Heat sink mounting for KSA1381 and KSC3503

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Alan0354

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Joined 2014
#1
I just received these transistors. I notice there is no metal backing on either side of these transistors. Is it important to even worry about which side to be in contact to the heat sink for heat dissipation?https://www.fairchildsemi.com/datasheets/KS/KSA1381.pdf

Also, if you look at the drawing in the data sheet, the only thing they show to distinguish the top side are the 3 circular indents on the surface. I look at my transistors, one side, there are 3 circular indents like the drawing. More important, the side with the 3 indents has the marking of 2SA1381. Can I safely assume that's the top side to count the pins?

Thanks
 
#3
rayma said:
The thermal resistance is lower using the rear side (opposite the markings).
The drawing on the data sheet defines the pinout with the marking on the top side.
Click to expand...
Do you know how much. Once you have plastic in between, it's not that good anyway. If you look at the transistor side way, the bottom is even thicker if you use the pins as the mid point. If the transistor inside is on the plane of the pins, it would be a lot closer to the top than bottom. I would say the distance from the bottom to the pins is double the distance from the pins to the top.
 
#4
Alan0354 said:
Do you know how much. Once you have plastic in between, it's not that good anyway. If you look at the transistor side way, the bottom is even thicker if you use the pins as the mid point. If the transistor inside is on the plane of the pins, it would be a lot closer to the top than bottom. I would say the distance from the bottom to the pins is double the distance from the pins to the top.
Click to expand...

The die is located below the plane of the leads. There are bond wires connected from the leads down to the die.
I don't think the thermal resistance is defined for heat sinking on the front surface.
 
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