PCB Design Noob - Critique my design (pic)

Community PCB Design
1

Greetings everyone. I’m new to PCB layouts, and I’m curious if I am doing anything wrong?

The board is 3.15" x 3.6". It is an arduino with one analog input, 7 LEDs, and two PWM outputs going to P-channel MOSFETs for high current switching. The purpose is to monitor a tilt sensor and the PWM outputs will control solenoids on a hydraulic valve to keep the sensor level. The LEDs are just for visual display of what is going to the PWM outputs. In the top right corner is a MAX232 chip for RS-232 connection to the computer. The wide traces are 200mil and will have to be 2oz to handle the 6 amp fuse. Actual load will be more like 1.5-3.5 amps, and there will only ever be one on at a time.

Any feedback would be appreciated.

Thanks,

Lance

2

When traces hit the pads they shouldn’t be so big. On Q2 and IC2 the middle trace is too close to the other pads.

3

You don’t seem to have any capacitors on the 7805 regulator. It might oscillate.

I can’t see a decoupling capacitor on the AVR.

4

You don’t need to run such wide traces for the logic, led, and similar signals; 10 mil should be fine. Also, for 6A, 150 mils of 1oz copper is fine, so 200 mils will be perfect. No need for 2oz, and that will save some money.

You don’t want to run traces under the tabs of the TO220 as they can short out, even with solder mask, if there’s a scratch or some conductive schmutz.

I’d add silkscreen labels to the LEDs stating what they mean, and add polarity marks and voltage range to the power connector.

/mike

5

Thanks for the suggestions. I have cleaned up the traces coming in to the TO220s.

There are capacitors to the left of the 7805, between it and the polarity protection diode. There are also 2 decoupling caps right next to the AVR, one on each side, near the middle of the long side of the chip. They just don’t have a very informational picture.

I used the trace width calculator here:

http://www.circuitcalculator.com/wordpr … alculator/

which says that 6 amps on 1oz copper requires a trace 364 mils wide. Going to 2oz copper takes the trace width down to 182 mils. Amusingly, I can find other trace width calculators that say the same, and I can find calculators that say I only need 107 mils of 1oz for 6 amps. It appears that current capacity of a trace goes down if it is inside the board due to lack of heat dissipation.

New image with the top silk turned on instead of the part labels.

-Lance

6

That calculator is showing 364 mils for inside layers (for a board with more than two layers), and 140 mils for outside layers. Outside layers can dissipate heat better.

/mike

7

You should run power through the cap from your 7805 rather than just having a trace branch off to it.

Avoid the off angle traces. They really make it look confusing.

It looks like you have a shared ground. Drop a ground fill on the bottom layer.