What are 6.5 Digit Multimeters Good For?
in [Design]
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From: Randomly on 17 Mar 2010 01:31 >http://www.tinaja.com/whtnu09.asp#d02-19-09 > >-- >Many thanks, > >Don Lancaster voice phone: (928)428-4073 >Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552 >rss: http://www.tinaja.com/whtnu.xml email: don(a)tinaja.com > >Please visit my GURU's LAIR web site at http://www.tinaja.com Thanks for the links, but I noticed you state there that one ounce copper is 0.68 milliohms per square for 25 micrometer thickness (1 mil). I think one ounce copper is 35.6 micrometers thick (1.4 mils) and the resistivity is 0.486 milliohms per square. or am I mistaken? --------------------------------------- Posted through http://www.Electronics-Related.com
From: JosephKK on 17 Mar 2010 02:48 On Tue, 16 Mar 2010 09:40:50 -0500, "Randomly" <fburfell2000(a)n_o_s_p_a_m.n_o_s_p_a_m.yahoo.com> wrote: > >>>You may be making measurement errors when you measure the traces, 1 amp >can >>>be a lot of current on small traces and you may be heating that trace up >>>quite a bit. Copper has a substantial thermal coefficient of resistance, >>>heat it up by 25C and the resistance goes up 10%. Try dropping your >current >>>to 0.1A and see how your measurements change. >> >>I think my measurements are accurate, and I often include a test trace >>whose geometry is suitable for accurate sheet resistance measurement. >> >>If I include a fab note demanding a minimum sheet resistance, or say >>"START WITH 1 OZ COPPER" I usually get below 600 uohms/square. If I >>just say "COPPERCLAD 1 OZ" I usually don't. > >Well if you are sure you are not heating your traces up when you measure >them it sounds like you need to talk to your fab about the issue. Get them >to explain their fabrication process and what the variables are that can >affect the sheet resistance. 1 oz copper is just an arbitrary standard, >what's important is to know what sheet resistance you can expect out of >them and how variable it can be. It's good to know what the sheet >resistances and dielectric constants of all the board options they offer so >you can get what you need out of them. If it's an important aspect of your >board design you have to specify it, you can't leave it to chance since >they may change suppliers, or processing, or subcontract it out etc. Talk >to them, find out what the options are and what they are comfortable with. >If you are not satisfied find another fab. > >What fab are you using? > >--------------------------------------- >Posted through http://www.Electronics-Related.com Damn you do not read very well do you? JL stated that he orders boards by sheet resistivity (al least when he thinks it matters, did you pick up on the test trace?).
From: JosephKK on 17 Mar 2010 02:54 On Tue, 16 Mar 2010 08:41:41 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon(a)My-Web-Site.com> wrote: >On Tue, 16 Mar 2010 05:02:11 -0700, >"JosephKK"<quiettechblue(a)yahoo.com> wrote: > >>On Sun, 14 Mar 2010 17:54:07 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon(a)My-Web-Site.com> wrote: >> >>>On Sun, 14 Mar 2010 18:46:36 -0700, >>>"JosephKK"<quiettechblue(a)yahoo.com> wrote: >>> >>>>On Fri, 12 Mar 2010 10:44:39 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon(a)My-Web-Site.com> wrote: >>>> >>>>>On Fri, 12 Mar 2010 09:33:25 -0800, D from BC >>>>><myrealaddress(a)comic.com> wrote: >>>>> >>>>>>In article <hndc5b$37k$1(a)news.albasani.net>, pNaonStpealmtje(a)yahoo.com >>>>>>says... >>>>>>> >>>>>>> On a sunny day (Thu, 11 Mar 2010 17:56:35 -0800) it happened D from BC >>>>>>> <myrealaddress(a)comic.com> wrote in <MPG.26033f321480b139896e5(a)209.197.12.12>: >>>>>>> >>>>>>> >6.5 digit multimeters sell around $1000.00. >>>>>>> >For electronics development, are these $1000 multimeters really >>>>>>> >necessary? >>>>>>> >What are they good for? >>>>>>> >>>>>>> They are not needed, all you need is a 5 Euro multimeter, >>>>>>> and in extreme cases a precise reference. >>>>>>> That means if you use one of those reference chips, you borrow >>>>>>> the very accurate multimeter for a day, measure your reference chip, >>>>>>> write it down, and use that to calibrate your cheap multimeter, >>>>>>> or o compute it's real value, >>>>>>> Saved: 1000$ >>>>>>> >>>>>>> Of course there are exceptions, >>>>>>> but in places where that counts they usually have a lot of ++++expensive stuff anyways. >>>>>>> Usually places where nothing really useful is done, like in CERN, or ITER, or LIGO, >>>>>>> etc. >>>>>> >>>>>>How about mohm measurements? Maybe that's handy. >>>>>>My DMM only goes to 0.1 ohm. >>>>>>I thought of measuring DCR of coils or pcb trace resistance for sim >>>>>>accuracy. >>>>>> >>>>>> >>>>> >>>>>Measuring milli-Ohms is tricky. Ideally you'd like 4-point-probe >>>>>measuring... voltage "viewing" pins are separate from current forcing >>>>>pins. >>>>> >>>>>I'd do it with an AC current source, so you can gain-up the resulting >>>>>voltage. >>>>> >>>>> ...Jim Thompson >>>> >>>>So, you know some interesting tricks to make an AC current source >>>>accurate to 0.01%? A lot of people would interested, especially if >>>>it was a clean sine source. With a good clean DC current source i >>>>have seen measurements all the way to 0.00002%. There be tradeoffs >>>>here. >>> >>>Why do need "accuracy" to 0.01%? What are you trying to measure to >>>that kind of accuracy? >>> >>> ...Jim Thompson >> >>Perhaps i wanted to get credible results on contact resistance >>repeatability. Or maybe i need to verify a current measuring shunt. > >If you do some kind of 4-point measuring arrangement, contact >resistance doesn't matter. > > ...Jim Thompson What i was measuring was the contact resistance of some relay contacts in the closed position, also connector contacts contact resistance. And, of course, it was the best 4-terminal connections i could make.
From: Randomly on 17 Mar 2010 09:36 >On Tue, 16 Mar 2010 09:40:50 -0500, "Randomly" = ><fburfell2000(a)n_o_s_p_a_m.n_o_s_p_a_m.yahoo.com> wrote: > >> >>>>You may be making measurement errors when you measure the traces, 1 = >amp >>can >>>>be a lot of current on small traces and you may be heating that trace = >up >>>>quite a bit. Copper has a substantial thermal coefficient of = >resistance, >>>>heat it up by 25C and the resistance goes up 10%. Try dropping your >>current >>>>to 0.1A and see how your measurements change. >>> >>>I think my measurements are accurate, and I often include a test trace >>>whose geometry is suitable for accurate sheet resistance measurement. >>> >>>If I include a fab note demanding a minimum sheet resistance, or say >>>"START WITH 1 OZ COPPER" I usually get below 600 uohms/square. If I >>>just say "COPPERCLAD 1 OZ" I usually don't. >> >>Well if you are sure you are not heating your traces up when you measure >>them it sounds like you need to talk to your fab about the issue. Get = >them >>to explain their fabrication process and what the variables are that can >>affect the sheet resistance. 1 oz copper is just an arbitrary standard, >>what's important is to know what sheet resistance you can expect out of >>them and how variable it can be. It's good to know what the sheet >>resistances and dielectric constants of all the board options they offer= > so >>you can get what you need out of them. If it's an important aspect of = >your >>board design you have to specify it, you can't leave it to chance since >>they may change suppliers, or processing, or subcontract it out etc. = >Talk >>to them, find out what the options are and what they are comfortable = >with. >>If you are not satisfied find another fab. >> >>What fab are you using? =20 >> =09 >>--------------------------------------- =09 >>Posted through http://www.Electronics-Related.com > >Damn you do not read very well do you? JL stated that he orders boards = >by=20 >sheet resistivity (al least when he thinks it matters, did you pick up on= >=20 >the test trace?). You've lost me. What did I say that was not valid? Perhaps my past experiences with cheap chinese pcb manufacturers has tainted my outlook but I am missing what point you are trying to make. --------------------------------------- Posted through http://www.Electronics-Related.com
From: John Larkin on 17 Mar 2010 13:14
On Wed, 17 Mar 2010 08:36:49 -0500, "Randomly" <fburfell2000(a)n_o_s_p_a_m.n_o_s_p_a_m.yahoo.com> wrote: >>On Tue, 16 Mar 2010 09:40:50 -0500, "Randomly" = >><fburfell2000(a)n_o_s_p_a_m.n_o_s_p_a_m.yahoo.com> wrote: >> >>> >>>>>You may be making measurement errors when you measure the traces, 1 = >>amp >>>can >>>>>be a lot of current on small traces and you may be heating that trace >= >>up >>>>>quite a bit. Copper has a substantial thermal coefficient of = >>resistance, >>>>>heat it up by 25C and the resistance goes up 10%. Try dropping your >>>current >>>>>to 0.1A and see how your measurements change. >>>> >>>>I think my measurements are accurate, and I often include a test trace >>>>whose geometry is suitable for accurate sheet resistance measurement. >>>> >>>>If I include a fab note demanding a minimum sheet resistance, or say >>>>"START WITH 1 OZ COPPER" I usually get below 600 uohms/square. If I >>>>just say "COPPERCLAD 1 OZ" I usually don't. >>> >>>Well if you are sure you are not heating your traces up when you measure >>>them it sounds like you need to talk to your fab about the issue. Get = >>them >>>to explain their fabrication process and what the variables are that can >>>affect the sheet resistance. 1 oz copper is just an arbitrary standard, >>>what's important is to know what sheet resistance you can expect out of >>>them and how variable it can be. It's good to know what the sheet >>>resistances and dielectric constants of all the board options they >offer= >> so >>>you can get what you need out of them. If it's an important aspect of = >>your >>>board design you have to specify it, you can't leave it to chance since >>>they may change suppliers, or processing, or subcontract it out etc. = >>Talk >>>to them, find out what the options are and what they are comfortable = >>with. >>>If you are not satisfied find another fab. >>> >>>What fab are you using? =20 >>> =09 >>>--------------------------------------- =09 >>>Posted through http://www.Electronics-Related.com >> >>Damn you do not read very well do you? JL stated that he orders boards = >>by=20 >>sheet resistivity (al least when he thinks it matters, did you pick up >on= >>=20 >>the test trace?). > >You've lost me. What did I say that was not valid? Perhaps my past >experiences with cheap chinese pcb manufacturers has tainted my outlook but >I am missing what point you are trying to make. > >--------------------------------------- >Posted through http://www.Electronics-Related.com I think a lot of board houses start with 1/2 or even 1/4 oz copper. That's ideal for etching fine-pitch traces, like 5/5 rules. Then they plate up surface traces and thru-holes, the "semi-additive" process. They tend to skimp on plating time. John |