JPH06209060A - Device and method for cooling semiconductor chip - Google Patents

Abstract

PURPOSE: To disclose a method and device for cooling a multi-chip module by using a buried heat pipe. CONSTITUTION: A semiconductor chip 10 is arranged in a multi-chip module via the cavity of a module substrate 12. The semiconductor chip is engaged to a heat pipe 38 that is buried into a substrate. The heat pipe propagates heat via a heat conduction junction layer 14 and delivers it out of the semiconductor chip.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to cooling multichip modules. More particularly, the present invention relates to embedding a heat pipe in a substrate of a multichip module to cool semiconductor chips mounted on the multichip module.

[0002]

An important goal in computer design is to fit the largest number of semiconductor chips, or ICs, into the smallest space. Factors such as board design, interconnect design, cooling method, and chip array density are highly relevant to the ultimate performance of the computer. Designers are trying to maximize the computing power of computers while making them as small as possible, but as a result, the packaging density of IC chips is increasing.
Along with this, the density of interconnects forming signal paths between ICs must be increased. Unfortunately, network dense interconnects tend to generate heat.

In addition, the higher the computational power, the faster the instructions can be executed. In order to have more instructions executed per second, the circuit must operate at a higher frequency. Operating at higher frequencies requires a higher energy input, which increases the energy generated in the device. A byproduct of high energy input is heat.

High computing power also means having the ability to execute larger instruction sets. As a result, semiconductor devices used within a given area need to have greater storage capacity to accommodate their increased capabilities. Therefore, more energy is required to operate a larger number of memory devices. In this case as well, an increase in the energy input leads to an increase in the energy that appears as heat. Therefore, cooling of these devices is a major consideration.

In a conventional computer, the circuit is simply cooled by convection of air circulated by a fan. However, the use of fans in conjunction with high density, multi-chip, mainframe computers requires large amounts of air for cooling, thus requiring a powerful blower and large ducts. Such clunky structures in computers took up valuable space and were noisy.

There are other ways to cool an IC, for example, Kucharek US Pat. No. 4,748,495.
U.S. Pat. No. 5,837,058 discloses a package for cooling a high density array of IC chips and their interconnections. In this configuration, I
The C chips are mounted as an almost flat array, separated by a flexible membrane mount, and a heat sink is connected to the IC. Therefore, all cooling structures are separated by the membrane mount and mounted on the top surface of the IC. Therefore,
A cooling fluid is pumped through the cooling structure and carries the coolant through a region above the IC.

Similarly, US Pat. No. 4,879,629 to Tustaninskyj et al. Discloses a liquid cooled multi-chip integrated circuit module that incorporates a seamless compliant member to provide leakage protection. In particular, the heat sink is placed directly on the top surface of the IC, while the top surface of the heat sink is provided with a conduit for carrying liquid coolant, which conduit is incorporated into the rigid cover. The compliant member seals the area of the conduit from the tip area to eliminate the risk of liquid coolant leakage.

Due to variations in the manner in which the IC is mounted on the substrate, the top surface of the IC appears to be tilted at various different angles, which impedes the conduction of heat to the heat sink. U.S. Pat. No. 5,005,638 to Goth et al.
Provide a structure for ensuring a solid contact between a heat sink and an IC. Goth discloses a barrel-shaped piston that is spring loaded and biased toward the IC chip to compensate for the small tip tilt by the spring. There, the heat rises from the IC chip through the barrel-shaped piston and reaches a large heat sink. Pump coolant through a heat sink to aid in heat dissipation.

Positioning the coolant fluid above the chip, as is the case in the prior art, unfortunately always presents a risk of coolant leakage. Should a leak occur, assuming that the coolant is conductive, the malfunction could be quite significant. Even if the coolant is not conductive, it will contaminate the chip and cause another reliability issue. Moreover, the structures required for fluid communication and heat sink-chip contact are usually very complex. Such complex structures require great care during assembly and are usually expensive to manufacture.

Finally, Chao US Pat.
No. 5,404 discloses a cooling device mounted on a printed circuit board. The printed circuit board has holes for receiving a cooling device composed of several layers including a heat spreader, a heat pipe and a heat sink. The heat spreader engages the semiconductor chip through a hole in the printed circuit board. The heat spreader is mounted on the lower surface of the printed circuit board, and the heat pipe is mounted on the heat spreader via an intermediate layer. The heat sink is connected to the heat pipe. Unfortunately, in such multilayer cooling devices, heat is not efficiently conducted, as each layer adds a resistive barrier to heat conduction. Furthermore, since the cooling device mounted outside as described above expands the space required for the printed circuit board, the overall shape factor of the system including the printed circuit board becomes large.

[0011]

SUMMARY OF THE INVENTION An object of the present invention is to provide a novel device and method for cooling an IC, in which the above-mentioned drawbacks of the conventional cooling means are improved.

[0012]

SUMMARY OF THE INVENTION The present invention is a method and apparatus for cooling a multichip module using an embedded heat pipe. The embedded heat pipe conducts heat out of the semiconductor chip located in the multi-chip module through the cavity of the module substrate.

In one embodiment, the module cooling device comprises a substrate having an integral heat conducting layer coupled to the heat pipe. The substrate is formed with a plurality of cavities for receiving semiconductor chips through the top surface of the substrate. The heat conductive layer is embedded in the bottom surface of the substrate. The upper surface of the heat conducting layer engages with the semiconductor chip through the cavity. A heat pipe that absorbs heat from the heat conducting layer engages the bottom surface of the heat conducting layer. The heat generated by the semiconductor chip is conducted through the heat conducting layer and dissipated by the heat pipe.

In another embodiment, the module cooling device comprises a substrate having a plurality of heat pipes embedded therein. A plurality of cavities are formed through the top surface of the substrate to receive the semiconductor chips. The upper surface of each heat pipe housed in the substrate engages with the semiconductor chip via the corresponding cavity. The heat generated by the semiconductor chip is conducted through the thermoplastic bonding layer and dissipated by the heat pipe.

[0015]

The following specification describes a method and apparatus for cooling a multi-chip module using an embedded heat pipe. Although specific materials and configurations are set forth in this description for a more complete understanding of the invention, those skilled in the art will understand that the invention may be practiced without these specific details. In other instances, well-known elements have not been described in detail so as not to obscure the present invention.

The present invention does not simply bolt the heat pipe, but integrates the heat pipe directly onto the multi-chip module (ie MCM) substrate. This is in sharp contrast to the prior art of adding a separate cooling structure to the MCM substrate. By directly embedding the heat pipe in the MCM, assembly of the product is much simpler and reworkable.

In the MCM package cooled according to the present invention, the coolant is sealed inside the substrate, so that the coolant is unlikely to leak, and therefore the risk of chip contamination is minimized. Moreover, the simplified construction of the cooling mechanism ensures that the manufacturing costs of the present invention are lower compared to conventional cooling devices. Also, the reliable contact between the cooling mechanism of the present invention and the IC chip provides more efficient heat transfer compared to conventional devices that required various make-up hardware to obtain reliable contact.

Referring now to FIG. 1, there is shown a multichip module just prior to installing the heat pipe. The mounting substrate 12 holds a plurality of semiconductor chips 10. In one embodiment, the mounting substrate 12 has a network of cavities 34 that extend completely through the thickness of the substrate 12. The semiconductor chips 10 are inserted into their cavities 34 by various methods known in the art.
An electrical interconnect (not shown) provided on the chip 10 and the upper surface 26 of the mounting substrate enables electrical communication between the chip 10 and an electrical interface with an external device. Conventional wire interconnects may be soldered to the chip 10 for this purpose. Alternatively, as disclosed in Conte US Pat. No. 5,121,293, more specific tape bonding (TA
B) Techniques can be used to form the interconnects. After mounting, it is preferable to pull the semiconductor chip 10 into the substrate 12 so that the bottom surface 36 of the semiconductor chip 10 is exposed. The heat conducting means 14 embedded in the bottom surface 28 of the mounting substrate 12 is to be engaged with the bottom surface 36 of the chip 10. An interference fit is sufficient to mechanically hold the heat transfer means 14 in place. Other mounting means such as cement, mechanical fasteners or other means known in the art are suitable for holding the heat transfer means 14 in place. In this way, a secure engagement is obtained between the bottom surface 36 of each chip 10 and the heat conducting means 14. In one embodiment, the heat conducting means 14 is copper slag. Obviously, instead of copper slag, other heat transfer devices known in the art are also acceptable.

A bonding process is used to ensure proper heat flow from the semiconductor chip 10 to the heat conducting means 14. The die mounting process includes supplying a small amount of heat conducting thermoplastic material to bond the die 10 to the heat conducting means 14. Initially the thermoplastic material is a fluid and flows to fill any voids in the joint. After curing, the bond is solid in that no further flow occurs, but the bond remains flexible. In one example, the thermoplastic material should be hexagonal boron nitride. Even if the mounting substrate 12 flexes during assembly, it is important that the compliance of the thermoplastic material maintain a strong thermal bond.

In one embodiment, the heat pipe 38 dissipates the heat stored in the heat transfer means 14. Heat pipe 3
8 is preferably formed from copper or aluminum. In order to transfer heat efficiently by conduction, it is preferable to attach the heat pipe 38 directly and securely to the heat conducting means 14. Conventional mechanical fasteners, such as screw tightening, can be used to lock the two structures together. Furthermore, there should be no air gaps between the contact surfaces that would impede heat transfer.

The heat pipe 38 functions similarly to a small refrigerator (not shown). In a typical closed circuit refrigeration cycle, heat is transferred to an evaporator that evaporates a liquid coolant, so that the coolant enters the compressor and the compressor delivers high pressure vapor to the condenser. The condenser dissipates the heat out of the system and condenses the coolant back into liquid form. afterwards,
The condensate returns to the evaporator through the pressure reducing expansion valve, from which the cycle is repeated. The principles used here are well known in the art and need not be described in further detail.

The same principle is applied to the heat pipe 38 used in the present invention. Heat pipe 38
Inside the hollow casing 24 is a chamber containing a coolant or coolant 18, and a wick 16.
In one embodiment, the coolant 18 is a dielectric fluorohydrocarbon. As shown in FIG. 2, one side of the heat pipe 38 is in contact with the bottom surface 32 of the heat conducting means 14, while the other side of the heat pipe 38 is separated. Of the heat pipe 38,
The region closest to the heat transfer means 14 acts as the evaporator 22, and the region farthest away functions as the condenser 20. Thus, as heat enters the evaporator 22 from the heat transfer means 14, the coolant 18 in that area evaporates and leaves the evaporator 22 and heads to the condenser 20. In the condenser 20, the vapor is cooled and the heat is transferred to the casing 2
It dissipates through 4 and returns to liquid form after exiting through heat dissipation surface 40.

After condensing in liquid form, the coolant 18 is drawn back by capillary action through the wick 16 and the evaporator 2
Enter 2. As is known in the art, capillary action is due to surface tension, ie, aggregation of liquid molecules and adhesion of the molecules to the surface of a solid. When the stickiness is greater than the cohesion, the liquid is drawn along the wick from the wet side to the dry side. Therefore, the coolant 18 is
A closed loop cycle is established by evaporating at 1, moving to the condenser 20, where it condenses to a liquid and is eventually drawn into the wick 16 and returned to the evaporator 22.

In one embodiment, a motherboard (not shown)
During final assembly into the mounting substrate 12, the mounting substrate 12 is flipped along with the associated devices. Therefore, the bottom surface 26 and the semiconductor chip 10 are all facing downward and face the motherboard.
As a result, the heat pipe 38 occupies the highest position on the mounting board 12. Heat pipe 3
Ideally, the condenser 20 of 8 is placed higher than the evaporator 22. With this particular orientation setting, heat travels upwards, thus optimizing heat transfer and heat dissipation from the heat generating device 10. Also, as the lighter vaporized coolant 18 rises from the evaporator 22, the denser and heavier condensed liquid coolant 18 is drawn back into the vaporizer 22 by gravity and the action of the wick 16. Fin 4 having a structure well known in the art
An optional second heat sink 42 with 4 can be added to the heat dissipation surface 40. The above configuration is only one of the configurations for attaching the heat pipe 38 to the heat conducting means 14.

In another configuration (not shown), the heat pipe may extend to one side of the heat transfer means. In this arrangement, the entire area closer to the heat transfer means acts as an evaporator, while away from the heat transfer means,
The remote part, which is not engaged with it, functions as a condenser.

FIG. 3 is a perspective view of an example of the multichip module 100. The semiconductor chips 120 to 123 are fitted into the upper surface 114 of the substrate 110 through a cavity. In the substrate 110, a group of heat pipes 150-1
Contains 71. For module 100 of this example,
The heat pipes 150 to 171 run along the length direction of the module 100.

FIG. 4 is a plan view of the module 100 of this example. The semiconductor chips 120 to 123 are arranged in a set of cavities 140 to 143 formed on the upper surface 114 of the substrate 110. The cavities 140 to 143 expose the upper surfaces of the heat pipes 150 to 171. The semiconductor chips 120 to 123 are arranged in the substrate 110 and are engaged with one or more heat pipes 150 to 171. The heat pipes 150 to 171 are semiconductor chips 120.
Dissipate the heat generated by ~ 123. In one embodiment, heat pipes 150-171 are preferably made of copper or aluminum.

In one embodiment, the heat pipe 150
The ends of ~ 171 that penetrate the surface 112 of the substrate 110 are closed. However, in other embodiments, the heat pipes 150-171 are completely enclosed within the substrate 110, depending on the thermal configuration of the system including the module 100.

The heat pipes 150 to 171 function similarly to the heat pipe 38 described above. Each heat pipe 150-171 has a coolant, i.e., a chamber containing a coolant, and a wick. In one example, the coolant is a dielectric fluorohydrocarbon. Semiconductor chips 120-1
The area of the heat pipes 150 to 171 closest to 23 functions as an evaporator, and the area of the heat pipes 150 to 171 farthest from the semiconductor chips 120 to 123 functions as a condenser.

Heat enters the evaporators of the heat pipes 150-171 from the semiconductor chips 120-123. After that, the coolant near the semiconductor chips 120 to 123 evaporates and moves away from the evaporator toward the condensers of the heat pipes 150 to 171. Coolant vapors are cooled in the condenser,
A heat pipe 150 penetrating the substrate 110 and the surface 112.
The coolant returns to liquid form as heat is dissipated through the ends of ~ 171. After condensing in liquid form, the coolant is drawn back by capillary action through the wick to the evaporator, thereby establishing a closed loop cycle.

FIG. 5 is a side view of an example of this example module 100. As shown, the semiconductor chip 120,
121 is fitted on the upper surface 114 of the substrate 110.
Further, the heat pipes 150 to 171 are the module 100.
Running along the length of. The semiconductor chip 120 is arranged in a cavity 140 formed in the upper surface 114 of the substrate 110. Similarly, the semiconductor chip 121 also has a substrate 110.
Is arranged in a cavity 141 formed in the upper surface 114 of the. The semiconductor chips 120 and 121 are heat pipes 15.
Engage with the upper surface of 1-156.

FIG. 6 is a cross-sectional view showing a portion of the module 100 of this example. As illustrated, the semiconductor chip 121 is arranged in the cavity 141. Cavity 14
1 is formed on the upper surface 114 of the substrate 110. Further, the heat pipes 150 to 156 are shown as viewed through the surface 112 of the substrate 110.

Between the semiconductor chip 121 and the substrate 110,
Also, the semiconductor chip 121 and the heat pipes 151 to 15
A contact joint part 144 is formed between the contact joint part 144 and the upper surface of 6.
The heat generated by the semiconductor chip 121 is applied to the contact bonding portion 14
4 and enter the evaporator of heat pipes 151-156. The heat generated by the semiconductor chip 121 is dissipated by the heat pipes 151 to 156 as described above.

In one embodiment, a heat conductive thermoplastic material is applied to the contact joint 144 to bond the semiconductor chip 121 to the cavity 141. The heat conducting thermoplastic material also ensures an efficient heat flow from the semiconductor chip 121 through the contact joint 144 to the top surface of the heat pipes 151-156. Initially, the thermoplastic material is a fluid and flows to fill all voids in the contact joint 144. After curing, the bond solidifies in that no further flow occurs, but the bond remains flexible. In one embodiment,
The thermoplastic material is hexagonal boron nitride. The compliant nature of the thermoplastic material maintains a firm thermal bond even when the substrate 110 flexes.

Other configurations of heat pipes known in the art are also suitable and, depending on space constraints or particular heat transfer applications, the heat pipes can be easily reoriented according to the present invention. Indeed, many modifications of the invention are possible and the actual scope of the disclosure should be determined by reference to the claims.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a multi-chip module in which a heat sink is integrated on a substrate.

FIG. 2 is a cross-sectional view of a multi-chip module in which integrated heat pipes are joined to a heat sink.

FIG. 3 is a perspective view of an example of a multi-chip module in which a set of semiconductor chips is arranged in a cavity on the upper surface of a module substrate.

FIG. 4 is a plan view of an example module showing semiconductor chips arranged in a series of cavities on the top surface of a substrate.

FIG. 5 is a side view of an example module showing a semiconductor chip disposed within a substrate and showing a heat pipe embedded in the substrate and running along the length of the module.

FIG. 6 is a cross-sectional view showing a portion of an example module and showing a semiconductor chip disposed in a cavity of a module substrate.

[Explanation of symbols]

 10 Semiconductor Chip 12 Mounting Substrate 14 Heat Conducting Means 16 Wick 18 Coolant 20 Condenser 22 Evaporator 24 Casing 38 Heat Pipe 100 Multi-chip Module 110 Substrate 120-123 Semiconductor Chip 140-143 Cavity 150-171 Heat Pipe

Claims (3)

[Claims] 1. A substrate having a plurality of cavities for receiving a semiconductor chip from the upper surface of the substrate; heat conducting means having an upper surface embedded in the bottom surface of the substrate and engaging with the semiconductor chip through the cavities; A semiconductor chip comprising: a heat pipe in which heat generated by a chip is transferred through the heat conducting means, engages with a bottom surface of the heat conducting means to dissipate the heat, and absorbs the heat from the heat conducting means; Cooling device. 2. A substrate having a plurality of cavities for receiving a semiconductor chip through an upper surface of the substrate, and an upper surface for engaging the semiconductor chip through the cavities to dissipate heat generated by the semiconductor chip. An apparatus for cooling a semiconductor chip, comprising a plurality of heat pipes contained inside. 3. Embedding a plurality of heat pipes having an upper surface that engages the semiconductor chip in a substrate for mounting the semiconductor chip; a semiconductor chip for receiving the semiconductor chip through the upper surface of the substrate. Forming a plurality of cavities that expose the upper surface of the heat pipe according to the dimensions of the semiconductor chip; A method of cooling a semiconductor chip comprising the steps of bonding to a top surface and a substrate.