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THERMAL INTERPOSER SUITABLE FOR ELECTRONIC MODULES
Abstract
A thermal interposer for use in providing a mating interface between a
heat sink and an electronic module includes an elongated body portion
having two opposing surfaces. On one surface, a plurality of press-fit
pegs are defined that extend upwardly and outwardly away from the
interposer body portion. On the other, opposing surface, a plurality of
contact arms are defined that extend, in cantilevered fashion, downwardly
and away from the interposer body portion. The press-fit pins are
configured to enter grooves formed in a heat sink in a manner to form
intimate, metal to metal, contact while the contact arms are configured
to contact the top surface of an electronic module with reliable normal
force.
1. A thermal interposer for providing a thermal interface between a
surface of an electronic module and a heat sink, the thermal interposer
comprising: a body portion, the body portion having opposing first and
second sides, the first and second sides configured to respectively
contact the electronic module surface and the heat sink, the body portion
including a plurality of cantilevered contact arms formed therein, each
contact arm including a base portion attached to the body portion and a
free end opposite the base portion, the contact arm being bent outwardly
away from the first side at an angle thereto, the free end terminating in
a contact face for contacting the electronic module surface when
installed; and the body portion further including a plurality of
attachment members disposed along the second side thereof, each
attachment member extending upward and away from the second side, each
attachment member having a base portion and an attachment point opposite
the base portion, each attachment member being received within
corresponding opposing grooves of the heat sink in a manner wherein the
attachment members intimately contact the grooves.
2. The thermal interposer of claim 1, wherein the attachment members
include pegs with pointed ends.
3. The thermal interposer of claim 1, wherein the contact arms are
arranged in rows upon the body portion, and the attachment members are
arranged around a perimeter of the body portion.
4. The thermal interposer of claim 3, wherein the attachment members are
further disposed on the body portion to surround each row of contact
arms.
5. The thermal interposer of claim 3, wherein the attachment members are
arranged in rows disposed between adjacent rows of contact arms.
6. The thermal interposer of claim 5, wherein pairs of attachment members
in different rows are aligned with each other such that an imaginary line
drawn through one of the pairs separates adjacent contact arms from each
other.
7. The thermal interposer of claim 1, wherein the attachment members are
arranged in a pattern on the body portion to divide the contact arms into
distinct rows of contact arms.
8. The thermal interposer of claim 1, wherein some of the attachment
members are disposed on the body portion proximate the contact arms base
portions such that each contact arm base portion has at least one
attachment member associated therewith to define a thermal transfer path
between the attachment member and the contact arm.
9. The thermal interposer of claim 1, wherein the attachment members have
a thickness equal to or greater than a width of the heat sink grooves.
10. The thermal interposer of claim 1, wherein the contact arms and the
attachment members are aligned lengthwise with respect to the body
portion.
11. The thermal interposer of claim 1, wherein the attachment members are
arranged in distinct first and second groups, the attachment members of
the first group being disposed along a portion of the perimeter of the
interposer, and the attachment members of the second group being disposed
interior of the interposer perimeter and aligned lengthwise with respect
to the body portion.
12. The thermal interposer of claim 11, wherein some of the contact arm
base portions and the attachment member base portions are disposed
perpendicular to each other.
13. The thermal interposer of claim 11, wherein the body portion further
includes a plurality of U-shaped openings, each opening being associated
with and disposed proximate a respective one of the second group
attachment members.
14. An interposer for providing a thermal interface between a surface of
an electronic module and a heat sink, the interposer comprising: a body
portion, the body portion including a plurality of sides cooperatively
defining a perimeter thereof, first and second surfaces extending between
opposing sides for respectively contacting an electronic module surface
and a heat sink when the interposer is disposed between the electronic
module and heat sink, and a plurality of cantilevered contact arms
disposed thereon, each contact arm including a base portion attached to
the body portion and a free end disposed opposite the base portion, each
contact arm being bent away at an angle from the body portion first
surface, each contact arm free end terminating in a contact face for
contacting the electronic module surface; and a plurality of attachment
members formed as part of the body portion and disposed on the body
portion second surface, each attachment member extending away from the
body portion second surface in a direction opposite that of the contact
arms, and having a base portion at one end joining with the body portion
and an attachment point at an opposite end of the attachment member, some
of the attachment members being disposed around the perimeter of the
interposer body portion and others of the attachment members being
disposed on the interposer body portion interior of the interposer body
portion perimeter; wherein the contact arm base portions and the
attachment member base portions are arranged perpendicular to each other
to define a plurality of heat transfer paths between the attachment
members and the contact arms.
15. The interposer of claim 14, wherein some of the heat transfer paths
are L-shaped.
16. The interposer of claim 14, wherein the attachment members are
configured to be received within corresponding opposing grooves of the
heat sink in a manner wherein the attachment members intimately contact
the heat sink grooves.
17. The interposer of claim 14, wherein the attachment members are
arranged in distinct first and second groups, the attachment members of
the first group being disposed along a portion of the perimeter of the
interposer, and the attachment members of the second group being disposed
interior of the interposer perimeter and aligned lengthwise with respect
to the body portion.
18. The interposer as set forth in claim 14, wherein the attachment
members are arranged in a pattern on the body portion to divide the
contact arms into distinct rows of contact arms.
19. The interposer as set forth in claim 14, wherein pairs of attachment
members in different rows are aligned with each other such that an
imaginary line drawn through one of the pairs separates adjacent contact
arms from each other.
20. The interposer as set forth in claim 14, further including a heat
sink, the heat sink including a plurality of grooves formed therein, the
interposer attachment members being aligned with and received within the
grooves.
Description
CROSS REFERENCE To RELATED APPLICATION
[0001] The Present Disclosure claims priority to U.S. Provisional Patent
Application No. 61/839,414, entitled "Thermal Interposer Suitable For
Electronic Modules," and filed 26 Jun. 2013 with the United States Patent
And Trademark Office. The content of this Application is incorporated in
its entirety herein.
[0002] The Present Disclosure claims the benefit of U.S. Provisional
Patent Application No. 61/839,412 (Molex Docket No. B2-022 US PRO),
entitled "Ganged Shielding Cage With Thermal Passages," filed on the same
day as the priority claim listed above, the content of which is hereby
incorporated herein.
[0003] Finally, the Present Disclosure also claims the benefit of
Co-Pending U.S. Patent Cooperation Treaty Patent Application No. ______
(Molex Docket No. B2-022 WO), entitled "Ganged Shielding Cage With
Thermal Passages," filed on the same day as the Present Disclosure, the
content of which is hereby incorporated herein.
BACKGROUND OF THE PRESENT DISCLOSURE
[0004] The Present Disclosure relates, generally, to thermal solutions to
heat transfer of electronic modules, and, more particularly, to a thermal
interposer having improved contact characteristics to improve heat
transfer between an electronic module and a heat sink.
[0005] There are many different styles of heat sinks used in the field of
electronics. In many electronic devices, such as routers, servers and the
like, different sets of circuits need to connect to associated circuits
of other electronic devices. This is commonly accomplished by way of
cable assemblies that typically include an electronic module terminated
to each end of the cable. The modules serve to connect the cable to a
corresponding connector on a circuit board within the device and with
respect to routers and servers, these cable assemblies operate at high
data transfer speeds, the operation of which generates heat.
[0006] Heat sinks are utilized to transfer heat generated by the module to
the exterior of shielding cage in which the module is inserted. Most of
these heat sinks are applied directly to the surface of the module and
thus require particular configuration for each module. Others rely upon a
thermal interface material, referred to as a "TIM," and these TIM
materials increase the thermal resistance of the overall assembly, as
well as the cost. Other heat sinks are rigidly attached by adherent
materials, such as solder, which may add to the overall thermal
resistance and also may affect the structural and mechanical operation of
the attachment. Solder also creates problems with certain materials used
in heat sinks, such as aluminum as oxide barrier may form on the aluminum
during soldering. Still further, due to the dissimilarity of solder with
aluminum, galvanic corrosion may occur in the finished heat sink.
[0007] Some have developed a thermal interposer that utilizes a plurality
of cantilevered contact arms arranged in a pattern on the interposer. The
interposer is rigidly attached to the heat sink by soldering, which
inhibits the contact arms from operating in an elastic manner. This rigid
attachment results in a permanent set across the face of the interposer
and induces plastic strain in the contact arms. This plastic strain does
not promote good Hertzian contact, and diminishes the elasticity of the
contact arms. When this occurs, the normal force between the contact arms
and the opposing surface of the module is reduced.
[0008] The Present Disclosure is therefore directed to an improved thermal
interposer that does not require a continuous rigid attachment and which
is particularly suitable for use with electronic modules, the interposer
having an attachment structure that retains a reliable normal force and
good Hertzian contact between the interposer and the electronic module.
SUMMARY OF THE PRESENT DISCLOSURE
[0009] Accordingly, there is provided a thermal interposer suitable for
electronic module applications, providing a reduced cost structure for
attachment to a heat sink and further providing reliable, beneficial
contact between the interposer and the electronic module. In accordance
with an embodiment of the following Present Disclosure, a thermal
interposer is provided for positioning between a heat sink and an
electronic module and the interposer is provided with a structure that
permits good, reliable contact with both the heat sink and the module,
without the need to use any thermal interface material.
[0010] The interposers of the Present Disclosure are formed from a flat
plate-like member that has a width matching or exceeding to some extent,
the width of the electronic module. On one surface of the module,
preselected, discrete portions of the plate-like member are bent
upwardly. These bent portions define a series of pegs or the like that
are configured to fit within selected grooves, or channels, that are
formed in the bottom surface of a heat sink member. Such a fit is a press
fit attachment accomplished with high mechanical pressure, creating in
effect, a solid joint between the interposer pegs and the heat sink. Such
a joint has low thermal resistance, much lower, and typically minimal, at
best, than that obtained using a thermal interface material. The press
fit application also serves to remove oxides from the aluminum surfaces
of the heat sink grooves which would otherwise increase the thermal
resistance and thereby improves heat transfer between the heat sink and
the module, by way of the interposer.
[0011] The press-fit pegs eliminate the need for a continuous rigid manner
of attachment of the interposer to the heat sink. This is important
because the interposer has a series of cantilevered contact arms stamped,
or otherwise, formed therein and these contact arms have their free ends
bent downwardly toward an opposing surface of the electronic module.
These arms are intended to be elastic and they remain so due to the
press-fit attachment. If the interposer were to be rigidly attached to
the heat sink, such as by way of solder, welding or the like, the solder
would form an attachment to the contact arms, especially near the radius
around which the contact rams flex. The presence of the continuous rigid
attachment would cause the contact arms to become plastic, rather than
elastic, and this condition would inhibit the application of reliable
normal forces by the contact arms onto the module surface.
[0012] The press-fit pegs are arranged in a pattern that separates them
into two distinct groups. A first group of such pegs are arranged around
a portion of the perimeter of the interposer body portion and in one
embodiment described herein, along two opposing, longitudinal edges of
the interposer. The second group of press-fit pegs are disposed interior
of the perimeter and are arranged between adjacent rows of contact arms.
The base portion of the press-fit pegs are arrange longitudinally as are
the contact arms but the press-fit pegs have their base portion oriented
perpendicular to the based portions of the contact arms. In this manner,
as described in one embodiment of the Present Disclosure, a series of
L-shaped heat transfer paths are defined between pairs of associated
press-fit pegs and contact arms.
[0013] These and other objects, features and advantages of the Present
Disclosure will be clearly understood through a consideration of the
following detailed description.
BRIEF DESCRIPTION OF THE FIGURES
[0014] The organization and manner of the structure and operation of the
Present Disclosure, together with further objects and advantages thereof,
may best be understood by reference to the following Detailed
Description, taken in connection with the accompanying Figures, wherein
like reference numerals identify like elements, and in which:
[0015] FIG. 1 is a perspective view of a single electronic module, in
place within one bay of a ganged shielding cage, utilizing an interposer
constructed in accordance the Present Disclosure;
[0016] FIG. 2A is a perspective view, taken from the bottom of the
shielding cage-module assembly of FIG. 1, with the bottom and some of the
side walls of the shielding cage removed for clarity, along with the
bottom half of the electronic module;
[0017] FIG. 2B is the same view as FIG. 2A, but with the electronic module
removed for clarity and illustrating the thermal interposer in place on
the bottom surface of the heat sink;
[0018] FIG. 3A is the same view as FIG. 2B, but with the cage side wall
removed and enlarged to illustrate the array of contact arms formed on
the thermal interposer;
[0019] FIG. 3B is a front elevational view of the thermal interposer in
place upon the heat sink and illustrating the manner of connection
therebetween;
[0020] FIG. 4A is a perspective view of the thermal interposer taken from
the bottom surface thereof;
[0021] FIG. 4B is a perspective view of the thermal interposer of FIG. 4A,
but in an inverted fashion, illustrating the top surface thereof with the
heat sink engaging pegs;
[0022] FIG. 4C is a top plan view of the thermal interposer of FIG. 4A;
[0023] FIG. 4D is a side elevational view of the thermal interposer of
FIG. 4A, along Line D-D;
[0024] FIG. 4E is an end elevational view of the thermal interposer of
FIG. 4A, along Line E-E;
[0025] FIG. 4F is an enlarged perspective view of a single contact arm
used in a known interposer attached to the heat sink rigidly by way of
solder in the shaded area; and
[0026] FIG. 4G is an enlarged view of a contact arm used in the
interposers of the Present Disclosure attached to the heat sink by way of
the attachment members.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0027] While the Present Disclosure may be susceptible to embodiment in
different forms, there is shown in the Figures, and will be described
herein in detail, specific embodiments, with the understanding that the
Present Disclosure is to be considered an exemplification of the
principles of the Present Disclosure, and is not intended to limit the
Present Disclosure to that as illustrated.
[0028] As such, references to a feature or aspect are intended to describe
a feature or aspect of an example of the Present Disclosure, not to imply
that every embodiment thereof must have the described feature or aspect.
Furthermore, it should be noted that the description illustrates a number
of features. While certain features have been combined together to
illustrate potential system designs, those features may also be used in
other combinations not expressly disclosed. Thus, the depicted
combinations are not intended to be limiting, unless otherwise noted.
[0029] In the embodiments illustrated in the Figures, representations of
directions such as up, down, left, right, front and rear, used for
explaining the structure and movement of the various elements of the
Present Disclosure, are not absolute, but relative. These representations
are appropriate when the elements are in the position shown in the
Figures. If the description of the position of the elements changes,
however, these representations are to be changed accordingly.
[0030] FIG. 1 illustrates a partial shielding cage 10 typically mounted to
a circuit board 11. The shielding cage 10 is of the ganged type, meaning
it has a plurality of bays 12 defined therein between side walls 14 of
the cage. Each bay 12 is configured to receive an electronic module 15
therein that provides a connection between a cable containing a plurality
of wires (not shown) and a connector mounted to the circuit board 11 and
disposed within the bay 12 of the cage 10. The electronic module 15 may
be designed for high speed data transmission and as such, generates heat
during its operation. This heat must be dissipated and therefore a heat
sink 16 is provided that either lies on top of the cage 10, or forms a
top wall, or ceiling 17, thereof.
[0031] As illustrated in FIG. 29, an interposer, or leadframe, 20 is
provided for the bay 12 in which the module 15 resides. The module 15 is
shown removed in FIG. 2B, as is the cage bottom, for clarity. The
interposer 20 can be seen to have an elongated body portion 21,
illustrated as a rectangle in the Figures. The interposer has a plurality
of side edges 22a-d that cooperatively define the body portion 21. The
interposer further has two opposing surfaces, shown as top and bottom
surfaces 23, 24, respectively and these surfaces make contact with the
heat sink 16 and the electronic module 15 as explained in further detail
below.
[0032] In order for the interposer 20 to function as a thermal
interposer--that is, one that transfers heat from the module 15 to the
heat sink 16 the interposer 20 is firstly provided with a plurality of
contact members, illustrated as cantilevered contact arms 25 that may be
stamped and formed in the interposer body portion. These contact arms 25
are defined by U-shaped openings 26 formed in the interposer body
portion; three parts of the openings 26 provide the cantilevered
configuration to the contact arms 25. The contact arms 25 have elongated
base portion 27 aligned lengthwise within the interposer body portion 21,
and which terminate in free ends 28, which may be coined, or otherwise
treated, to form. contact surfaces 29 at the free ends. In use, these
contact surfaces 29 make contact with the top surface 15c of the
electronic module 15.
[0033] A plurality of attachment members 30 are disposed on the other
(top) surface of the interposer. These attachment members 30 are
illustrated as press-fit pegs 32 having base portions 33 where they are
bent up from the interposer body portion. These base portions 33
terminate in pointed ends 34 having a generally triangular configuration,
although other configurations may be suitable. The interior attachment
members 30 have U-shaped openings that define their shape and permit them
to be bent out of the plane of the interposer body portion into the
desired upright shape. These attachment members 30 are configured to be
received within grooves 40 formed in the bottom surface 16b of the heat
sink 16. The pointed ends 34 of the attachment members 30 permits the
attachment members to be reliably inserted into the heat sink grooves 40
in such a manner that good and intimate metal-to-metal contact is made,
with good heat transfer capabilities and low thermal resistance
properties, about equal to that Obtained from a solid attachment. Thus,
it is preferred that the attachment members 30 are slightly thicker than
the width of the heat sink grooves 40.
[0034] As shown in the Figures, the grooves 40 run lengthwise within the
heat sink 16 and the spacing between the grooves 40 defines an intended
spacing between the attachment members 30. It can be seen that the
contact arms are arranged on the interposer body portion in a manner that
defines a plurality of rows, running both lengthwise and crosswise
(transversely) within the perimeter of the interposer 20. The attachment
members 30 are arranged in what may be considered as two distinct groups
of attachment members 30. The first group of attachment members 30 are
those that are disposed substantially around the perimeter of the
interposer, shown as positioned on side edges 22a, 22b, 22c in FIG. 4C
and will be referred to herein as an "exterior" group of attachment
members 30.
[0035] The second group of attachment members 30 are those remaining
members disposed inwardly from the side edges of the interposer and will
be referred to herein as an "interior" group of attachment members 30.
The interior attachment members 30 are disposed in rows that are
positioned between rows of contact arms in FIG. 4C. As such, the interior
attachment members serve to divide the contact arms 25 into groups. In
FIG. 4C, two imaginary lines LA and CA are drawn in respective
longitudinal and crosswise directions, interconnecting interior
attachment members for the CA line and both interior and exterior
attachment members for the LA line. The CA lines define crosswise rows of
contact arms, while the LA lines define lengthwise rows of contact arms
25. Cooperatively, the lines define imaginary boxes CAB that surround
groups of contact arms 25. These groups can either be arranged in the
lengthwise or crosswise direction. Likewise, the imaginary lines separate
adjacent contact arms 25 from each other. Still further it is preferred
that the interior attachment members 30 are disposed close to where the
contact arm body portions meet the interposer body portion. As
illustrated, the location of the attachment members 30 with respect to
the contact arms defines a series of individual thermal transfer paths
"TP" between associated pairs of contact arms and attachment members 30.
As shown, the thermal transfer paths are L-shaped.
[0036] The structure of this interposer and the grooves of the heat sink
provide for a semi-rigid attachment of the interposer that differs from
other rigid attachment structures, such as solders. With interposers 20
of the Present Disclosure, heat generated within the module 15 is
transferred to the interposer 20 by way of conduction between the contact
arms 25 and the interposer body portion 21. The heat then travels from
the interposer body portion 21 to the attachment members via the thermal
transfer paths TP, and into the body of the heat sink by way of contact
with the walls of the heat sink grooves 40. Most heat sinks 16 are made
out of aluminum, which is prone to oxidation, and the use of dissimilar
metals promotes galvanic corrosion. The oxidation that occurs on aluminum
surfaces makes soldering difficult and moreover, increases the thermal
resistance of the overall structure, as does any thermal interface
material such as adhesive, tape, gap filling pads, etc. Still further, as
shown in FIG. 4F, a solder attachment method creates problems with the
contact arms of such an interposer in that the body portion of the
interposer and part of the base of the contact arm are attached to the
heat sink as shown in the shaded area of FIG. 4F. Because of this area of
attachment, plastic strains will occur along the entire width of the
contact arm where it is joined to the body of the interposer, at arrow Z.
Deflection of the interposer contact arms in this structure when the
module is inserted into the shielding cage bay will cause plastic strain
and the contact arm no longer becomes entirely elastic. This will
detrimentally affect the normal forces required between the contact arms
and the electronic module top surfaces.
[0037] Utilizing interposers of the Present Disclosure eliminates these
problems. The plastic strains which occur in the interposer contact arms
occur in the body portion 21 of the interposer 20 as shown by Arrow Z in
FIG. 4G, thereby reducing, if not altogether eliminating, permanent set
in the contact arms. This will maintain the normal force applied by the
contact arms in the range desired by the designer to achieve good
Hertzian contact. The attachment between the interposer and the heat sink
is metal-to-metal and thus there is an overall reduced thermal
resistance.
[0038] While a preferred embodiment of the Present Disclosure is shown and
described, it is envisioned that those skilled in the art may devise
various modifications without departing from the spirit and scope of the
foregoing Description and the appended Claims.