JPH0680757B2 - Semiconductor module - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a semiconductor module in which a plurality of semiconductor elements are mounted on a wiring board and cooling means for cooling the elements is provided, and particularly to a large computer. The present invention relates to a semiconductor module suitable for use and a cooling device therefor.

[Conventional technology]

Semiconductor devices used in high-speed data processing devices, etc., have higher integration and higher power consumption of semiconductor elements in order to improve the data processing speed, and as a result, the amount of heat generated from semiconductor elements is cooled by forced air cooling or other cooling means. The limit that can be cooled has been exceeded. Therefore, in a semiconductor device used in a large-scale computer or the like, it has been considered to cool the semiconductor element using a liquid such as water or a boiling refrigerant.

As one method for effectively cooling a plurality of semiconductor elements mounted on a wiring board by using a cooling liquid such as water, there is an individual cooling method for cooling each semiconductor element, which is disclosed in JP-A-61-2203.
It is disclosed in Japanese Patent Publication No. 59.

In this semiconductor element individual cooling method, as shown in FIG. 6, a cooling plate is joined on the semiconductor element, and a housing having a cooling liquid flow path and a cooling plate are connected by a bellows to flow in the housing. This is a method of cooling a semiconductor element by bringing a cooling liquid into contact with a cooling plate.

By doing so, it is possible to guide the cooling liquid to the vicinity of the semiconductor element, thereby enhancing the cooling effect of the semiconductor element and suppressing an increase in the thermal resistance of the semiconductor element.

[Problems to be solved by the invention]

In the above-mentioned conventional technique, the wiring board and the semiconductor element, and the semiconductor element and the cooling plate are all solder-bonded. For this reason, when a thermal strain occurs between the wiring board and the housing and a position shift occurs, the displacement is absorbed by the deformation of the bellows, but the stress generated at that time is directly caused by the wiring board and the semiconductor. It will be added to the solder joint with the element.

Bellows generally have a property that they are easily deformed in the axial direction but are hard to be deformed in the direction perpendicular to the axis. For this reason, great stress is generated with respect to the positional deviation between the wiring board and the housing in the horizontal direction. On the other hand, the fatigue life of the solder joint between the wiring board and the semiconductor element has a small decrease under compressive stress, but has a characteristic that the life is remarkably decreased under shear stress, that is, under the above-mentioned horizontal stress.

Due to this, when the wiring board is increased in size to several tens of mm or more, the solder joint between the wiring board and the semiconductor element is caused by thermal strain in the shearing direction due to temperature fluctuations during semiconductor module assembly or use due to solder joining. Has a problem that its fatigue life is shortened and the reliability of the device is significantly impaired.

The object of the present invention is to reduce the stress applied to the solder joint between the wiring board and the semiconductor element even when the bellows is deformed due to the thermal strain between the wiring board and the housing. It is to provide a semiconductor module capable of suppressing the reduction of life.

[Means for solving problems]

The present invention provides a plurality of semiconductor elements mounted on a wiring board,
A cooling plate joined to the semiconductor element and cooled by contact with a cooling medium, a housing having a flow path of the cooling medium brought into contact with the cooling plate, and a connection between the housing and the cooling plate. In a semiconductor module including a bellows for bringing a cooling medium in the housing into contact with the cooling plate, a member is used, one of which is joined to an end of the cooling plate and the other of which is joined to the wiring board.

By directly fixing the cooling plate and the wiring board in this manner, the stress due to the deformation of the bellows is hardly applied to the solder joint between the wiring board and the semiconductor element, and the wiring board and the semiconductor element are fixed to each other. It comes to the department. Therefore, it is possible to prevent the fatigue life of the solder joint between the semiconductor element and the wiring board from decreasing.

The cooling plate may be individually provided for each semiconductor element as shown in FIGS. 1 to 3, or one cooling plate may be provided for each of a plurality of, for example, two or three semiconductor elements. .

The cooling plate and the semiconductor element are preferably joined by solder. Since the solder has excellent thermal conductivity, it is possible to reduce the thickness of the solder and enhance the cooling effect of the semiconductor element.

The semiconductor element mounted on the wiring board may be directly soldered to the wiring board as shown in FIGS. 1 to 3, or the semiconductor element may be housed in a chip carrier and connected to the outside of the chip carrier. Alternatively, the leads may be taken out and the leads and the wiring board may be soldered. An example of a semiconductor device housed in a chip carrier is shown in Japanese Patent Application Laid-Open No. 58-43553, and the present invention can also be configured in this way.

As a method of manufacturing the bellows, for example, JP-A-61-2203
The method described in Japanese Patent Publication No. 59 can be applied.

As a method of fixing the cooling plate to the wiring board, as shown in FIGS. 1 and 2, a skirt may be provided on the cooling plate and the skirt may be joined to the wiring board by soldering or the like.
As shown in the figure, a cooling plate fixing member may be separately mounted on the wiring board, and the cooling plate may be joined thereto.

As shown in FIGS. 1 and 2, two bellows are attached to one cooling plate, one is used as a flow path for flowing the cooling medium from the housing to the cooling plate, and the other is returned from the cooling plate to the housing. It may be a flow path. Alternatively, as shown in FIG. 3, only one bellows may be provided for each cooling plate. The inside of one bellows may be divided into two flow paths, and a continuous flow may be imparted to the cooling medium as in FIGS.

As the semiconductor element, for example, an LSI (Large Scale Integration) chip can be used.
The case where an LSI chip is used will be described below as an example.

As the cooling medium, a liquid such as water or a gas can be used, but among these, it is preferable to use the liquid.

[Action]

In the present invention, the cooling plate corresponding to each LSI chip is attached to the wiring board mechanically or by soldering, and even if an external force is applied to the cooling plate, the relative displacement with respect to the board, whichever is It never happens. As a result, under the condition that the back surface of the LSI chip, that is, the surface not bonded to the wiring board, is fixed to the cooling plate with solder or the like, thermal strain caused by temperature difference or thermal expansion difference between the wiring board and the housing is generated. Even if it occurs, the strain can be absorbed by the deformation of the bellows, and the stress generated at that time will be supported by the mounting part between the cooling plate and the substrate,
No external force is applied to the solder joint between the LSI chip and the wiring board, and there is no risk of damage or shortening of the thermal fatigue life. At the same time, since the cooling plate and the LSI chip are metallically connected, it is possible to achieve highly efficient cooling with a thermal resistance of 0.5 ° C / W or less in terms of cooling performance.

Further, in the present invention, a structure in which a skirt is attached to the lower portion of the cooling plate to form a cap, and the LSI chip is hermetically sealed by the substrate and the cooling plate is posted as an idea. This prevents the cooling water from directly contacting the LSI chip and damaging the LSI chip even if water leakage occurs due to corrosion or damage from the thin bellows portion or the like. Further, by completely replacing the inside of the hermetically sealed interior with an inert gas such as He, it is possible to prevent corrosion damage to the LSI wiring and solder joints, and the reliability as a semiconductor module can be significantly improved.

〔Example〕

 Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an example in which a cooling plate is provided for each LSI chip, and a skirt is attached to the cooling plate and joined to a wiring board. In FIG. 1, the housing 1 provided with a circulation path for the cooling water 13 has a cooling element 6 corresponding to each LSI chip 9.
8 are provided. The cooling element 68 has a cooling plate 6 and two metal bellows 2 for supplying and discharging a refrigerant thereto. The cooling plate 6 has a cooling fin 4 that efficiently transfers the heat from the LSI chip 9 to the refrigerant and a cap 3 that seals the refrigerant.

Reference numeral 5 is a skirt, one end of which is fixed to the cooling plate and the other of which is joined to the wiring board with solder 11. housing,
Bellows and caps are made of metal with high corrosion resistance, such as SU
It is preferably composed of metals such as S, Ti and Ti alloys, Ni and Ni alloys. The cooling fin 4 is made of metal C having excellent thermal conductivity.
It is preferably composed of u, Ni, Ag or the like or ceramic AlN, SiC, Al ₂ O ₃ or the like. Further, it is preferable that the skirt 5 is made of Fe--Ni alloy or the same ceramic material as the substrate material so that the coefficient of thermal expansion of the skirt 5 is the same as that of the wiring substrate. Diffusion bonding and high melting point brazing such as Ag brazing, Ni brazing, and Au brazing are used for the bonding between each component. The back side of the LSI chip is S
Cr-Ni-Au metallization is applied on the insulating film made of iO _2, and low melting point solder 7
It is joined to the cooling fin 4. The wiring board and the skirt are airtightly bonded with the same low melting point solder 11 as described above via a metallized layer. A Pb-Sn-In alloy or the like can be used as the low melting point solder. In addition, a space with an LSI chip 6
7 is filled with He.

According to the present embodiment, since the LSI chip and the cooling fin are metallically joined by the low melting point solder, the thermal conductivity is high and the cooling performance is excellent, and the cooling plate is soldered to the wiring board. Even if a displacement due to heat or the like occurs between the substrate and the housing, the stress due to the deformation of the bellows is hardly applied to the solder joint 10 and the fatigue life of the solder joint is not reduced. Furthermore, because the LSI chip is completely hermetically sealed in a He atmosphere, even if water leaks from the cooling element joint or bellows, the LSI chip will not be damaged, and the chip wiring or solder joints will not be damaged. Parts will not be corroded or damaged by moisture. Therefore, the reliability of the semiconductor device can be improved.

FIG. 2 is a sectional view of a semiconductor module showing another embodiment of the present invention. In FIG. 2, the housing 1 to the cooling plate 6 have the same structure as that of the embodiment shown in FIG.
The skirt 5 is made of the same mullite ceramic material as the wiring board 12, and is brazed 19 to the cooling fin 4. The cooling fin 4 made of Ni and the LSI chip 9 are made of Pb-Sn having a melting point of 90 to 150 ° C. via a metallized layer 8 formed on the SiO ₂ oxide film.
-In-based solder 7 is used for joining. The wiring board 12 is the cooling plate 6
The chip mounting portion is recessed in conformity with the dimensions of the above, and the side surface of the recess and the side surface of the skirt 5 are joined with the solder 11 via the metallized layers 23 and 25 formed there, and hermetically sealed. . The low melting point solder 11 used for sealing is of a composition having a slightly lower melting point than the low melting point solder 7. The solder of the solder joint portion 10 is 95Pb-5Sn solder having a melting point of 280 ° C.

According to this embodiment, as in the embodiment of FIG. 1, there are great effects in improving the cooling performance of the LSI chip, the service life of the solder joint 10 and the reliability of the LSI chip.

FIG. 3 shows still another embodiment of the present invention, in which a cooling plate fixing member 38 is attached on a wiring board, and the cooling plate and the cooling plate are joined by solder 34. In this embodiment, when the metal bellows 2 is connected to the housing 1, the metal bellows is connected to the flange 31, and the O-ring 30 is provided between the flange 31 and the housing 1. The metal bellows is held between the housing and the cooling plate by its spring action.

The cooling plate fixing member 38 is made by punching out a ceramic plate made of the same material as the wiring board, as shown in FIG.

According to this embodiment, the shape of the cooling plate can be simplified. Also, the cooling plate fixing member 38 can be easily manufactured, and the assembly of the semiconductor module can be simplified as compared with the case shown in FIG.

FIG. 5 and FIG. 6 show a semiconductor module of the type in which a conventional LSI chip is individually cooled. In Figure 5
Reference numeral 49 is a heat conductive grease, 51 is a lead, 52 is a bonding wire, 53 is a chip carrier (package), and 54 is a solder joint. In the structure of FIG. 5, the cooling water is
Since the heat transfer path is short because it is sent to the vicinity of the LSI chip, and there is no space in the middle of the heat transfer path, the cooling performance is greatly improved compared to the type that cools only by heat conduction using a cooling fin or the like. ing. Further, with respect to the thermal strain caused by the temperature difference or the thermal expansion difference between the wiring board 12 and the housing 1, the action of the bellows 2 and the thermal conductive grease 49 can absorb the displacement in the vertical and horizontal directions. It can be said that the thermal fatigue life of the solder joint between the wiring board and the wiring board does not easily decrease.

However, on the other hand, grease is used that has a thermal conductivity that is worse than that of metal by an order of magnitude or more for the purpose of providing variability at zero stress in the heat transfer path from the LSI chip to the cooling water. Since it is difficult to reduce the temperature to several tens of μm or less due to its surface tension, it is difficult to improve the cooling performance to a thermal resistance of 1 ° C./W or less. For this reason, if the LSI chip comes to be used when the amount of heat generated per chip exceeds 40 W in the future, there is a problem that this cooling structure cannot cope with it.

FIG. 6 shows a semiconductor chip individual cooling type disclosed in JP-A-61-220359. In FIG. 6, 61 is a low melting point solder joint portion, and 66 is a solder joint portion. In the structure shown in FIG. 6, since the distance from the cooling water to the LSI chip 9 is shorter and the heat transfer path is made of metal or ceramic with good thermal conductivity, the cooling performance is better than that of the structure shown in FIG. It is remarkably improved, and good results of thermal resistance of 0.5 ° C / W or less are obtained. However, in the structure of FIG. 6, since the cooling plate 6 and the wiring board 12 are fixed by soldering, all the thermal strain between the housing 1 and the wiring board 12 must be absorbed by the bellows 2.

Also, because the LSI chip is rigidly joined to the cooling body on the wiring board and housing side by soldering, if a displacement due to thermal strain occurs between the wiring board and the housing, the displacement is absorbed by the deformation of the bellows. However, the stress generated at that time is directly applied to the solder joint between the wiring board and the LSI chip.

For this reason, the fatigue life of the solder joint portion 10 between the LSI chip and the wiring board tends to be shortened.

〔The invention's effect〕

As described in detail above, according to the present invention, it is possible to reduce the stress generated by the displacement of the wiring board and the housing from being applied to the solder joint between the semiconductor element and the wiring board, and to reduce the fatigue life of the solder joint. Can be suppressed.

In addition, by bonding the periphery of the cooling plate to the wiring board and hermetically sealing the semiconductor element, there is an effect that reliability can be expected to be improved without being damaged by moisture or water leakage accident. can get.

[Brief description of drawings]

FIG. 1 is a sectional view of a semiconductor module showing an embodiment of the present invention, FIG. 2 is a sectional view of a semiconductor module showing another embodiment of the present invention, and FIG. 3 is a further embodiment of the present invention. FIG. 4 is a sectional view of the semiconductor module shown in FIG. 4, FIG. 4 is a plan sectional view of the cooling plate fixing member shown in FIG. 3, FIG. 5 is a sectional view of a semiconductor module showing a conventional example, and FIG. 6 is a semiconductor module showing the conventional example. FIG. 1 ... Housing, 2 ... Metal bellows, 5 ... Skirt, 6 ... Cooling plate, 9 ... LSI chip, 10 ... Solder joint, 13 ... Cooling water, 38 ... Cooling plate fixing member.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hiroshi Wachi 4026 Kuji Town, Hitachi City, Hitachi, Ibaraki Prefecture Hitachi Research Laboratory, Ltd. (72) Asahiko Shida 4026 Kuji Town, Hitachi City, Ibaraki Prefecture Hitachi, Ltd. (56) References JP-A-60-160150 (JP, A)

Claims (7)

[Claims] 1. A wiring board, a plurality of semiconductor chips mounted on the wiring board, a plurality of cooling plates joined to each of the semiconductor chips and cooled by contact with a cooling medium; And a plurality of bellows for connecting the housing and each of the cooling plates to each other to bring the cooling medium in the housing into contact with each of the cooling plates. And a plurality of members, one of which is joined to the end of each cooling plate and the other of which is joined to the wiring board. 2. The semiconductor module according to claim 1, wherein the member is a skirt arranged between the cooling plate and the wiring board. 3. The semiconductor module according to claim 2, wherein the skirt is provided on the entire circumference of the cooling plate, and the semiconductor chip is hermetically sealed by the skirt. 4. The semiconductor module according to claim 3, wherein a space around the semiconductor chip hermetically sealed by the cooling plate and the skirt is filled with an inert gas. 5. The wiring board according to claim 2, wherein the wiring board has a plurality of dents, and the respective ends of the skirt are inserted into the dents and soldered. And semiconductor module. 6. The semiconductor module according to claim 1, wherein the member is a cooling plate fixing member arranged on the wiring board. 7. The semiconductor module according to claim 6, wherein the cooling plate fixing member is shared between the adjacent semiconductor chips.