| Step 1.
Prepare cold plate and heat sink surfaces by drilling
clearance holes on one surface and drill and tap opposite
accordingly (see sketch). If
a spacer block is used to increase distance between surfaces,
performance is greater if the spacer block is on cold side
of system.
Step 2. Grind or lap
flat cold plate (within +/- .001") in module area.
Thoroughly clean and degrease thermoelectric module, heat
sink, and cold surface.
Step 3. Heat sink
surface must be solderable (either copper or copper plated
aluminum). Clean module area of heat sink surface by light
abrasion and degrease thoroughly. Pretin with indium-tin
eutectic type solder and flux.
Step 4. Module surface
should be degreased and fluxed lightly. Heat pretinned and
cleaned heat sink surface to 120 to 130°C (250 to 265°F).
The module should not go above 138°C or the internal
solder will reflow. Place module in position on surface,
wait a few seconds for solder on module to melt and excess
flux to boil out. When all solder is molten, module will
have tendency to float on solder. Light swishing of module
will enhance wetting.
(Note: If after all solder is molten there
is a slight dragging effect on the module, a deficiency
of solder is indicated. Remove module and add additional
solder to heat exchange surface. Cool unit and solidify
solder.) If more than one module is used in the assembly,
the flattened cold side surfaces of the module must be
kept in a common plane during the soldering operation
(Step #3). This can best be accomplished by first fastening
the modules, cold face down and in proper array, to a
ground flat plate of metal or graphite with double-faced
tape. This assembly of modules and flat plate facilitates
soldering of the modules to the heat sink, while insuring
that all module cold surfaces are maintained in a common
plane and properly arrayed.
Step 5. After assembly
cools, rinse thoroughly to remove all traces of flux residue.
Step 6. Assembly is
now ready for bolting to cold plate. Apply a thin continuous
film of thermal grease (Wakefield Engineering Type 120 or
Dow Type 340) to module top surface and to module area on
cold plate and mate surfaces. Gently oscillate module back
and forth, exerting uniform downward pressure, noting efflux
of thermal compound around edges of module. Continue motion
until resistance is felt.
Step 7. Before bolting,
best results are obtained by preloading in compression the
cold plate/heat exchanger/module assembly, applying a light
load in line with center of module, using clamp or weights.
For two module assemblies, use 3 screws located on module
center line, with middle screw located between modules.
To preload, torque middle screw first. Bolt carefully, by
applying torque in small increments, alternating between
screws. Use a torque limiting screw driver. The recommended
compression for a TEC assembly is 150 to 300 pounds per
square inch of module surface area. Using the following
equation we can solve for torque per screw:
-
| T = (C
x D x F x in2) / (# of screws) |
T = torque per screw (in-lbs)
C = torque coefficient (0.20 as received, 0.15 lubricated)
D = nominal screw size (4/40 = 0.112, 6/32 = 0.138,
8/32 = 0.164)
F = Force (lbs / in2)
in2 = Module surface area (length x width)
Check torque after one hour and retighten if
necessary. Use Stainless Steel Screws, fiber insulating
shoulder washers, and steel spring (Belleville or split
lock type) washers (see sketch
in Assembly Tips).
CAUTION
1. To assure good thermal grease interfaces
there should be no bowing of either surface due to torquing.
To prevent bowing, apply less torque if one or both surfaces
are less than 1/8 inch thick copper or 1/4 inch thick aluminum.
2. Lead wires are soldered to module tabs
with bismuth/tin solder (136°C). If lead wire replacement
is necessary, use bismuth/tin solder.
use lead / tin solder (180°C).
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