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SHOCK HARDENED MOUNTING AND COOLING OF A 
SEMICONDUCTOR DEVICE 



RIGHTS OF THE GOVERNMENT 
[0001] The invention described herein may be manufactured and used by or for the 
Government of the United States for all governmental purposes without the payment of any 
royalty. 



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BACKGROUND OF THE INVENTION 
[0002] In a series of three issued U.S. Patents we have heretofore described the 
environment incurred by military munitions devices during their ballistic termination 
encounter with a target, particularly a hardened target. We have also discussed in these 
patents the frequent need to study events attending this terminal encounter from of course 
a safely remote location. These three issued patents are identified as U.S. 6,380,906; 
6,453,790 and 6,456,240 all of which became known during the year 2002 and all of which 
are hereby incorporated by reference herein. It is believed helpful in appreciating these 
three patents as well as the present invention to recognize that the use of moderate power 
radio frequency communication apparatus in an environment calling for its shock 
hardening against large physical stresses represents a combination in the technical arts 
that has remained largely unexplored until recent years. It is possible to attribute this 
unexplored status to the fact that moderate power radio frequency communications, the use 
of class U C" nonlinear amplifier stages in such communications and the shock hardening 
aspects of such apparatus have each been considered to lie in the black art or empirical 
design arenas and therefore have either been avoided whenever possible or explored in 
secrecy. Our inventions are believed to represent part of an emergence of this technology. 

[0003] The occurrence of deceleration forces measuring in the tens of kilo-G or in 
excess often thousand times the force of gravity during a target encounter event i.e., during 
a probable time of remote study interest, is of course one of the major components of a 
target encounter environment to be expected in this technology. Another component of this 
environment is of present interest and concerns a need to limit the temperature excursion 
incurred in a power semiconductor device employed in communicating data from the 
moving munitions device to a safely remote location e.g. to limit temperature in a transistor 
or integrated circuit device included in a telemetry transmitter apparatus embedded in the 
munitions device. An additional aspect of this environment is the need to limit the physical 
size and weight of components associated with the invention in order to make them 
compatible with the space and weight limitations imposed on a ballistic munitions device 
and the incurred G forces at impact. A yet additional aspect of this environment is the 
frequent need for a low impedance electrical connection between one or more terminals of a 
mounted electrical device and a true ground node of the employed electrical circuit. 

[0004] The present invention is believed to contribute additional knowledge to the 
art of accomplishing data communication under these unusual environmental conditions 



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and in fact provides a frequently needed component that can be beneficially used in such 
systems as the communication apparatus described in the incorporated by reference herein 
patents. The invention is not however limited to use in such environments and may in fact 
provide utility in other environments including for example routinely encountered static 
semiconductor device applications. 

[0005] The present invention therefore addresses the need to mount for example a 
semiconductor device in order to assure both its physical integrity and its safety from 
thermal damage during a brief but nevertheless high stress interval of usage. In a 
situation typical of the presently described military munitions study environment an 
involved semiconductor device can be for example of the field effect transistor type as is 
used in the final amplifier stage of a ultra high radio frequency or very high radio frequency 
transmitter apparatus that receives energization for one quarter of a second during an 
actual use event extending from before to during an impact of the munitions device with a 
target. This semiconductor device may also be of the integrated circuit, power diode or 
other types of semiconductor devices and the invention may in fact also find utility in the 
mounting of non-semiconductor devices such as power dissipating resistive components and 
heat dissipating electromechanical devices. 



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SUMMARY OF THE INVENTION 

[0006] The present invention provides a thermally effective G-force tolerant, space 
and weight conserving and low electrical impedance mounting for a semiconductor device or 
other energy-dissipating component of an electrical apparatus. 

[0007] It is therefore an object of the present invention to provide an impact 
resistant mounting for a thermal energy dissipating electrical device. 

[0008] It is another object of the present invention to provide an impact resistant 
mounting for a thermal energy dissipating electrical device usable in the space and weight 
limited environment of a ballistic munitions device. 

[0009] It is another object of the invention to provide an impact resistant mounting 
for a thermal energy dissipating electrical device that also enables achievement of a low 
electrical impedance between the mounted electrical device and a true ground node of an 
attending electrical circuit. 

[0010] It is another object of the invention to provide a physically robust mounting 
for a plastic encapsulated semiconductor device. 

[001 1] It is another object of the invention to provide a mounting arrangement for a 
semiconductor device that benefits from both heat absorbing and heat dissipating 
characteristics. 

[0012] It is another object of the invention to provide a physically robust mounting 
for a pulse operated semiconductor device, a mounting having thermal capacity to absorb 
pulse related energy before significant conduction to a dissipating surface can commence. 

[001 3] It is another object of the invention to provide a physically robust mounting 
for a pulse operated semiconductor device that can in time conduct thermal energy to 
surrounding conductors such as an array of printed circuit board traces. 

[0014] It is another object of the invention to provide a physically robust mounting 
for a pulse operated semiconductor device that achieves physical shock immunity through 
use of relatively large mounting elements and surfaces. 

[0015] It is another object of the invention to provide a mounting arrangement for a 
relatively small semiconductor device of the SO-8 package size. 

[0016] It is another object of the invention to provide a small semiconductor device 
mounting arrangement that may be conveniently expanded, possibly in standard size 
increments, to accommodate larger semiconductor devices. 



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[0017] It is another object of the invention to provide a heat sinking arrangement for 
a semiconductor device that also provides desirable electrical conductivity for electrical 
currents originating in said semiconductor device and in physically adjacent electrical 
circuits. 

[0018] It is another object of the invention to improve the state of the electrical art 
with respect to impact resistant radio frequency energy sources of higher operating 
frequency and moderate operating power capabilities. 

[0019] It is another object of the invention to provide a semiconductor device 
mounting arrangement that is readily fabricated from common materials. 

[0020] It is another object of the invention to provide a semiconductor device 
mounting arrangement that uses soldering techniques in achieving a combination of 
thermal conductivity, electrical conductivity and structural integrity. 

[0021] It is another object of the invention to provide a semiconductor device 
mounting arrangement that provides both intra surface and inter surface via electrical 
conductor functions for a printed circuit board. 

[0022] It is another object of the invention to provide a semiconductor device 
mounting arrangement that is comparable to a shirt cuff-link in both physical size and in 
mounting arrangement. 

[0023] These and other objects of the invention will become apparent as the 
description of the representative embodiments proceeds. 

[0024] These and other objects of the invention are achieved by impact resistant 
semiconductor device mounting and cooling apparatus comprising the combination of: 

[0025] a printed circuit board having electrical conductors arrayed on first and 
second surfaces thereof and having a shaped transverse opening located in a selected 
portion thereof; 

[0026] an integral metallic heat sink member of first cross section shape conforming 
with said printed circuit board shaped transverse opening and disposed within in said 
transverse opening; 

[0027] said integral metallic heat sink member having a second cross sectional 
shape orthogonal of said first cross sectional shape and inclusive of a wing element portion 
extending along said printed circuit board first surface; 

[0028] said integral metallic heat sink member having a third cross sectional shape 
orthogonal of both said first cross sectional shape and said second cross sectional shape and 



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including a recessed saddle portion parallel with said printed circuit board along a first 
cross sectional extremity and a grooved recess parallel with and adjacent said printed 
circuit board second surface along a second cross sectional extremity. 



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BRIEF DESCRIPTION OF THE DRAWINGS 

[0029] The accompanying drawings incorporated in and forming a part of the 
specification, illustrate several aspects of the present invention and together with the 
description serve to explain the principles of the invention. In the drawings: 

[0030] FIG. 1 shows an enlarged perspective view of a miniature heat sink element 
for a semiconductor mounting arrangement in accordance with the present invention. 

[0031] FIG. 2 shows a dimensioned end view of a FIG. 1 heat sink element. 

[0032] FIG. 3 shows a mounting arrangement for a FIG. 1 and FIG. 2 depicted heat 
sink element. 

[0033] FIG. 4 shows a dimensioned elevation view of a FIG. 1 - FIG. 3 heat sink 
element. 

[0034] FIG. 5 shows a top view of a FIG. 1 - FIG. 4 heat sink element. 
[0035] FIG. 6 shows a top view of a FIG. 1 - FIG. 5 heat sink element with a 
mounted semiconductor device received thereon. 



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DETAILED DESCRIPTION OF THE INVENTION 
[0036] FIG. 1 in the drawings shows an enlarged perspective view of a miniature 
heat sink element 100 of a semiconductor mounting arrangement in accordance with the 
present invention. As shown in the FIG. 1 drawing the heat sink 100 may be considered to 
be of a generally Tee shaped cross sectional configuration (as viewed from its FIG. 1 right or 
left most ends), and to include the tee stem portion 102, the tee stem depth portion or 
saddle - inclusive portion 104 and the pair of integral transverse wings or tee arms shown 
at 106 and 108. The FIG. 1 heat sink is preferably composed of gold or copper or some other 
metal of good thermal and electrical conductivity. Although the metal aluminum is often 
considered to have such thermal and electrical characteristics, and is indeed a suitable 
material for some uses of the present invention heat sink, copper or some metal providing 
desirable soldering characteristics is preferable for incorporating the FIG. 1 heat sink into 
the circuit assemblies described in the ensuing paragraphs herein and most uses of the 
invention. 

[0037] FIG. 2 in the drawings shows an end view of the FIG. 1 heat sink element 
together with representative or typical dimensions for such a heat sink element as utilized 
in the pulsed low electrical duty cycle and high impact forces environment described herein. 
Notably the FIG. 3 heat sink element (herein simply "heat sink") includes a pair of wing- 
like elements 201 that are received on top of a tee section heat sink tee stem or body 
element 202 to form a tee-like structure when viewed from an endmost viewpoint. The 
FIG. 3 heat sink also includes a slot-like cut 204 usable in holding the FIG. 2 structure 
securely in a printed circuit board in order to achieve an impact-resistant assembly. The 
preferred direction of the applied impact forces is indicated at 206 in the FIG. 2 drawing, 
the most preferred direction of this force being in the downward direction of FIG. 2; the 
FIG. 2 structure is also found to have substantial impact force tolerance in other directions 
appearing in the FIG. 2 and FIG. 4 drawings. 

[0038] As indicated by the dimensions appearing in the FIG. 2 drawing the heat 
sink element of the present invention is typically made to be of a rather small physical size, 
a size that is actually comparable with for example a naturally occurring individual peanut 
or cherry pit or shirt cuff-link. This small physical size and the attending relatively small 
physical mass are of course helpful in limiting the magnitude of the large physical force 
received by the heat sink during a target impact event, an event such as a smart munitions 
device encountering a hardened target. In this regard it may be recalled that the force F, 



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generated during a physical deceleration of a moving physical mass M, at a rate A, is 
predicted by the familiar Newtonian physics mathematical relationship of F = M A or that 
the generated force is directly proportional to the amount of mass and its rate of 
deceleration; the force F in the environment of the present invention is contemplated to be 
as great as that produced by an acceleration A, of some fourteen thousand (14,000) times 
the force of gravity. 

[0039] Equally important with respect to the present invention the small physical 
size of the FIG. 1 - FIG. 4 heat sink is compatible with the physical size of a family of 
semiconductor devices that are convenient for use in the electronic circuits embedded in a 
present day smart munitions device — electronic circuits such as a radio frequency energy 
generating- telemetry transmitter or a warhead fuse circuit such as a hard target penetrator 
fuse. In particular the FIG. 2 and FIG. 3 represented dimensions are compatible with the 
industry standard eight pin or SO-8 plastic package that is often used to contain a single 
field effect transistor semiconductor device or a small integrated circuit device. The SO-8 
package may for example be conveniently used to contain the 30 watt-rated radio frequency 
field effect transistors made by Polyfet Devices of Camarillo, CA. Such transistors have for 
example proven to be desirable for use in the class "C" final amplifier stage of a 300-500 
megahertz telemetry transmitter used in the manner discussed in the above incorporated 
by reference herein patents in our smart munitions development work. When provided 
with the heat sink of the present invention this 30 watt transistor is found to be capable of 
generating a somewhat surprising 42 watt level of radio frequency energy with an overall 
power in to power out efficiency near seventy percent in the short duty cycle environment 
characterized by a munitions device telemetry transistor. (A munitions device telemetry 
transistor can for example be thought of as having an actual in-use operating life 
measurable in milliseconds of time up to about one quarter of a second; however 
transmitter tuning and other human interventions often extend the required operating 
time to at least an integral number of seconds. The heat sink and mounting arrangement 
of the present invention of course should preferably accommodate the full extent of such 
duty cycle possibilities.) 

[0040] Returning now to the description of the present invention heat sink as 
provided in the FIG. 1 through FIG. 4 drawings, FIG. 3 in these drawings shows how the 
FIG. 1 and FIG. 2 heat sink 100 may be mounted in a printed circuit board 302 during for 
example fabrication of the above-described telemetry transmitter. In the FIG. 3 cross 

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sectional view drawing the wing 201 portions of the heat sink 100 are shown to be received 
on the top most surface of printed circuit board 302 while the body or tee leg portion 202 of 
the heat sink passes through an aperture 304 of appropriate rectangular configuration that 
has been pre disposed in the printed circuit board 302. The relationship of the heat sink tee 
stem portion 202 with the aperture of the printed circuit board 302 may be, for discussion 
convenience, likened to the relationship of a cuff link with the shirt cuff it retains. As 
called-for by this analogy the heat sink tee stem 202 passes through the printed circuit 
board 302 and is retained in this position by an attached but movable orthogonal member 
engaged within slot 204 and soldered over all possible surfaces. 

[0041] The printed circuit board 302 may be made to have a thickness of 0.062 inch 
or 1/16 of an inch and may be made from the fiberglass - resin composite material 
identified as FR-4/G10 by its many manufacturers and also by Military Specification. This 
thickness dimension is compatible with and is actually an extension of a convenience 
concept by which dimensions for the FIG. 1 through FIG. 4 heat sink are assigned in one 
sixteenth of an inch-compatible measurement units; units that are a number of increments 
of printed circuit board thickness. Such units are in fact also compatible with the 
dimensions to be expected in a segment of transmission line of the fifty ohm characteristic 
impedance "strip line" type. Other measurement units may of course be used with the 
present invention, including measurements convenient to the metric system when 
appropriate. The FR4 printed circuit board material is generally said to be usable up to a 
frequency of some 500 megahertz and is therefore suited to the 300-500 megahertz band of 
operation of the herein often referred-to telemetry transmitter. For munitions telemetry 
usage the printed circuit board 302 may have some unusual lateral shape such as the shape 
of a crescent in order to for example be conveniently fitted into space available in the 
trailing end portion of a munitions device. A crescent space of some one inch by one inch 
cross sectional size and radius between five and 14 inches has, for example, been used to 
contain a telemetry transmitter printed circuit board of this configuration in some of our 
experimental work. 

[0042] Also appearing in the FIG. 3 drawing is an end view or cross sectional view of 
a locking plate or keeper member or flange member 300 used to retain the heat sink 100 
captive in the printed circuit board 302. The keeper or flange member 300 preferably 
engages the slot 204 of the body or tee leg 202 in a manually inserted but snug fit that is 
ultimately fixed into permanence by a flowing solder attachment to the heat sink 100 as is 



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described in detail in paragraphs following herein. Two of the slots 204 are disposed in the 
heat sink body 202 as may be best appreciated in the FIG. 4 drawing view. These slots 204 
may be cut to 0.025 inch top to bottom dimension in FIG. 3 (to mate with 0.250" x 0.500" x 
0.024" thick copper sheet material keepers) and to a depth of up to 0.030 inch into the heat 
sink body; desirably such cutting is accomplished by way of a saw cut. Preferably two of the 
keeper or flange members 300, one at each end of the heat sink body portion 202, are used 
with the slots 204 in order to retain the heat sink 100 captive in the printed circuit board 
302. The slots 204 may of course be extended around the total periphery of the heat sink 
body 202 and thus engaged by additional keeper or flange members of appropriate length in 
order to increase the engagement area of the slot or keeper members with the printed 
circuit board surface and achieve greater impact resistance tolerance when needed. 

[0043] The keeper or flange members 300 are preferably made of sufficient lateral 
surface size as to provide the heat sink 100 with a significant capability of resisting impact 
forces directed upwardly in the FIG. 3 drawing. Soldering of the keepers or flanges 300 as 
well as the wing-like elements 200 to printed circuit board conductors on each side of the 
printed circuit board 302 also adds to the impact resistance of the installed heat sink 100 
and also to the heat conduction capability of the assembly. The keeper or flange members 
300 may be made of the same material such as copper as the heat sink body portion 202 or 
alternately of some other, preferably solder-capable, material such as brass where greater 
hardness and resistance to impact force bending is needed. 

[0044] FIG. 4 in the drawings shows a dimensioned elevation view of the FIG. 1 heat 
sink element 100 as it is tailored to receive a semiconductor device contained in the above- 
described eight pin SO-8 size package. From the FIG. 4 view it may also be appreciated 
that the heat sink of the present invention need not be limited to this SO-8 package and 
may for example be easily extended to the sixteen pin SO-16 package or to other types and 
other sizes of package, including packages intended for non semiconductor device usage for 
example. For use with the SO-16 package for example the 0.2 inch saddle width dimension 
shown in FIG. 4 may be merely doubled to 0.40 inch and the overall width shown in FIG. 4 
increased to 0.525 inch. Again other dimensions are entirely possible when attended by 
accommodation of the resulting changes in heat sink mass, thermal conductivity and other 
characteristics. 

[0045] The wings 201 used to retain the heat sink 100 on the top surface of printed 
circuit board 302 in the FIG. 3 drawing appear at the upper right and left in the FIG. 3 



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view. The wing dimensions as shown in FIG. 2 are compatible with the printed circuit 
board thickness dimension 0.062 inch units of measure already described herein. When 
made in accordance with these dimensions the heat sink tee leg portion lies 1/3 within the 
printed circuit board 302 in the FIG. 3 drawing and 2/3 extending below the printed circuit 
board. For space and mass conservation purposes it may be desirable to limit the extent of 
this 2/3 extension by either pre assembly or post assembly shortening of the tee leg portion. 
Similarly shortening may be applied to the wing dimensions shown in FIG. 2 where mass 
and size limitations are imposed and sufficient surface area contact remains with the 
printed circuit board to dissipate the encountered impact force. The overall heat sink depth 
dimension of 0.325 inch shown in the FIG. 4 drawing is also compatible with the 0.062 inch 
unit of measure arrangement and is selected in accordance with the SO-8 device package 
size usage of the illustrated heat sink. 

[0046] The space intermediate the wings 201 in the FIG. 4 drawing, i.e., the space 
400 where the semiconductor device package is received, may be referred-to as the heat 
sink saddle area and is arranged to provide the lowest possible thermal resistance between 
a mounted semiconductor device and its ultimate thermal energy dissipation media. This 
lowest possible thermal resistance is achieved by way of the substantial surface area 
available in the saddle region area 400 for receiving heat from the semiconductor device 
and the contemplated low thermal resistance connection established in the saddle area with 
the semiconductor device i.e., the connection established at the surface 406 in FIG. 4. 
Although silicone paste based heat conducting media as commonly used in the electronics 
industry may be used in the saddle area 400 to make an effective thermal connection with a 
semiconductor device the completely metal connection described below herein is preferred 
because of its lower thermal resistance. Indeed many of the characteristics of the present 
invention heat sink are arranged in contemplation of this all-metal connection. 

[0047] The substantial cross sectional area of the wings 201 and the resulting ability 
of these elements to conduct heat away from the saddle area 400 may be appreciated in 
both the FIG. 4 and FIG. 5 drawings. This substantial wing cross sectional area of course 
also contributes to the thermal mass of the heat sink 100 and is thereby of significant 
temperature limiting benefit in the short duration or pulse operated environment of the 
munitions device telemetry function contemplated in the referred-to application of the 
present invention heat sink. The substantial wing cross sectional area also is effective to 
communicate saddle area heat to the copper or other conductor material located on the 



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upper surface of the printed circuit board 304 - especially in view of the preferred use of 
solder between the lower wing surface and the printed circuit board conductor. A top view 
of the saddle area 400 of a present invention heat sink and the adjoining wings 201 appears 
in the FIG. 5 drawing. The lines appearing at 408 and 410 in FIG. 4 may at first blush 
appear to be portions of or extensions of the saddle area 400 and the saddle surface 406. 
Actually however these lines 406 and 408 represent the intersection of the lower surface of 
the wings 201 with the heat sink body portion 202 and thus merely happen to coincide with 
the elevation of the saddle surface 406 in the illustrated embodiment of the invention. 

[0048] A top view of a packaged semiconductor device 600 mounted in the saddle 
area 400 of a present invention heat sink appears in the FIG. 6 drawing. Also appearing in 
the FIG. 6 drawing are the leads 602, 604 606 and 608 by which the semiconductor device 
600 is later to be electrically interconnected with other elements of a telemetry transmitter 
or other circuit utilizing the present invention heat sink. In the case of a single transistor 
being contained in the saddle 400-mounted semiconductor device, one pair of leads such as 
leads 604 and 606 on each side of the semiconductor device 600 may be commonly 
connected both within and external of the semiconductor device 600. Actually SO-8 
transistor packages normally include four leads on each side of the transistor package 
however in the case of one transistor used with the present invention heat sink, four of the 
resulting leads are also common to the transistor source electrode and the metal window 
area of the SO-8 package described in ensuing paragraphs herein and therefore may be 
removed before transistor mounting. Notably the direct connection of a transistor source 
element to the metal of the window area 610 as espoused herein, in addition to providing a 
good thermal path for transistor heat also provides a desirably low electrical inductance 
path for the transistor's source current to follow. Passing such current through the 
inductance of bond wires normally disposed within a transistor package can be quite 
detrimental to the operation of a transistor amplifier functioning in the 300 - 500 
megahertz frequency region. 

[0049] Before departing from the saddle area 400 and its containment of the 
mounted semiconductor device 600 it is also desirable to consider that the arm or wing 
elements 201 as shown in the FIG. 6 drawing provide additional support and stabilization 
for the semiconductor device 600 in the saddle 400 by way of the physical abutment 
occurring at 612 and the other similar locations in FIG. 6. By way of this physical 
abutment the semiconductor device 600 is restrained from motion in at least one direction 



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even though the shock and shock excited vibration arising from a target impact event may . 
be sufficient to stretch the metal located within the window area 610 or otherwise establish 
vibrations in the semiconductor device, the printed circuit board and the heat sink 
structures. This physical abutment restraint is usually solder filled, but may be assisted by 
adding other suitable filler materials such as an organic sealer or a hardenable substance 
such as an epoxy between the semiconductor device surface and the adjacent surface of the 
arm or wing elements 201. 

[0050] The heretofore discussed drawings of FIG. 3, FIG. 4 and FIG. 6 may also be 
though of as representing three different cross sectional views of the present invention heat 
sink, three cross sectional views that are each oriented mutually orthogonal with respect to 
the remaining two views of the heat sink. Cross sectional shading is omitted in all but the 
FIG. 3 of these potential cross sectional views for convenience and clarity purposes. The 
arrows at 110, 112 and 114 in the FIG. 1 drawing show directions of viewing that are 
appropriate for these three different cross sectional views and are identified with one 
possible set of cross sectional view identification numbers. Other cross sectional view 
identification number ordering may of course be assigned as desired. A cross sectional 
interpretation of the FIG. 3, FIG. 4 and FIG. 6 drawings is believed helpful in 
understanding the formal description language relating to the invention included in the 
attached claims. 

[0051] The enclosed dotted line window area at 610 in the FIG. 6 drawing of a SO-8 
package-contained semiconductor device represents the outline of a lower face exposure 
metal panel window of the semiconductor device 600. In some transistor types such as in 
the Lateral Drain Metal Oxide Silicon (LDMOS) transistor this metal window is in fact 
physically and electrically connected with one transistor element, such as the transistor 
source element, of a transistor received in the saddle-mounted device package 600 (i.e., the 
transistor layers are fabricated on the top surface of the metal window area 610 with for 
example the transistor source electrode being both formed on and connected with the 
window metal; package enclosure material is added to the transistor after this fabrication). 
This transistor fabrication arrangement enables the transistor within the dotted line 610 to 
be intimately connected electrically and thermally with the transistor package window 
metal. Notably such intimate connection also continues into the saddle area in the present 
invention heat sink and moreover allows for the transistor metal to heat sink connection to 
be accomplished by way of metallic soldering-in order to obtain the lowest possible thermal 



14 



resistance in the transistor heat dissipation path. A metal to metal connection, even when 
accomplished by way of tin/lead solder, is of course far superior to an insulated connection 
(as often accomplished with a mica washer and silicone grease for example) in its low 
thermal resistance and heat transferring ability. 

[0052] Fabrication of transistor layers on the top surface of the window area defined 
by the dotted line 610 and direct connection of this window area to the heat sink 100 also of 
course provides the desired lowest possible electrical resistance and electrical impedance 
between a transistor electrode and the true ground node of the electrical circuit utilizing 
the transistor. The direct soldering connection of a metal transistor fabrication substrate to 
the heat sink of the present invention of course entails heating of the semiconductor layers 
of the transistor to solder flow-promoting temperatures for at least the short interval of a 
soldering event. The resulting semiconductor device temperatures, temperatures in the 500 
to 600 degrees Fahrenheit or 260 to 315 degrees Centigrade range when eutectic-proximate 
tin/lead solder is used, appear to be satisfactorily tolerated by at least silicon semiconductor 
devices. Semiconductor devices made from gallium arsenide and germanium and other 
semiconductor materials may be threatened by temperatures of this range and thereby may 
call for the use of threaded fasteners or thermally conductive adhesives or other lower 
temperature attachment arrangements at the semiconductor device to heat sink interface 
in the present invention. 

[0053] Soldering may be used to electrically connect the wings 201 of the FIG. 1 and 
FIG. 2 heat sink 102 into the topside printed circuit board electrical circuit and thus 
enables use of the wings 201 as printed circuit board surface mounted conductors, i.e., as 
conductors communicating between other topside conductors of the printed circuit board or 
topside to bottom side communication conductors. This heat sink conductor concept thus 
enables the tee stem body 202 of the heat sink to communicate electrical currents and 
thermal energy through the printed circuit board 302. The electrical conduction of these 
conductive attributes in fact represents a significant attribute of the present invention, i.e., 
such conduction may be attributed to the general principle that the present invention heat 
sink adds significant via conductor capability to a printed circuit board in which it is 
installed. This via conductor ability may especially be observed, by way of the large cross 
sectional areas involved, to be significantly more effective than the usual plated through or 
otherwise arranged circular via holes in connecting front side printed circuit board 
conductors with backside conductors. Good via conductors are of course of significant 



15 



assistance in obtaining the desired performance from a circuit operating in the presently 
considered 300-500 megahertz frequency band. As has been stated in one corollary to the 
familiar Murphy's law, nothing is so effective in turning an amplifier circuit into an 
oscillator circuit as a small amount of inductance in a ground path. 

[0054] Fabrication of the FIG. 1 heat sink element 100 in the present semiconductor 
device mounting arrangement invention may be accomplished through use of an individual 
molding or casting sequence that is tailored for the preferred copper or copper inclusive 
material. Other materials such as brass or possibly aluminum may also be used for the 
heat sink and fabricated by these processes. Aluminum is however difficult or impossible to 
solder using at least conventional tin/lead processes and the electrical and thermal 
conductivity of both brass and aluminum is somewhat lower than that of the preferred 
copper metal. In addition use of such molding or casting processes can result in metal grain 
structures characterized by lower thermal and electrical conductivity than is achieved with 
other fabrication arrangements and can result in exterior heat sink surfaces that are 
sufficiently rough as to require smoothing for achieving effective thermal and electrical 
contact with a semiconductor device package. In view of these limitations therefore the 
preferred arrangement for fabrication of at least small quantities of the FIG. 1 heat sink is 
through use of machining commenced with conventional rolled soft copper bar stock. 

[0055] During such individual heat sink element machining it is possible to 
commence with a billet or blank or having the overall 0.25 by 0.25 by 0.325 inch dimensions 
shown in the FIG. 2 and FIG. 4 drawings and to then perform milling machine or other 
machine-tool cutting operations to remove metal from the areas 208 and 210 identified in 
the FIG. 2 drawing and from the saddle region 400 defined in the FIG. 4 drawing. 
Alternately it is also possible to commence fabrication of the heat sink 100 with a length of 
bar stock. Such stock may be first machined and then severed into individual heat sink 
element lengths or severed first and then machined to achieve the illustrated shapes. 
Notably a simple straight three-cut or four-cut straight line machining sequence is 
sufficient to achieve FIG. 1 represented shape using this individual heat sink element 
machine tool fabrication process. Moreover at least two of these machine cuts can be 
performed on a multiple heat sink blank wherein the individual heat sink elements are 
taken from the blank by segregation of adjacent heat sink surfaces 402 and 404 as are 
shown in the FIG. 4 drawing. A small milling machine such as a computer-controlled 
machine is convenient in performing these machining steps. In view of the well known 



16 



chip-reattachment properties and chip pile difficulties encountered in machining metallic 
copper stock it is well to include a degree of patience or hesitation in the heat sink 
machining operations. 

[0056] It is also feasible to machine the FIG. 1 heat sink elements from a multi 
element blank or billet in which the individual heat sink elements are originally adjacent at 
the surfaces 212 and 214 in the FIG. 2 drawing—through use of a sawing or other cutting 
segregation procedure. Machining in this manner enables single cut formation of the slot 
like cuts 204 and the saddle regions 400 in a plurality of heat sink elements. Additionally 
it is of course also possible to machine the FIG. 1 heat sink elements from a multi element 
blank or billet in which the individual heat sink elements are originally adjacent at the 
surfaces 216 and 218 in the FIG. 2 drawing~by use of another sawing or cutting 
segregation sequence. As may be observed from this number of fabrication possibilities the 
optimum method of fabrication is perhaps best defined by available equipment rather than 
by limitations of the fabricated heat sink. 

[0057] The relatively small size and mass of the present invention heat sink element 
also lends to the use of a screw machine or punch press die fabrication process to meet 
larger quantity heat sink needs. Rearrangement of the described configuration of the heat 
sink can make use of such equipment easier while maintaining the underlying function of 
the device. 

[0058] The significance of a well considered heat sink in critical electrical circuitry, 
such as in many moderate power radio frequency circuits, may perhaps be better 
appreciated by recognizing that some of the large semiconductor manufacturers have 
recently adopted the practice of selling their moderate and large power radio frequency 
semiconductor devices with a factory installed heat sink already mounted in place. 
Although this practice limits a user's freedom to employ the semiconductor device in 
unusual physical arrangements it has doubtless been found helpful in assuring the 
achievement of adequate cooling and limiting heat-associated semiconductor device 
problems. The large and fixed shape of such semiconductor device plus heat sink 
combinations almost universally prohibits their use in our munitions related work; 
especially when the impact loading forces of our environment are considered. This is 
perhaps another illustration in support of our belief that the combination of impact loading 
and moderate radio frequency power in a single electrical circuit is a specialized area that 
has received little attention in the electronic art. 



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[0059] The present semiconductor device mounting invention is therefore believed to 
improve the art of impact hardened and moderate radio frequency energy electrical circuits; 
some of the more significant advantages provided by the invention may be summarized as 
follows. 

Downward movement of the mounted semiconductor device is restricted by 
wing-bars received on top of the receiving printed circuit board; 

Upward movement of the mounted semiconductor device is restricted by 
plates received in semiconductor body slots; 

Bars and interlocking plates are soldered to an available 2-side plated 
printed circuit board; 

Heat transfer is above, through and below the preferably copper printed 
circuit board 

Low inductance grounding is above, through and below the preferably 
copper printed circuit board; 

Certain transistors such as LDMOS devices have the source element 
soldered-in a heat sink saddle area by way of a metal window located at the 
bottom of selected plastic packages. 

The heat sink retaining bars and plates are disposed at package ends and do 
not interfere with transistor heat sink center (source) and side-located (gate 
and drain) leads. 

[00601 The invention is believed to make a needed contribution to the art of 
relatively high powered semiconductor devices that must operate in a physically stressful 
and significant impact inclusive environment. 

[0061] The foregoing description of the preferred embodiment has been presented for 
purposes of illustration and description. It is not intended to be exhaustive nor to limit the 
invention to the precise form disclosed. Obvious modifications or variations are possible in 
light of the above teachings. The embodiment has been chosen and described to provide the 
best illustration of the principles of the invention and its practical application in order to 
thereby enable one of ordinary skill in the art to utilize the invention in various 
embodiments and with various modifications as are suited to the particular scope of the 
invention as determined by the appended claims when interpreted in accordance with the 
breadth to which they are fairly, legally and equitably entitled. 



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