Microelectronic package with device cooling

A microelectronics package has improved device cooling. The package includes a lead frame defining an upper and lower surface. An active electronic device, such as an integrated circuit, is positioned above the upper surface of the lead frame. An encapsulating package is molded around both the lead frame and the active electronic device to form the microelectronic package. A cooling tube is integrally molded within the encapsulating package and typically formed of a thermally conductive material such as copper. A cooling fluid, such as air or a liquid, can be moved through the cooling tube for discharging the heat generated by the active electronic device.

FIELD OF THE INVENTION 
This invention relates to a microelectronic package with improved device 
cooling, and more particularly to a microelectronic package having a lead 
frame, an active electronic device, and an encapsulated package molded 
around the lead frame and the active electronic device with improved 
cooling of the active electronic device. 
BACKGROUND OF THE INVENTION 
Microelectronic packages are continuously increasing in computational 
capacity and performance through increased circuit density and improved 
sub-micron circuit technologies, increased input-output capabilities, 
multi-chip module technology, and a larger integrated circuit chip 
relative to the size of the package. With this increased performance, 
there is an increase in the power density, resulting in an increase in the 
operating temperature of the package. It is well known by those skilled in 
the art that the reliability of a package is directly related to its 
operating temperature. The optimum performance of a microelectronic 
package is obtained only when the heat generated by a chip or plurality of 
chips (i.e., an active electronic device) is efficiently removed. 
Some of these electronic packages include a lead frame with an upper and 
lower surface and an active electronic device, such as an integrated 
circuit or chips mounted on a silicon die and positioned above and 
attached to the upper surface of the lead frame with a thermally 
conductive adhesive. An encapsulating package is molded around the lead 
frame and chip and forms a typically substantially flat, rectangular 
configured microelectronic package. In some applications, cooling fins are 
mounted on top of the package by a heat conductive adhesive and acts as a 
heat sink. Typically air is blown over the fins. In this type of 
microelectronics package, approximately 94% of the heat generated by the 
chips propagates into the silicon die towards a die adhesive and the lead 
frame, with the remaining 6% propagating into the epoxy molding compound 
layer adjacent the chips and forming the encapsulating package. 
Typical package designs place the chips above the lead frame so that when 
the package is mounted onto a circuit board, the high heat side of the 
package faces the circuit board. With a typical 0.020 inch stand-off of 
the package from the circuit board, the majority of the heat generated 
into the electronics package migrates towards the small gap between the 
electronics package and the circuit board. Air cooling is accomplished by 
blowing with forced flow, or using the natural buoyancy-induced convective 
flow of air. 
However, the low thermal capacity of the air requires a large volumetric 
air flow to adequately cool a microelectronic package. Heat sinks 
sometimes are mounted on the outside surface of the package to increase 
the package surface area for cooling. Sometimes the heat sinks may be 
metallic, conductive dies positioned within the package. For example, one 
thermal management technique includes a molded-end heat slug inserted in 
the package. The slug is a solid material having a higher thermal 
conductivity than the epoxy molding compound forming the body of the 
package. Typically, the heat slug can be aluminum or copper and forms a 
direct heat conduction path to the surface of the package. Air cooling is 
then used to expel the heat away from the slug. 
This type of arrangement is expensive and difficult to manufacture and does 
not always provide an acceptable means for reducing the generated heat. 
SUMMARY OF THE INVENTION 
The foregoing problems are overcome with the microelectronic package which 
includes improved device cooling of the present invention. The 
microelectronic package includes a lead frame defining an upper and lower 
surface. An active electronic device, such as an integrated circuit, is 
positioned above and attached to the upper surface of the lead frame with 
a thermally conductive adhesive. An encapsulating package, such as formed 
from an epoxy molding compound is molded around the lead frame and active 
electronic device and forms the microelectronic package. A cooling tube 
can be integrally molded within the encapsulating package. A cooling fluid 
is delivered through the cooling tube. The cooling fluid could be air or 
refrigerant or some other liquid. 
In one aspect of the present invention, the cooling tube is mounted in 
spaced relation above the active electronic device. In still another 
aspect of the present invention, the cooling tube is mounted against a 
lead frame opposite the active electronic device. 
The active electronic device can be one or more integrated circuits, and in 
a preferred aspect of the present invention, the cooling tube is formed in 
a serpentine configuration within the package. The cooling tube is formed 
of a thermally conductive material such as copper or aluminum. The cooling 
tube typically has a diameter of about 0.025 inches and an inner diameter 
of about 0.015 inches. The cooling tube has two ends that extend outward 
from an edge face of the package.

DETAILED DESCRIPTION OF THE INVENTION 
Referring now to FIG. 1, there is illustrated generally at 10 a 
microelectronic package of the present invention having improved cooling 
of an active electronic device, such as an integrated circuit or series of 
chips. FIG. 2 illustrates an exploded view of the various components of 
this improved microelectronic package 10. As illustrated, a lead frame die 
paddle 12 has top and bottom surfaces 14, 16 and receives the active 
electronic device on its top surface 14. Typically, the active electronic 
device 18 is a multi-chip module on a silicon substrate. The device 18 can 
include several active chips or integrated circuits bonded to the silicon 
substrate. For purposes of clarity, the active electronic device 18 will 
be referred to hereafter as a chip. The lead frame 12 includes a 
substantially planar, peripheral portion 20 extending outward from the 
chip 18 to form a plurality of leads 21 that connect to a circuit board. 
An epoxy molding compound body (package) 22 is molded over the lead frame 
and forms the substantially flat, rectangular package 10 having side faces 
24 as illustrated. Although a rectangular configured package 10 is 
illustrated and preferred, the package 10 can be almost any configuration 
desired by those skilled in the art. 
In accordance with the present invention, at least one cooling tube 30 is 
integrally molded within the encapsulating package in a typically 
serpentine manner as illustrated. The cooling tube 30 is formed of a 
thermally conductive material, such as copper or aluminum, and can be 
about 0.025 inches outer diameter and about 0.015 inches inner diameter. 
In one aspect of the present invention, the cooling tube 30 is spaced from 
the top surface 14 of the lead frame 12 and chip 18 as shown in FIGS. 3 
and 4. During manufacture, the cooling tube 30 is typically cantilevered 
over the chip 18 and supported by inserts in the mold or supporting 
elements on the lead frame (not shown). Then the epoxy molding compound is 
molded over the cooling tube 30, lead frame 12 and chip 18. 
In another aspect of the present invention, a second cooling tube 32, 
either singularly or in combination with the other cooling tube 30 is 
placed on the back side and mounted adjacent and preferably against the 
lead frame on the opposite side of the chip 18. In either configuration, 
however, the cooling tubes 30, 32 have two ends 34, 36 that extend outward 
from a side face 24 of the package 10. The illustrated figures show the 
two cooling tubes 30, 32 in the two locations as described above. Because 
the cooling tube 30 is formed from a high heat conductive material, such 
as copper or aluminum, heat generated by the integrated circuit is 
conducted through the cooling tube 30 and removed from the package 10. 
In a preferred aspect of the present invention, a cooling fluid is pumped 
through the cooling tube 30. The cooling fluid can be air such as provided 
by a normal fan 40 used in a personal computer 42, shown schematically in 
FIG. 3. In still another aspect of the present invention, the cooling 
fluid can be a liquid, such as water, or even a refrigerant. As shown 
schematically in FIG. 2, the refrigerant could be cycled by a refrigerant 
system 44 with flash vaporization and act as a two-leg natural convection 
loop so that the refrigerant flows through the refrigerant line, indicated 
by dotted line 46 without the need for any refrigerant pump. The heat 
generated by the chip 18 will provide part of the convective loop power 
necessary for moving the refrigerant. 
It should be understood that the foregoing description of the invention is 
intended merely to be illustrative thereof and that other embodiments, 
modifications, and equivalents may be apparent to those skilled in the are 
without departing from its spirit.