheered. > >Beer time. Actually, yes! John
From: John Larkin on 3 Jan 2010 19:58 On Sun, 03 Jan 2010 21:52:39 +0000, John Devereux <john(a)devereux.me.uk> wrote: >John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> writes: > >> On Sun, 03 Jan 2010 07:04:40 +0000, John Devereux >> <john(a)devereux.me.uk> wrote: >> >>>John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> writes: >>> >>>> On Fri, 01 Jan 2010 18:33:34 +0000, John Devereux >>>> <john(a)devereux.me.uk> wrote: >>>> >>>>>Bill Sloman <bill.sloman(a)ieee.org> writes: >>>>> >>>>>> On Jan 1, 6:00�am, Spehro Pefhany <speffS...(a)interlogDOTyou.knowwhat> >>>>>> wrote: >>>>>>> On Thu, 31 Dec 2009 09:10:22 -0700, the renowned Don Lancaster >>> >>>[...] >>> >>>>>>> >It is NEVER right the first time. >>>>>>> >>>>>>> Keep firing people who have that attitude and it eventually will be! >>>>>> >>>>>> Perhaps. But if the survivors are sufficiently nervous of getting >>>>>> fired that they triple-check every aspect of the circuit before they >>>>>> commit to a printed circuit layout, you may find that you get to the >>>>>> final layout more slowly than you would have if you'd gone through a >>>>>> throw-away prototype layout along the way. >>>>> >>>>>I'm going through this right now. New (208 pin!) microcontroller, ADC, >>>>>connectors, SMPS chip. I can spend an extra couple of days re-checking >>>>>everything, and I just *know* I will still miss a couple of things. Or I >>>>>can just go ahead and make the damn board. >>>>> >>>>>I think I'll just go ahead and see how it turns out. At some point it's >>>>>actually quicker and cheaper to debug using the real thing. >>>> >>>> You have to debug the real thing anyhow, so it makes sense to try to >>>> do the final product first pass. That saves a lot of time and teaches >>>> good disciplines. And you may be able to sell it. >>> >>>That *is* what I am doing. But don't you find there is eventually a >>>point of diminishing returns with respect to "paper" analysis and >>>prototyping? The last bug you did have on a rev A board, couldn't you >>>have found it by staring at the design for another week, checking >>>datasheets, going through the operation in your head? Maybe prototyping >>>some more bits of the circuit? >> >> Sure, there's a point of diminishing return. But a tradeoff of a week >> of checking to avoid a board spin is clearly worth it. Most of the >> time, in hardware or software, a bug just makes you look at an error >> that was in plain sight and would have been prevented by checking. We >> check enough that maybe 80% or so of our boards are sellable at first >> etch. I suspect we could do a little better, 90% maybe, and that would >> be worth it. > >We usually hand-build a prototype of the "first etch", and use it as a >development board for the firmware. After fixing any remaining bugs, I >am then sufficiently confident of the design to go to "production" >(typically only 50-100pcs for our stuff). This is actually the most >expensive cost, the solder stencil costs more than the bare boards! We do 6 and 8 layer boards mostly, 1000+ vias being common, and the first run, usually 5-10 boards, costs around $1000, depending on turn time. I think we're paying about $150 for a stainless stencil. John
From: krw on 3 Jan 2010 20:40
On Sun, 03 Jan 2010 17:02:05 -0500, Spehro Pefhany <speffSNIP(a)interlogDOTyou.knowwhat> wrote: >On Sun, 03 Jan 2010 14:15:52 -0600, the renowned krw ><krw(a)att.bizzzzzzzzzzz> wrote: > >>On Sun, 03 Jan 2010 10:08:15 -0800, John Larkin >><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >> >>>On Fri, 01 Jan 2010 19:19:42 -0600, krw <krw(a)att.bizzzzzzzzzzz> wrote: >>> >>>>On Fri, 01 Jan 2010 17:40:54 -0500, ehsjr <ehsjr(a)nospamverizon.net> >>>>wrote: >>>> >> >><snip> >> >>>>>You've got a steadier hand than I'll ever have. >>>>>I have to do it with a Dremel mounted in a drill press >>>>>adapter, and slide the board against guides clamped to >>>>>the bed. Even then ... :-( >>>> >>>>Sounds like you need a small milling machine. >>> >>>We had one of those PCB mills, on indefinite loan from a customer who >>>wasn't using it. It was such a hassle that we wound up not using it >>>too. >> >>Gotta be better than fence clamped to a drill press. > >With the spindle Morse taper Loctited in so that the side forces don't >loosen it up! Goina need a bigger hammer! |