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I'm going to purchase a PYNQ-Z1 FPGA development board from Digilent (Link: https://store.digilentinc.com/pynq-z1-python-productivity-for-zynq/). However, some of the comments on the linked page say that the board runs very hot and they should have included a heatsink or fan.

As the board is rather expensive and I want to protect it from damage, I'm thinking of also buying a heatsink. The main chip is a ZYNQ XC7Z020-1CLG400C (BGA, 0.8mm ball pitch, 17x17 mm package).

So I did some research and found at least one heatsink designed for this size of chip, linked here: https://www.digikey.com/product-detail/en/advanced-thermal-solutions-inc/ATS-55170D-C1-R0/ATS1264-ND/1284978

I'm wondering whether it's a good idea to install this heatsink, or whether it's unnecessary or even dangerous, or whether a different kind of heatsink would be better. At 9.5mm in height, I'm also worried that this heatsink might interfere with the Arduino interface, but I would need better measurements to be sure.

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    \$\begingroup\$ I can't imagine it'd cause any problems if properly installed. At least, no electrical problems. \$\endgroup\$ – Hearth Apr 29 '18 at 18:49
  • \$\begingroup\$ I assume that you are planning to plant the heatsink on top of the FPGA chip itself. It would improve your thermal situation a little, but not dramatically. The epoxy (which the IC case is made of) has a fairly high thermal resistance. The FPGA is intended to be heatsunk to the PCB. \$\endgroup\$ – Nick Alexeev Apr 30 '18 at 4:00
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Adding a heat-sink won't hurt your board or any other board connect to it. Also fitting one which is too large is not an issue either, as long as it does not touch anything but the top of the chip.

Before you go though all the trouble have a look at the applications which cause it to heat up so much and what speed they are running. It could well be that the circuit you are planning to program into it will not heat it up.

There is a power estimation tool in Vivado which can give you some idea of the energy it will use before you program the board.

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Since the pre-complied demo code already makes the chip hot (as per user's reviews), adding a heat sink is an utmost right idea. The simple "adhesive" types are suited for this job, without damaging anything.

However, your selected sink might be a little too small for the job. It will definitely lower the BGA temperature to some degree, but I would advise to use some much bigger sink, and preferably of more "omni-directional" type (since you are not planning to use a fan, yet), something like this one.

enter image description here

As per picture of your board, there are bypass caps that seems to be higher than the BGA case, so a bigger heat sink might not sit flat, which would in unacceptable. The caps can be easy accommodated if you make accommodating cuts in the sink, by drilling 1-2mm deep in right spots on sink body. It is a common practice when space is limited. If the sink is encroaching into Arduino interface space, you can saw-off a portion of sink fins to make it fit.

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  • \$\begingroup\$ Thank you. When you say the sink might be a little too small for the job, that seems vague...If I knew the operating and desired temperatures, could I calculate the ideal size of heatsink? I'm thinking of getting an angled-fin version such as digikey.com/product-detail/en/advanced-thermal-solutions-inc/… . It's shorter and hopefully less likely to bump into Arduino shields. An alternative is to plug extenders into the Arduino headers to make them taller. \$\endgroup\$ – N.E.C. Apr 29 '18 at 20:54
  • \$\begingroup\$ @N.E.C., no, it is very unlikely that you can calculate much. Note, that all the sinks we considered have defined their thermal impedance under a certain external flow conditions, 200LFM, 500LFM, etc. What is your LFM flow? You don't know. Likely zero, or slow free convection in obscured situation. So, bigger is better, trust me. Looking at board power supplies, the FPGA can dissipate up to 11 W, and maybe 5-6 W typical. This is substantial. Your new sink selection won't handle this. \$\endgroup\$ – Ale..chenski Apr 29 '18 at 21:20

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