JPH04305965A - Multichip module and manufacture thereof - Google Patents

Abstract

PURPOSE:To propose a water cooling system for electronic computers which are greater in cooling performance and moreover excellent in assemblability. CONSTITUTION:An insulation board 6 is bonded (soldered or the like) on chips 2 laid out on a board 1. A border board is arranged to come into contact on this layout. Cooling fins 5 are bonded on the board 4 at a relative position to the chips. When a hat 7 is caped on the fins and water is adapted to flow, the water forcibly runs in the cooling fins, thereby enabling the heat generated from the chips to be removed efficiently. There are proposed different systems which enhance assemblability, such as sealing structure which uses an O ring at an adjustment stage and air-tight sealing structure at an adjustment end stage.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cooling structure for effectively removing heat generated from a multi-chip module, particularly a multi-chip module using large integrated circuit chips.

0002

[Prior Art] Multi-chip modules used in large-scale electronic computers have a structure in which multiple integrated circuits are mounted on a single wiring board. This is extremely important as it affects performance. In recent years, the cooling method has been shifting from the conventional air cooling method to a water cooling method, and several proposals have been made. As an example, JP-A-59-2004
95, as shown in FIG. 5, a method is adopted in which cooling structures 101 are individually attached to the top surface of the chip 2, and the cooling structures are connected using flexible pipes 102 such as bellows. was. This method has been proven to have extremely excellent cooling performance. However, when trying to assemble a module based on this method, the structure is complex, so it requires a lot of assembly man-hours.
Very advanced technology was required to complete the cooling structure with high reliability.

0003

SUMMARY OF THE INVENTION An object of the present invention is to provide a cooling structure that is easy to assemble and has excellent cooling performance. In particular, the purpose is to simplify the structure by omitting the bellows, which was the biggest factor that made assembly difficult. Furthermore, another object of the present invention is to provide a cooling structure in which cooling efficiency is not affected by variations in height between chips that are unavoidable due to manufacturing technology. Still another object is to provide a multi-chip module in which chips can be easily replaced in the event that an integrated circuit chip fails.

0004

[Means for Solving the Problems] In order to achieve the above object, in the present invention, fins are arranged on a flexible boundary plate at positions corresponding to individual chips to be cooled. The chip is cooled by forcing a refrigerant (cooling water, etc.) to flow through the fins while the plate is in contact with the chip.

[0005]

[Operation] When refrigerant is flowed through such a structure, since the boundary plate is flexible, it is pressed against the chips by the pressure of the refrigerant, causing the individual chips to vary in height or tilt due to alignment errors. The heat generated from the chip is transferred from the boundary plate to the refrigerant through the fins.

Although this structure has a certain degree of cooling performance even without fins, it is extremely effective to increase the heat transfer area by providing fins in order to improve the cooling performance. Furthermore, in order to increase the heat conduction efficiency, it is important to minimize the thermal resistance of the heat conduction path. For this purpose, a material with high thermal conductivity is used for the fins and the boundary plate, and the two are connected by a metal with high thermal conductivity, such as by soldering or brazing. Furthermore, although the chip and the boundary plate are brought into contact with each other, in order to reduce the thermal resistance, a highly thermally conductive gas such as helium is filled. Alternatively, it is effective to apply thermal conductive grease or the like.

[0007]

EXAMPLES The present invention will be explained in detail below based on examples.

FIG. 1 shows an embodiment of the present invention. Board 1
A 10mm2 chip 2 is placed on top of the CCB (Control
This figure shows a case in which the modules are arranged in 4 rows by 4 columns using the Collapse Bonding method, and the structure of the module is partially represented by a cross section.

On the boundary plate 4, on the surface opposite to the chips to be cooled, fins 5 are provided corresponding to each chip.
are arranged in 4 rows x 4 columns. Here, a copper plate with a thickness of 0.2 mm is used for the boundary plate 4, and a copper block is cut for the fins 5 to form fins in the shape of 5 (each fin has a thickness of 0.2 mm, They are 0.2 mm apart, 2 mm high, and integrally molded on a 10 mm 2 x 0.5 mm (t) bottom plate, and both are joined by silver brazing.

On the other hand, an insulating plate 6 was bonded to the surface of the boundary plate that was in contact with the chip. This is unnecessary when the back surface of the chip is at zero potential, but in this example, since it was not at zero potential, it was provided for the purpose of preventing all the chips from being electrically connected by the boundary plate 4. It is something. A material having high thermal conductivity and high electrical insulation properties is suitable for this insulating plate, and ceramics such as SiC (Hitaceram SC-101: registered trademark) are also suitable. However, this time, we will use a plate of high thermal conductivity AlN ceramics (10 x 10 x 0
．． Ti-Ni-Au was vapor-deposited on one side of the 3mm) and bonded to the boundary plate using high melting point solder (Au-Sn - melting point 280°C). (Solder is not limited to the above, and can be selected as long as it has a higher melting point than the solder used in the subsequent process.Also, the thinner the insulating plate is, the lower the thermal resistance will be, (0.2 to 0.5 mm is preferable considering the properties.) The boundary plate prepared as described above was joined to the hat 7 as shown in FIG. The hat 7 is provided with a pair of supply/drain ports 72 and a partition wall 71 for circulating the refrigerant to the fins. It was made of Kovar, which has a coefficient of thermal expansion similar to that of the substrate 1, and was plated with gold. When joining the boundary plate to this hat, the lower surface 751 of the flange portion 75 was hermetically sealed with solder while the fins 5 were inserted into the grooves (refrigerant passages 76 in FIG. 3) formed by the partition wall 71. At the same time, a spacer 73 (frame-shaped with a square cross section) made of the same material as the hat 7 (gold-plated Kovar) was hermetically sealed with solder on the opposite surface of the boundary plate 4. In this case, a solder having a lower melting point than that used to bond the insulating plates 6 (Sn-Ag - melting point 221° C.) was used, and the solder was reflowed all at once in a vacuum furnace. Note that the groove 74 provided in the flange portion of the hat is provided for the purpose of reducing the heat capacity of the flange portion and clarifying the solder connection range during solder reflow.

[0011] The connection surface 751 after reflow must not leak when refrigerant is flowed through the hat, and must be hermetically sealed. Also, the joint surface 731 with the spacer on the opposite side
Also, when considering the inclusion of He, airtight sealing is required.

[0012] When the cooling structure prepared in this manner is placed on the substrate, the structure is completed in appearance. Here, two methods are possible for connecting the interface 10 between the spacer 73 and the substrate 1 depending on the method of thermal contact between the chip 2 and the insulating plate 6. That is, when the chip 2 and the insulating plate 6 are in simple contact or in contact with each other with thermally conductive grease applied, the interface 10 does not necessarily need to be hermetically sealed and may be simply screwed together. It is possible to use a structure in which it is screwed through an O-ring. In this case,
If the chip is found to be electrically defective after assembly, it is extremely easy to replace it.

On the other hand, H is formed on the contact surface between the chip 2 and the insulating plate 6.
When encapsulating e, it is necessary to hermetically seal the interface 10. This method uses solder that has a lower melting point than the solders that have been used so far (for example, Pb-Sn solder).
A reflow method using a melting point of 183° C. is preferred.

[0014] Regarding the above two methods, in this example, two were used in combination. That is, a groove for fitting the O-ring 8 is provided around the boundary surface 10 of the spacer 73 along its center line, and in the stage of adjusting the electric circuit, the circuit is adjusted while being cooled using the O-ring. When the adjustment was completed, it was hermetically sealed and He was encapsulated. To enclose He, connect a pipe 9 to one place of the spacer 73 as shown in FIG.
Finally, pipe 9 was sealed and cut.

The cooling function of the cooling structure assembled in this way will be explained. That is, when cooling water is flowed as a refrigerant through the pair of suction/drainage ports 72, the boundary plate 4 is deflected by the water pressure as shown in FIG. is guaranteed. In order to make full use of this function, it is necessary to keep the following two points in mind.

(1) The dimensions of the refrigerant passage 76 include the fins 5.
Allowing room for rotation: In order to utilize the flexibility of the boundary plate, the fins 5 must not come into contact with the partition wall 71 of the hat and be prevented from rotating. Therefore, the dimensions of the passage must be larger than the fins 5, and the gap between them is 0.2 to 0.5 m on one side for a 10 mm2 chip.
A value of about m was appropriate. (If this gap is too large, the flow of water between adjacent passages will increase, and if an abnormality occurs such as dirt clogging one of the fins, the water will flow avoiding that fin. As a result, variations in cooling performance tend to occur.) (2) Adjust the water pressure appropriately: The force that bends the boundary plate 4 and brings it into contact with the chip 2 is generated by water pressure. If you gradually increase the water pressure when you start flowing cooling water, the cooling performance will increase rapidly with the water pressure, but after a certain pressure, the cooling performance will gradually stop changing. This is because, after the chip 2 and the insulating plate 6 have almost sufficient contact, the cooling performance hardly changes even if the pressure is increased. Furthermore, if the pressure is increased too much, the solder bumps 3 connecting the chip 2 and the substrate 1 are likely to be damaged. therefore,
The pressure must be maintained at an appropriate value (in the case of this example, about 1 to 2 atmospheres).

In this embodiment, a copper plate was used as the boundary plate 4. It is desirable that this material not be corroded by the refrigerant, have a coefficient of thermal expansion as close as possible to that of the hat 7, and have as high a thermal conductivity as possible. From this point of view, the material of the boundary plate 4 is Ti, Ni,
Pt, Mo, Ag, etc. are also applicable. The material of the fins should preferably have the same coefficient of linear expansion as the above-mentioned materials and a high thermal conductivity. From this point of view, it is also effective to manufacture the fins from highly thermally conductive ceramics (AlN, Hitaceram, etc.). However, in the case of AlN, it begins to chemically dissolve upon contact with water. In order to prevent this, the surface of the AlN fin is treated to increase its water resistance, for example, (1) the surface is oxidized to form Al2O3 on the surface.

(2) It is effective to deposit a water-resistant substance by vapor deposition or the like (ion plating of a metal such as Pt, deposition of glass using Parylene (trade name), etc.). Further, as the shape of the boundary plate 4, a flat plate was used in the above embodiment. However, as shown in FIG. 4, it is also effective to form a bellows 41 around the fins to be joined. That is, if a boundary plate formed in this manner is used, the flexibility in the vertical direction is increased, and contact with the chip 2 as shown in FIG. 3 can be easily obtained, which is more effective.

[0019]

According to the present invention, excellent cooling performance can be obtained without employing the complicated structure disclosed in the above-mentioned known examples. Specifically, (1) there is no need to use an independent cooling member for each chip, and bellows and cooling members can be omitted. ■Since the refrigerant does not need to pass through narrow diameter pipes such as bellows, the flow resistance of the refrigerant is significantly reduced. ■As the structure is simpler and easier to assemble, assembly reliability increases and variations in thermal resistance depending on location are reduced. There are advantages such as Regarding cooling performance, in the case of the above-mentioned known example, the cooling member was soldered to the back side of the chip 2, so the thermal resistance from the chip to the cooling member is larger in the present invention, and this part is The thermal resistance increases by about 30 to 50%. However, as for the overall cooling structure, the cooling rate was 1℃/W in the known example, but the cooling rate was 1℃/W.
．． The thermal resistance is about 2° C./W, and cooling of about 40 W is possible.

[0020] According to the present invention, another great advantage is that the thickness of the module can be reduced. In other words, when large-scale electronic circuits are required, such as in large-scale computers, many modules like the one shown in Figure 1 are often stacked on top of each other. , it is possible to obtain high-performance functions in a small size. From this point of view, the suction/drainage ports shown in FIG. 1 do not necessarily need to be located on the top surface of the module, but may be appropriately selected such as provided on the side surface. In addition, in the above embodiment, the cooling water is
Although a method has been described in which the book passages 76 are made to flow in parallel, this is not an essential condition, and a method such as allowing the books to flow in one passage and then moving to the next passage may also be considered.

[0021] There are many applications for water cooling systems using fins for water cooling electronic computers (for example,
Application No. p63-156760 (Publication No. p02-
007456)). In these methods, although fins are arranged on the back surface of the chip, a method of forcing water to flow through them is not adopted. In order to improve cooling performance, it is extremely important not only to sprinkle water onto the fins, but also to adopt a structure that forces water to pass through the fins. The present invention presents a practical method for this purpose, that is, a method that is easy to assemble and has high cooling performance. Therefore, if the present invention is applied to devices that require large-scale, high-speed electronic circuits, such as electronic computers, a significant effect can be obtained in improving the performance thereof.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing one embodiment of the basic structure of the present invention.

FIG. 2 is an explanatory diagram showing an airtight sealing method.

FIG. 3 is an explanatory diagram showing a state of contact with a chip according to the present invention.

FIG. 4 is an explanatory diagram of a structure in which bellows are formed on the boundary plate.

FIG. 5 is a diagram for explaining a conventional structure.

[Explanation of symbols]

1...Substrate, 2...chip, 3...Solder bump, 4...Boundary plate, 5...fin, 6...Insulating board, 7...hat, 8...O-ring, 9...Sealed tube.

Claims (6)

[Claims] 1. A multi-chip module mounting a plurality of semiconductor chips, wherein a metal plate is provided in contact with the semiconductor chips, and cooling fins are provided at opposing positions on the surface of the metal plate opposite to the semiconductor chips. A multi-chip module characterized in that the cooling fins are joined together and a refrigerant is forced to flow through the cooling fins. 2. The multi-chip module according to claim 1, wherein an insulating plate is interposed between the semiconductor chip and the metal plate. 3. The multi-chip module according to claim 1, wherein thermally conductive grease is interposed between the semiconductor chip or the insulating plate and the metal plate. 4. The multi-chip module according to claim 1, wherein the semiconductor chip is hermetically sealed and then a highly thermally conductive gas is sealed therein. 5. According to claim 1 or 2, a cooling structure in which thermally conductive grease is applied on the semiconductor chip is provided at the stage of adjusting the electronic circuit of the multi-chip module, and at a stage when the adjustment of the electronic circuit is completed. A method for manufacturing a multi-chip module, which comprises hermetically sealing the semiconductor chip and filling it with a highly thermally conductive gas. 6. An electronic computer comprising a multi-chip module employing the cooling structure according to claim 1 or 2.