Direct heatpipe attachment to die using center point loading

Details Direct heatpipe attachment to die using center point loading Direct heatpipe attachment to die using center point loading

2000-09-29

2002-10-22

Thompson, Gregory (Department: 2835)

Electricity: electrical systems and devices

Housing or mounting assemblies with diverse electrical...

For electronic systems and devices

C165S080200, C165S104330, C174S015200, C257S715000, C257S719000, C361S704000

Reexamination Certificate

active

06469893

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the field of computer component assembly and in particular to an assembly of a die to a heat conductor.
2. Discussion of Related Art
In the design and manufacture of computer hardware, meeting certain thermal requirements can be essential. In particular a silicon microchip (die) placed into a circuit package, can have a requirement to remove heat generated by the microchip during operation. The circuit package may have a barrier of plastic covering the die. In the case of laptop computers, a heatpipe acting as a heat conductor may be attached to the circuit package containing the die to help carry off the heat. As illustrated in
FIGS. 1
a
and
1
b
, the heatpipe
116
can have a metal part called a spreader plate
104
that is placed between the circuit package
110
and the heatpipe
116
to thermally mate the smaller heatpipe contact area to the circuit package
110
. The heatpipe
116
, circuit package,
110
, and spreader plate
104
are clamped to a printed circuit board substrate (substrate)
112
using several fasteners
102
. The clamping process can places unequal forces (loads) F
1
& F
2
(only two fasteners are shown for clarity but four or more fasteners may be used) on the heatpipe
116
and spreader plate
104
. There can potentially be as many unequal forces applied as there are fasteners
102
. As a result, some of the computer components (heatpipe
116
, spreader plate
104
, circuit package
110
) may flex and/or shift. With movement of the computer components
116
,
104
,
110
, thermal interface materials
108
,
114
placed between the heatpipe
116
and the spreader plate
104
and between the spreader plate
104
and the circuit package
110
may take on a varying thickness. A varied thickness in the thermal interface materials
108
,
114
as well as an increase in thermal interface material
108
,
114
thickness will both increase thermal resistance.
Illustrated in
FIGS. 1
a
,
1
b
, and
1
c
is an apparatus to provide the clamping force using fasteners
102
such as screws or bolts. These fasteners
102
connect the spreader plate
104
to the substrate
112
with the circuit package
110
in between. Each fastener
102
applies a force (F
1
, F
2
) that contributes to the total clamping force (F
1
+F
2
). The spreader plate
104
and the substrate
112
place in compression a first thermal interface material (TIM
1
)
108
, the circuit package
110
, and a second thermal interface material (TIM
2
)
114
. Even small differences in the dimensions of the spreader plate
104
or the circuit package
110
or in the torque applied
113
to each fastener
102
is sufficient to cause one fastener
102
to have a force different F
1
≠F
2
from the other fasteners
102
. As a result, the spreader plate
104
may tilt (
FIG. 1
b
) and the thermal interface materials
108
,
114
can each take on a varying thickness. In addition, if the forces (F
1
, F
2
) applied are too great for the spreader plate
104
stiffness, the spreader plate
104
may bow (
FIGS. 1
a
&
1
c
). If the spreader plate
104
is sufficiently stiff, the spreader plate
104
may tilt as a result of the unequal forces F
1
, F
2
(
FIG. 1
b
). Both bending and tilting of the spreader plate
104
are simultaneously possible with the result that TIM
1
108
can flow in response thereby creating a non-uniform TIM
1
108
thickness. The second thermal interface material (TIM
2
)
114
, positioned between the spreader plate
104
and the heatpipe
116
, is outside the clamping force (F
1
+F
2
) but can still flow in response to the movement of the spreader plate
104
, with the result of a non-uniform TIM
2
114
thickness. The consequence of non-uniform TIM
108
,
114
thicknesses is reduced performance because of a local and/or overall temperature increase in the circuit package
110
.
Additionally, in response to these unequal loads (F
1
, F
2
), TIM
1
108
and TIM
2
114
may develop voids, and TIM
1
108
and TIM
2
114
may separate from the spreader plate
104
and/or the heatpipe
116
. As a result, an increase in the thermal resistance recurred by TIM
1
108
and TIM
2
114
on to thickness differences and voids/separations can occur.
Connecting the spreader plate
104
to the heatpipe
116
may be accomplished without a thermal interface material by using a close fit of the components such as an interference fit that requires tight dimensional tolerances between mating surfaces. To minimize thermal resistance, close direct contact is required to avoid air gaps between the two mating parts. Alternatively, the connection may be accomplished with the thermal interface material between the heatpipe
116
and the spreader plate
104
. The thermal interface material (TIM) should also be thermally conductive and may be a grease, a solder, selected from a range of adhesives, or other materials. The interface dimensions, the thermal interface material, and a method of holding the computer components in a stacked position (stack), are important.
When an adhesive or solder is used as the thermal interface material, and bond strength is required, proper assembly force is necessary to ensure good bond strength. If no bond strength is required, a thermal interface material may be used that does not set up as do the adhesives and solders. However, regardless of whether a TIM sets up like an adhesive or does not set up such as with a grease, during the time the TIM can flow or deform requires the thickness to be controlled as well as the creation of gaps and voids to be minimized. Such voids may exist within the TIM and gaps can exist at the TIM surfaces. Additionally, the thickness of the material may be applied unevenly. As a result, heat conduction through the material and interface surfaces will be less efficient.


REFERENCES:
patent: 5307236 (1994-04-01), Rio et al.
patent: 5424918 (1995-06-01), Feips et al.
patent: 5549155 (1996-08-01), Meyer, IV et al.

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