Reading my posts, you may think I only do thermal tests…today I’ve built 3 potted drop ins built out a Convoy M1…and yes, did another thermal test.
I’ve seen comments made often about Fujik Heatsink Compound and it’s effectiveness compared to RTV Silicone. I only use Fujik as a thermal thread lock, but saw an opportunity to set up a new test.
The contenders:
Fujik Heatsink Compound (50 ml tube - Silicone Filuid* - greaselike - white……….*yes, they misspelled it on the tube)
Permatex Black RTV Silicone
Insulcast RTVS Potting Compound –2pt
Most of you probably have never heard of the Insulcast, but I’m including it because its what I use to attaching my mcpcb and it’s a good soft set potting compound.
The test setup:
I used a piece of 1”x1”x1/8” aluminum angle 2’ long. I wrapped the angle with monofilament .5mm diameter. The monofilament was wrapped in a spiral fashion around the aluminum angle and the wraps were spaced 1/4” apart. (more on this later)
I cut 3 pieces of aluminum flat stock 1”x1.5” -sanded one side flat to 600 grit. I then spread each of the materials to be tested on a 1.5” section of the monofilament wrapped aluminum angle.
I pressed a piece of the 1”x1.5” flat stock into the test material -I weighted each test piece with an 8oz weight, placed it in a curing oven at 65c for 24 hours.
The monofilament created a .5mm gap between the aluminum angle and the 1x1.5 test blocks…this gap was filled with only the test material (and the monofilament wraps)…any heat passing from the aluminum angle to the test blocks had to pass through .5mm of the test material…consistent gap -no metal to metal contact.
A fly in the ointment: I like the Insulcast because it is thin. When I mount a mcpcb with it, I add about 3 or 4 drops into the pill -yes drops -not globs or smears. Fujik is a little thicker than toothpaste -Insulcast is about as thick as syrup (Aunt Jemima not Karo…there is a difference). When I press the mcpcb into Insulcast, any excess is easily squeezed out from under the mcpcb and fills the voids around the perimeter. Also it sticks, but not as tenaciously as Fujik or RTV silicone making removing the star easier. The Fly: when I set up the test block with the Insulcast, a good portion of it dripped out of the gap (remember, it’s thin) -I would estimate I still had only about 75% coverage -since I’m probably the only using Insulcast, I decided to proceed with the test.
Enough about Insulcast -this is really a test between Fujik and RTV silicone.
I mounted the angle onto two steel spring clamps. I attached a piece of blue masking tape to the top surface of the aluminum test pieces (I used an infrared thermometer to take the temperature readings, the masking tape corrects the emissivity of the aluminum surface). I cut off the exposed monofilament strings leaving only the portion embedded in the test material. I heated the underside of the angle with a propane torch, concentrating on the leg that did not have the test pieces on the opposite side. Each torch pass lasted about 1/2 seconds.
I immediately read the temperature of each test sample and had someone record it. I continued reading right to left -left to right -right to left -ect. I chose the set with the highest temperature difference.
I allowed the assembly to cool then repeated the test a total of 6 recorded times -each run had a different number of torch passes:
Higher temperature means better thermal conductivity.
R1 | R2 | R3 | R4 | R5 | R6 | avg | |
Fujik | 97 | 105 | 118 | 122 | 136 | 152 | 121.7 |
RTV Silicone | 96.5 | 105 | 118.5 | 122 | 135 | 152 | 121.5 |
Insulcast | 103.5 | 112 | 126.5 | 130 | 142.5 | 163.5 | 129.6 |
all temperatures are F
Well I’m surprised, I always though Fujik had some kind of thermal filler…but it looks like Fujik is no better (or worse) than RTV Silicone…actually, it is just RTV Silicone.