Functionally graded metal substrates and process for making same

The invention provides for a functionally-graded metal substrate that is made of at least two metal compositions, a functional insert and a surrounding body that surrounds the functional insert. In a preferred embodiment of the invention a functional insert powder composition of loose powder metal is placed in a compact of a surrounding body powder composition and both metal compositions are sintered in a sintering furnace to form a sintered part. The sintered part is infiltrated in part or in whole with a molten metal compound to produce a functionally graded metal substrate having a density of at least 90% of theoretical. A heat-generating component such as a chip can be attached to the metal substrate for use in microelectronic packaging. When the functionally-graded metal substrate has two discrete compositions of copper/tungsten the surrounding body which has a CTE that ranges from about 5.6ppm/.degree. C. to about 7 ppm/.degree. C. constrains the expansion of the functional insert which has a thermal conductivity that ranges from about 200 W/mK to about 400 W/mK.

FIELD OF INVENTION 
This invention relates generally to a process for producing metal 
substrates and the resultant metal substrates. More specifically, this 
invention relates to a process for making metal substrates and the 
resulting metal substrates having two or more discrete portions of metal 
compositions. 
BACKGROUND 
Metal substrates are usually made of a single metal, a single metallic 
alloy, a single metal matrix composite (MMC) or a combination of clad 
metallic film layers. Metal substrates made of metal matrix composites, in 
particular, offer broad design flexibility because an MMC is a composite 
that contains at least two metals, one of which is a substantially higher 
melting refractory metal or reinforcement compound. A substrate that is an 
MMC can be tailored to control certain physical characteristics, such as 
mechanical, thermal, electrical, and chemical properties by varying the 
relative proportions of the two or more metals to satisfy end use 
specification requirements. 
Metal substrates have long been used in microelectronic packaging to house 
circuit chips, dice, electrical components, and the like. In such 
applications, one or more heat-generating components are mounted on a 
metal substrate that is conventionally termed a flange or a carrier 
substrate. Once these components are mounted, the carrier substrate is 
usually mounted on a printed circuit card or circuit board. Metallic 
carrier substrates are good electrical conductors and are especially 
suited to house components or chips that require electrical grounding. For 
example, an application in which chip grounding is necessary is laterally 
diffuse metal oxide semiconductors (LDMOS) which house field effect 
transistors (FET). 
When a carrier substrate is used for microelectronic packaging, the thermal 
conductivity (TC) and the coefficient of thermal expansion (CTE) are among 
the most important properties considered in the design of carrier 
substrates. The carrier substrate is generally made of a material having 
high thermal conductivity so that there is high heat transfer away from 
the heat-generating component. Microelectronic packages must also be 
dimensionally stable to prevent warping, delamination between the chip and 
the carrier substrate, or even cracking of the chip during thermal 
cycling. Thus, the carrier substrate must be designed such that its 
thermal expansion approximately matches or is slightly higher than the 
expansion of the chip. Typically, the CTE of a chip is about 2.8 
ppm/.degree. C. for a silicon chip and about 5.6 ppm/.degree. C. for a 
gallium arsenide chip, for example. 
A common problem in the design of microelectronic packages, however, is 
that material candidates having high thermal conductivity also have a high 
CTE. For example, copper has a thermal conductivity of about 400 W/mK, 
however, the CTE of copper is about 17 ppm/.degree. C. Thus, a metal 
substrate containing a high concentration of copper yields unacceptable 
results in most microelectronics applications. Compared to metal 
substrates made of a single metal or metallic alloy, MMC carrier 
substrates can be better designed to match the thermal expansion 
characteristics of the chip or other heat-generating component attached to 
the carrier substrate while also providing improved heat transfer. For 
example, copper/tungsten and copper/molybdenum composites are commonly 
used in electronic packaging applications and have a thermal conductivity 
that ranges from about 130 W/mK to about 180 W/mK depending on the copper 
content of the composite. This is considerably less than the thermal 
conductivity of copper. 
While MMCs offer broad design flexibility, certain end use performance 
characteristics of metal substrates are compromised due to the homogeneity 
of the metal substrates in the x-y plane. It is desirable to provide a 
metal substrate that has at least two discrete portions of material 
compositions in the x-y plane with each material composition having 
distinct material properties. It is desirable to provide a metal substrate 
that has improved thermal conductivity to dissipate heat generated by a 
die situated in a localized area as well as a surrounding area that 
constrains the expansion of such localized area. It is also desirable to 
produce a metal substrate that can be used in microelectronic packaging to 
improve heat dissipation of chips and heat-generating components while 
maintaining dimensional stability and minimal warpage during thermal 
cycling. It is further desirable to produce a functionally graded metal 
substrate that achieves these objectives at a lower cost. 
SUMMARY OF THE INVENTION 
The invention herein provides for a functionally-graded metal substrate 
that is made of at least two metal compositions and has at least two 
discrete portions, a functional insert and a surrounding body, in the x-y 
plane. The functional insert is intimately bonded to the surrounding body. 
The functionally-graded metal substrate is characterized by two or more 
discrete portions each having different mechanical properties, thermal 
properties, electrical and magnetic properties, chemical composition or 
aesthetic features. 
When the functionally-graded metal substrate is used in microelectronic 
packaging applications a heat generating chip is attached directly to the 
functional insert which is surrounded by the surrounding body. The 
functional insert preferably has a thermal conductivity that is greater 
than the thermal conductivity of the surrounding body. The functional 
insert conducts heat away from the chip to the environment or to a heat 
sink. Although the CTE of the functional insert is higher than the CTE of 
the surrounding body, the otherwise detrimental expansion of the 
functional insert is constrained by the surrounding body when the 
temperature of the microelectronic package increases. 
The process for making functionally-graded metal substrates comprises: 
filling the cavity of a metal body with a functional insert and sintering 
the metal body and the functional insert simultaneously. In another 
embodiment of the invention, the process further comprises infiltrating 
the sintered metal body or the sintered functional insert or both with a 
molten metal compound. 
In accordance with a preferred embodiment of the invention the metal body 
is a compact of powder metal or a surrounding body powder composition, and 
the functional insert is a loose powder metal or functional insert powder 
composition. The preferred process comprises: compacting a surrounding 
body powder composition to form a compact having a cavity therein, filling 
the cavity with a functional insert powder composition that is preferably 
a loose powder, sintering the surrounding body powder composition and the 
functional insert powder composition simultaneously, and infiltrating the 
sintered surrounding body or sintered functional insert or both with a 
molten metal. The cavity can be formed while forming the compact or after 
the compact is formed. The resulting functionally-graded metal substrate 
has two discrete portions, a functional insert and a surrounding body that 
surrounds the functional insert, preferably, in two dimensions in the x-y 
plane. 
In a particularly preferred embodiment of the invention, the functional 
insert powder composition and the surrounding body powder composition both 
comprise either copper and tungsten or copper and molybdenum. The 
concentration of copper in the functional insert powder composition is 
greater than the concentration of copper in the surrounding body powder 
composition. The cavity formed for making the functional insert portion of 
the substrate preferably extends from a first surface of the compact to a 
second surface of the compact, such as from the top to the bottom of the 
compact, for example. Upon sintering, the sintered functional insert 
composition has a greater porosity than the sintered surrounding body 
composition, and upon infiltration, the sintered functional insert 
composition achieves full density. The result is a functionally-graded 
metal substrate that has a density greater than at least about 90% of 
theoretical throughout. 
The resulting functionally-graded metal substrate finds particular use in 
housing microelectronic components. A heat-generating component, such as, 
for example a chip, can be attached directly to the functional insert. The 
functional insert which can have a thermal conductivity up to about 400 
W/mK, is preferably greater than the thermal conductivity of the 
surrounding body. The surrounding body preferably has a CTE that is lower 
than the CTE of the functional insert, and thus the surrounding body 
controls or constrains the expansion of the functional insert along its 
contact surfaces as the functional insert conducts heat away from the 
heat-generating component. 
In another embodiment of the invention, the process for making 
functionally-graded metal substrates comprises: compacting a surrounding 
body powder composition to form a compact having a cavity therein, 
compacting a functional insert powder composition to form a compact, 
filling the cavity with the compact of functional insert powder 
composition, and sintering the functional insert powder composition and 
the surrounding body powder composition. 
Alternative embodiments of the invention also include sintering a solid 
metal surrounding body having a cavity therein containing a functional 
insert powder composition to form a functionally-graded metal substrate, 
or diffusion bonding or brazing a solid metal functional insert to a solid 
metal surrounding body. Infiltration can follow sintering in embodiments 
which include sintering the surrounding body containing a functional 
insert powder composition or a compact of insert powder composition.

DETAILED DESCRIPTION OF THE INVENTION 
The invention herein provides for a process for making a 
functionally-graded metal substrate and the resulting substrate that has 
at least two discrete areas, a functional insert and a surrounding body, 
in the x-y plane. The functional insert is surrounded by the surrounding 
body, preferably, in at least two dimensions. The discrete areas of the 
functionally-graded metal substrate have distinct physical characteristics 
which are governed by the metal composition in each discrete area. 
The functionally-graded metal substrate comprises at least two metal 
compositions that represent at least one surrounding body and at least one 
functional insert. Metals that make up the surrounding body and the 
functional insert can include an elemental metal, a metallic alloy or a 
metal matrix composite (MMC). The functional insert and the a surrounding 
body may include the same metals but in varying concentrations or 
compositions. Materials that can be used according to the invention herein 
include, for example: metals such as copper, nickel, iron, beryllium, 
aluminum, silver; metallic alloys such as copper beryllium, copper-zinc 
(bronze), copper-tin (brass), 64% iron/36% nickel (Invar.TM.) and 54% 
iron/29% nickel/17% cobalt (Kovar.TM.), copper-iron, nickel-niobium, 
nickel-silver, nickel-copper, iron-copper, iron-copper-carbon, 
iron-copper-nickel, iron-chromium, iron-copper-tin, 
copper-nickel-titanium-aluminum, nickel-copper-titanium; and metal matrix 
composites such as copper/tungsten, copper/molybdenum, aluminum/silicon 
carbide, aluminum/aluminum nitride, copper/aluminum, silver/Invar.TM., 
copper/cubic boron nitride, copper/diamond and copper/high conductivity 
carbon fiber. 
When the functionally-graded substrate having two different metal 
compositions is used in microelectronic applications, a heat-generating 
component, for example, a chip, is attached directly to the functional 
insert and the functional insert is surrounded by the surrounding body. 
The functional insert preferably has a thermal conductivity that is 
greater than the thermal conductivity of the surrounding body, and the 
surrounding body preferably has a CTE that is lower than the CTE of the 
functional insert. The surrounding body thus controls or constrains the 
expansion of a functional insert along its bonded surfaces as the 
functional insert conducts heat away from the heat-generating component. 
In accordance with the invention herein, a process for making a 
functionally-graded metal substrate comprises: filling the cavity of a 
metal body with a functional insert and sintering the metal body and the 
functional insert simultaneously. In another embodiment the process 
further comprises infiltrating the sintered metal body or the sintered 
functional insert or both with a molten metal compound. The result is a 
functionally-graded metal substrate having a functional insert and a 
surrounding body that surrounds the functional insert, preferably in at 
least two dimensions, in the x-y plane. 
In accordance with a preferred embodiment of the invention, the metal body 
is made from a compact of a surrounding body powder composition, and the 
functional insert is made from a functional insert powder composition. 
FIG. 1(a) shows a surrounding body powder composition 2, which is pressed 
preferably with cavity 4 formed therein. FIG. 1(b) shows the pressed 
compact containing the surrounding body powder composition on alumina 
sintering plate or sagger plate 6 and functional insert powder composition 
8 in cavity 4. Functional insert powder composition 8 is preferably a 
spray-dried powder and is placed in a loosely packed arrangement. Metal 
powders that can be used for the surrounding body powder composition and 
the functional insert powder composition can be any metal powders that are 
used in metal sintering processes and are well known in the art. 
The sintering plate is then placed in a sintering furnace and fired at a 
temperature such that sintering causes the insert powder composition to 
bond with the surrounding body powder composition. The surrounding body 
powder composition is sintered to a density that is at least 90% of 
theoretical, preferably at least 97% of theoretical, and even more 
preferably at least 99% of theoretical. The sintered functional insert 
composition is porous after sintering having a density that is less than 
the density of the sintered surrounding body and preferably about 70% or 
less of theoretical. 
Next, the sintered functional insert composition is infiltrated with molten 
metal such that the sintered functional insert achieves a density of at 
least 90% of theoretical, preferably at least 97% of theoretical, and even 
more preferably at least 99% of theoretical. The result is a 
functionally-graded metal substrate having a functional insert and a 
surrounding body that surrounds the functional insert in at least two 
dimensions. 
In accordance with a particularly preferred embodiment of the invention, 
the compact of surrounding body powder composition contains copper and 
tungsten powder comprising from about 5% to about 50% by weight copper, 
preferably, from about 5% to about 40%, and more preferably, from about 
10% to about 30% by weight copper powder. Copper can be introduced in the 
compact in the form of copper powder or copper oxide powder or both. The 
functional insert powder composition comprises copper and tungsten powder 
that is from about 20% to about 80% by weight copper, preferably, from 
about 30% to about 50%, and more preferably, from about 30% to about 45% 
by weight copper powder. The functional insert powder composition is 
preferably sintered in loose powder form. The sintered functional insert 
composition is relatively porous infiltrated preferably with copper, and 
more preferably, oxygen-free high conductivity (OFHC) copper. Infiltration 
is conducted in a nitrogen/hydrogen environment at a temperature ranging 
between about 1100.degree. C. and about 1150.degree. C. to produce a 
functional core having high thermal conductivity relative to the 
surrounding body. 
Alternatively, in another preferred embodiment the compact of surrounding 
body powder composition contains copper and molybdenum powder comprising 
from about 5% to about 50% by weight copper, preferably, from about 5% to 
about 40%, and more preferably, from about 10% to about 30% by weight 
copper powder. Copper can be introduced in the compact in the form of 
copper powder or copper oxide powder or both. The functional insert powder 
composition comprises copper and molybdenum powder that is from about 20% 
to about 80% by weight copper, preferably, from about 30% to about 50%, 
and more preferably, from about 30% to about 45% by weight copper powder. 
The functional insert powder composition is preferably sintered in loose 
powder form. The sintered functional insert composition is relatively 
porous infiltrated preferably with copper, and more preferably, 
oxygen-free high conductivity (OFHC) copper. Infiltration is conducted in 
a nitrogen/hydrogen environment at a temperature ranging between about 
1100.degree. C. and about 1150.degree. C. to produce a functional core 
having high thermal conductivity relative to the surrounding body. 
The functionally-graded metal substrates of the invention herein can be 
used to house microelectronic components. FIG. 3 illustrates a flow scheme 
that summarizes the process for making copper/tungsten or 
copper/molybdenum functionally-graded metal substrates for microelectronic 
packages in accordance with the preferred embodiment of the invention. 
Copper/tungsten or copper/molybdenum spray dried powder is prepared 101 
and then dry pressed to form a compact of the surrounding body having at 
least one cavity therein 102. Copper/tungsten functional insert powder 
comprising from about 20% to about 80% by weight copper is spray dried 103 
and the functional insert powder composition in loose powder form, is 
placed in the cavity of the compact of the surrounding body powder 
composition 104. The compact of the surrounding body and the functional 
insert powder compositions are fired in a furnace during the sintering 
process 105. The functional insert composition undergoes infiltration 106 
with copper to produce a functionally-graded metal substrate. 
Subsequently, the surfaces of the metal substrate are ground to desired 
dimensions 107 followed by metal plating 108 in preparation for further 
processing of the microelectronic package. 
FIG. 4 is a scanning electronic microscope (SEM) micrograph of a 
cross-sectional area of the functionally-graded metal substrate in 
accordance with the invention herein. The surrounding body portion 
designated by vertical (a) portion of the micrograph contains 
copper/tungsten metal matrix composite containing from about 15% by weight 
copper and about 85% by weight tungsten. The functional insert portion 
designated by vertical (b) portion of the micrograph is a copper/tungsten 
metal matrix composite containing from about 40% by weight copper and 
about 60% by weight tungsten. 
FIG. 5 illustrates functionally-graded metal substrate 10 as a carrier 
substrate of a microelectronic package 20. Heat-generating chip 22 is 
attached directly to functional insert 14 by brazing, soldering, epoxy 
adhesive or attachment means that are well known in the art. Functional 
insert 14 conducts heat away from heat-generating chip 22 to the 
environment or to a heat sink attached thereon (not shown). Preferably, 
functional insert 14 has a thermal conductivity that is greater than the 
thermal conductivity of the surrounding body and surrounding body 12 has a 
CTE that is lower than the CTE of functional insert 14. The CTE of 
surrounding body approximately matches or is slightly greater than the CTE 
of the heat-generating chip and controls the expansion of the functional 
insert during thermal cycling. For example, a functionally-graded 
substrate in which the functional insert and the surrounding body are 
comprised of copper/tungsten or copper/molybdenum, the functional insert 
has a thermal conductivity that ranges from about 200 W/mK to about 400 
W/mK and the surrounding is body has a CTE that ranges from about 5.6 
ppm/.degree. C. to about 7 ppm/.degree. C. where the CTE is measured at 
ambient temperature. Thus, a metal substrate having a functional insert 
with high thermal conductivity improves the thermal dissipation of the 
metal substrate while maintaining low thermal expansion in the area where 
the chip is attached. 
The process of making spray-dried agglomerates from powder metal 
compositions and the process of compaction, sintering, and infiltration 
are well known in the art. These processes are described in U.S. Pat. No. 
5,686,676 which is hereby incorporated by reference herein. Metal powders 
are mixed by means of mechanical mixers such as high shear mixers, 
blenders and mills in the presence of a liquid, preferably water. Once the 
metal powders are mixed, they can be formed into a compact in any 
conventional manner. For example, a free flowing agglomerate powder is 
poured into a die and pressed with either a hydraulic or mechanical press 
to form a compact. The dimensions of the compact are determined by the 
size of the desired finished part and the die, taking into account the 
shrinkage of the compact during the sintering operation. Sintering is 
preferably accomplished using either a batch furnace or a continuous 
pusher type furnace. Sintering residence time and temperature depends upon 
the melting temperature or the eutectic temperature of the metal powder 
composition. The sintering temperature is greater than at least one metal 
of the powder metal compositions. Infiltration is well known in the art 
and metal compositions that are used for infiltration are generally those 
having a melting temperature of about 1400 deg. C or less. 
It has been found that if one of the powder compositions that is used 
contains a metal that is capable of forming a eutectic composition, then a 
denser substrate can be produced. This phenomenon is described in U.S. 
Pat. No. 5,686,676 which is hereby incorporated by reference herein. An 
example of a powder metal system that can form a eutectic composition 
during sintering is copper-copper oxide. Sintering compacts containing 
copper oxide or a combination of copper and copper oxide is conducted at 
temperatures from about 1050.degree. C. to about 1400.degree. C. Even more 
preferably, the compacts can be sintered in a reducing atmosphere, which 
for example, contains hydrogen, nitrogen or moisture, for example. 
In accordance with another embodiment of the invention, the process 
comprises: compacting a surrounding body powder composition to form a 
compact having a cavity therein, compacting a functional insert powder 
composition, filling the cavity with the compact of functional insert 
powder composition, and sintering the functional insert powder composition 
and the surrounding body powder composition simultaneously. The cavity can 
be formed in the compact of surrounding body powder composition while 
forming the compact or after the compact is formed. 
FIG. 6 shows a compact containing functional insert powder composition 8 
before it is placed into a compact containing surrounding body powder 
composition 2. The functional insert powder composition is pressed to a 
size that will fit into the cavity of the surrounding body composition. 
The two compacts are sintered together to a density that is at least about 
90% of theoretical, preferably at least about 97% and at least about 99% 
of theoretical. Both powder metal compositions can be pressed in a single 
tool. A multi-action press having a specialized feedshoe (receptacle on 
tool to fill cavities) can be used to press both powder metal compositions 
in a single tool. 
If the sintered part containing the sintered surrounding body and the 
sintered functional insert has a low density, for example, less than about 
95% of theoretical, the sintered part can be infiltrated with molten 
metal. In another embodiment of the invention the process comprises: 
compacting a surrounding body powder composition to form a compact having 
a cavity therein, compacting a functional insert powder composition, 
filling the cavity with the compact of functional insert powder 
composition, sintering the functional insert powder composition and the 
surrounding body powder composition simultaneously, and infiltrating the 
sintered surrounding body or the sintered functional core or both. 
In another embodiment of the invention the metal body is a solid, wrought 
metal body. The process for making a functionally-graded metal substrate 
comprises: placing a functional insert powder composition into the cavity 
of a solid surrounding body and sintering the functional insert powder 
composition. The cavity can be formed by machining the solid surrounding 
body or by other well-known techniques. In another embodiment the process 
further comprises infiltrating the sintered functional insert with a 
molten metal composition. 
In yet another embodiment of the invention, the process for making a 
functionally-graded metal substrate comprises: placing a solid functional 
insert into the cavity of a solid surrounding body and brazing the solid 
functional insert to the solid surrounding body. The cavity can be formed 
by machining the solid surrounding body or by other well-known techniques. 
The solid, functional insert, preferably a wrought metal, is attached or 
bonded to the metal body using conventional brazing technology. 
Alternatively, the solid functional insert can be attached by either 
pressure-assisted or pressureless diffusion bonding to form a 
functionally-graded metal substrate. 
After the functionally-graded metal substrate is made, it can undergo one 
or more secondary operations. End use dimensions can be achieved by 
double-disk grinding the metal substrate according to a process well known 
in the art. The functionally-graded metal substrate can also be plated by 
conventional plating processes, such as electroless plating or 
electrolytic plating, for example. More specifically, in a microelectronic 
packaging application, the functionally-graded metal substrate can be 
nickel plated or nickel and gold plated via electroless or electrolytic 
plating operations. 
The functional insert of the functionally-graded metal substrate can be any 
geometric shape. For example, FIG. 7 shows functional insert 14 has 
tapered or angled walls. The cross-sectional area of the functional core 
is increasingly larger toward the bottom of the functionally-graded metal 
substrate. The tapering can facilitate greater thermal dissipation from 
the top down if a heat-generating component is attached to functional 
insert 14, for example. 
The functional insert can extend partially or completely through the 
surrounding body. The functional insert of FIG. 7 shows that the 
functional insert extends from top surface 15 of functionally-graded metal 
substrate 10 to bottom surface 16. FIG. 8 shows functional insert 14 
extends from the top surface of substrate 10 to a location within 
surrounding body 12. 
Functionally-graded metal substrates can be made in a variety of shapes, 
sizes and configuration as shown in FIG. 9 and FIG. 10. In addition, the 
functionally-grade metal substrate herein can have one or many functional 
inserts. FIG. 11 shows a functionally-graded metal substrate that has a 
plurality of functional inserts of varying sizes and shapes. If used in 
microelectronic packaging, the functionally-graded metal substrate can 
house several components such as dice, diodes, resistors, and capacitors, 
for example. The functional inserts can be distributed throughout the 
substrate wherever needed per end use requirements. Limitations on the 
size of the functional insert or the volume of functional insert relative 
to the total volume of the functionally-graded metal substrate depends 
upon the end use application, desired performances, and the functional 
insert and surrounding metal compositions. Such limitations may be 
determined through routine experimentation by one skilled in the art. For 
example, if the functionally-graded metal substrate herein is used in 
microelectronic packaging, the volume of the functional insert relative to 
the total volume of the substrate must be large enough to physically 
accommodate a heat-generating component and to facilitate improved heat 
transfer. The surrounding body must be large enough to constrain the 
dimensional expansion of the functional insert which has a CTE that is 
greater than the surrounding body. 
In addition, functionally-graded metal substrates can be made in an array 
which consists of a repeated pattern of metal substrates. An array of 
functionally-graded metal substrates is illustrated in FIG. 12. A large, 
functionally-graded metal substrate can be prescribed so that the array 
can be singulated into several individual metal substrates having a 
functional insert 14 and a surrounding body 12. 
The several embodiments discussed provide for a surrounding body that 
surrounds the functional insert in the x-y plane. Preferably, the 
surrounding body surrounds the functional insert in at least two 
dimensions, but the surrounding body can also surround the functional 
insert in one dimension. FIG. 13 is a perspective view of a 
functionally-graded metal substrate in which the surrounding body 24 
surrounds 26 the functional insert in one dimension. 
In order to more fully and clearly describe the present invention so that 
those skilled in the art may better understand how to practice the present 
invention, the following examples are given. These examples are intended 
to illustrate the invention and should not be construed as limiting the 
invention disclosed and claimed herein in any manner. 
Working Example 
The following working example are provided to illustrate more thoroughly 
the present invention: 
Heat Sink Made by Sintering and Infiltration 
A. Preparation of Surrounding Body Powder Composition 
A copper/tungsten (15%/85% by weight) spray dried powder was made using the 
quantity of ingredients listed below. 
______________________________________ 
Tungsten 423.6 lbs 
Cuprous Oxide 84.0 lbs 
Deionized water 105.1 lbs 
Cobalt 2.7 lbs 
Isopropyl Alcohol 18.5 lbs 
Benzotriazole 3.3 lbs 
Acrylic Emulsion 12.5 lbs 
______________________________________ 
Benzotriazole corrosion inhibitor (Cobratec.RTM. 99 available from PMC 
Specialties Group, Inc., Cincinnati, Ohio) was dissolved in isopropyl 
alcohol and particulate cuprous oxide was then added to the benotriazole 
solution. The mixture was set aside for 12 hours. 
Deionized water and cobalt metal (mean particle size of about one micron) 
were mixed in a mixing tank for ten minutes. Next, tungsten metal (mean 
particle size of about one micron) was ball milled for about four hours 
and then slowly added to the ingredients in the mixing tank and mixed for 
two hours. The mixture of cuprous oxide, benzotriazole and isopropyl 
alcohol was added and mixed for 30 minutes. Rhoplex.RTM. B-60A acrylic 
emulsion was then added to the mixture which was then mixed for an 
additional 30 minutes. The mixture was recovered and spray dried in a 
Bowen No. 1 Tower spray drier at 25 psi and an outlet temperature of about 
270.degree. C. to about 280.degree. C. The spray dried agglomerate powder, 
which after screening (65 mesh) exhibited a Hall meter flow rate of about 
30 seconds per 50 grams of powder. 
B. Preparation of Functional Core Powder Composition 
A copper/tungsten (30%/70% by weight) functional powder composition was 
made by first making spray dried tungsten. Teledyne C-10 tungsten powder 
(306.8 grams) and deionized water (88 grams) were milled in a tumbling 
ball mill for three hours until the particle size of the tungsten was 
finer than about 10 microns. An acrylic emulsion, Rhoplex.RTM. B-60A, made 
by Rohm and Haas was screened through a 100 mesh screen before being 
weighed out in an amount of 5.2 grams. The Rhoplex was slowly added to the 
tungsten slurry and mixed for a minimum of ten minutes. 
The mixture was then spray dried in a Bowen No. 1 Tower spray drier at 25 
psi and an outlet temperature of about 270-280.degree. C. The spray dried 
agglomerate powder after screening (65 mesh) exhibited a Hall flow rate of 
about 20 seconds per 50 grams of powder. 
The spray dried tungsten powder (70 grams) was then blended with RL copper 
powder (30 grams) made by OMG Metal Products, Research Triangle Park, N. 
C. in a blending jar with a disrupter bar and blended for 5 minutes. The 
mixture was then screened through a 60 mesh screen. 
C. Preparation of Compact and Sinter 
Green compacts of the surrounding body powder composition were made by 
filling a die with copper/tungsten (15%/85%) powder from Step A and 
compressing the powder in a press at a pressure of 25,000 psi to form a 
green compact. The die was rectangular in shape and had a solid 
rectangular shaft built within. Thus, the resulting green compact had a 
through-hole that extended the thickness of the compact. 
Next, the green compact was placed on alumina setter plates and the entire 
volume of the hole was filled with the functional powder composition 
described in step B above. The compact was sintered in a BTU reducing 
furnace at 1125.degree. C. at a rate of one inch/min of the compact. The 
atmosphere in the BTU furnace was 100% hydrogen having a dew point of 
+20.degree. C. 
D. Infiltration 
After the compact was sintered, the resulting sintered flange was placed on 
the setter for the infiltrating furnace. Oxygen-free high conductivity 
(OFHC) copper compacts or preforms were prepared for infiltration. 
Approximately 20% in excess of OFHC copper was placed on the area of the 
flange to be infiltrated, that is, the surface area of the flange that, 
prior to sintering, consisted of the functional powder composition. The 
sintered flange was then heated to 1100.degree. C. in a dry (&lt;-400C.) 
hydrogen/nitrogen (25%/75%) atmosphere for about 5 minutes. The result was 
a functionally-graded metal substrate having a functional insert and a 
surrounding body. 
E. Secondary Finishing 
The proper flatness and desired thickness of the functionally-graded metal 
substrate was achieved by double-disc grinding the surfaces. The heat sink 
was tumbled to remove the burrs. The metal substrate was nickel plated by 
the well-known electroless nickel plating process 
(plate/sinter/plate/sinter process) to a thickness of about 100 
micro-inches of nickel. Finally, the metal substrate was electrolytically 
plated with gold to a thickness of about 75 micro inches and a flatness of 
about 0.2 to about 0.3 mils/inch. 
Other modifications and variations of the present invention are possible in 
light of the above teachings. For example, the functional insert and the 
surrounding body of the functionally-graded metal substrate embodiments 
described herein can comprise a variety of metal compositions for use in 
end-use applications other than microelectronic applications. It is to be 
understood, however, that changes may be made in the particular 
embodiments described above which are within the full-intended scope of 
the invention as defined in the appended claims.