Upgrading Ultra96-V2 to the passive heatsink - how to

My team kind of inherited the original design of the Ultra96 platform. From early on when we started working on the project I started making a checklist of things I wanted to change if the opportunity arose. The first change I wanted to make was to the power architecture, which I lobbied hard for along with other tweaks and changes we wanted to make to improve the board. That was accomplished with the release of the Ultra96-V2. The one thing that was still missing from my wish list when we released V2 was the fan bracket.

I won't lie, I hated the fan bracket. That is not to say that it didn't do its job just fine, but in my mind I viewed this platform as a low power entry into the UltraScale ecosystem. When my brain sees (and hears) a fan, I don't think low power. Do any of your handheld or peripheral devices have a fan? No. Fan = noise, Fan = perception of higher temperatures (meaning higher power draw) which didn't paint the right picture in my mind. The catch was, it worked fine. Like so many other things, people don't want to mess with thermal solutions if they are working. My window to push my agenda (heh, heh) opened when we decided to offer an industrial temp version of the design.

My devious end goal was to design a passive heatsink solution that would allow for industrial temp operation (with the use of a fan or some sort of airflow) but would also provide enough thermal relief that we could replace the fan bracket on the commercial version with a lower cost, more reliable (no moving parts) solution. Now I won't rehash the whole design, but we were able to accomplish that with the new custom heatsink design from Boyd. I talked more about it in a previous blog - Thermal relief is critical - design example around Ultra96-V2

I wanted to set the stage for why I'm writing this blog on how to upgrade your design to the new thermal relief solution. I like when things have context. All that being said, below you'll see my first hand step by step thermal solution swap.  Here is the before shot of the Ultra96-V2 and the heatsink. Note the side view of the Ultra96-V2 for the 2 wires that you must remove from the board.

If you have a soldering iron, just heat them up and pop them out. If not, you can just cut the wires, just make sure they don't hang off the board and short to anything (including each other)

You may have a heatsink where the gap pad material may have come off of the pedestals. Don't be alarmed, part of the tradeoff on these materials is that adhesiveness can sometimes result in a material with greater thermal impedance (less efficient transfer). If this happens to you as it did to me, just use tweezers or some other probe to gently lift the pad off the plastic and place them back on the pedestals

Once you have the gap pads in the right place (the large rectangular pad has never come loose from what I've seen so matching up the smaller pads with the pedestals is pretty straight forward) you are ready to remove the Ultra96-V2 from its fan bracket and attach it to the new heatsink. Keep the screws as you will use them to reattach the board to the new heatsink.

Align the board so that the large rectangular pad aligns with the Xilinx device as shown below. Make sure you haven't soldered any pins or headers onto the bottom side of the board as they will interfere when mating the boards. I had a PMBus header that I had put on which had to be removed before mounting, but the stock unmodified board will not have anything interfering with the heatsink.

Then just line up the screw holes and try to place the board down directly on top of the threads so you don't shift the pads when you compress them together. Tighten them like a wheel, opposite corners first.

After you've tightened down all 4 screws, double check the gaps and make sure the pedestal pads are contacting the board and IC as well as that the large pad is contacting the Xilinx device.

At this point you are good to go with your new thermal solution. The new solution allows you to run more intensive AI applications because of it's better thermal dissipation properties. That being said, you will notice it gets pretty hot when under heavy load. A small desk fan (yeah, I know, fan) will drop the heatsink temperature almost immediately. You can see in this pic I got creative and actually mounted the fan from the bracket assembly to the back side of my heatsink which did a remarkable job of cooling it down, letting me run any application on the board that I wanted to run.

If you have any questions about this upgrade please feel free to reach out.

Ultra96-V2Ultra96-V2

New Heatsink - https://www.avnet.com/shop/us/products/avnet-engineering-services/aes-acc-u96-phs1-3074457345642330680/