Feedback Application Note Product
CPU Heat Sink
For cooling CPUs: Pentium, PIII, PII, K6, K7, & others
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Heat Sink + Fan to keep your 1
GHz CPU
cool !
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P/N: 5180 for AMD K6 Socket 7 Overall size: 50 x 50 x 24mm Thermal resistance ~ 1.9 oC/W For up to 16 W applications P/N: CCI-087 for Pentium III Socket 370 Overall size: 55 x 55 x 33mm Thermal resistance ~ 1.4 oC/W For up to 25 W applications P/N: CCI-087 A
for Pentium III Socket
370 1 GHz
Overall size: 55 x 65 x 33mm Thermal resistance ~ 1.0 oC/W
For up to 35 W applications |
Custom Heat Sink
Short Lead Time: tooling in ~ 5 weeks & production
in ~6 weeks
Just-In- Time deliveries: from our California
warehouse
Satisfied customers: SONY, Apple Computer,
& Dell Computer
Detail Catalog available, or Fax / e-mail your sketch for a match.
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Extrusion - Over 600 shapes available.
· Cut to Length· Drill, punch, tap, or notch
· Special machining· Special finishes
· Flatness: 0.004 in/in (extruded)
· Flycut to 0.001 available Roughness: 90m (extruded)
· Flycut to < 64 available
Finishing options include: anodizing, chromating, irriditing, painting, silk screening, washing, & degreasing.
Secondary operations include: broaching, chamfering, cutting, deburring, drilling, epoxy bonding/isolation, fly cutting, milling, punching, reaming, sanding, slotting, stamping, tapping, tumbling, & brazing.
Machined or Bonded Fin
| Medium Fin Density | High Fin Density |
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Natural Convection |
Forced Convection |
| Fin Gap ~ 0.2" | Fin Gap ~ 0.1" |
| Fin Thickness ~ 0.06" | Fin Thickness ~ 0.05" |
| Height to 5" | Height to 5" |
| AL/Cu Fin & AL Base | AL / Cu Fin & AL/Cu Base |
How does the bonded-fin perform better then regular extrusion?
The denser and taller fins can provide additional surface area by about 4 times more than the regular extrusion. The heat dissipation is hampered by additional heat resistance at the joints (base, epoxy, & fins) and low dissipation efficiency* of the long and thin fins. However, the increase in surface area overcomes all these and can give 2 to 3 times more cooling power than regular extrusions.
*The long and thin fins are ~ 85% effective in dissipating heat as those thicker and shorter fins.
Cold Pack provides
Extremely Low Thermal Resistance
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Mounting Plate accepts 120
mm muffin fans
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Ball bearing fan 50x50x10 mm 12VDC MTBF ~ 40,000 hours at 25 oC, Metal clip for attaching to the Socket, Thermal tape to interface with the CPU
Liquid
Cold Plate
(low
footprint) provides Extremely Low
Thermal Resistance
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Direct Contact - up to 12”x 6” x 0.5” |
Pipe Series - up to 24” x 6” - plate only 0.25” thick |
Flow Rate of ~ 1.5 to 2 GPM is the optimal. Pressure drop is ~3 psi for 2-Pass and ~ 4 psi for 4-Pass. Three sizes of pipe available: 1/4”OD, 5/16”OD, & 3/8”OD.
Smaller pipe has the advantage of compact size and lighter overall weight.Thermal Resistance in oC/W for various products.
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Pipe |
Pipe |
DC
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DC
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W |
L |
2-Pass |
4-Pass |
2-Pass
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4-Pass
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3 |
5 |
~0.07 |
N/A |
~0.03 |
N/A |
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4 |
6 |
~0.06 |
N/A |
~0.02 |
N/A |
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5 |
6 |
~0.06 |
~0.04 |
~0.02 |
~0.02 |
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5 |
12 |
~0.03 |
~0.02 |
~0.015 |
~0.01 |
Minor
variations on thermal resistance across the plate. Various Flanges available.
Plate thickness: DC Series - 0.5”,
Pipe Series - 0.25” or 0.375”,
custom design.
Keep Your Device Cool with a Heat Sink
The hot device should be kept cool with heat sink to enhance its reliability. The total heat load, Q, on the hot side is the sum of the active heat loads.
For DC-DC converter the heat load is the wattage difference between the input and output. Proper heat sink is needed for the hot side.· Keeping your device as low as practical is a good practice.
· D T = Q x Q Temperature rise is the heat load, Q,
times the thermal resistance, Q .
Natural Convection Heat Sink
Normally used for low-power applications, its thermal resistance,
Q , 2.0 0C /watt for dimensions of 5 "x3 "x l" A natural convection heat sink should be positioned so that:1. heat can be dissipate upward through the fins,
2. no significant obstructions to impede air flow.
· Any other heat-generating components near by the
heat sink would increase the ambient air temperature.
· A black anodized finish on aluminum heat sink can
lower the Q by 4 %.
· The Q is proportional to inverse of total surface area.
It is desirable to use a heat sink as large as practical
without blocking the air flow. However, too reduce the
Q by one-half, the extruded heat sink volume has to be
increased by a factor of four.
· The structure member of an enclosure or mounting
frame is often used to remove heat from a device.
This technique is effective for small amount of heat.
Forced Convection Heat Sink
Substantial cooling power can be achieved by using forced convection.
· The Q can be reduced to below 0.2 0C / watt.
· Three general ways of applications:
1. mount the fan or blower to one side of the heat sink and force air through the heat sink parallel to the extrusion direction,
2. mount the fan or blower near the center of heat sink
on top of the fin and force the air downward to the base and through two open sides,
3. same as b. except force the air upward from the base and through two open sides.
These methods should be carefully assessed from the complete package point of view to reach a best solution for a particular application.
· A black anodize finish does not improve much for the force convection heat sink.
· Linear Feet per Minute (LFM) equals to the Cubic Feet per Minute (CFM) of the fan or blower divided by the orifice area in square feet.
· The fan, a moving device, has a much lower MTBF than the TEC. Easy maintenance to the fan should be considered in designing the cooling assembly.
· How to estimate the OS of a heat sink?
1. Find the heat sink's Length (in inch) & surface area (S in inch2 per inch).
2. Compute the figure of merit (F).
F = 0.008 x square root of L.
3. Q (0C/Watt) = 1 I ( S x F).
Example: L = 5 in, S = 20 in2 per in, then F = 0.008 x ~5 =0.0178, Q = 2.8.
If forced air cooling is used, find the fan's CFM Calculate the LFM and tweak the figure of merit,
F = 0.011 x square root of (L X LFM / 1O0)
Example: CFM =400,
orifice 2 ft2, LFM= 400/2,
F = 0.011
x square root of(5 x 200 /100) = 0.0347, 1.4. Then, AT is only half of that without a fan.
· The "Stacked fin" heat sink is better than extrusion in
Lower thermal resistance 30%
Lower weight 30%
Smaller size & faster delivery.
Ambient Temperature
Temperature of the air near the device under consideration, do not confuse with the room temperature. In most cases it is much hotter than room temperature, especially if the device is inside a enclosure without adequate air circulation.