Hello,
I noticed that the LMS7002 on the LimeSDR mini heats a lot. My question is: Is there any thermal pad between the LMS7002 chip and the the metal shield on the top ?
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Hi, @tonymontana
By default there is no thermal pad between the LMS7002 chip and the the metal shield on the top.
I also noticed the chips got very hot in the warm weather we have had recently. Cooler today, and I measured 50C on the LMS7002. The FPGA gets to almost the same temperature. I am just in the process of fitting a copper plate under the screening can - soldered to it, and heat sink compound to connect thermally to the LMS7002. I’ll try and get some temperatures with and without it.
On this schematic on IC1, there is thermal pad recommendations.
What is the 1) 2) 3) ?
Can we deduce that there is a thermal pad between the metal cap and the LMS7002 chip ?
No thermal pad between the metal cap. Its easy to remove if you want to see for yourself.
I have soldered a copper plate to the inside of the lid, with a little thermal compound to bond to the chip, as shown in attached photo. Running the LimeSDR from HDSDR tuned to an FM radio station, I measured the following temperatures with an infra red thermometer underneath the LimeSDR. I measured underneath because the shiny metal lid gives a false reading on top of the Lime chip:
Lime chip 41.8 degC FPGA/USB i/f 45.4 deg C.
Previously, the Lime chip was at least as warm as the FPGA and USB i/f.
Tony
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what size is the “copper plate”?
a link to your part you used would be great or dimensions like Height, Width and Length would be great.
i took the shielding off my mini and the best i can say is that chip is about the same height as the chip close to the usb connector.
I used a couple of thin pieces of copper plate soldered together, then soldered to the lid - no part number! I seem to remember I used a piece of old plumbing pipe made flat with a hammer, and sanded more flat with an emery disc. It’s approx 13mm square and 3mm thick. The thickness is such that the screening box nearly touches the pcb when the copper plate is flush against the chip.
Tony
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I recently bought two LimeSDR mini, and i would like to bring down the operating temperate of LimeSDR mini for optimum RF performance and longevity of the board. In that regard, I would like to know how easy is it to remove the the silver lid/shielding and re-attach (I bought some thermal pads and compound and would like to apply).
Another question, this maybe a very dumb question (I have zero knowledge about electronics), can I apply the thermad pad to the entire PCB or just the three chips is enough? The thermal compound I got is this one https://www.amazon.de/gp/product/B00UYTTXSM/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1
I appreciate a lot if someone could help me in this regard. Thanks a lot in advance
The LMS7002 transceiver is under the screen and I think most of the heat comes from the MAX10 FPGA. Also not sure if introducing materials into that space might have some effect on RF performance.
@Zack, could you advise, please.
Thanks a lot Andrew. Regarding the usage of thermal pads (I am very newbie to this), are there any precautions that I should take while putting it on top of Altera MAX 10? (I made the conductivity and everything about the thermal pads are good)
Regarding the RF performance what I observed was that, running srsenb at band 7 LTE is not possible at high temperatures (Tx wont cannot get calibrated at high temperatures). So currently, I am using a tab fan near LimeSDR mini (crude method 
) to cool and it (its quite effective), through this I am able to have a very stable link at band 7 LTE any higher frequency.
Hi @herlesupreeth,
Indeed, active cooling is the best option for this small board. You can check fans we have tested:
https://wiki.myriadrf.org/LimeSDR-Mini#Additional_Components
There is a provision to mount 30mm x 30mm fans on the board. Notice these oval holes - these are for fan mount.
Thank you Jack. Is it okay to have the heatsink over the entire PCB on the bottom part of LimeSDR mini?
From 60 degrees C to max 38 degrees C with a small 5V quiet fan. (the 5V you can get from the solder points on the Lime SDR mini). The enclosure is a cheap one from ebay.
Nice!!! Can you please show me the picture of how you soldered the fan connector to LimeSDR mini board?
Don’t know if the raster between the 2 solderings points is 2,54mm. I just soldered the 2 wires from the fan directly to the soldering points on the lime sdr mini. It was already half a year ago but i am sure the + 5V is at solder point J10 and (i think) the point next to it is an eartpoint but you have to measure if 5V is between them. After that the fan is always on. There is a possibility to choose the fan is running at some temperature hysteresis which you can switch on with lime suite but maybe better you search for it on this forum. I am sure i have seen it somewhere here…
