Note: Descriptions are shown in the official language in which they were submitted.
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~IOFT~ CED E~EMICONDVCTOR COMPONENT El;AC~RINa
BACXGROUND OF THE INVENTION
The present invention relate6 generally to an improved
thermally conductive and preferably electrically lnsulatlve
interface means for mounting a fully encapsulated semiconductor
device or apparatus onto a mounting ~urface, and more
particularly to 6uch an interface means for providing a thermally
conductive mounting medlum between the ~heath portlon of ~n
encapsulat.ed semiconductor apparatu~ and a chassis mountlng
surface. In accordance with the pre~ent inv~ntion, ~ enhanced
thermal cc,nductance is provided between the encapsulated device
and the mounting surface, particularly through the elimination
and/or reduction of unexpelled, retained, or captùred air between
the individual ~urface~ making up the outer surface of the fully
encapsulated devi~e and its mating mounting ~urface on a chas~is
or the like.
It has long been known that a thermally conductive
interface i~ desirable betw~en a semiconductor devic~ and a
mounting pad such as an electrical cha6sis or the like. In this
connection, an electrically insulative thermally conductiva layer
i9 used a~ a mounting pad between the cha~si~ member and the
6urface of the sheath portion of an encapsulated semiconductor
apparatu~. Such arrangement~, when appropriately de~igned in
connection with the present invention, have been found to enhance
the electrical propertie~ and life of the semiconductor device
without adding significantly to the size and bulk of the
semiconductor device, and without inter~ering with other normal
assembly operation~. The interface per ~e may be applied
directly to a surface of the fully encapsulated semiconductor
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levice, or, alternatively, to the chassis surface or other
surface upon which the semiconductor device is mounted.
Recently, fully encapsulated semiconductor devices have
been widely commercially utilized. In order to provide an
appropriate interface means between the sheath portion of thQ
encapsulat,2d semiconductor apparatus and the chassis mountlng
surface, ~illcone grea~e, or other mean~ have typlcally been
sugge~ted ~o a~ to reduce the occurrence~ and pre~ence of air
which i~ unexpelled, retained or otherwise captured between the
mating mounting surface0. Such retained or captured air provide~
an increased thermal impedance between the encapsulated
semiconductor device or as~embly and the mounting surface, and
hot spots may develop during Qxposure o~ the ~emlconductor device
to certain normally expected and encountered electrical
operational parameter~. The present invention has been found to
reduce the occurrences and presence of retained or captured air
between the mating surface~ of the encap~ulated semiconductor
apparatus and the chassis. In order to achieve this reduction of
retained or captured air, a relatively thin layer of moderately
soft and pliable material is provided, with this layer being
thermally conductive and preferably electrically insulative. The
combination of properties including the selection of cros~-
sectional thicknes~ along with the softnes~ and pliability has
been found to effectively reduce or eliminate the quantity of
retained or captured air, thus improving the thermal properties
of the assembly. The improvement in thermal properties, of
course, expand~ the capability and lifetime of the ~emiconductor
device being utilized in combination with the overall interface
arrangement.
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Th~ combination of physical properties and thickness of
the interfac~ layer have been found to provlde no impediment to
normal a~sembly operations or proces~ing. In other words, the
pre~ence o~ the interface layer does not detract from the
efficacy of normal assembly operationR, nor ha~ lt been ~ound to
add any ~ignificant time to normal assembly operations. Thus,
the interface layer of the present invention is compatible with
those operations normally encountered in typical a~sembly and
proce~sing program~. In order to enhance the thermal conductance
lo between the encapsulated 0emiconductor apparatu~ and the mounting
surface, an interface i8 provided which is both soft and pliable,
and which i6 tough, durabl~ and capable of with~tanding exposure
to those certain a~sembly processes and operations normally
encountered with this type of device.
In order to ach~ove these improved re~ults, c~rtain
properties and/or characteristics are required for the interface
layer. Specifically, the layer is designed to be soft and
pliable, with a thickne6s le6~ of than about lO mils. The
hardne3s of the layer should preerably be between lO and 30
d~rometer on the A-Shore scale. The pliable characteri~tic
permits the reduction and/or ellminatlon of retalned or captured
air, with the thickness being such that good thermal conductivity
is achieved between the sheath portion of the encapsulated
semiconductor device and the mounting surface.
The desirable properties and/or characteristics required
for the interface layer are not readily found in natural-
occurrinq substances. The present invention, therefore, ~esks to
provide this unusual combination of characteristics, including
the physlcal property-of being soft and pliable, along with the
characteristic of thermal conductivity.
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SUMMARY OF THE INVENTION
In accordance with the present invention, a thermally
conductive interface means is provided for interposition between
the sheath portion of an encapsulated semiconductor apparatus and
a mounting surface to enhance the thermal conductivity between
the encapsulated semiconductor device and the mounting surface
wherein the interface means comprises a generally soft pliable
Plastic layer of a synthetic resin, which is, nevertheless,
tough, durable and of low thermal imPedance or resistance.
In this connection, the plastic layer is a synthetic
resin selected from the group consisting fo silicone rubber.
epoxy resin, polyester, and polyurethane. The soft pliable layer
preferably has a hardness of about 10 durometer on the A-Shore
scale, with a range of hardness between 10 and 60 having been
found to be acceptable.
In order to enhance the thermal conductivity of the
material, the resin is preferably compounded with a substance to
enhance such conductivity. In particular, the materials employed
for enhancement of thermal conductivity include such electrical
insulators as alumina, boron nitride, aluminum nitride and
mixtures thereof, mixtures of alumina and boron nitride, finely
divided metallic particles such as finely divided copper,
aluminum, steel or the like. Such materials may be added to the
silicone rubber in an amount ranging from between about 20% to
50% by volume of compound solids, balance resin solids.
Therefore, it is a primary object of the present
invention to provide an imProved interface means for mounting and
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interposit.ioning between the sheath portion of an encapsulated
semiconductor device ancl the mounting surface therefor, wherein
the interface means comprises a generally soft pliable plastic
layer of a 6ynthetic resin having a hardness of between about 10
and 60 durometer, A-Shore scale.
It is yet a further object of the present invention to
provide an interface means for mounting between the sheath
portion of an encapsulated aemiconductor apparatu~ and a mounting
surface therefor, wherein a soft pliable pla~tic layer of
~ynthetic resin i~ provided, with the synthetic resin being
selected from the group con6i~ting of silicone rubber, epoxy,
polyester and polyurethane, and wherein the plastic material iB
filled with finely divided solids to enhance thermal
conductivity.
Other and further objects of the present invention will
become apparent to those skilled in the art upon a study of the
following spec~fication, appended claims and accompanying
drawing.
IN THE DRAWING
Figure 1 i8 a perspective view of a common type of
encapsulated semiconductor device utilized in the past, and
illustratlng a metallic lnterface mean~ in the form of a ground
plane secured to a planar surface of the sheath portion: and
Figure 2 i~ a perspective view of a fully encapsulated
semiconductor apparatus, with the interface means of the present
invention interposed between the sheath portion of the
semiconductor device and the mounting surface therefor; and
Figure 3 is a side elevational vlew of the Pully
encap~ulated ~emiconductor device illustrated in Figure 2, and
illustrating the device mounted upon the ~urface of a typical
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chassis, and with a mounting ~crew being utilized to secure the
device OlltO the chassis surface.
DESCRIPTION OF THE PREFERRED EMBODIMENT
In accordance with the preferred embodim~nt o~ the
present invention, and with particular reference to Figurea 2 and
3 of the drawin~, a fully encapsulated semiconductor apparatus 10
is shown, with the sheath portion being utilized in order to
fully enclose or ~fully encapsulate~ a semiconductor device
therewithin. Specifically, the fully encapsulated semiconductor
apparatus 10 includes a sheath portion 11 from which there are
extendlng conductive tab members 12-12. The nut ~nd bolt
comblnation 14 couples semiconductor apparatus 10 to ba~e
mounting plate or chassis 15. As a still further mounting means,
a mounting clip may be employed to mechanically bia~ the
sem$conductor device against the surface of the chassis.
Encapsulated semiconductor devices and/or apparatus of the type
illustrated in Figures 2 and 3 are, of course, commercially
available.
With continued attention being directed to Figures 2
and 3, interface means 16 is provided which i8 di~posed along the
base portion of fully encapsulated ~emiconductor apparatus 10.
Interface means 16 i~ in the form of a generally soft pliable
plastic layer or pad of a synthetic resin substance selected from
the group consisting of silicone rubber, epoxy, polyester and
polyurethane, preferably filled or compounded with a thermally
conductive particulate solid such as alumina, boron nitride,
mixtures of alumina and boron nitride, aluminum nitride, or
finely divided metallic particles. Layer 16 LB, in turn,
uniformly bonded to a planar surface of the sheath portion 11 of
the encapsulated semiconductor device lO. In order to provide
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for and facilitate sub~equent ~sembly proce~es~ adhe~31ve layer
17 may be utilized over the outer ~urface of interfacn layer 16.
The outer surface of inter~ace layer 16 may he coated with a fllm
of adhesive in order to facilitate bonding to the sur~ace of a
chassis or other mounting member in lieu of the nut and bolt
combination 14 as illustrated in Figure 3. Suitable adhesives
such as pressure sensitive adhesives, thermally actuated
adh~sives or solvent based adhe~ives may be u~d. A releasQ film
for covering the pressure ~ensitive adhesive film when utilized
lo may be employed. Such adhesives such as the pressure sensitiYe
adhesives are, of course, commercially available.
With attention being directed to Figure 3 of the drawing,
semiconductor device 10 is shown mounted upon the surface of
chassis 15, with layer 16 forming the interface between the
encapsulated semiconductor device 10 and chas~is 15 being shown
in place. As indicated, the layer 16 is formed in place on the
surface of encapsulatiny sheath 11, and thus neither impedes nor
otherwise restricts or retards the assembly processes and/or
operations normally encountered with this type of device.
When utilized, adhesive layer 17 provlde~ for ~ufflclent
adhesion and cohe~lon so as to provlde a system o~ approprl~te
strength and durabllity. The thickne~ is, as lndicated, A~
small as possible, preferably less than about 0.7 mil so as to
provide little, if any, impedance or re~istance to thermal
conductance. The softness characteristic or property of the
layer, which is preferably in the range of between 10 and 30
durometer on the A-Shore scale, is adequate to reduce the
presence and~or occurrences of captured, retained, or unexpelled
air and it is this f~ature which provides for the advantageous
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characteri~tics of the system. Durometer hardness on thls scale
ranging from between 10 and 60 have been found suitable.
In the preferred embodiment, layer 16 consists of
silicone rubber, having a thickness of between about 5 and 10
mils. Such a thickness has been found to provide adequate
pliability so as to reduce the presence of retained or captured
air, along with adequate mechanical toughness without detracting
from the electrical integrity of the overall device.
ALTERNATE PREFERRED EME30DIMENT
In an alternate preferrQd embodiment, laver 16 iB form~d
in place on the eurface of mounting ~urface or cha6si~ 15, and i5
deslgned to receive the encap~ulated semlconductor device 10
thereon. In such an arrangement, therefore, the interface film
is applied directly to the outer surface of cha6sis 15. In a
subsequent ae6embly operation, therefore, sheathed semiconductor
devices are mounted in place in a configuration consi6tent with
the requirements of the assembly. Other feature~, ~uch a~
interface thickne6s and properties remain the eame as previously
~et forth.
As indicated in Figure 1, the conventional transistor
and/or other semiconductor utilized in the past employs a
metallic ground plane for direct contact with the cha~sis. In
certain applications, however, the utilization of such a metallic
member renders it difficult to achieve a fully uniform and fully
contacting pair of mating surfaces. In such instances, the
uneven characteristics or non-planar characterietic~ of the
metallic member of the semiconductor device and/or the chassie
member reduces the area of contact between the metallic pad
member oP the ~emiconductor device and the surface of the
mounting chas~is.
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It will be appreclated that thoee skilled ~n the art may
depart from the example ~iven hereinabove without departing from
the spirit and scope of the present invention.
What is claimed is:
