1. Home
  2. Electronics Design
  3. When to use copper pour/fill

When to use copper pour/fill

I've known about the existence of copper pours for some time, but I suppose didn't think I needed one, and up until now, probably didn't.

A little background: I have a little home project that uses a 50MHz quad flat pack microcontroller with integrated 10/100 Ethernet MAC/PHY, which connects to a RJ45 jack with integrated magnetics. So there's a minimal amount of external components required for my Ethernet interface. Also on the board is an I2S audio DAC going to a standard pair of RCA line out jacks, and a simple linear power supply. I designed a double sided PCB with little regard to EMC, and it works, but when the Ethernet cable is plugged in, the nearby TV shows interference. (Which I find somewhat amazing considering the TV is not getting signal from an antenna, but from CATV).

So, after a little Googling I see what I essentially need to do with the Ethernet traces/components, and it involves copper pour along with keeping some traces near each other. But my question is: is there a reason to not apply copper pour to the entire board? My current train of thought is to copper pour both sides and connect it to ground. But is there much advantage to doing this? I'll have to use copper pour between the micro and Magjack, but is it worthwhile to use everywhere?

I know this is probably a very subjective question, with lots of variables. I'm looking for any input anyone has. For the record, the audio quality the current design is generating is fine. It's just that the Ethernet I/F is generating interference.

Reply to
hondgm
Loading thread data ...

snipped-for-privacy@yahoo.com wrote in news:267cad6a-f016-45ad-8a61- snipped-for-privacy@v41g2000yqv.googlegroups.com:

I had a similiar problem. It turned out to be the smps powering my PC has no CMC this would cause mild picture snow on a TV on the same circuit in an adjacent room.

You could try a line filter on your linear regulator and maybe RF shielding around your device.

Reply to
Hammy

It's likely the cable that's acting as an antenna. Yes, copper pours (or better, planes) are always a good idea, but I don't think this is your problem. You might try putting a couple of ferrite beads in line with your Ethernet signals, or better, an RJ-45 with the magnetics built in. There are also ferrite lumps you can place around the cable, with maybe a loop of cable through the ferrite material. We had to do this on our base station to pass CE compliance tests. You often see these "lumps" on cables (even power cables) for the same reason.

Reply to
krw

I see no reason not to apply copper fill to the whole board. The only place (that I can think of) where you generally _don't_ want copper fill is underneath a free-running oscillator, in which case you're defending against a temperature-dependent capacitance between the fill and your oscillator's frequency-determining components.

I probably get more use out of copper fill as a handy place to build dead-bug circuit additions than for any EMI advantages.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" was written for you.
See details at http://www.wescottdesign.com/actfes/actfes.html
Reply to
Tim Wescott

You may not need a copper pour. OTOH the Ethernet traces need to be trated as transmission lines; with full respect to consistant spacing, impedance, and termination and adding a ground plane undernath them will impact all 3. For all signals above 1 MHz, treating as needing transmission lines will rarely hurt and will normally benefit you.

The other comments made seem reasonable as well.

Reply to
JosephKK

I'd be looking at some ethernet cards, they all follow similar rules for those signal pairs from the connector over to the chip. Although looking inside the back of a gigabit connector where the toroids are not potted is scary, very, very busy in there.

Grant.

Reply to
Grant

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.