I have a board (an evaluation module for a USB-to-HDMI chip from Microchip) that has a feature I haven't seen before. On top of the 3 DC-DC regulators, there is a clear substance that appears to completely cover these 3 regulators (the IC's and related passives). The clear substance seems to be something between hot glue and clear epoxy – it's harder than hot glue, but softer than epoxy. I've attached a picture of the board below – the three regulators are along the bottom of the board, in between the 2-pin header and the 7-pin header. It's hard to see the clear substance in the photo (because it's clear..), but you can kind of see the reflection.
I understand that DC-DC regulators are typically an electrically noisy section of the board, and given the rest of the board has a lot of high-speed signals, I'm wondering if this offers some sort of EMI attenuation. My only other hypothesis is that it is intended to silence the high-pitched ringing you sometimes hear from these regulators. I would love to hear if anyone knows for sure what this is for, though!
Best Answer
This is an eval board and is sold in an unprotected format. The components along that edge are vulnerable to fingers and errant connector plugging missions.
I think it's just a blob of clear epoxy intended to protect the smallest and most vulnerable SMT parts from being accidentally pried off of the board. The other edges of the board are relatively protected or have larger, more sturdy parts.