Exposed pad and ground

[FreshmanNewbie]

I'm using this device - ATSAMD21G17A

While I measured the connection between the exposed pad and the ground, they seem to be unconnected.

When I went and check on section 10, problem 20, on page 30 of this Checklist, I found the below:




Which effectively says us to connected the exposed pad to ground pins of the device and the PCB.


My question:

1. Should the exposed pad of a device always be connected to the ground? If so, why? If the exposed pad should always be connected to the ground, then why do manufacturers, in this case, Microchip, do not connect the exposed pad and ground pins of the device together internally?

Like, is the exposed pad solely for thermal dissipation or does it serve as a ground pin as well?

Can the exposed pad be left floating in any case, if I am taking care of thermal dissipation?

 

[std_match]

The recommendation is to connect the exposed pad to MCU ground, but a circuit can work without the connection.
Read more here:

https://www.nxp.com/docs/en/engineering-bulletin/EB806.pdf

 

[KlausST]

Hi,

For me personally there is only one answer:
--> It depends. Follow the datasheet recommendation.

Klaus

 

[FvM]

If the question is about required procedure, the answer is pretty clear. Exposed pad must be grounded because specified in the datasheet. If it's more informational, I presume that chip attachment is similar to linked NXP device. I remember cases where exposed pad wasn't clearly connected to chip substrate but nevertheless affected electrical behaviour. Maybe due to capacitive coupling or because epoxy glue doesn't provide isolation.

 

[barry]

1. Should the exposed pad of a device always be connected to the ground? If so, why? If the exposed pad should always be connected to the ground, then why do manufacturers, in this case, Microchip, do not connect the exposed pad and ground pins of the device together internally?

Like, is the exposed pad solely for thermal dissipation or does it serve as a ground pin as well?

Can the exposed pad be left floating in any case, if I am taking care of thermal dissipation?

No, no, no. READ the data sheet. Theres no rule that says you must ALWAYS connect the pad to ground. Sometimes you must absolutely NOT connect it to ground.

 

[dick_freebird]

The ground plane may also be your best thermal-spreader plane.

Depending on technology the die backside could be isolated from
frontside circuitry, in which case the pad would be floating, and
floating conductors are untrustworthy. As ground "should be"
the quietest, that's the easy recommendation.