Finished PCB that uses lots of Sparkfun parts.

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ADmoney
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Finished PCB that uses lots of Sparkfun parts.

Post by ADmoney » Wed May 28, 2008 2:19 am

Hello all, I've finished a PCB that makes use of the Arduino, Sparkfun accelerometer (memsic 2125 i believe), a GSR sensor, RF modules from Sparkfun (315 Mhz), muscle wire output, and Soundgin mini-synth. Circuit schematic and PCB top copper / bottom copper is located here: http://tiny.cc/DvaaM.

I'm pretty confident about my board, I've done several designs before, although this is a more "complex" one I've done. I've double checked everything, made sure I've got nice power decoupling caps, fat traces on all power/gnd signals. Top layer is mostly power planes, bottom layer is mostly ground plane save the horizontal 3.7v signal. For power, I'm using 3.7v Li-On batteries that get boosted up to 5v for the whole circuit In addition, the 3.7v is used to power 4 pairs of muscle wires. It's also going through a voltage reg to 1.5v for the GSR so I don't have to use an external battery for that. What else... I've got loads of jumper pins that are mostly used to connect external stuff like batteries, sensors etc. If anyone wants to briefly look at schematics and give feedback that would be good.

One question though - does it make a difference if my power / gnd planes copper pours are thatched, like criss cross design? I've heard that it helps to dissipate heat or whatever... but I'm just going with a solid fill.

TIA

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leon_heller
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Post by leon_heller » Wed May 28, 2008 3:39 am

It won't make any difference. It's sometimes done so that the copper can be recovered.

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Philba
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Post by Philba » Wed May 28, 2008 10:01 pm

That is done to make soldering easier - that's the heat they are talking about. Basically, a copper plane will soak up a lot of heat and make soldering a lot harder. You can do the same if you use thermals.

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Post by NleahciM » Thu May 29, 2008 2:32 pm

Philba wrote:That is done to make soldering easier - that's the heat they are talking about. Basically, a copper plane will soak up a lot of heat and make soldering a lot harder. You can do the same if you use thermals.
Thermals are just as effective at doing this.

Cross hatching is useful for RF and flex circuits. I've heard some people mention that it is useful for some techniques that people use for making their own PCBs. Otherwise - I don't know of any good reasons to do it.

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bigglez
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Re: Finished PCB that uses lots of Sparkfun parts.

Post by bigglez » Fri May 30, 2008 3:00 pm

Greetings TIA (No First Name Supplied),
ADmoney wrote:does it make a difference if my power / gnd planes copper pours are thatched, like criss cross design? I've heard that it helps to dissipate heat or whatever... but I'm just going with a solid fill.
Hatching ground planes has advantages for the board house,
the lower copper mass makes soldering easier (as already
pointed out) although thermals relieve the issue. Also, the
lower copper mass reduces warping during processing and
soldering, and is less likely to give rippled solder coat under
the solder resist (if used). Most board houses do HAL (Hot
Air Leveling) so this is less of an issue. It may save wieght
in large boards with large plane areas.

If the planes are used for heatsinking the solid area will
have a lower thermal resistance than the same area with
hatching (not the other way around as you had heard).

It would be unwise to have solid plane areas without
thermals, due to soldering difficulty.

For RF applications it is common to staple the ground
planes (with vias) to form a WGBC (waveguide beyond cut-off).
This is only applicable to RF techniques above about 1GHz.
More info here.

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ADmoney
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Location: Cape Town

Post by ADmoney » Sat May 31, 2008 1:32 am

Thanks for the reply... TIA means thanks in advance, my name is Adrian.

OK so i thought thermals were the X or + pattern around the vias that are connected to power / ground layer. Does thermal mean the pattern used as well on the copper pour? In any case I guess I'll just use the X pattern for my ground and VCC polygons.

NleahciM
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Post by NleahciM » Sat May 31, 2008 5:46 am

ADmoney wrote:Thanks for the reply... TIA means thanks in advance, my name is Adrian.

OK so i thought thermals were the X or + pattern around the vias that are connected to power / ground layer. Does thermal mean the pattern used as well on the copper pour? In any case I guess I'll just use the X pattern for my ground and VCC polygons.
No - you were right to begin with - the X/+ on the pad is a thermal. When your whole plane is in that cross hatch pattern, it's called cross hatching. And if you you should get one thing from this thread - it should be that cross hatching is not going to help you.

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