Forums

pc motherboard grounds

Started by John Larkin August 25, 2012
On Sat, 25 Aug 2012 18:24:02 -0700, Jeff Liebermann <jeffl@cruzio.com>
wrote:

> >This might explain: ><http://smallformfactors.com/pdfs/RTD.Win07.pdf> > EDITOR: Should the pads for the PC/104 mounting holes be grounded? > > BLAZER: The PC/104 specifications do not say anything about > grounding the mounting holes.
PC/104 is NOT the PC spec. That is an entirely different form factor/bus/architexture altogether.
On Sat, 25 Aug 2012 18:50:27 -0700, Jeff Liebermann <jeffl@cruzio.com>
wrote:

> The idea is to prevent >ground loops and keep the noise level down.
That is because the spec allows several different vendor devices to end up on your backplane, dingledorf. They are also hot swap capable. Again, it is an entirely different concept than a PC is.
On Sat, 25 Aug 2012 19:01:17 -0700, Jeff Liebermann <jeffl@cruzio.com>
wrote:

>FCC Part 15: ><http://ecfr.gpoaccess.gov/cgi/t/text/text-idx?c=ecfr&sid=83a8c3f5180c5c04dc038e32b563925f&rgn=div5&view=text&node=47:1.0.1.1.16&idno=47> >etc... None of the voluminous specifications include anything on >implimentation specifics such as grounding.
Are you so dumb as to think that emissions testing would pass without it back in the TTL early CMOS days? They were far more emissive then than now. In order to comply with the FCC emissions standards, intelligent designers in the PC industry ALL tied their ground planes to their mobo/chassis mounting holes. You guys all lost some basic common sense somewhere along the way.
On Sat, 25 Aug 2012 20:07:53 -0700, SoothSayer
<SaySooth@TheMonastery.org> wrote:

>On Sat, 25 Aug 2012 19:01:17 -0700, Jeff Liebermann <jeffl@cruzio.com> >wrote: > >>FCC Part 15: >><http://ecfr.gpoaccess.gov/cgi/t/text/text-idx?c=ecfr&sid=83a8c3f5180c5c04dc038e32b563925f&rgn=div5&view=text&node=47:1.0.1.1.16&idno=47> >>etc... None of the voluminous specifications include anything on >>implimentation specifics such as grounding.
> Are you so dumb as to think that emissions testing would pass without >it back in the TTL early CMOS days? They were far more emissive then >than now.
Amazing. Back in the TTL and early CMOS daze, presumably the 1970's, there was S-100, Multibus, DEC Unibus, and such. They radiated badly, mostly because of the long unterminated wire lengths. (Wires make good antennas, components do not). However, as computahs progressed, and technology improved, the bus lengths shrank, as did the number of components that needed interconnection, thus reducing radiated EMI somewhat. However, at the same time, the power consumption of the CPU started climbing. Today, Intel CPU's are hovering around 75-100 watts. Tricky methods, such as "spread spectrum" clocks really didn't reduce the radiation as much as it took advantage of a stupid loophole in the FCC part 15 specifications. You have only to turn on a 2-way radio in a room full of computers to test the effectiveness of the current EMI/RFI reduction efforts. I would say that it's about the same as the 1970's with the added bonus of having to deal with more EMI/RFI producing devices.
> In order to comply with the FCC emissions standards, intelligent >designers in the PC industry ALL tied their ground planes to their >mobo/chassis mounting holes.
Also amazing. We had a simple test to determine if the PCB was properly bypassed. We would fire up a spectrum analyzer with a small discone or biconical antenna, and put it near the board. If attaching it to the base plate (usually a piece of aluminum sheet metal with PEM standoffs installed) had any effect on the radiated RFI, there was a problem. Only when mounting and grounding the board to the baseplate were we sure that there were no circulating currents going through the sheet metal, which would eventually act as an antenna in the final product. Relying on the case for grounding is not a great idea.
> You guys all lost some basic common sense somewhere along the way.
I prefer a balanced sense as in a Kelvin bridge. Common (ground) sense measurements are inaccurate. -- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
On Sat, 25 Aug 2012 19:53:21 -0700, SoothSayer <SaySooth@TheMonastery.org>
wrote:

>On Sat, 25 Aug 2012 20:03:43 -0400, "krw@att.bizzzzzzzzzzzz" ><krw@att.bizzzzzzzzzzzz> wrote: > >> The FCC has their own ideas and even they don't >>care what you do with the screws. > > This isn't about screws, idiot. It is about industry wide and fully >adopted and accepted circuit board design standards.
Cite these "standards", AlwaysWrong.
> You are a goddamned retard, Williams.
*Everyone* here knows you're AlwaysWrong.
On Sat, 25 Aug 2012 20:07:53 -0700, SoothSayer <SaySooth@TheMonastery.org>
wrote:

>On Sat, 25 Aug 2012 19:01:17 -0700, Jeff Liebermann <jeffl@cruzio.com> >wrote: > >>FCC Part 15: >><http://ecfr.gpoaccess.gov/cgi/t/text/text-idx?c=ecfr&sid=83a8c3f5180c5c04dc038e32b563925f&rgn=div5&view=text&node=47:1.0.1.1.16&idno=47> >>etc... None of the voluminous specifications include anything on >>implimentation specifics such as grounding. > > Are you so dumb as to think that emissions testing would pass without >it back in the TTL early CMOS days? They were far more emissive then >than now.
Cite the specification that requires it, AlwaysWrong, or admit that you're just making it up as you go.
> In order to comply with the FCC emissions standards, intelligent >designers in the PC industry ALL tied their ground planes to their >mobo/chassis mounting holes.
Cite the specification that requires this.
> You guys all lost some basic common sense somewhere along the way.
You never had any, AlwaysWrong. Of course, the janitor, and village idiot, don't need any sense at all. I suppose we all have our places in the orgainization. Someone has to keep the pipes clear.
On Sat, 25 Aug 2012 20:04:51 -0700, SoothSayer <SaySooth@TheMonastery.org>
wrote:

>On Sat, 25 Aug 2012 18:50:27 -0700, Jeff Liebermann <jeffl@cruzio.com> >wrote: > >> The idea is to prevent >>ground loops and keep the noise level down. > > That is because the spec allows several different vendor devices to end >up on your backplane, dingledorf.
Irrelevant, AlwaysWrong.
> They are also hot swap capable.
Completely irrelevant, DimBulb.
> Again, it is an entirely different concept than a PC is.
Moving goal posts again, Dimmie?
On Sat, 25 Aug 2012 18:00:06 -0700, John Larkin
<jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

>On Sat, 25 Aug 2012 17:53:41 -0700 (PDT), Bob Boblaw ><larrymoencurly@my-deja.com> wrote: > >>On Saturday, August 25, 2012 9:34:54 AM UTC-7, John Larkin wrote: >> >>> The mounting holes on PC motherboards: are they usually >>> connected to the PCB ground plane? >> >>I haven't seen a mounting hole that was plated-through, but any copper rings surrounding a hole was always (?) connected to ground. OTOH other copper foil running right next to the hole isn't always ground, and I've measured 5V and 3.3V on some; in one case the copper on the left side of the hole was connected to the 5V supply and the copper on the right went the 3.3V (FIC brand PA-2007 or VA-503+ motherboard)
>I wonder why they are not plated. A non-plated hole is a secondary PCB >fab operation. The ring+vias thing looks like more work.
We had a problem with plated holes, where they couldn't keep the tolerance on the holes in spec for the mounting tabs. We had to have the plating removed.
>Maybe they are worried about stress/cold flow fracturing the plating? >We do plated mounting holes, no extra vias, grounded to internal >planes, and I've never seen a problem.
The extra vias seem to be a good idea, though. There's no cost, so...
Sooth Sayer is probably another sock puppet for Always Wrong. You can 
change your handle, but the asshole stench always comes through.


On 2012-08-25, SoothSayer <SaySooth@TheMonastery.org> wrote:
> L thought you have been claiming to have laid out PWAs for the last > several years. > > This is a no brainer.
No, you are.
> If you had ever assembled your own PC at any time, you would know the > answer simply by examining the fastener/stud pack that comes with the > motherboard.
The machine screws and standoffs come with the case. if they wanted the hole insulated ther's just design the PCB with no electrical connection to the holes. I've seem a few cases that used a combination of plastic ans metal standoffs, not so mant recently. Some standffs have 6-32 thread others have M3, some have one end 6-32 and M3 at the other. On the board I measured all the bolt holes were connected to ground. -- &#9858;&#9859; 100% natural --- Posted via news://freenews.netfront.net/ - Complaints to news@netfront.net ---