Exposed IC Therma pad on TOP layer between inductors

Is it a good practice to expose the IC (LTC3868) thermal pads between two inductors. Would it cause noise to be coupled into the IC ? The design is for a buck converter running at 608kHz. The thermal pad is circled in yellow. The left SN2 and corresponding CAP+ on either sides are the inductors. The voltage being bucked is from 12v to 8v 60A.

Hello anishkgt,

This is a question for a design engineer, that can look over your entire design.
Hopefully one of the engineers on the TechForum can add to this post, with their recommendations.

Thank you David. Am i posting in the wrong section ? Is there a place in the forum for Designers ?

It’s not entirely clear to me what is meant by “expose the thermal pads” in this case. Are you speaking of removing the solder mask, extending a copper land region, something else…?

Per this note on page 9, the exposed pad on the package is intended to be connected to the circuit reference node (“ground”). That’s a common recommendation, because even if the pad is electrically isolated from the die, it has some amount of capacitive coupling to it and can potentially be a path for unwanted signals. By connecting it to the circuit’s reference node, the amount of noise that can be capacitively coupled into the die through it is quite limited.

Laying out the current-carrying path poorly is more likely to be cause for noise problems. That’s a topic well-covered in many application notes like this one.

And if you were speaking of solder mask deletion, an exposed trace usually does do convective heat transfer somewhat better than a soldermask-covered one. Other considerations such as corrosion resistance, contact hazards, etc. also need to be considered however, and often take precedence.


I meant exposing the copper, that is deleting the solder mask. Thank you. I can’t seem to find any evaluation boards for the LTC3868. Don’t they have any ?

Hi anishkgt,

They don’t appear to have a demo board for the LTC3868 at this time. However, I did find a couple demo boards for the LTC3869, the DC1807A-A and the DC1807A-B. These are pretty similar parts, so you may get some “best practice” layout ideas from the design files of those boards. If you scroll down in the respective links above, you will find the design files for each version.