5V Pins under IC must all be connected?

[Eggnoggicus]

Hey everyone,

I finished routing the entirety of my PCB but the DRC seems to require that all the 5V pins on my Atmega32U4 have to be connected to each other somehow. That being said, all the 5V pins of a microcontroller are internally connected so that shouldn’t be an issue. Is there any other way to fix this, or is this a problem with my schematic? Thank you!

[dsa-t]

Do I have to provide VCC to every VCC pin on Atmega32u4 MCU?

[Piotr]

My way of connecting VCC is by going with it under uC and then distributing it through corners and VCC pins to other elements. You can see it here:

Approaching PCB track routing for a newbie

Positioning for me is the main work in designing PCB. If each element is where it is needed than routing is simple. Till now all my PCBs are 2 layers and all of them have GND plane taking 100% of bottom layer. So except GND I design my PCBs as 1 layer. I use microcontrollers in QFP packages without thermal pad at bottom. This allows me to go with VCC under the microcontroller and go out through all corners and all VCC pins. That way GND and VCC don’t disturb my signal connections. At all digi…

You seem to not knowing that each VCC pin should get blocking capacitor as close to it as possible. uC at my picture (AtXmega serie) has each VCC pin located next to GND pin so capacitors just connect adjacent pads.

[davidsrsb]

This is not a KiCad issue, so I will close it soon. Read the others comments carefully. When I lay out one of these, I always place a 0603 decoupling capacitor right next to each power pin and use a solid ground plane, connecting to each GND pin and each capacitor. Then the details of the Vcc track become much less critical. I have had no problems passing MIL STD EMC tests doing this.

[BobZ]

Generally be very careful about leaving any pins unconnected on any IC. I think about a quad op amp (such as LM324) for example. If you are using three of the four op amps, the fourth one should be properly biased, such as a ground follower for example. If you leave the inputs to the fourth op amp disconnected it could cause the other amplifiers to misbehave.

[paulvdh]

In short, pins on an IC package cost money, and thus there are good reasons to put multiple GND and power pins on an IC.

Also agree with davidrsb. There is no decent GND plane on this PCB, and I also do not see any decoupling capacitors. Rick Hartly made a 2h and 19 minute video over the importance of a good GND plane in PCB design, and it’s worth watching all of it at least twice. So make some time free for it and grab some popcorn.

[nickmBY]

@paulvdh

and I also do not see any decoupling capacitors.

Well, there are some! They are so huge that they are hard to see. Just have a look at the caps left and right of the X-tal. I even don’t know what package that is …

This thread can be closed I think.

[paulvdh]

Those footprints on the nets XTALP and XTALN are not decoupling capacitors, they are the capacitors for the crystal itself.
The footprint in the center / top of the PCB (only one pad shown) is connected to the +5V net and may be a decoupling capacitor. But the size of these is indeed also quite unusual.

[davidsrsb]

Enough advice for the OP, this is not a how to design your circuit forum