User Manual
13
Thermal Solutions Design Guide | Specifications subject to change
Overview
The watt density tables on he following page show
the maximum allowable power for each heater type,
expressed in watts per square inch, or centimeter, of
effective area. The rating depends upon the heater’s
insulation/internal adhesive, heat sink control
temperature, and the mounting method.
If watt density exceeds the maximum rating, the heater
is in danger of overheating and premature failure. To
obtain more power:
• Select a larger size heater
• Consider other heater insulation materials, e.g. mica
• Change the mounting method
• Use proportional control to reduce power as the
heat sink temperature rises
• Contact Minco for product and design assistance
In addition to wattage, you should calculate the current
(I) through the heater leadwires to keep it within the
maximum rating for the AWG wire size used.
Using watt density charts
1. Look up the effective area for the heater model in
question. This is total heater area minus borders
and lead attachment space (calculated by Minco).
2. Divide the power requirement in watts by this area
to obtain watt density.
3. Draw a line from the heat sink temperature (at
the bottom of the chart) to the line labeled with
the mounting method and/or insulation you have
chosen.
4. The maximum watt density is indicated by the
value on the left or right axis that corresponds with
that intersection.
Maximum Watt Density
Calculate maximum allowable power
100
90
80
70
60
50
40
30
20
10
25 50 75 100 125 150 175 200 225 250
Watts / in²
Operating Temperature (°C)
15.5
14.0
12.8
10.9
9.3
7.8
6.4
4.7
3.1
1.6
Watts / cm²
CLAMPED
FACTORY MOUNTED
All-Polyimide Heaters
Maximum Watt Density by Mounting Method
2mil/50μm Polyimide
110
100
90
80
70
60
50
40
30
20
10
-200 -100 0 100 200 300 400 500 600
Watts / in²
Operating Temperature (°C)
17.1
15.5
14.0
12.4
10.9
9.3
7.8
6.2
4.7
3.1
1.6
Watts / cm²
0.020” (0.5mm) MICA
0.010” (0.3mm) MICA
Mica Heaters
Maximum Watt Density with Clamping
60
50
40
30
20
10
0
-75 -50 -25 0 25 50 75 100 125 150 175 200
Watts / in²
Operating Temperature (°C)
9.3
7.8
6.4
4.7
3.1
1.6
0
Watts / cm²
PSA
STRETCH TAPE OR
CLAMPED
#15 EPOXY
Polyimide/FEP Heaters
Maximum Watt Density by Mounting Method
1mil/25μm Adhesive
2mil/50μm Polyimide