Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
il2
S~LF-CO~JT~TNEl~ THF.R~ TRANSFER
INTEGR~TED CIR(~UIT CAR~IER PACK~E
The invention enhances tne internal convective operation of an integrated circuit carrier package. Typicallyt
the semiconductor die is secured in a small hermetically sealed chamber with some inert gaseous atmosphere. This
invention expands this chamber via a network of cooling substructures which allow the working ~luid to circulate and
exchange heat energy with cooler portions of the package. The invention hence has a coolant flow self-perpetuated
by the heat generated by the semiconductor die. A completely self-contained and independent cooling system is
summarily conslructed. In a typical installation of such integrated circuits as in a minicomputer, no coolant circulation
system is required. This reduces mass of said system as well as costs at an efficiency level between a large area finned
heatsink and a external coolant circulation system.
The design of the invention begins at the semiconductor placement site. Here, the semiconductor is fastened
10 toastructurecomposedoffusedsphericals.ThesefusedsphericalsprovideacombinationoEthermalduty.Firstly,such
a structure provides a greatened surface area which is generally several times greater than that of the semiconductor
die itself. This improved thermal area boosts convective heat transfer to the working fluid and aids in reduction of the
die temperature. The fused spheroid structure also has specific characteristics when a liquid is employed as the working
fluid. The larger surface area and the porous nature of this structure controls any violent boiling effects that may be
induced in such a situation. The secondary function of the structure is heat conduction to the main heat transfer device.
Heat conduction from the semiconductor material continues through an electrical isolation layer and the thin
wallcoolantshellstoahighlyconductivespacerandstem.Thisstemalsoservesasachargingvalveassemblyforwhich
the internal volume can be readily evacuated and filled with ~he requisite working fluid (gaseous or liquid). This
conductive stem is essentially encompassed in a fused spheroid structure. This spheroidal structure encompasses the
20 upper portion of the invention in a form or shape of a diagonally arranged finned porous heatsink. This provides a low-
mass large area heat tranfer surface which is enhanced for specific flow characteristics and radiadve discharge
properties.
Convection of heat from the semiconductor die is from all exposed surfaces including the spheroid base. The
working fluid is heated in the primary chamber. If the working fluid is gaseous at standard conditions, it will rise in
temperature and pressure. If a liquid is employed as a working fluid, phase changes such as boiling may occur. The
highpressuregasorvapouristhencollectedindomedstructuresandisforcedthrougheitheranaperture,orifice,nozzle,
and/or valve. The selection of this component is dependent on the nature of the working fluid. A gaseous coolant can
undergo a pressure and temperature drop æ it passes through a restriction. Similarly, a vapour may revert to a liquid
insuchathermodynamiceffect.Theworkingfluidinpassingthroughthisstageencountersalargesurfaceareatypically
~o at a cooler temperature than itself. This is the secondary chamber which contains a mass of spheroids. Here thermal
convection occurs from the working fluid to this area and subsequently reduces the fluid temperature. This complete
structure is known as the thermal transfer module. Multiple transfer modules are networked in a fashion which allows
the working fluid to flow across several of these modules in sequence. The network is arranged in a geometry which
- 1 -
~7~ ,ff~
will provide subsequently cooler modulcs along a single tlOw path. Two module types are typically employed in this
fashion. A module as described above is both a fluid^collecting and heat-transfering unit, whereas a strictly heat-
transfering type unit may be also employed in coordinates of cooler andlor non-collective locals. These modules are
interconnected by coolant ducts which carry the working fluid from unit to unit, The working fluid eventually reaches
the coolant retum chamber where it opens a set of valves to reenter the primary chamber. These valves are generally
located above the die and base structure so as to permit a coolant stream to directly cool the semiconductor die. The
circulation of the working fluid is perpetuaUy driven by the themmal energy generated by the semiconductor circuit.
The thermal transfer modules are arranged geometrically to not only take advantage of generally cooler
coordinates, but also a fused mass of spheroids. The general form or shape of this structure is essentially a set of
o diagonally arranged fin-like structures. The diagonal structure provides a violently turbulent obstacle to a forced flow
of air typically encountered in many applications. It is an optional requirement of the invention to generally be in a
forced airflo v environment. Although the imvention will function e~ficiently in a static environment, a dynamic airflow
willenhancetheoperationoftheinvention.Theaveragetemperatureofthefin-likestructurecanbecontrolledtowithin
several degrees of this forced air stream. Should a s~atic situation be required, the radiative discharge characteristics
of the external spheriod structure may be enhanced accordingly. An orientation criteria also exists for the invention.
When a gaseous working fluid is employed, the invention will operate under any orientation (ie. horizontal, vertical).
Thisisalsotrueforsomeliquidworkingfluidswhichwillnotboilorvapourizeundertherequisiteoperationaldomain.
Should a boiling effect be employed in cooling, special attention as to orientation of the vapour collection domes must
be made. The major components of the thermal transfer apparatus also exert some benificial functions. Generally, these
20 components serve as a conductive heat sink to the semiconductor circuit as well as the above mentioned functions.
Typically, a majority of the materials employed will be metallic in nature and they will provide an electromagnetic
shield to the semiconductor die. The invention is readily hardened to immunity from such phenomena as electromag-
netic pulses (~MP) and cosmic rays.
Construction of said invention begins with the formation of the vessal layers. This can be accomplished by
astampingformationprocessintherequiredshapeorform.Theinternalvessallayermustalsohaveanadditionalvalve,
orifice etc. An micro-aperture can be bored using a high-powered laser drill, or a valve, nozzle etc. can be beam welded
into position. The external vessal layer is then filled with a measured amount of spheriods into the formed cavities and
the internal layer is positioned on top. A seam welding operation is then performed on the perimeter of this assembly
and spot welds are strategically implemented on the internal areas. Material selection for these components is
30 important. They must be optimized with respect to thermal properties and knowledge of the chemical characteristics
of the working fluid. This will prevent material reactions which may corrode or foul the assembly and reduce its
usefulness. As an example, copper may be used as the metal in the assembly with an inert gas(es) such as helium etc.
Stainless-type steels may be employed when the coolant is a flourocarbon liquid as an alternative example. The vessal
assembly is completed by the affixing of the charging assembly by a welding process. The final step would be to fuse
the external fin-like spheriods into shape or form. This would be implemented in a die-form with a measured amount
of spheriods and fused into permanent shape. The process of such nature is well described in the art of U.S. Patent
- 2 -
#3,825,064. ~imilMly, the spheriod dic base can be manufactured.
The radiative coating(s) to this external spheriod structure can be applied by various methods including
electrochemical plating, plasma or ion deposition, oxidization etc. Selection of the coating and its combinations relys
on knowledge of the temperature application and the physical phenomena of radiative transfer that occurs within this
spheriod structure. Coating selection and application can become a major thermal transfer mechanism when properly
implemented. Multiple coatings can be built-up on the spheriod surface which exhibit a hi8h emissivity with a
selectively reflective and absorptive characteristics. This would facilitate absorption of low energy photons, and
reflection of high energy radiation. An example implementation would be to plate a reflective metal such as gold,
chromium, nickel etc. onto the spheriod structure. An ion implantation technique can then be utilized to coat a highly
10 emissive material such as carbon onto the majority of the externally accessible surfaces. This would effect a reflective
inner core where temperature gradients are high and an exterior surface with high emissivity. Particular coating
combinations may also provide surface discharge characteristics of interesting photonic effects due to quantum
properties. An example of this would be a surface which essentially converts heat energy into visible light. The
material(s) may be either inorganic or even organic which has been bioengineered for such a use.
Theheatexchangeapparatusoncecompletedintheabovefashionisreadyforassemblytotherestofthecarrier
package. A base carrier is completed with thepin grid array and electrical traces. A dielectric isolation layer is generally
affixed with adhesives to this assembly. Finally, the thermal exchanger is affixed to the base assembly with generally
some form of adhesives. The self-contained thermal transfer carAer package is now ready to accept the semiconductor
circuit(s).Thesemiconductordie(s)is/areaffixedtothespherAodbasewhichisthensecuredinthecenterofthethermal
20 package. These operations typically will take place in a facility known as a clean room to prevent particulate
contamination. Once the semiconductor assembly is affixed, circuit connections to the gAd can be made on an
automated wire machine. The cover plate is then secured iDto place to seal the carrier package. The package is then
ready to accept its coolant. An evacuation of the trapped gases inside the unit is made through the charging valve. At
this point, the actual working fluid either gaseous or liquid may be introduced into the internal chambers through the
charging valve. The self-contained thermal transfer carAer package is now ready for testing, veAfication and
application.
Features, objects, and concepts of this invention are more readily understood visually through the aid of a
drawing, specifically:
l~IG. 1 is an isometric view of a self-contained thermal transfer apparatus implemented in a pin grid array package
30 format;
FIG. 2 is a cross-sectional view through the central diagonal fin-like structure illustrating the major components of the
invention;
FIG. 3 is an anatomical top view of the same apparatus illustrating geometAc placement of the components which
-3-
invoke the invention.
A more definitive descrip~ion of tne components of the invention can be made with respect to illustrative
ordering. Specifically, the semiconductor die at 1 is affixed to a spheroid base 2. This base is essentially a fused mass
of spheroids with generally complimentary thermal expansion proper~ies to the semiconductor die material. Fixation
of the die to this base can be implemented by such techniques as adhesives, soldering or direct fusion. The primary
chamber 3 contains the working fluid which is in direct contact with 1 and 2. This working fluid will exchange the
majority of its thermal energy in the secondary chamber 4. The working fluid gains thermal energy from the
semiconductor material 1 and its base 2 and proceeds through the coolant pass-through openings 5. These opening 5
are initiated in the dielectric isolation layers 20. The working fluid is essentially directed to the collection domes 6.
o Here, the working fluid is forced through an aperture 7 or other fluid related component as previously described into
the secondary chamber 4. The working fluid encounters a large surface area created by a mass of spheroids 8. A transfer
of energy from the fluid to the surface occurs thus reducing the energy state of the coolant. The working fluid will pass
through several of these heat-transfer modules 9. These modules 9 are connected in a network by coolant ducts 10 in
a fashion described previous. The working fluid eventually flows to the coolant return chamber 11 where it passes
through a coolant return valve 12. The fluid has now returned into the primary chamber and completed a cycle of the
perpetual circulation function. The primary chamber 3 containing the semiconductor die 1 and base 2 is accessed by
removal of coverplate 30.
Working fluid loading, maintenance etc. is accomplished through the charging valve 13 and charging duct
14. Here both the primary chamber 3 and secondary chamber 4 can be evacuated through this valve and replaced with
20 coolant.Valvel3andductl4arecomponentsoftheconductivestudlSandconductivespacerl6.Thiscolumnofhighly
conductive material transfers a portion of the heat generated by the semiconductor circuit to the external surroundings.
This stud 15 and the transfer modules 9 are conceiled within an external structure of fused spheroids 17. As previously
described, these fused spheriods have a diagonal fin-like form. Not only are ~he spheriods fused amongst themselves
as per description, but they are fused to the external vessal layer 18. This vessal layer effects the shape and form of
the secondary chamber 4. The internal vessal layer 19 effects the shape and form of the boundary between the primary
chamber 3 and secondary chamber 4. The coupling of these two vessal layers produces the heat exchanger vessal 29.
The dielectric isolation layer 20 isolates these layers from the electrical network.
Electrical connections to the semiconductor circuit 1 are made through connection wires 21. These wires 21
terlninate at connection pads 22 which route signals through electrical traces 23 to the contact pin grid array 24. These
30 pins 24 are extended through pin holes 25 in the base carrier material 26. The base carrier material generally will have
dielectric isolation characteristics necessary to prevent shorts. The pin grid array 24 is completed with pin seals 27.
To provide for proper electrical insertion in various applications, a package index notch 28 is supplied.
