Re: [Elecraft] Heat Sink Compound Question
Chuck……. Great information for the K3 Radio’s Ray WA6VAB K3 From: Charles K0MV Sent: Tuesday, March 29, 2022 6:30 PM To: elecraft@mailman.qth.net Subject: Re: [Elecraft] Heat Sink Compound Question Hi Tony, I posted this reply last November. This topic appeared on the list previously from last October "sticky thermal pads for K3 LPA Mosfets". One of my LPA Mosfets went bad in my K3s. I saw a comment on the reflector about these devices failing and I'm guessing the heat sink design is subject to production variation. I used to design switching power supplies. Reliability is a very strong function of device temperature so keeping cool is important. I hate to take time to fix stuff, so try to fix it so it never fails again. I replaced both of them but also improved the thermal design. As Ray WA6VAB mentioned, I got mine from RF Parts. The epitome of outstanding thermal design is the Intel I7 processor heat sinking. The processor and the heat sink are polished, shiny, and very flat. The best thermal compound is a silver based paste included with the heat sink. It does 100 watts over a couple of square inches so very low thermal resistance (remarkable!). Any gaps compromise the performance. There is a very good tutorial on this here: https://forum.digikey.com/t/thermal-interface-materials I examined the bottom cover and found the surface of the metal to be uneven and this inhibits heat transfer (raises the thermal resistance). I also found the bottom cover may not be perfectly flat. Moreover, the typical flexible thermal pads are not as good as alternatives. I polished the K3s bottom cover where the heat sink attachments are with a Dremel tool and polishing pad and automotive rubbing compound, a fine abrasive. You can see it becomes more shiny and I verified that with a microscope. I got a larger diameter flat washer for placing under the screw head on the outside of the K3s. This places compression over a larger area to help heat transfer. Digikey part number H734-ND. Since Elecraft has different board revisions you should check that the tabs of the MOSFETs can be grounded. If so, then there is a type of thermal pad that is very good. From the data sheet: High-PERFORMANCE, cost effective thermal interface material Used where electrical isolation is not required, Tgon TM 800 is ideal for where electrical contact and thermal transfer are desired. High thermal conductivity of 5 W/mK in Z axis and 240 W/mK in the X-Y axis. This type not only has low thermal resistance across it, but also a low thermal resistance in the plane of the pad helping to spread the heat out. Digikey part number 926-1471-ND manf part number A15037-112. Use just a very small amount of the silver based thermal compound. I run FT8 so the duty cycle is 50%. It's been several months and no problems (1000s of QSOs)--at least yet! Good luck and 73, Chuck K0MV On 3/29/22 15:24, Tony wrote: > All: > > It seems that thermal compounds are not all the same and I was > wondering which type is best to use for transceiver applications? I > understand Elecraft uses thermal pads these days, but what type of > compound was used prior to the switch? > > Just purchased a produced called MX-5 from Arctic which is commonly > used for CPU applications and was wondering if it can be used for HF > transceivers, kits etc. > > See: > https://www.amazon.com/gp/product/B08T64M68V/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&th=1 > > Thanks, > > Tony > > __ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:Elecraft@mailman.qth.net > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > Message delivered to k...@altaeng.com -- Charles K0MV __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to wa6...@gmail.com __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
Re: [Elecraft] Heat Sink Compound Question
Hi Tony, I posted this reply last November. This topic appeared on the list previously from last October "sticky thermal pads for K3 LPA Mosfets". One of my LPA Mosfets went bad in my K3s. I saw a comment on the reflector about these devices failing and I'm guessing the heat sink design is subject to production variation. I used to design switching power supplies. Reliability is a very strong function of device temperature so keeping cool is important. I hate to take time to fix stuff, so try to fix it so it never fails again. I replaced both of them but also improved the thermal design. As Ray WA6VAB mentioned, I got mine from RF Parts. The epitome of outstanding thermal design is the Intel I7 processor heat sinking. The processor and the heat sink are polished, shiny, and very flat. The best thermal compound is a silver based paste included with the heat sink. It does 100 watts over a couple of square inches so very low thermal resistance (remarkable!). Any gaps compromise the performance. There is a very good tutorial on this here: https://forum.digikey.com/t/thermal-interface-materials I examined the bottom cover and found the surface of the metal to be uneven and this inhibits heat transfer (raises the thermal resistance). I also found the bottom cover may not be perfectly flat. Moreover, the typical flexible thermal pads are not as good as alternatives. I polished the K3s bottom cover where the heat sink attachments are with a Dremel tool and polishing pad and automotive rubbing compound, a fine abrasive. You can see it becomes more shiny and I verified that with a microscope. I got a larger diameter flat washer for placing under the screw head on the outside of the K3s. This places compression over a larger area to help heat transfer. Digikey part number H734-ND. Since Elecraft has different board revisions you should check that the tabs of the MOSFETs can be grounded. If so, then there is a type of thermal pad that is very good. From the data sheet: High-PERFORMANCE, cost effective thermal interface material Used where electrical isolation is not required, Tgon TM 800 is ideal for where electrical contact and thermal transfer are desired. High thermal conductivity of 5 W/mK in Z axis and 240 W/mK in the X-Y axis. This type not only has low thermal resistance across it, but also a low thermal resistance in the plane of the pad helping to spread the heat out. Digikey part number 926-1471-ND manf part number A15037-112. Use just a very small amount of the silver based thermal compound. I run FT8 so the duty cycle is 50%. It's been several months and no problems (1000s of QSOs)--at least yet! Good luck and 73, Chuck K0MV On 3/29/22 15:24, Tony wrote: All: It seems that thermal compounds are not all the same and I was wondering which type is best to use for transceiver applications? I understand Elecraft uses thermal pads these days, but what type of compound was used prior to the switch? Just purchased a produced called MX-5 from Arctic which is commonly used for CPU applications and was wondering if it can be used for HF transceivers, kits etc. See: https://www.amazon.com/gp/product/B08T64M68V/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&th=1 Thanks, Tony __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to k...@altaeng.com -- Charles K0MV __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
Re: [Elecraft] Heat Sink Compound Question
then there is INDIUM,, which is wired thin metal thermal foil, some believe the conductivity to be better than the paste https://www.indium.com/products/thermal-interface-materials/ On 3/29/2022 6:56 PM, David Gilbert wrote: Thermal pads are a compromise between heat conductivity and ease of use. Thermal paste can be applied in a thinner layer, and if done uniformly will therefore have less thermal resistance. You're good. 73, Dave AB7E On 3/29/2022 2:24 PM, Tony wrote: All: It seems that thermal compounds are not all the same and I was wondering which type is best to use for transceiver applications? I understand Elecraft uses thermal pads these days, but what type of compound was used prior to the switch? Just purchased a produced called MX-5 from Arctic which is commonly used for CPU applications and was wondering if it can be used for HF transceivers, kits etc. See: https://www.amazon.com/gp/product/B08T64M68V/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&th=1 Thanks, Tony __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to n...@arrl.net __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
Re: [Elecraft] Heat Sink Compound Question
Thermal pads are a compromise between heat conductivity and ease of use. Thermal paste can be applied in a thinner layer, and if done uniformly will therefore have less thermal resistance. You're good. 73, Dave AB7E On 3/29/2022 2:24 PM, Tony wrote: All: It seems that thermal compounds are not all the same and I was wondering which type is best to use for transceiver applications? I understand Elecraft uses thermal pads these days, but what type of compound was used prior to the switch? Just purchased a produced called MX-5 from Arctic which is commonly used for CPU applications and was wondering if it can be used for HF transceivers, kits etc. See: https://www.amazon.com/gp/product/B08T64M68V/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&th=1 Thanks, Tony __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
Re: [Elecraft] Heat Sink Compound Question
Tony, Elecraft has always used the thermal pads. 73, Don W3FPR On 3/29/2022 5:24 PM, Tony wrote: All: It seems that thermal compounds are not all the same and I was wondering which type is best to use for transceiver applications? I understand Elecraft uses thermal pads these days, but what type of compound was used prior to the switch? Just purchased a produced called MX-5 from Arctic which is commonly used for CPU applications and was wondering if it can be used for HF transceivers, kits etc. See: https://www.amazon.com/gp/product/B08T64M68V/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&th=1 Thanks, Tony __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to d...@w3fpr.com __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
[Elecraft] Heat Sink Compound Question
All: It seems that thermal compounds are not all the same and I was wondering which type is best to use for transceiver applications? I understand Elecraft uses thermal pads these days, but what type of compound was used prior to the switch? Just purchased a produced called MX-5 from Arctic which is commonly used for CPU applications and was wondering if it can be used for HF transceivers, kits etc. See: https://www.amazon.com/gp/product/B08T64M68V/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&th=1 Thanks, Tony __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
