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QMX TN0110 Heat Sink

 

Just when you thought this topic met a fateful end, I've attached images of an adhesive heat sink applied to the PA MOSFETs in my low band QMX.? Because the TN0110 MOSFET's have the flat side facing up, that arrangement lends itself nicely to a low-profile heat sink.? ?In addition to the self-adhesive compound, it's compressed against the MOSFETs by the quarter-twist plastic tab on the LCD display.? ?

I make no claim that it's any more effective than the existing steel washer configuration but decided to try it anyway.??

Paul, W9AC

? ??
 

Paul?

That is super neat and tidy!

JZ KJ4A?

On Thu, Jan 11, 2024, 4:44?PM Paul Christensen <w9ac@...> wrote:
Just when you thought this topic met a fateful end, I've attached images of an adhesive heat sink applied to the PA MOSFETs in my low band QMX.? Because the TN0110 MOSFET's have the flat side facing up, that arrangement lends itself nicely to a low-profile heat sink.? ?In addition to the self-adhesive compound, it's compressed against the MOSFETs by the quarter-twist plastic tab on the LCD display.? ?

I make no claim that it's any more effective than the existing steel washer configuration but decided to try it anyway.??

Paul, W9AC

? ??
 

Paul,

Very nice! Looks like a Raspberry Pi heatsink ?- I like the mechanical assembly!?

Tony - AC9QY?

On Thu, Jan 11, 2024 at 3:47?PM John Z <jdzbrozek@...> wrote:
Paul?

That is super neat and tidy!

JZ KJ4A?

On Thu, Jan 11, 2024, 4:44?PM Paul Christensen <w9ac@...> wrote:
Just when you thought this topic met a fateful end, I've attached images of an adhesive heat sink applied to the PA MOSFETs in my low band QMX.? Because the TN0110 MOSFET's have the flat side facing up, that arrangement lends itself nicely to a low-profile heat sink.? ?In addition to the self-adhesive compound, it's compressed against the MOSFETs by the quarter-twist plastic tab on the LCD display.? ?

I make no claim that it's any more effective than the existing steel washer configuration but decided to try it anyway.??

Paul, W9AC

? ??
aa0jr Jakob
 

Nice job!
As a further improvement, I would drill a metric 3 threaded hole into the heatsink aligned with the screw hole in the PCB. The added screw will conduct heat from the PCB to the heatsink and keep the sandwich together. Remove the sticky tape and replace it with a tiny amount of thermal conducting paste on the flat of each FET. Such a heat sink would certainly outperform the original washer solution and, sorry Hans, look better.
73
 

Did you do any thermal modelling on this ??


(Thermal tape is a pretty poor heat conductor when uncompressed .. )

Use a fixing screw instead to apply pressure to the sink -FET interface and apply the thinnest possible layer of thermal grease to the packs point of contact?
 

The main thing to remember about heat sinks is unless there¡¯s a heat transfer path out of the assembly (i.e. convection, conduction, or radiation), ?a heat sink only slows down the temperature rise of the devices being heat-sunk. This is fine for low-duty cycle transmissions but it won¡¯t help much for long transmissions like WSPR. Adding a small raspberry pi fan on top of the heat sink would help but not much in a closed case environment. The best you can do in a closed case is conduct the heat to the board using a metal bolt of some sort and hope the entire board acts as a heat sink. As Bruce mentioned, a VERY thin layer of heat sink compound between the FETs and heat sink will improve the rate of heat transfer.

On Fri, Jan 12, 2024 at 4:43?PM Bruce Akhurst <bruce@...> wrote:

Did you do any thermal modelling on this ??


(Thermal tape is a pretty poor heat conductor when uncompressed .. )

Use a fixing screw instead to apply pressure to the sink -FET interface and apply the thinnest possible layer of thermal grease to the packs point of contact?
aa0jr Jakob
 

A good point, Tony, about the accumulation of heat energy that cannot escape. Disperse the heat through the PCB may help a bit. My ultimate solution to bring the heat out of the box is using a solid piece of Alu or better Copper bolted down on top of the FET. Fins are not required. Extend the side of the piece such that it touches the housing and fix it to the housing wall with screws through the wall. Add a minimal amount of heat sink compound. I am tempted to retrofit this to my QMX before I go digital again.
73
 

Direct heat conduction to a metal case is the best solution and copper strapping is the?way to go. Aluminum isn¡¯t as good of a heat conductor but it¡¯ll do in a pinch.

I once did an experiment with a system inside a plastic case where I lined the entire inside of the case with copper tape. This created a poor-mans Faraday cage as well as a large surface area for heat dissipation. The power transistors were strapped with multiple stranded wires (enough to completely cover the transistors) and soldered to the copper tape lining the case. It sure wasn¡¯t pretty but it worked well.

Another clever concept was developed by a mechanical engineer friend of mine. The board had exposed copper ground pads regularly spaced along its periphery, each tied to the internal PCB ground planes. He used small L-brackets soldered to each of these pads which were then soldered to the bottom half of the metal case. With appropriate spacing of the brackets, he accomplished both EMI shielding and excellent heat transfer. Rework was a pain but hey, there ain¡¯t no free lunch.?

Tony - AC9QY

On Fri, Jan 12, 2024 at 10:41?PM aa0jr Jakob via <aa0jr=[email protected]> wrote:
A good point, Tony, about the accumulation of heat energy that cannot escape. Disperse the heat through the PCB may help a bit. My ultimate solution to bring the heat out of the box is using a solid piece of Alu or better Copper bolted down on top of the FET. Fins are not required. Extend the side of the piece such that it touches the housing and fix it to the housing wall with screws through the wall. Add a minimal amount of heat sink compound. I am tempted to retrofit this to my QMX before I go digital again.
73

 

Been away for a few days but having a look at the new heatsink, adding machine screws is easily accomplished.?

1) A hole can be drilled into the heat sink's center to compress it with a thin layer of compound against the quad set of TN0110 MOSFEts.? At the moment compression is accomplished with the LCD display's plastic quarter-turn tab.? Functional but not as good as a screw passing through.??

2) The heat sink can be moved flush with the back enclosure edge.? A new #4 hole (or two) can be drilled into the bottom enclosure and *tapped* into the heatsink.? ?

3) Finally, a row of multiple holes can be placed along the front and back side bottom enclosure for ventilation.? With enough holes, it may not even require forced air flow, especially with the heat sink bolted against the enclosure.?

The current quad arrangement has the MOSFET source leads at ground potential. I've not considered the viability of reconfiguring the circuit to ground the drain instead.? A simple device rotation isn't possible for several reasons, a diode across the D-S leads being once.? Changing to a P-channel device may offer some possibilities to divert heat from the physically larger drain lead to a grounded heat sink.??

Paul, W9AC

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