JPH05166969A - Semiconductor device - Google Patents

Abstract

(57) [Abstract] [Purpose] This is caused by the stress applied from the Cu foil to the Al ₂ O ₃ plate when the thickness of the Cu-clad Al ₂ O ₃ substrate is reduced to improve heat dissipation from the mounted semiconductor element. Prevent cracks that are easy to do. [Structure] To secure insulation between Cu foils on both sides, the edges of the Ci foil and Al
The difference in dimension provided between the end surface of the ₂ O ₃ plate and Al ₂ O ₃
When the thickness of the plate is 0.26 to 0.29 mm, the stress is balanced on both sides by suppressing the range to 0.5 mm or less to prevent the occurrence of cracks. In addition, stress balance is improved by providing Cu foils on both sides with a pattern that overlaps vertically.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device on an insulating substrate made of alumina having a copper foil on its surface, such as a power module used for motor control, inverters for air conditioners or NC control. The present invention relates to a mounted semiconductor device.

[0002]

2. Description of the Related Art Electronic devices have been remarkably developed in recent years, and high integration, small size, and light weight have been rapidly advanced, and semiconductor devices play a central role in these. Among them, the power module used for control as described above is usually miniaturized by accommodating a plurality of elements including an element of an auxiliary circuit in a single container in addition to a power semiconductor element. In such a power module, in order to insulate elements from each other or between elements, the elements are mounted using an insulating substrate having brazable metal foils on both sides. Previously, alumina (Al ₂ O ₃ ) was mainly used as the ceramic for the insulating substrate of this power module, but with the miniaturization and high functionality of new elements, the thermal conductivity has increased. Higher aluminum nitride (AlN) substrates have come into use.

[0003]

[Problems to be Solved by the Invention] The thermal conductivity of AlN is 80-
140 W / (m ・ k), about 5 times that of Al ₂ O ₃ 17 W / (m ・ k)
Although it can be expected that the heat dissipation through the substrate will be greatly improved, it is limited to special applications due to the high price. Therefore, it is conceivable to reduce the thickness of the inexpensive Al ₂ O ₃ substrate to improve the heat conduction, but reducing the thickness lowers the stress resistance. That is, 0.635m which was used conventionally
The bending strength of an Al ₂ O ₃ substrate with a thickness of m is 8 kg, whereas when it is thinned to 0.275 mm, the bending strength becomes 2 kg, which is 75%.
Also drops. Therefore, cracks may occur due to heat history during assembly.

It is an object of the present invention to use an insulating substrate made of inexpensive Al ₂ O ₃ as a material and having good heat conduction by reducing the thickness thereof, and moreover, a semiconductor device which is free from cracks during the assembly heat history. Shall be provided.

[0005]

In order to achieve the above-mentioned object, the present invention mounts a semiconductor element on one surface of an insulating substrate having a Cu foil stretched on both surfaces of a flat plate made of Al ₂ O _3. In the semiconductor device, the absolute value of the dimensional difference between the edges of the Cu foil on both sides and the end faces of the Al ₂ O ₃ plate is 0.5 mm or less. Further, it is effective to have a pattern in which the Cu foils on both sides are vertically overlapped with each other when viewed from the direction perpendicular to the substrate surface. Further, it is effective that the thickness of the Al ₂ O ₃ plate is 0.26 to 0.29 mm.

[0006]

[Operation] Cu foil on both sides of the insulating substrate is Al₂O₃Up to the edge of the board
When stretched, the creepage distance is Al₂O₃Insulation only with the thickness of the plate
Since the pressure resistance cannot be obtained, the end face is not stretched. sand
That is, as shown in FIG.₂O₃From both sides of board 1 from the edge
Cu foil 2 to the position where only the dimensions A and B were pulled down,
3 is stretched. Identify where cracks occur in the assembly heat history
Looking up, the larger of A and B, namely Al₂
O₃The edge of the Cu foil that has the largest pull-down from the edge of plate 1
Lower Al₂O₃It was found that the plate cracked. this
If the pulling down of the Cu foil on both sides is different, the
Cu with different pulling force and larger pull down
It is considered that the stress is concentrated on the edge of the foil. Assembly heat history
Al when cooled in₂O₃To ceramic generated on both sides of the plate
If the tensile stress of the
For the A-B value of the stress value with a certain physical constant calculated
Figure 3 shows the dependence of As the basis of calculation, Al₂O₃Board
The thickness of 1 is 0.27mm, the thickness of Cu foils 2 and 3 is 0.25mm respectively.
And When cooling the figure, the solid line 31 is the Al of the Cu foil 2.₂O₃On board 1
The tensile stress exerted, the dotted line 32 being the Al of the Cu foil 3. ₂O₃Board
The tensile stress exerted on 1. The tensile stress is
Al₂O₃The distance increases from the end face of the plate 1.
That is, as shown by the line 31, the Al of the Cu foil 2 ₂O₃To board 1
Boss tensile stress is when the value of AB becomes positively large.
It becomes large and becomes small when it becomes negative. Reverse
And the Al of the Cu foil 3 as shown by the line 32₂O₃Pull on plate 1
Tensile stress is small when the dimension AB is positively increased.
It becomes small and becomes large when it becomes negatively large. Both of these
To the absolute value of size AB₂O₃The board does not break
There will be an appropriate range for Take it a step further, AB =
Set to 0 and make the Cu foil pattern perpendicular to the insulating substrate surface.
If you make it overlap vertically when viewed from the direction,
Cu foil is Al₂O₃The stress on the plate will be balanced and the turtle
There is no risk of cracking.

[0007]

Example: A thickness of 0.25 is formed on an Al ₂ O ₃ plate 1 having a thickness of 0.275 mm.
A power module was assembled using a ceramic insulating substrate having Cu foils 2 and 3 of mm. When the restraint dimension R = | AB | was changed by changing the tensioning of the Cu foils 2 and 3, various cracks occurred in the Al ₂ O ₃ plate due to the heat history of assembly. FIG. 1 shows the relationship between the crack generation rate and R. As is clear from the figure, cracks do not occur when the dimension R is 0.5 or less, and cracks rapidly increase when the dimension R exceeds 0.5. When the insulating substrate was prepared by setting R ≦ 0.5 with reference to this result, the power module could be manufactured without causing defects during assembly.

FIG. 4 is a plan view of the upper and lower surfaces of an insulating substrate according to another embodiment of the present invention, in which the patterns of the Cu foils 2 and 3 on the Al ₂ O ₃ plate 1 have a line-symmetrical shape and the substrate surface It is designed to overlap when viewed from the direction perpendicular to. Conventionally, the Cu foil 2 on the side on which the element is mounted is patterned, but the Cu foil 3 on the side to be soldered to the Cu substrate as the heat radiator is not patterned. By doing so, the stress generated during the thermal history during assembly is balanced. The Cu foil 3 serves as a path for heat radiation from the device to the heat dissipation board together with the solder layer below, but since the Cu foil 3 is always present immediately below the device mounted on the Cu foil 2, heat dissipation is ensured. Has no effect on.

[0009]

According to the present invention, when the thickness of the insulating substrate on which the semiconductor element is mounted is reduced to improve the heat dissipation and reduce the cost, the edge of the Cu foil stretched on both sides and the semiconductor of the Al ₂ O ₃ plate are used. By setting the absolute value of the distance difference from the element surface to 0.5 mm or less, the stress exerted on the Al ₂ O ₃ plate of the Cu foil on both sides can be balanced, resulting in damage to the Al ₂ O ₃ plate. Is less. This enables high integration and miniaturization. Further, by providing the Cu foils on both sides of the insulating substrate with a pattern that vertically overlaps each other, it is possible to further balance the stress.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the absolute value of a spare dimension and the crack occurrence rate showing the effect of the present invention.

FIG. 2 is a sectional view of an end portion of an insulating substrate according to the present invention.

FIG. 3 is a diagram showing the relationship between the stress calculation values on both sides of the insulating substrate and the spare dimensions.

FIG. 4 is a plan view showing Cu foil patterns on both sides in another embodiment of the present invention, as shown in (a) and (b).

[Explanation of symbols]

1 Al ₂ O ₃ plate 2 Cu foil 3 Cu foil

Claims (3)

[Claims] 1. A semiconductor element is mounted on one surface of an insulating substrate having a copper foil stretched on both sides of a flat plate made of alumina, wherein the dimensions of the edges of the copper foil on both sides and the end surface of the alumina plate are different. A semiconductor device characterized in that the absolute value of the difference is 0.5 mm or less. 2. The semiconductor device according to claim 1, wherein the copper foils on both sides have a pattern in which they are vertically overlapped with each other when viewed in a direction perpendicular to the substrate surface. 3. The semiconductor device according to claim 1, wherein the thickness of the alumina plate is 0.26 to 0.29 mm.