Hi
I am making a footprint for http://www.ti.com/lit/ds/symlink/tlv757p.pdf. The footprint for the DRV0006A on Pg39 has 2 vias on the ground pad but is causing DRC issues for m. I am wondering if it is okay to remove the via?
If you can extend connections to the thermal pad to outside the package, you will get enough heat out not to need the vias to inner planes.
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I can draw a trace and connect to ground in the PCB. Is that okay?
What exact DRC error did you get?
How did you make the vias?
We have footprints in the official lib for quite similar parts that should work. (The process is explained towards the end of Tutorial: How to make a footprint in KiCad 5.1.x (From scratch)?)
The DFN/QFN generator of our scripting repo should be able to produce such a footprint.
A zone with pad connection set to solid might be a better choice. You want as much copper as possible connecting to the center pad.
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Hi,
Could you exaplin the meaning of the lst sentence a bit more? What does a zone with pad connection set to solid mean? Does the zone refer to some sort of area around the center pad? Also what does setting the pad connection to solid actually do without a copper pour since I plan to have a trace connecting to this?
But my center pad is alreay as big as possible. How would adding a zone help? I understand increasing the number of vias or connecting to a pour to increase the amount of copper, but making a zone around the pad (put a large area of copper and connecting it to ground), isnt something i can do since I already have a gnd plane. Is not connecting through vias enough?
Why did you think that the copper pour can only be connected to the GND Net?
And, if you look closely, you will see that the Vias connect to the back side copper pour as well. In this example, there is 4 times the total copper, and ~2x the copper exposed to the air (using the TLAR method of calculation).
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My pad on the center is already as big as it can be. I dont understand where I should insert the coppe pour. I can connect the center pad through vias to gnd but dont understand the zone part since I cant extend my copper like you have.
This board has multiple Copper Zone pours. Again, look at the image, the pour does not have to connect to GND. In the examples above, it must connect to the same NET as the VIAs (as such it can only surround the individual pad, and not the entire footprint with pads on different Nets).
Last question, “Did you not notice the ‘Zone priority level’ setting?”
At some point you might want to show that you have given some of your own effort in resolving your design issue.
The best thing would be if you could post a screenshot of your board. That way we can more easily understand what your problem is. Maybe also show us the DRC error you get when adding the vias. (As i requested in my first post already)
If you need more copper (either by connecting to the back side by use of vias or by connecting the center pad to a large copper area) depends on how you use the part.
The manufacturer suggestions come from the ratings given in the datasheet and assume nominal environment temperature. If your part is somewhere hot you might need more cooling to achieve the same result. If you do not get near the maximum ratings (so if the ic is overpowered for this usecase) and you are in a cool environment you might not need to worry about thermal conduction that much.
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