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2.1. Cooling and thermal Resistance

All characterization is made at 27ºC ambient, not junction temperature, without any cooling or forced ventilation of the sensor.

Thus the actual increase in noise will be less than the 17% from 27ºC to 80ºC, as the junction temperature is already above the 27ºC for the measurement.

The noise contribution is mainly from Thermal noise, thus it is proportional to Temperature in Kelvin. However, a part of the noise comes also from power supply noise, usually the power supply noise will also increase with temperature, again following the same physical law's. A cross section of the package is shown in the sensor specification.





However, we think we have no customer that actively cools the sensor. We would estimate that you will only achieve a marginal improvement by active cooling of the sensors compared to cooling over heat conduction by thermally coupling the Invar to a heat sink. Especially considering the high effort to provide active cooling, we would only consider this if your application requires extremely long exposure times and you would be limited by dark current integration. Furthermore, for exposure times in the range of hundreds of milli-seconds or even seconds, Dragster is maybe not the ideal sensor. It's strength is in high line rates, thus exposure times typically is less than 1 ms.

 

Thermal resistance dragster:

Material (Invar) : FeNi42 = CTE 5.3 10e-6 /K

Thermal conductivity: K =15.1 W/m/K

Thickness of Invar: 2e-3
Length (center to screw hole) 31.75e-3
Width of plate 25e-3

Cross section: 50e-6m2

Conductivity plate: 0.755e-3 Wm/K, 31mm length -> 0.023 W/K

-> center to screw hole: 42K/W
-> assumign 4 screw holes: 10.5K/W

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Vertical thermal resistance to cooling body with 2mm x 63mm contact area.

Cross Section of Invar (2mm x 63mm) 378e-6m

conductivity vertical plate: 0.0057 Wm/K

conductivity vertical 2mm 2.85 W/K

-> Thermal resistance vertical through 2mm Invar 0.35K/W

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Thermal resistance 100um air gap:


Thermal conductivity Air : K
0.024 W/m/K

conductivity air gap under die: 9e-6 Wm/K
conductivity 100um air gap under die: 0.09W/K

-> thermal resistance 100um air gap 11K/W

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Thermal resistance 200um thick glue (assuming low density polymere)

K = 0.16

-> thermal resistance 200um glue 3.3K/W

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Thermal paste (silver based) K = 8

-> 200um -> 0.06K/W

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Regarding the LCC version ,  we have the following :

The cross section is 3.95 e-4 m2 :

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Thermal Conductivity of Tg 135 neglecting the vias contribution : 0,49 W/m/K

Thickness of Invar: 1.5e-3 m

conductivity vertical : 0.49 x 3.95e-4 = 0.193e-3 Wm/K

conductivity vertical 1.55 mm:   0.1245 W/K

-> thermal resistance :  8 K/W

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