Datasheet

1
4
Introduction
Design
Guide
Polyimide
Heaters
Silicone
Rubber
Heaters (foil)
Standard
Polyimide
& Rubber
Rubber
Heaters
(wire-wound)
Mica Heaters
Thermal-Clear
Heaters
All-Polyimide
Heaters
Sensors,
Controllers &
Accessories
Reference
|
Flexible Heaters Design Guide | www.minco.com
Description of
Thermal System
Warm a test instrument in an avionics
system from as cold as -45°C to 70°C
within two minutes with ±2°C accura-
cy. The instrument is a cylinder 1.25"
(32 mm) diameter and 3.5" (89 mm)
tall, providing a heating area of 3.9 ×
3.5" (100 × 89 mm). The available volt-
age on the aircraft is 28 VDC.
Maintain 96 sample vials, each con-
taining 10 ml of human blood, at
37°C. The vials are positioned in
drilled blind holes in an aluminum
block measuring 4.0" × 6.0" × 1.5"
(102 x 152 x 38 mm) with a total mass
of 500 g. The sample temperature
must never exceed 40°C at 24 VDC.
A 300 mm silicon wafer placed on a
325 mm diameter aluminum chuck
must be heated from 40°C to 220°C
during processing. Input voltage is
208 VAC.
Wattage
requirements
From Thermal Calc*, we need 60 watts
warmup power and 25 watts mainte-
nance power.
From Thermal Calc*, we need 60 watts
for warmup and maintenance.
From Thermal Calc*, we need 800 watts
to reach the required temperature
within the time limit.
Electrical
parameters
R = E²/W = 28²/60 = 13.1 Ω R = E²/W = 24²/60 = 9.6 Ω R = E²/W = 208²/800 = 54.1 Ω
Heater selection Commercial and military avionics sys-
tems typically specify Polyimide insulat-
ed heaters. Model HK5482R12.1L12A is
selected.
Specifying polyimide because it is
resistant to most chemicals and does
not outgas, the best choice is
HK5491R9.4L12B
The required temperature exceeds the
limit for polyimide heaters, and the vac-
uum process does not allow silicone
rubber. An All-Polyimide heater, factory
mounted to the chuck, is required.
Actual wattage Wattage is 28²/12.1 = 65 W Wattage is 24²/9.4 = 61 W Wattage is 208²/54.1= 800 W
Watt density Watt density = W/effective area =
65/9.8 in² = 6.6 W/in² (1.0 W/cm²)
Watt density = W/effective area =
61/21.54 in² = 2.8 W/in² (0.4 W/cm²)
Watt density = W/effective area =
800/109.9 in² = 7.3 W/in² (1.1 W/cm²)
Installation For this cylindrical shape heat sink, a
BM3 Shrink Band is selected.
Any type of heater mounting will han-
dle the watt density. We recommend
acrylic PSA for fast availability of proto-
types.
Factory lamination of AP heaters pro-
vides optimum heat transfer and allows
operating temperatures higher than
other adhesives.
Leadwire current AWG 26 current rating is 5.0 A. Actual
current is:
I = 28/12.1 = 2.3 A (OK).
AWG 24 leadwire current rating is 7.5 A.
Actual current is:
I = 24/9.4 = 2.6 A (OK).
AWG 20 leadwire current rating is 13.5
A. Actual current is:
I = 208/54.1 = 3.8 A (OK).
Control The CT325 controller will be used to
control the heater.
A custom control circuit integrated into
the system electronics will control the
heater. The controller is designed for a
1000 Ω platinum RTD element input.
All electrical and motion control of the
wafer processing system is centrally
controlled by a computer. Thermal con-
trol is integrated into the system.
Sensor An S665 Thermal Tab RTD provides easy
installation in the prototype test sys-
tem.
A 1000 Ω platinum Thermal-Tab™ RTD
sensor is used. The customer tests the
sensor in several positions around the
aluminum block to determine the opti-
mum location.
An S247 thin film RTD element with
high-temperature extension leads will
be cemented into a hole in the platen.
Custom options Experiments confirm the power
requirements, but also show that the
sensor measures only one point rather
than the average temperature of the
cylinder. In the final custom design an
integrated Thermal-Ribbon strip sensor
wraps around the circumference of the
cylinder to measure the average tem-
perature.
Testing showed that edge losses
required 20% higher watt density
around the periphery of the heater to
equalize temperature within the block.
A custom design with profiled power
output, integrated sensor, and 40°C
thermal fuse provides a complete ther-
mal system in one package.
The leads exit is located at the center of
the heater to fit with the design
requirements of the machine.
*Thermal Calc is an on-line tool available at www.mi
nco.com to assist in estimating heater wattage requirements from known
parameters.
Examples of Thermal Systems