JPH11121662A - Cooling structure for semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve heat dissipation characteristics by providing, between a plurality of semiconductor chips of different heights and a heat dissipation member, a heat-conductive member comprising a fin which contacts the heat dissipation member, for sure contact to a single heat dissipation member. SOLUTION: Semiconductor chips 1a, 1b, and 1c are jointed to the upper surface of a substrate 2 with a solder 6, and a heat-conductive member 7 is provided between the semiconductor chips 1a, 1b, and 1c and a heat dissipation member 4. Related to the heat-conductive member 7, a face facing the heat dissipation member 4 is provided with a cut, which is set up to form a fine fin 8. The fine fin 8, in bowed state, always contacts a surface of the heat dissipation member 4. Thus, when the semiconductor chips 1a, 1b, and 1c generate heat, it is transferred to a solder 10 and the heat-conductive member 7, and then to the heat dissipation member 4, so a low thermal resistance is realize. Since the heat-conductive member 7 is filled with a grease 9, still lower thermal resistance is realized.

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 a semiconductor device having a semiconductor chip or the like mounted thereon.

[0002]

2. Description of the Related Art In a conventional multi-chip type semiconductor device, in order to dissipate heat by directly adhering a plurality of semiconductor chips to one heat radiating member, when the package is a hermetic type, the semiconductor chip and the heat radiating member are connected. And soldering between them to achieve high thermal conductivity. When the package is a non-hermetic type, a member having good thermal conductivity is sandwiched between the semiconductor chip and the heat radiating member to reduce the thermal resistance of the contact portion.

In the case of actually manufacturing a multi-chip type semiconductor device, there are some variations in the height of all the semiconductor chips, and some means have been reported to transfer the heat of the semiconductor chips to the heat radiating member. I have. JP 7-24536
In Japanese Patent Publication No. 2, an elastic body for absorbing variations in height is interposed between the semiconductor chip and the heat radiating member. JP-A-6-2
In Japanese Patent No. 24334, a step or a depression is provided on the surface of a heat dissipating member facing a semiconductor chip, and the semiconductor chip is attached with an adhesive having a uniform thickness.

The above structure is a useful means for reducing the thermal resistance even if the height of the semiconductor chip varies.

However, the amount of heat generated has increased along with the speeding up of the semiconductor chip, so that the amount of thermal deformation of each component generated when operating the semiconductor device cannot be ignored. When the power is turned on, the semiconductor chip generates heat, and the heat causes each component to expand and deform. Also, when the power is turned off, the heat drops,
Each part shrinks and deforms. By repeatedly turning on and off this power, a heat transfer member that adheres to the semiconductor chip,
Alternatively, when the heat radiating member has high rigidity, a compressive / tensile stress is generated in the semiconductor chip or a connection portion between the semiconductor chip and the substrate, and there is a possibility that the semiconductor chip may be broken by a long-term operation.

[0006]

If the height of the semiconductor chip varies in the initial state assembled as described above, the semiconductor chip having the highest height comes into contact with the heat radiating member. A gap is formed between the semiconductor chip having a low height and the heat radiating member, thereby causing a problem that the thermal resistance is significantly increased.

Further, when the semiconductor chip generates heat, the substrate and the frame expand due to heat, and a gap may be generated between the semiconductor chip and the heat radiating member due to deformation due to a difference in thermal expansion between the substrate and the frame. Also in this case, there has been a problem that the thermal resistance increases according to the gap.

On the other hand, in contrast to the case where the gap is opened, there is also a portion that is deformed in a direction in which the semiconductor chip and the heat radiating member approach each other due to heat generated by the semiconductor chip. In this case, the semiconductor chip is compressed between the heat radiating member and the substrate, and an excessive compressive stress is generated in a solder portion connecting the semiconductor chip to the substrate. Therefore, there has been a problem in that a repeated load is applied to the solder due to power on / off of the semiconductor device, and the solder connection portion is broken by fatigue.

It is an object of the present invention to apply an excessive compressive load to a solder joint of a semiconductor chip without adjusting the height of all the semiconductor chips and even when the power of the semiconductor device is turned on and off. Instead, it is an object of the present invention to provide a multi-chip type semiconductor device in which semiconductor chips having different heights are collectively brought into contact with one heat radiation member without fail and heat radiation characteristics are improved.

[0010]

The object of the present invention is to provide, as shown in FIG. 1, a plurality of semiconductor chips 1a, 1b,
In the multi-chip type semiconductor device having the structure in which the semiconductor chip 1c is mounted and the heat of the semiconductor chip is radiated by the heat radiation member 4, the plurality of semiconductor chips 1a, 1b,
This is achieved by providing a heat transfer member 7 filled with grease between the semiconductor chip 1c and the common heat dissipation member 4 for the plurality of semiconductor chips.

According to the present invention, the following effects are produced by the above means to solve the above-mentioned problems. The heat transfer member was made of a metal having excellent heat conductivity, and fine fins were formed on a surface of the heat transfer member facing the heat radiating member. Further, grease was filled in the gaps between the fine fins. The heat transfer member is in close contact with the semiconductor chip, and the fine fins formed on the heat transfer member
In the bent state, it always contacts the heat radiating member. The fine fins absorb variations in height of the initial semiconductor chip and deformations generated during assembly, and thermally connect the semiconductor chip and the heat radiating member. Further, grease is filled in the gaps between the fine fins to improve heat transfer characteristics to the heat radiating member.

[0012]

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

(Embodiment 1) FIG. 1 is a cross-sectional view showing a structure of a package, which is a multi-chip type semiconductor device of the present invention. A plurality of semiconductor chips 1a, 1 having different heights
b, 1c are mounted on the upper surface of a substrate 2 made of ceramics or the like, the frame 3 is arranged around the upper surface of the substrate 2, and the frame 3 and the heat radiating member 4 are tightened with screws or the like via an O-ring 5 so as to be airtight. It is a formula package.

FIG. 2 is an enlarged sectional view showing the structure of FIG. 1 in detail. The semiconductor chips 1a, 1b, 1c (only one semiconductor chip 1 is shown in FIG. 2) are joined to the upper surface of the substrate 2 by solder 6, and the semiconductor chips 1a, 1b, 1c
The heat transfer member 7 is provided between the heat transfer member 4 and the heat transfer member 4.

The heat transfer member 7 is formed of a metal having good heat conduction and excellent workability, for example, aluminum, and has a cut in the surface facing the heat radiating member 4 to generate fine fins 8. . The fine fins 8 are always in contact with the surface of the heat radiating member 4 in a bent state. The gap between the fine fins 8 is filled with grease 9 having good thermal conductivity.

With the above configuration, even when the heights of the plurality of semiconductor chips 1a, 1b, 1c are varied, the fine fins 8 are always in contact with the heat radiating member 4 due to the bending of the fine fins 8. Further, the gap between the fine fins 8 is filled with the grease 9, so that the heat transfer efficiency is improved.

The manufacturing process of the semiconductor device according to this embodiment will be described with reference to FIG. First, the semiconductor chip 1 is joined to the substrate 2 with the solder 6 having a high melting point. This joint
The semiconductor chip 1 and the solder 6 are arranged at predetermined positions, and after applying a temperature at which the solder 6 melts, cooling is performed.

Next, the solder 1 having a lower melting point than the solder 6
At 0, the substrate 2 and the frame 3 are joined, and the semiconductor chip 1 and the heat transfer member 7 are joined. This joint is installed at a predetermined position, and a temperature at which the solder 10 is melted is applied and cooled. Thereafter, the gap between the fine fins 8 formed in the heat transfer member 7 is filled with viscous grease 9 having good thermal conductivity. The fine fins 8 of the heat transfer member 7 are formed by making a cut with a cutter and raising the portion.

The heat dissipating member 4 includes a heat dissipating fin 4a and a cap 4b joined to the heat dissipating fin 4a to form a flow path 4c. The materials of the radiation fin 4a and the cap 4b in the present embodiment are as follows.
Copper with good heat conductivity and excellent workability. Heat radiation fins 4
a and the cap 4b are joined with the solder 6. This joining is performed by disposing the solder 6 at a predetermined position between the radiation fin 4a and the cap 4b, applying a temperature at which the solder 6 melts, and then cooling it.

Finally, the heat dissipating member 4 is fastened to the frame 3 via the O-ring 5 with screws (fastening by screws is not shown) to obtain an airtight package structure.

With the above-described package structure, even if the heights of the semiconductor chips 1a, 1b, 1c vary as shown in FIG.
Since the heat transfer members 7 connected to b and 1c are in contact with the heat radiation member 4, they are always thermally connected.

When the semiconductor chips 1a, 1b, 1c generate heat, heat is transmitted to the solder 10 and the heat transfer member 7 and is transferred to the heat radiating member 4, thereby realizing a low heat resistance. Further, by filling the heat transfer member 7 with the grease 9, lower heat resistance is realized.

FIG. 3 is a bird's-eye view in which a part of the semiconductor device of the present invention is cut away. The heat radiating member 4 has a flow path 4c, a cooling water inlet 4d, and a cooling water outlet 4e. Cooling water inlet 4d
Cooling water flowing into the cooling water outlet 4e through the flow path 4c
The heat radiation member 4 is always cooled by flowing out of the
The cooling characteristics of the semiconductor chip are improved.

(Embodiment 2) The deformation that occurs when assembling the semiconductor device of the present invention will be described with reference to FIGS.

FIG. 4 is a cross-sectional view showing a state in which heat enough to melt the solder 10 is applied to the whole to join the frame 3 to the substrate 2 with the solder 10. Since the melting point of the solder 6 connecting the semiconductor chips 1a, 1b, 1c to the substrate 2 is higher than that of the solder 10, the solder 6 does not melt at the temperature at which the solder 10 melts. FIG. 4 shows a state where each member is expanded and deformed by heat at a temperature at which the solder 10 melts. By cooling this, the solder 10 solidifies and the frame 3 is joined to the substrate 2. When this cooling is performed, deformation occurs due to the difference in the coefficient of thermal expansion between each member, particularly, the substrate 2 and the frame 3. An example is described below.

FIG. 5 is a cross-sectional view in which the frame 3 is joined to the substrate 2 after cooling from the state of FIG. However, the frame 3 is made of a material having a larger coefficient of thermal expansion than the substrate 2. Therefore, the frame 3 expands more due to the heating and tends to contract by cooling. As a result, the frame 3 is deformed so as to fall inward on the basis of the portion joined to the substrate 2, and the substrate 2 is also deformed to follow the shape.

FIG. 6 is a cross-sectional view in which the frame 3 is joined to the substrate 2 after cooling from the state of FIG. However, the frame 3 is made of a material having a smaller coefficient of thermal expansion than the substrate 2. Therefore, the substrate 2 tends to contract by cooling as much as the substrate 2 expands due to the heating. As a result, the frame 3 is deformed so as to fall outward with reference to the portion joined to the substrate 2, and the substrate 2 is also deformed into a convex shape following this.

As described above, when the coefficient of thermal expansion of the frame 3 is larger than that of the substrate 2, the substrate 2 is deformed into a concave shape, and when the coefficient of thermal expansion of the frame 3 is smaller than that of the substrate 2, the substrate 2 becomes convex. Deform to.

In the semiconductor device of the present invention, heat can be efficiently transmitted to the heat radiating member 4 even if these deformations occur. This structure will be described with reference to FIGS.

FIG. 7 is a cross-sectional view in which the heat radiating member 4 is fastened with screws in a state where the substrate 2 to which the frame 3 is joined is deformed into a concave shape (FIG. 5) (fastening with screws is not shown). FIG. 8 is a cross-sectional view in which the heat radiating member 4 is fastened with screws in a state where the substrate 2 to which the frame 3 is bonded is deformed into a convex shape (FIG. 6).

In FIGS. 7 and 8, the heat radiating member 4 has higher rigidity than the frame 3, so that the frame 3 is deformed following the heat radiating member 4. The deformation of the substrate 2 caused when the frame 3 is joined to the substrate 2 is reduced by fastening the heat radiating member 4 to the frame, but the deformation is concave in FIG. 7 and convex in FIG. Remains.

When the substrate 2 is deformed into a concave shape as shown in FIG. 7, the distance between the semiconductor chip and the heat radiating member 4 is such that the semiconductor chip 1b disposed at the center is separated and the semiconductor chip 1a disposed at the peripheral part. , 1c approach. Conversely, when the substrate 2 is deformed in a convex shape, the distance between the semiconductor chip and the heat radiating member is such that the semiconductor chips 1a and 1c arranged in the peripheral portion are far from each other and the semiconductor chip 1b arranged in the central portion is close. Regardless of the deformation state, in the case of the structure of the present invention, the fine fins 8 of the heat transfer member 7 are always in contact with the heat radiating member 4 in a bent state.

Therefore, in the present embodiment, the semiconductor chips 1a, 1b, 1c and the heat radiating member 4 are thermally connected via the heat transfer member 7 even if the assembly is deformed.

Thus, all the semiconductor chips 1a,
The heat generated in 1b and 1c is transmitted to the heat transfer member 7 filled with the grease 9, and conducts the heat to the heat radiating member 4, thereby realizing low heat resistance. Further, as an alternative to the grease 9, a viscous gel or oil or wax having good heat conductivity may be used.

[0035]

According to the present invention, the heat of the semiconductor chip can be efficiently transmitted to the heat dissipating member even when the height of the semiconductor chip at the time of assembly is uneven.

Further, by repeating heat generation and heat radiation,
Even if the substrate and the frame are deformed and the gap between the semiconductor chip and the heat radiating member changes, the heat of the semiconductor chip can be efficiently transmitted to the heat radiating member. In addition, since the heat transfer member absorbs the gap that changes due to the heat generated by the semiconductor chip, the force applied to the joint between the substrate and the semiconductor chip can be reduced, and the gap is given to the joint by repeated heat generation and heat radiation. Low damage, no creep breakage of solder.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a semiconductor device according to an embodiment of the present invention, on which semiconductor chips having different heights are mounted.

FIG. 2 is an enlarged cross-sectional view of a semiconductor chip mounting portion showing one embodiment of the present invention.

FIG. 3 is a bird's-eye view of a partially cut-away semiconductor device showing one embodiment of the present invention.

FIG. 4 is a cross-sectional view of a semiconductor device according to an embodiment of the present invention when a substrate and a frame are joined by applying heat.

FIG. 5 is a cross-sectional view of a semiconductor device showing deformation occurring after bonding a substrate and a frame according to an embodiment of the present invention.

FIG. 6 is a cross-sectional view of a semiconductor device according to an embodiment of the present invention, showing a deformation that occurs after a substrate and a frame are joined.

FIG. 7 is a sectional view showing a deformation after assembling the semiconductor device according to the embodiment of the present invention;

FIG. 8 is a sectional view showing a deformation after assembling the semiconductor device according to the embodiment of the present invention;

[Explanation of symbols]

1, 1a, 1b, 1c ... semiconductor chip, 2 ... substrate, 3 ...
Frame: 4 heat dissipating member, 4a ... heat dissipating fin, 4b ... cap, 4c ... flow path, 4d ... cooling water inlet, 4e ... cooling water outlet, 5 ... O-ring, 6 ... solder, 7 ... heat transfer member, 8 ...
Fine fins, 9: grease, 10: solder.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Tadakatsu Nakajima 502 Kandachicho, Tsuchiura-shi, Ibaraki Pref.

Claims (1)

[Claims] In a semiconductor device having a structure in which a plurality of semiconductor chips are mounted on a substrate and heat of the semiconductor chips is radiated from a heat radiating member, the plurality of semiconductor chips having different heights and the plurality of semiconductor chips are provided. A cooling structure for a semiconductor device, wherein a semiconductor chip and a heat radiating member are connected via a heat conducting member having a fin that contacts the heat radiating member between the semiconductor chip and a common heat radiating member.