Integrated circuit package including a heat pipe

A plastic-encapsulated integrated circuit includes a package formed of plastic, an integrated circuit embedded in the package, and heat-dissipating means for conducting heat from the integrated circuit, which means include a hermetically sealed container formed of a heat conductive material embedded in the package and extending from the integrated circuit to at least an outer surface of the package, and a volatile fluid disposed in the container. In operation, the volatile fluid absorbs heat from the integrated circuit when it changes from the liquid state to the vapor state, and dissipates heat when it changes from the vapor state to the liquid state.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to the packaging of integrated circuits. 
2. State of the Art 
When designing integrated circuits, thermal factors must be considered 
because of the heat which the circuits generate during operation. 
Typically, integrated circuits are encapsulated by polymeric material that 
has relatively low thermal conductivity and, therefore, does not 
effectively dissipate heat that the chips generate. In low-power 
integrated circuit devices, lead frames have been relied upon for 
dissipating heat by thermal conduction. For dissipating heat in higher 
power integrated circuits, metal heat spreaders or heat sinks have been 
attached to the outside of the package or incorporated directly into the 
package as an insert during the molding step. 
SUMMARY OF THE INVENTION 
The present invention provides a plastic-encapsulated integrated circuit 
that includes a package formed of plastic, at least one integrated circuit 
embedded in the package, and heat-dissipating means for conducting heat 
from the integrated circuit, which means include a hermetically sealed 
container formed of a heat conductive material embedded in the package and 
extending from the integrated circuit to at least an outer surface of the 
package, and a volatile fluid disposed in the container. The volatile 
fluid absorbs heat from the integrated circuit while converting from a 
liquid to a vapor state, and dissipates the heat while converting from a 
vapor state to a liquid state. That is, the volatile fluid absorbs heat 
from the integrated circuit when it changes from the liquid state to the 
vapor state, and dissipates heat when it changes from the vapor state to 
the liquid state. 
Preferably, the container includes first and second frusto-conical portions 
disposed adjacent the integrated circuit and the outer surface of the 
package, respectively, and an intermediate cylindrical portion 
interconnecting the first and second portions. The intermediate portion is 
preferably of smaller cross-section than the first and second portions. 
Also, the container is preferably formed of metal so as to exhibit a high 
coefficient of thermal conductivity. Further, the lower end of the 
container preferably is bonded to the integrated circuit, as by a 
heat-conductive adhesive.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
As shown in FIGS. 1-3, an integrated circuit chip 110 is mechanically 
bonded to a metal die pad 112 and is electrically connected to a lead 
frame 114 by whisker wires 116. The chip 110, die attach pad 112, whisker 
wires 116, and inner portions of the lead frame elements 114 are 
encapsulated within a polymer package 120. The encapsulation process can 
comprise, for example, a conventional transfer molding process. (After 
encapsulation, the outer portions of the lead frame can be bent into a 
suitable configuration to facilitate mating with a connector.) 
The integrated circuit chip 110 in FIGS. 1 and 2 further includes a 
miniature container or pipe 130 which forms a hermetically sealed chamber 
partially filled with a volatile fluid 132 for increasing the 
heat-dissipating capacity of the chip. The container 130, which is 
embedded within the package 120 during the molding step, is formed of a 
relatively conductive heat conducting material, such as aluminum or 
copper. A bottom surface 135 of the container 130 is bonded to an upper 
surface of the chip by a conventional suitable adhesive, such as a 
heat-conductive adhesive (e.g., a polymer epoxy which contains a metal 
filler like silver) for promoting thermal conductivity. The interior of 
the container 130 is at a partial vacuum. 
In practice an upper surface of the container 130 lies flush with the outer 
surface of the package 120 or, alternatively, projects beyond the package 
120. 
In practice, the container 130 is shaped to present relatively larger 
surface areas at its upper and lower ends in order to maximize the heat 
absorption and dissipation properties of the container material. The 
depicted container 130 has an hourglass-like shape, comprising generally 
frusto-conical upper and lower portions 134, 136 interconnected by a 
cylindrical intermediate portion 138. 
The dimensions of the container 130 must be quite small. For example, it is 
expected that the diameters of the container 130 at the top and bottom 
ends thereof will be in the range of about 0.20 to about 1.20 inches, the 
diameter of the container 130 at the center of its height will be in the 
range of about 0.05 to about 0.25 inches, and the overall height from 
end-to-end will be in the range of about 0.15 to about 0.50 inches. 
In practice, the container 130 is formed by a suitable process and then is 
bonded to the chip surface prior to the molding of the package, so as to 
become embedded in the package following the package-molding step. 
In operation, the container 130 acts as a "heat pipe" wherein fluid, which 
normally is in a liquid state at the lower end of the container 130, 
vaporizes upon absorbing sufficient heat from the chip. As the vapor rises 
toward the upper, cooler end of the container 130, it condenses and 
thereby emits heat. Thus, the volatile fluid should be one, such as 
alcohol, that vaporizes at a relatively low temperature. Preferably, the 
fluid should vaporize at a temperature no greater than about 40.degree. C. 
As a result of operation of the above-described device, thermal energy 
generated by the chip is dissipated through the lead frame and, also, 
heats and vaporizes the fluid in the container 130. The heated vapor rises 
toward the top of the container 130 where it gives off heat. Upon 
recondensing, the fluid gravitates as a liquid back to the bottom of the 
container 130 to be revaporized. 
The foregoing has described the principles, preferred embodiments and modes 
of operation of the present invention. However, the invention should not 
be construed as limited to the particular embodiments discussed. Instead, 
the above-described embodiments should be regarded as illustrative rather 
than restrictive, and it should be appreciated that variations may be made 
in those embodiments by workers skilled in the art without departing from 
the scope of present invention as defined by the following claims.