How do you design these days?
in [Design]
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From: krw on 3 Jan 2010 20:43 On Sun, 03 Jan 2010 16:49:45 -0800, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >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. What good does that do? I guess I don't see the purpose of the insulator without a pad to solder to. Got a picture? > But I guess you could do multilayer breadboards with >layers of kapton tape and copper foil tape. Stained-glass folks sell >copper tape. We use it for testing EMI and ESD shields, too. >You could make pretty good transmission lines! I hunk of 30ga wire on a ground plane isn't bad. Al *lot* of 30ga wires on a ground plane isn't bad, either.
From: John Larkin on 4 Jan 2010 01:33 On Sun, 03 Jan 2010 19:43:46 -0600, krw <krw(a)att.bizzzzzzzzzzz> wrote: >On Sun, 03 Jan 2010 16:49:45 -0800, John Larkin ><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: > >>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. > >What good does that do? I guess I don't see the purpose of the >insulator without a pad to solder to. Got a picture? Under the SO8... ftp://jjlarkin.lmi.net/BB_fast.JPG John
From: John Devereux on 4 Jan 2010 03:57 John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> writes: > 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: >>>>> [...] >>>>>>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. That does change the equation. We have a couple of 4 layer boards, but mostly I try to keep to two layers. The one I just did uses a fairly bloated "single-chip" microcontroller, with external SDRAM and a TFT LCD interface. I have managed to maintain a fairly good groundplane on one side but this is the most that I would attempt on two-layer. Cost of a couple of prototype boards is $140, that will allow me to assemble a prototype, program some firmware and bring the design to the point where I can confidently build 50 pcs next time. (Stencil cost is ~$300 unless my assembly company can put someone elses on it too). -- John Devereux
From: Baron on 4 Jan 2010 11:52 Spehro Pefhany Inscribed thus: > > With the spindle Morse taper Loctited in so that the side forces don't > loosen it up! > > Best regards, > Spehro Pefhany I've never had a Morse taper fitting loosen due to side forces or had to use Locktite on one. -- Best Regards: Baron.
From: Joel Koltner on 4 Jan 2010 13:53
"krw" <krw(a)att.bizzzzzzzzzzz> wrote in message news:ngu1k5lciqj2c6h9svs4m69eu4nu9ih7ut(a)4ax.com... > 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. My experience is that it's almost always is cheaper to have boards made out of house (particularly as soon as you have enough vias that you're better off with plated-through holes rather than just soldering in jumper wires) than on a milling machine *so long as you can wait for a week-long turn*. E.g., I can get, say, a 6"x8" boards with solder mask, silkscreen, plated-through holes/vias, and 6/6 traces and spaces for something like $100 if I'm willing to wait a week, whereas having our guys make a board like that with the LPKF machine we have is probably more like $500 and they start to look worried with designs rules tighter than about 8/8. But it is nice to have around if you just need a single side+ground plane board (which often works fine for the RF test boards I do) and can live without a silkscreen or soldermask and would like the board *today*. ---Joel |