Copper Pour on PCB Tips

dwelve

Hi,

I've designed a double-sided Prop-based board (dip version) and have everything laid out and routed. I copper poured ground to the top layer and am wondering if I should put a copper pour on the bottom layer.

If I do put a copper pour on the bottom side, what NET should I tie it to? I have an unregulated +11.1 V, and regulated +5V and +3.3V power NETs. Should I make the bottom side GND, +3.3V (powers prop and eeprom, sd card, two other ICs), or +5V (powers four ICs)? Or should I not even bother with copper pouring the bottom side? The fasting switching speeds are the Prop itself, serial communications of at most 115,200 baud rate, and SPI on the sd card... also, I have a Bluetooth module breakout board that sits on the board. I used through-hole parts for everything... (I suspect that ground planes on both sides might exhibit unwanted capacitance and a slight charge buildup if I'm not careful).

My protoboard with wires everywhere (even for power) doesn't seem to exhibit too many problems, so I'm wondering If I'm just over-doing it... but just for future reference I want to know what the best practices are for something like this.

Thanks.
dwelve

mctrivia

always net both sides ground

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Need to make your prop design easier or secure? Get a PropMod has crystal, eeprom, and programing header in a 40 pin dip 0.7" pitch module with uSD reader, and RTC options.

dwelve

Thanks, mctrivia, I'll probably net both sides ground, then! Just out of curiosity, what are the advantages and disadvantages of net'ing both sides ground versus net'ing the other side +3.3 V or +5V?

Thanks again.
dwelve

Peter Jakacki

Generally speaking you don't "always" do things the same way. Generally I pour ground on one side and a mix on the other so that VDD is poured in and around the logic with perhaps VCC (+5V) and then ground filling in the rest. The clearance rules for these large pours of copper need to be increased as narrow voids between large areas of copper tend not to etch as nicely and sometimes the blank pcbs have copper whiskers shorting across (which BBT should reject) . Unregulated power normally doesn't need a copper pour really as a good short track to the regulator and power devices is all that is needed.

Talking about grounds though I usually make sure that I place a 2-pin jumper (0.1" pin strip) as a test ground somewhere accessible on the pcb.

*Peter*

mctrivia

the reason for ground is it absorbs stray radiation from your signal traces and having a good ground plane stops all kind of strange problems.

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Need to make your prop design easier or secure? Get a PropMod has crystal, eeprom, and programing header in a 40 pin dip 0.7" pitch module with uSD reader, and RTC options.

Peter Jakacki

Because the VDD and VCC pours are capacitively coupled to the ground via the numerous (hopefully) decoupling capacitors and the pcb itself then these areas form an effective ground plane for high-frequency signals as they are low impedance at these frequencies. Also the power plane one side with the ground plane on the other also creates an image plane where EM fields are nulled out by the equal return currents otherwise the ground plane can become an EM radiator itself in certain places.

*Peter*

Phil Pilgrim (PhiPi)

One thing to be careful of: Don't assume that, just because you've done a copper pour and connected it to Vss, you've created a ground plane. If the copper pour is broken up by signal traces, you need to examine it carefully and plot the paths of your return currents to make sure that heavy currents, for example, take a direct path to the power source without encountering sensitive circuitry along the way. (In fact, it's often desirable to add isolation channels to a groundplane to guarantee this.) Also, if your layout software doesn't do it for you, you need to check for galvanic "islands" in your pour that don't connect anywhere.

-Phil

william chan

Why eagle don't allow copper pour?

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www.fd.com.my
www.mercedes.com.my

mctrivia

eagle does. use the polygon tool and rename it to the net you want it to be attached to.

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Need to make your prop design easier or secure? Get a PropMod has crystal, eeprom, and programing header in a 40 pin dip 0.7" pitch module with uSD reader, and RTC options.

Philldapill

I've been trying to figure out how to do that for some time now, mctrivia. I LOVE eagle. I've learned so much in the past week...

mctrivia

Eagle is a great program though not always the easiest to use. Glad I could help.

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Need to make your prop design easier or secure? Get a PropMod has crystal, eeprom, and programing header in a 40 pin dip 0.7" pitch module with uSD reader, and RTC options.

Timothy D. Swieter

When using the polygon tool, be sure to watch your line width, your design rules and the orphan check box. Do take the time to read through the help file to understand the options. I use EAGLE for my designs and use copper pours/polygons.

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Timothy D. Swieter, E.I.
www.brilldea.com - Prop Blade, LED Painter, RGB LEDs, 3.0" LCD Composite video display, eProto for SunSPOT
www.tdswieter.com

OwenS

In particular, if you have any active analogue circuitry on the board (I.E. op-amps and such), give it a ground plane of it's own so it doesn't have to put up with 80Mhz noise