PCB Layout Help

[CapeCAD]

Hello CapeCAD,

I've seen this before on boards before but I never knew what the purpose was. I still don't actually. The feature is available in the PCB layout software I use (PCB Artist). Would you be able to explain how cooper fill areas affect the performance or help the pcb? Is it standard practice to use copper fill areas on the signal planes?

Amir

If you ask any PCB vendor they will want this on all layers of every board. When you avoid having large open areas with etched copper the board does not have to be etched as long, there is less compensation required, there is less chance of voids in the inner layer pre-preg, and less pre-preg is needed to fill in large voids.

You will mostly see this used with power supplies and loads but any board would benefit in one or all of the following:

Electrically the poured copper provides shielding around the noisy traces.

Mechanically the poured copper helps keep the board from warping - especially during reflow - and reduces the chance of over or under etched traces due to compensation.

Thermally the extra copper helps to dissipate the heat, even if it is not connected to the hot traces. This becomes noticable when viewed with a thermal imaging camera.

 

[akahrim]

If you ask any PCB vendor they will want this on all layers of every board. When you avoid having large open areas with etched copper the board does not have to be etched as long, there is less compensation required, there is less chance of voids in the inner layer pre-preg, and less pre-preg is needed to fill in large voids.

You will mostly see this used with power supplies and loads but any board would benefit in one or all of the following:

Electrically the poured copper provides shielding around the noisy traces.

Mechanically the poured copper helps keep the board from warping - especially during reflow - and reduces the chance of over or under etched traces due to compensation.

Thermally the extra copper helps to dissipate the heat, even if it is not connected to the hot traces. This becomes noticable when viewed with a thermal imaging camera.

Hello CapeCAD,

Thank you for explaining copper pour areas.

Amir

 

[akahrim]

Hello Alec_t,

This circuit works wayyyyyyyyyyyyyyyyyy better than the one I threw together. Thanks for your help.

Amir

 

[akahrim]

Hello Kubeek, Dougy, and Ronv,

Thank you all so much for the help. I completely scrapped the old circuit I was working on and I'm moving in the direction you all suggested. I breadboarded a circuit similar to the one Alec_t suggested above and its works well. I saw the circuit that Ronv designed that incorporates all of your suggestions. There are two components that I'm a little confused about. How does C2 and R5 affect the performance of the circuit? I am working on doing this in LTSpice so I can test it out.

Amir

 

[ronv]

I used an LM324 instead of the LT1013 because the LT1013 doesn't like to drive the capacitance of the FET. The 324 when driving a capacitive load has trouble deciding if it wants to run in class A or class B mode so sometimes has little oscillations. Adding the load (R5) forces it into class A all the time.

C2 rolls off the frequency response giving the circuit more stability. I "tuned" it using the 51 ohm and C2 for good phase margin. If you use different parts let us know. The 324 comes in a single package LM124 I think it is. It's an oldie but...

 

[akahrim]

Hello Ronv,

Thanks for the explanation. I still have so much to learn. You mentioned the IPB011N04l in your earlier post. I had this lying around and it seems to work. In terms of this circuit, it can handle the current load so I threw it in. What mosfet parameters do you think would be important to focus on if I wanted to improve the design?

Amir

 

[dougy83]

That FET is just really overrated and has a very large gate capacitance. It will work, but so would many smaller FETs

 

[akahrim]

Hello Dougy83,

If I find a mosfet with lower gate capacitance, how will that affect performance? I am thinking that the lower gate capacitance means it requires less current to turn on. This is easier for the Op Amp to handle. Now that the gate capacitance is lower the mosfet will respond faster and the overall feedback loop will be faster. By faster, I mean that the op amp output will settle on a voltage that makes the negative input equal to the positive input faster.