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BS170 Heat flow experiment with results

mux_folder2001 All Messages By This Member #129539 开云体育 I have attached a PDF file that describes an experiment with the goal of determine where the heat flows in a BS170. The PDF contains pictures of the fixture and a graph of the results. The essence of it is that, given equal opportunity, heat will flow as follows: Best flow is through the case. Second best flow is the drain lead. A distant third is the source lead. Last is the gate lead. The graph will give you a sense of how much difference there is between them.? The transistor is configured in a DC circuit and is dissipating 767mw continuously in the test. I should have put that in the PDF file but I forgot to. Tony AD0VC
Sandy All Messages By This Member #129544 开云体育 Hey Tony - That is an interesting result. There is no substitute for actual measurement. This suggests that case contact with the pad is important. I always install the BS170s first with the screw and washer ensuring they are all flat and only then solder in place. Thanks for your efforts! Sandy KB3EOF On 9/11/24 22:18, mux_folder2001 via groups.io wrote: toggle quoted message Show quoted text I have attached a PDF file that describes an experiment with the goal of determine where the heat flows in a BS170. The PDF contains pictures of the fixture and a graph of the results. The essence of it is that, given equal opportunity, heat will flow as follows: Best flow is through the case. Second best flow is the drain lead. A distant third is the source lead. Last is the gate lead. The graph will give you a sense of how much difference there is between them.? The transistor is configured in a DC circuit and is dissipating 767mw continuously in the test. I should have put that in the PDF file but I forgot to. Tony AD0VC
Paul - AI7JR All Messages By This Member #129545 开云体育 I wonder if it tells what we want to know... "Wrap the BS170 case with copper tape and solder it to another copper plate." In the QMX, only the flat side is connected to the heat sink... (Assuming the washer and screw aren't very significant!) If that were taken into account, heat extraction via the case and via the drain lead might be more comparable, maybe even swapped? You're making the assumption that temperature at the measurement point is a proxy for power flow on the path. But the actual temperature is a function of the thermal resistance from the measurement point to the environment... It seems to me that you'd need to standardize the thermal resistance of what you attach the measurement points to, in order to measure relative power flow. This is giving me a headache! Am I making it harder than it has to be? Paul -- AI7JR On 9/11/24 20:42, Sandy via groups.io wrote: Hey Tony - That is an interesting result. There is no substitute for actual measurement. This suggests that case contact with the pad is important. I always install the BS170s first with the screw and washer ensuring they are all flat and only then solder in place. Thanks for your efforts! Sandy KB3EOF On 9/11/24 22:18, mux_folder2001 via groups.io wrote: I have attached a PDF file that describes an experiment with the goal of determine where the heat flows in a BS170. The PDF contains pictures of the fixture and a graph of the results. The essence of it is that, given equal opportunity, heat will flow as follows: Best flow is through the case. Second best flow is the drain lead. A distant third is the source lead. Last is the gate lead. The graph will give you a sense of how much difference there is between them.? The transistor is configured in a DC circuit and is dissipating 767mw continuously in the test. I should have put that in the PDF file but I forgot to. Tony AD0VC -- Paul -- AI7JR
Hans Summers All Messages By This Member #129547 Very nice experiment, Paul Nice to see some real experimental data.? I agree with Paul AI7JR, it would perhaps be interesting to measure with only the flat of the transistor face against the copper, since practically in a transceiver the curved part of the body is not touching the copper. I don't think there's any problem with the?measurements though; all the copper plates are the same size with the same dissipation to the environment so it's a reasonable relative comparison. 73 Hans G0UPL toggle quoted message Show quoted text On Thu, Sep 12, 2024 at 7:47?AM Paul - AI7JR via <paul.hanchett=[email protected]> wrote: I wonder if it tells what we want to know... "Wrap the BS170 case with copper tape and solder it to another copper plate." In the QMX, only the flat side is connected to the heat sink... (Assuming the washer and screw aren't very significant!) If that were taken into account, heat extraction via the case and via the drain lead might be more comparable, maybe even swapped? You're making the assumption that temperature at the measurement point is a proxy for power flow on the path. But the actual temperature is a function of the thermal resistance from the measurement point to the environment... It seems to me that you'd need to standardize the thermal resistance of what you attach the measurement points to, in order to measure relative power flow. This is giving me a headache! Am I making it harder than it has to be? Paul -- AI7JR On 9/11/24 20:42, Sandy via wrote: Hey Tony - That is an interesting result. There is no substitute for actual measurement. This suggests that case contact with the pad is important. I always install the BS170s first with the screw and washer ensuring they are all flat and only then solder in place. Thanks for your efforts! Sandy KB3EOF On 9/11/24 22:18, mux_folder2001 via wrote: I have attached a PDF file that describes an experiment with the goal of determine where the heat flows in a BS170. The PDF contains pictures of the fixture and a graph of the results. The essence of it is that, given equal opportunity, heat will flow as follows: Best flow is through the case. Second best flow is the drain lead. A distant third is the source lead. Last is the gate lead. The graph will give you a sense of how much difference there is between them.? The transistor is configured in a DC circuit and is dissipating 767mw continuously in the test. I should have put that in the PDF file but I forgot to. Tony AD0VC -- Paul -- AI7JR
dl8lrz Reiner All Messages By This Member #129550 Very informative measurement by Tony. The heat is therefore primarily dissipated via the FET housing and the drain wire, i.e. onto the board. I don't have such convenient measuring technology. A measurement on a closed QMX would also be interesting: - a sensor between the FETs (FET temperature) - a sensor on the board (board temperature) - an air temperature sensor between the board/display - a sensor on the lower housing shell This would show where the heat dissipation should be improved (cooling hoods on the FETs or board to housing). 73 Reiner ? ?
John Z All Messages By This Member #129551 Tony,? That was a very well done experiment. Bravo! It should do much to dispel the "all the heat leaves via the leads" myth that resurrects from time to time on this forum. Thank you for that excellent work OM. 73 JZ KJ4A? toggle quoted message Show quoted text On Thu, Sep 12, 2024, 5:15?AM dl8lrz Reiner via <dl8lrz=[email protected]> wrote: Very informative measurement by Tony. The heat is therefore primarily dissipated via the FET housing and the drain wire, i.e. onto the board. I don't have such convenient measuring technology. A measurement on a closed QMX would also be interesting: - a sensor between the FETs (FET temperature) - a sensor on the board (board temperature) - an air temperature sensor between the board/display - a sensor on the lower housing shell This would show where the heat dissipation should be improved (cooling hoods on the FETs or board to housing). 73 Reiner ? ?
Daniel Conklin All Messages By This Member #129557 That's not a lot of heat for each individual FET. The original QCX had them all standing up separately. I wonder if having them clamped down on a thin metal surface with an insulating PCB material underneath is a cause of heat accumulation. -- 73, Dan - W2DLC
Nate Reik N8BTR All Messages By This Member #129560 Great work, thanks for sharing!? ? I bet if you did just the flat of the transistor somehow, it'd be very close to the drain lead, but my guess is the case would still flow more heat than the drain lead. ? Either way, this shows us that BOTH the case and the leads are significant. The gate lead is just under half that of the case as far as temp rise. In fact, combining all 3 leads... it appears you still have more heat coming from them (combined), I believe.? ? -Nate N8BTR
mux_folder2001 All Messages By This Member #129564 开云体育 Hi Hans, I assume you were addressing me (Tony) as the one who did the experiment. I was looking for a basic grasp of heat flow in the device. Of course I intend to look at the flat washer mounting as well but I think this provides a basis for comparison. I am also going to look at other transistors, like the TN0110 because I am curious how they compare to the BS170. Tony AD0VC toggle quoted message Show quoted text From: [email protected] <[email protected]> on behalf of Hans Summers <hans.summers@...> Sent: Thursday, September 12, 2024 12:21 AM To: [email protected] <[email protected]> Subject: Re: [QRPLabs] BS170 Heat flow experiment with results ? Very nice experiment, Paul Nice to see some real experimental data.? I agree with Paul AI7JR, it would perhaps be interesting to measure with only the flat of the transistor face against the copper, since practically in a transceiver the curved part of the body is not touching the copper. I don't think there's any problem with the?measurements though; all the copper plates are the same size with the same dissipation to the environment so it's a reasonable relative comparison. 73 Hans G0UPL On Thu, Sep 12, 2024 at 7:47?AM Paul - AI7JR via <paul.hanchett=[email protected]> wrote: I wonder if it tells what we want to know... "Wrap the BS170 case with copper tape and solder it to another copper plate." In the QMX, only the flat side is connected to the heat sink... (Assuming the washer and screw aren't very significant!) If that were taken into account, heat extraction via the case and via the drain lead might be more comparable, maybe even swapped? You're making the assumption that temperature at the measurement point is a proxy for power flow on the path. But the actual temperature is a function of the thermal resistance from the measurement point to the environment... It seems to me that you'd need to standardize the thermal resistance of what you attach the measurement points to, in order to measure relative power flow. This is giving me a headache! Am I making it harder than it has to be? Paul -- AI7JR On 9/11/24 20:42, Sandy via wrote: Hey Tony - That is an interesting result. There is no substitute for actual measurement. This suggests that case contact with the pad is important. I always install the BS170s first with the screw and washer ensuring they are all flat and only then solder in place. Thanks for your efforts! Sandy KB3EOF On 9/11/24 22:18, mux_folder2001 via wrote: I have attached a PDF file that describes an experiment with the goal of determine where the heat flows in a BS170. The PDF contains pictures of the fixture and a graph of the results. The essence of it is that, given equal opportunity, heat will flow as follows: Best flow is through the case. Second best flow is the drain lead. A distant third is the source lead. Last is the gate lead. The graph will give you a sense of how much difference there is between them.? The transistor is configured in a DC circuit and is dissipating 767mw continuously in the test. I should have put that in the PDF file but I forgot to. Tony AD0VC -- Paul -- AI7JR
Hans Summers All Messages By This Member #129565 Hi Tony ? I assume you were addressing me (Tony) as the one who did the experiment. Yes, sorry to have called you Paul accidentally.? ? I was looking for a basic grasp of heat flow in the device. Yes I agree, it is very informative.? Another comment Nate's post just now made me think of... in QMX the area under the flats of the transistors is - intentionally - bare copper, so as to conduct heat away as well as possible. The drain lead, on the other hand, is a 50 mil trace. Your experiment shows the heat conduction out of the transistor where each of the heatsinks is equivalent?(the same size). On a real QMX the heatsink on the case flat is much better than the heatsink connected to the drain (which is just a copper trace). I think this is likely to make the case-conducted heat even more high relative to that conducted by the drain lead.? 73 Hans G0UPL
ajparent1/kb1gmx All Messages By This Member #129578 Carefully crack open a device and look at the construction. ? The drain lead is part of the lead frame to which the die s bonded. Memory says the back of that leadframe is the flat side of the device.?? ? The gate and source are via bond wires to the die.? Hence there is less heat transfer to the leads. ? The ideal device is one where the drain is bonded to an accessible tab? for example VN7000 (to92 with tab out the top) and the IRF510. In both cases the direct mechanical (or solder) contact has greatly increased heat transfer.? ? The yabut of it all is the source lead carries the most current and the wire bond to the lead is the limiting factor.? ? Enough current and the that fine wire vaporizes.? ? Its one of the things that limits? power handling of the device.?? ? ? -- Allison ------------------ Post online only,? direct email will go to a bit bucket.
Donald S Brant Jr All Messages By This Member #129673 On Thu, Sep 12, 2024 at 10:43 AM, ajparent1/kb1gmx wrote: Enough current and the that fine wire vaporizes.? ? Its one of the things that limits? power handling of the device.? ? ? Here's a discussion of bond wire fusing currents. ? Bond wire fusing is actually helpful, as many semis fail short and the fusing of the wire acts as a fuse which disconnects the failed component.?? I used to use heated bond wires as targets to align the IR and visible channels of IR microscopes.? I could reliably run an Amp through 1 mil gold wire without it fusing. 73, Don N2VGU ? ?
Dean - KC9REN All Messages By This Member #129744 I sanded a couple of these BS170s a while back to show what they look like inside and posted pictures here but it looks like the pictures have been deleted. (I think that happens automatically after some time on these groups) I think I tossed them out but I can look around just in case and I'll repost if I find them. Dean - KC9REN ? On Thu, Sep 12, 2024 at 09:43 AM, ajparent1/kb1gmx wrote: toggle quoted message Show quoted text Carefully crack open a device and look at the construction. ? The drain lead is part of the lead frame to which the die s bonded. Memory says the back of that leadframe is the flat side of the device.?? ? The gate and source are via bond wires to the die.? Hence there is less heat transfer to the leads. ? The ideal device is one where the drain is bonded to an accessible tab? for example VN7000 (to92 with tab out the top) and the IRF510. In both cases the direct mechanical (or solder) contact has greatly increased heat transfer.? ? -- Allison ------------------ Post online only,? direct email will go to a bit bucket.

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