JPH04312932A - Semiconductor device and brazing method thereof - Google Patents

Abstract

PURPOSE:To reduce a void generation, improve heat dissipation, and not to cause pellet cracks generation by a method wherein wettability of a brazing material on a brazing surface of a semiconductor device is made excellent. CONSTITUTION:On at least one brazing surface of a semiconductor substrate 1 making a part of a semiconductor pellet and a heat conduction material 2 making a package, grooved parts 3 comprising V-shaped or U-shaped grooves are formed in parallel or radially. If a preform brazing material is set in a central part on the brazing surface to perform a reflow, a melted brazing material 4 can expand along the grooves all over the grooved parts 3.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a technique for brazing semiconductor pellets, and more particularly, to a semiconductor device having a structure in which one principal surface of a semiconductor pellet disposed in a package is brazed to the inner surface of the package to form a heat conduction path. It concerns techniques that can be used effectively.

0002

BACKGROUND OF THE INVENTION Conventionally, in brazing semiconductor pellets, mechanical holding of semiconductor pellets to a package, For purposes such as electrical connection and heat dissipation, the package includes a bonding process in which the semiconductor pellet is fixed face-up in a predetermined position in the package prior to wire bonding.

By the way, the present inventor has studied the generation of voids accompanying the brazing of large semiconductor pellets.

[0004] The following are the techniques studied by the present inventor, and the outline thereof is as follows.

[0005] That is, WSI (wafer scale integration)
When the size of semiconductor pellets becomes larger, such as in the case of tegration, a semiconductor pellet with bump electrodes is mounted on a base on which a circuit pattern is formed, and the ceiling surface is in contact with the semiconductor pellet whose upper surface is metallized. A cap having a U-shaped cross section is covered, and the connecting portion between the cap and the base and the contact surface between the upper surface of the semiconductor pellet and the inner surface of the cap are fixed by brazing. With such a configuration, heat generated from the semiconductor pellet during use can be released to the cap via the brazing surface, and further heat can be dissipated to the atmosphere.

[0006]

[Problems to be Solved by the Invention] However, in the semiconductor device that dissipates heat through the cap as described above,
No consideration was given to the increase in voids in the brazed part of large semiconductor pellets, which increase the brazing area, and there is a problem that heat dissipation from the PN junction of LSI decreases due to the increase in voids in the brazed part. was discovered by the present inventor.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a technique that can prevent an increase in voids and a decrease in heat dissipation performance.

The above objects and novel features of the present invention will become apparent from the description of this specification and the accompanying drawings.

[0009]

[Means for Solving the Problems] Among the inventions disclosed in this application, a brief overview of typical inventions will be as follows.
It is as follows.

That is, in a semiconductor device in which a heat dissipating surface of a semiconductor pellet is brazed to a package, grooves arranged so as to extend outward from a brazing material mounting portion are formed on at least one of the semiconductor pellet or the package. It is provided on one brazing surface.

[0011]

[Operation] According to the above-mentioned means, the groove provided on the brazing surface functions like a capillary tube in the longitudinal direction of the groove for the molten brazing material, and improves the wetting and spreading of the brazing material. The filler metal penetrates into the surface densely. Therefore, it is possible to reduce the occurrence of voids, increase the bonding surface area, improve heat dissipation properties, and reduce the occurrence of pellet cracks.

0012

[Embodiment] As shown in FIG. 1, the present invention has a semiconductor substrate 1 (
The feature is that a grooved portion 3 is formed on the brazing surface of the semiconductor pellet (semiconductor pellet) and the brazing surface of the thermally conductive material 2 (package), and these both surfaces are joined by a brazing material 4. The grooved portion 3 is processed into a shape that allows the melted brazing material 4 to easily flow during brazing. Here, the semiconductor substrate 1 is, for example, a silicon single crystal substrate, the thermally conductive material 2 is, for example, aluminum nitride, and the brazing material 4 is, for example, a PbSn-based solder material.

In FIG. 1, a semiconductor substrate 1 and a thermally conductive material 2 are shown.
However, as shown in FIG.
The brazing surface of the semiconductor substrate 1 may be a smooth surface 5, or the brazing surface of the semiconductor substrate 1 may be a smooth surface 5 by providing a brazing material 4 only on the thermally conductive material 2, as shown in FIG.

4 and 5 show details of the shape of the grooved portion 3, FIG. 4 shows an example in which a sawtooth or V-shaped groove 6 is formed, and FIG. 5 shows an example in which a U-shaped groove 7 is formed. An example is shown. When forming the grooves 6 and 7, methods such as photoetching, mechanical grinding, laser processing, etc. can be used. Further, a metallized layer 8 is formed on the surfaces of the grooves 6 and 7. The metallized layer 8 is provided for the purpose of improving wetting of the brazing material 4. For example, the metallized layer 8 is made of gold as a base,
The surface is coated with multiple layers of chrome, copper, and gold,
Alternatively, a combination of an adhesive layer made of multiple layers of chromium, titanium, and tungsten from the bottom, a barrier layer made of nickel, copper, platinum, palladium, molybdenum, etc., and an oxidation prevention layer made of gold, silver, etc. provided on this barrier layer. can be used.

6 and 7 show plan views of the grooved portion 3 on the semiconductor substrate 1. FIG. 6 shows the case where the grooves are formed in parallel, and FIG. 7 shows the case where the grooves are formed radially outward from the center. It shows.

As described above, by providing the grooved portion 3 having the shape of the groove 6 or the groove 7, the groove on the horizontal plane becomes
It acts like a capillary tube along its length. On the other hand, a groove perpendicular to its length behaves like a barrier because a position is found such that its contact angle is a threshold value. Spreading across the grooves is particularly suppressed if the crests between the grooves have sharp edges. Therefore, the directionality of the spread of the brazing filler metal 4 is better in FIG. 4 than in FIG. 5. In this way, the brazing material 4 travels along the groove 6 (or groove 7) to the grooved part 3.
Since it permeates throughout the entire area, it is possible to reduce the occurrence of voids and improve heat dissipation.

Note that the vertical depth y of the groove, which determines the wetting and spreading of the brazing filler metal 4, is determined by the surface tension of the molten brazing filler metal γl,
If the density of the molten brazing material is ρ, the gravitational acceleration is g, and the radius of curvature of the surface of the molten brazing material is replaced by an equivalent radius, Re is expressed by Equation 1.

[0018]

[Equation 1] y= 2γl/ρgRe Furthermore, for a groove with a semicircular cross section or a groove with a rectangular cross section with a base angle of 90°, Re ≒2.5y, and if the groove shape is even sharper, , Re is made smaller. In addition, for a base angle of 60°, Re ≒y, base angle 3
For 0°, Re≈0.35y. However, in reality, the above effect can be obtained by using grooves at 150 μm (60 Ru) when the unevenness of the grooves is treated as surface roughness.
The value is as follows.

Next, a method for brazing a semiconductor device according to the present invention will be explained with reference to FIGS. 8 to 11.

As shown in FIG. 8(a), a preform brazing material 9 processed to a predetermined size is placed on the thermally conductive material 2, and a groove is formed on the preform brazing material 9. The semiconductor substrate 1 is placed with the processing section 3 facing down. In this state, when the installation atmosphere (for example, an atmosphere containing an inert gas with O2 of 10 ppm or less, or a gas containing 10 to 20% H2 added thereto) and a load of 10 is applied, the result is shown in FIG. 8(b). As shown in the figure, the preform brazing material 9 melts and spreads from the center of the grooved portion 3 to the outside as described above, so that a bonding layer of the brazing material 4 is obtained.

FIGS. 9 and 10 are plan views showing the shape and placement of the preform brazing filler metal 9. Here, an example is shown in which the semiconductor substrate 1 is square. 9 corresponds to the groove arrangement in FIG. 6, and a preform brazing material 9 having a rectangular bar shape and a length corresponding to the width of the semiconductor substrate 1 is placed in the center of the semiconductor substrate 1 in the longitudinal direction of the grooves. They are arranged orthogonally. Further, FIG. 10 corresponds to the groove arrangement in FIG. 7,
A sugar cube-shaped preform brazing material 9 is arranged at the center of the grooved part 3.

Furthermore, FIGS. 11 and 12 show the case where the semiconductor substrate 1 is a rectangle having a short side 11a and a long side 11b, and a preform brazing material 9 is placed at the center in the direction of the short side 11a and between the long side 11b. Place it. When reflowing is performed in this state, the wetting and spreading distance of the preform brazing material 9 can be shortened.

As described above, according to the above embodiment,
Due to the capillary effect of the grooves formed on the brazing surface, it is possible to control the wetting and spreading of the brazing material as well as its direction, and furthermore, by supplying the brazing material from the center of the brazing surface, the generation of voids can be reduced. . As a result, LSI
It will also be possible to cope with larger sizes. Furthermore, since the surface area contributing to solder bonding is larger than the apparent solid surface area, heat dissipation and bonding strength can be improved.

[0024]

[Effects of the Invention] Among the inventions disclosed in this application, the effects obtained by the typical inventions are briefly explained as follows.
It is as follows.

That is, in a semiconductor device in which a heat dissipating surface of a semiconductor pellet is brazed to a package, grooves arranged so as to extend outward from a brazing material mounting portion are formed on at least one of the semiconductor pellet or the package. Since it is provided on one brazing surface, it is possible to reduce the generation of voids and increase the bonding surface area, thereby improving heat dissipation and reducing the occurrence of pellet cracks.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing the main parts of a semiconductor device according to the present invention.

FIG. 2 is a sectional view showing another example of the shape of the grooved portion according to the present invention.

FIG. 3 is a sectional view showing still another example of the shape of the grooved portion according to the present invention.

FIG. 4 is a cross-sectional view showing an example of the groove shape of the grooved portion.

FIG. 5 is a cross-sectional view showing another example of the groove shape of the grooved portion.

FIG. 6 is a plan view showing an example of groove arrangement.

FIG. 7 is a plan view showing another example of groove arrangement.

FIG. 8 is an explanatory diagram showing the brazing method of the present invention.

9 is a plan view showing the shape and placement state of the preform brazing material corresponding to the groove arrangement of FIG. 6; FIG.

10 is a plan view showing the shape and placement state of a preform brazing material corresponding to the groove arrangement of FIG. 7; FIG.

FIG. 11 is a plan view showing the shape and placement state of a preform brazing material corresponding to a rectangular semiconductor substrate shape.

[Explanation of symbols]

1 Semiconductor substrate 2 Thermal conductive material 3 Groove processing section 4 Brazing filler metal 5 Smooth surface 6 Groove 7 Groove 8 Metallized layer 9 Preform brazing filler metal 10 Load 11a Short side 11b Long side

Claims (4)

[Claims] 1. A semiconductor device in which a heat dissipating surface of a semiconductor pellet is brazed to a package, wherein grooves arranged so as to extend outward from a brazing material placement part are formed in at least one of the semiconductor pellet or the package. A semiconductor device characterized in that it is provided on one brazing surface. 2. The semiconductor device according to claim 1, wherein the groove is V-shaped or U-shaped and is formed radially from the center of the brazing surface to the periphery. 3. The semiconductor device according to claim 1, wherein the grooves are V-shaped or U-shaped and are formed parallel to each other at regular intervals between opposing sides of the brazing surface. 4. A semiconductor device in which a heat dissipating surface of a semiconductor pellet is brazed to a package, wherein the surface area of the soldering surface of one of the semiconductor pellet or the package is located in the center between at least one opposing side of the soldering surface of the semiconductor pellet or the package. A method for brazing semiconductor devices, characterized in that brazing is performed by placing a preform brazing material smaller than the area and reflowing in this state.