JPS60233833A - Semiconductor device - Google Patents

Abstract

PURPOSE:To increase the repeating withstand strength against the variability in humidity by a method wherein, in the installation of an electrode with solder on a metallic layer adhered to the surface of a semiconductor pellet, the electrode is so tapered as to have a large area in the front and a small area at the bottom, and the tapered surface is surrounded by the solder as well as the bottom surface. CONSTITUTION:In fixing the electrode 6 with the solder 5 on the semiconductor pellet 3 provided with the metallic layer 4 on the surface, the electrode 6 is treated as follows instead of being formed to a plate. That is, the front of the electrode 6 is made larger in parallel with the pellet 3, and its bottom is made smaller in the presence of the tapered side wall. In such a manner, the tapered surface is surrounded by the solder 5 as well as the bottom surface; thus, the withstand strength against the repeating variation in temperature is improved. Besides, the heat dissipation is improved by reducing the thermal resistance of solder at the center.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a semiconductor device and a structure in which semiconductor pellets and electrodes are brazed to bamboo.

[Background of the invention]

FIG. 1 shows a conventional electrode brazing structure of a semiconductor device. A semiconductor pellet 3 having a metal 4 arranged on its main surface for connection to equipment is connected to a base 1 and an electrode through soldering materials 2 and 5. 6
It has a structure sandwiched between.

In the case of semiconductor devices, thermal stress is generated due to differences in thermal expansion coefficients between members due to temperature changes during actual operation. In particular, it is thought that the cause of the deterioration of the solder materials 2 and 5 is the repeated shear core force that changes.

When the semiconductor device shown in FIG. 1 is actually operated, the temperature of each member fluctuates as the heat loss generated in the semiconductor pellet 3 fluctuates due to fluctuations in the current flowing through the semiconductor device. In particular, when the load of a circuit using the semiconductor device fluctuates greatly, the range of temperature fluctuation also increases. Therefore, the brazing material 2
, 5 bear the shear core force, and the semiconductor pellet 3 bears the tensile and compressive stresses.

Now, the coefficient of thermal expansion of the semiconductor pellet 3 is α11, the coefficient of longitudinal elasticity E1, the thickness is hl, the coefficient of thermal expansion of the electrode 6 is α2, the modulus of longitudinal elasticity is E2, the thickness is h2, the modulus of transverse elasticity of the solder material 5 is G, the thickness is If h3 is the maximum diameter of the bonded part and 2xo, then applying the shear lag theory, the shear core force τ in the solder material 5 is
(support) is approximated by the following equation, where the temperature fluctuation range is ΔT.

However, regarding k, it becomes the following formula.

In equations (1) and (2), the value of τ(X) is the elastic limit τ of the solder material 5.
When it exceeds 0, τ(phantom Στ0 and nashi, shear strain γ
can be approximated to a quadratic equation of the distance X from the center of the semiconductor pellet, and becomes the following equation.

r=a x2+b x+c - (3) However, a, b, and c are constants determined by the dimensions and physical property values of each member, and a>O.

In equations (1) and (2), αs = 3.5X10-', α2 =
8 X 10-' r El ""11X103Kp/
++i, &=30X103Kp/+i, C+=0.0
78 to 9Δ-, h1=Q, 3 cabinets, h3=Q, 5 spaces,
h” = 0.05 throat, 0.1 tone.

The calculation for ΔT=1000 is shown in FIG.

From Fig. 2, we can see that the shear stress τ is towards the end, that is, x =
It can be seen that it reaches a maximum at x o and rapidly approaches zero near the center. Furthermore, the smaller the thickness h3 of the solder material 5, the larger the maximum value of τ.

Further, it has been found from another experiment that the following equation holds true as the withstand capacity N for the number of repetitions of temperature fluctuation.

However, C1 is a constant determined by the type of solder material.

According to equation (4) and FIG. 2, there is an electrode brazing structure shown in FIG. 3 as a conventional example in order to improve the repeatability N.

That is, by making the cross-sectional shape of the electrode 6 which is bonded to the solder material 5 into a convex spherical shape, the thickness of the solder material 5 is increased at the end where the shear force τ is large. This structure reduces the maximum value τ□0 of the shear stress τ.

However, in the structure shown in FIG. 3, since the thickness of the recording material around the semiconductor pellet 3 gradually increases, the semiconductor pellet 3
The disadvantage is that the amount of heat generated is difficult to dissipate. As a general example, if copper is used for the electrode 6 and solder is used for the solder material, the thermal conductivity of the solder is 1/10 that of copper, and the thermal resistance of the solder around the semiconductor pellet 3 is becomes larger.

Therefore, the heat dissipation performance of the semiconductor device is reduced, and the temperature of the semiconductor device tends to rise during operation.

Semiconductor devices often have a specified maximum guaranteed temperature during operation, and a reduction in heat dissipation is a drawback in that large amounts of power cannot be consumed.

Furthermore, the fact that machining the electrode 6 into a convex spherical shape is difficult in practice makes it difficult to realize the structure shown in FIG.

Furthermore, although FIG. 4 is also a conventional example, the lateral dimension of the cross section perpendicular to the surface of the electrode 6 connected to the semiconductor pellet 3 is smaller than that of the semiconductor pellet 3, and the solder material 5 is placed on the side surface of the electrode 6. It also has a raised structure. In this structure, since the surface of the metal 6 facing the semiconductor pellet 3 is flat, the poor heat dissipation of the case shown in FIG. 3 is improved.

However, with the structure shown in this figure, during bonding, air that enters from the outside is trapped inside the solder material and tends to form voids. Stress concentration occurs in these pores, which often reduces the withstand capacity N for the number of repetitions of temperature fluctuations, and heat dissipation is also poor due to the very low thermal conductivity of the air sealed inside. was a major drawback.

Furthermore, FIG. 5 is also a conventional example. As can be seen from the figure, electrode 6
By providing a step at the end of Fig. 3.

As in FIG. 4, the thickness of the sheath material at the end of the semiconductor pellet 3 is increased. In the case of Fig. 5, the purpose is to prevent solder from rising to the end 7 of the semiconductor pellet 3, so there are the following drawbacks in terms of withstanding repeated temperature changes during the mounting operation of semiconductor devices. .

That is, as shown in FIG. 4, the holes are sealed inside the solder material, and when the holes generated in the center of the semiconductor pellet 3 flow out to the periphery together with the solder material during brazing, the stepped portion of the electrode 6 It tends to accumulate at 8. The presence of pores causes stress concentration as described above.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the drawbacks of the prior art described above, increase the withstand capacity N for the number of repetitions of temperature fluctuations, and provide a semiconductor device having an electrode brazing structure with good heat dissipation. It is.

[Summary of the invention]

The present invention is characterized in that the cross-sectional area of the electrode increases in the plane facing the main surface of the semiconductor pellet and in the direction parallel to the main surface as the electrode moves away from the main surface. The main surface has a sloped surface, and a brazing material is provided between the main surface and the flat and sloped side surfaces.

[Embodiments of the invention]

FIG. 6 shows an embodiment of the present invention.

The cross section of the electrode 6 perpendicular to the surface connected to the semiconductor pellet 3 has a trapezoidal shape, and the length of the base thereof is smaller than the dimension of the metal 4 coated on the semiconductor pellet 3 for connecting to the solder material 5. be.

As mentioned above, since the thickness of the solder material connected to the periphery of the semiconductor pellet 3 is thicker than that at the center, the resistance against repeated temperature changes is improved, and the thickness of the solder material connected to the center portion of the semiconductor pellet 3 is increased. Since it is thin, the thermal resistance of the solder material 5 is reduced. In addition, when manufacturing this device, the solder material 5 is
The solder material 5 flows from the center of the semiconductor pellet 3 toward the periphery, and since the flowing solder material 5 tends to rise up the inclined side surface to the height of the bottom of the electrode 6, the generation of voids is suppressed.

The advantage of the present invention over the conventional rows shown in FIGS. 3 and 4 is that in the case of FIG. pellet 3
The heat generated by the electrode is easily transmitted evenly over the entire surface of the electrode. In contrast to FIG. 4, the solder material connected to the periphery of the semiconductor pellet 3 bulges up and the amount of the solder material becomes thicker, so the shear center force of the solder material in this part becomes smaller according to equation (2).

Furthermore, FIG. 7 shows the calculation results of the relationship between the number n of temperature changes in turning and the peeling rate of the solder material for the semiconductor devices having the three structures shown in FIGS. 3.4.6. Here, Xi represents the dimension of a crack in the solder material measured with the periphery of the solder material contacting part of the semiconductor pellet as the origin. In this calculation, the volume of the solder material 5 is calculated under the same conditions for all three.

In FIG. 7, first, the curve in FIG. 4 is obtained by translating the curve in FIG. 6 to the left. The reason for this is that at the beginning of the deterioration of the solder material, the surrounding area leaks, and at this time, in the case of Fig. 6, the cross-sectional shape of the electrode 6 is trapezoidal, so the amount of solder material in the surrounding area is smaller than that in Fig. 4. will increase. The difference in the amount of solder material in this peripheral area is the difference in the initial value of the solder material in FIG. 7. If the crack in the solder material advances toward the center and the amount of solder material is uniform in the area, there will be no difference in the crack growth speed between the two structures.

In the structure shown in FIG. 3, since the amount of solder material gradually decreases toward the center of the semiconductor pellet 3, the speed of crack propagation increases at an accelerating rate with the number n of repetitions of temperature change.

In addition, in the case of Fig. 5, since the electrode metal 6 has a certain thickness even at the peripheral part, which is the starting point of the solder metal crack, the electrode metal 6 has a certain thickness at the peripheral part as shown in Fig. 6. It is obvious that the thermal stress is greater than that of the metal 6. In other words, in Figure 5, the thermal stress in the peripheral area is larger than in Figure 6, so
This means that the crack initiation time is earlier, and in the relationship shown in FIG. 7, the crack starts at a smaller n than the curve shown in FIG. 6.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to obtain a semiconductor device having an electrode brazing structure with a large withstand capacity N for the number of repetitions of temperature fluctuations and good heat dissipation.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of a conventional semiconductor device, and Figure 2 is a cross-sectional view of a conventional semiconductor device.
3 to 5 are cross-sectional views showing other conventional semiconductor devices, and FIG. FIG. 7, a cross-sectional view showing an embodiment, is a diagram showing the solder tolerance in the semiconductor device of FIG. 6 in relation to the position of the solder. DESCRIPTION OF SYMBOLS 1...Pace, 2,5...Brazing material, 3...Semiconductor pellet, 4...Metal, 6...Electrode. Kaya 4 illustrations! 5 Continuation of figure 1 page @ inventor Masami Fujii

Claims (1)

[Claims] 1. The electrode to be brazed to the surface of the semiconductor pellet has a plane facing the main surface and an inclined side surface that increases the cross-sectional area of the electrode in a direction parallel to the surface as it moves away from the surface. A semiconductor device characterized in that a brazing material is provided between the main surface and the flat and inclined side surfaces.