JPH07120736B2 - Semiconductor rectifier - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to a semiconductor rectifying device, and is particularly used for a rectifying device for an AC generator of a vehicle.

(Prior Art) An example of a semiconductor rectifying device related to the present invention has a structure shown in FIG. In the figure, 1 is a silicon chip, 2 is a heat dissipation container molded in a bowl shape, and the silicon chip 1 is one first main surface (lower surface in the figure) of which the solder layer 3a forms a concave bottom of the heat dissipation container 2. Mounted on the second main surface (upper surface in the figure) of the silicon chip 1 and the solder layer 3b.
Is connected to the lead wire 4 and the electrodes are led out. In order to protect the silicon chip 1, the encapsulation material 5 made of silicone resin is filled in the recess of the bowl-shaped heat dissipation container 2 to cover the silicon chip 1 and the heat dissipation container 2 and the lead wire 4. And an envelope that integrally seals and.

By the way, conventionally, the heat dissipation container 2 has been made of copper having good heat conductivity or a clad material of copper / invar / copper. However, the coefficient of linear expansion of copper at 20-200 ℃ is 16.
At 7 × 10 ^-6 / ℃, it was much larger than that at 2.5 × 10 ^-6 / ℃ in silicon, so the silicon chips in the rectifying element were often damaged. Also copper / invar / copper [layer thickness ratio
The linear expansion coefficient of 20 ~ 200 ℃ in the clad material of 1/1/1]
Although it is 11.2 × 10 ^-6 / ℃, which is much smaller than that of copper, the result of the fracture test of the repeated cycle of 50 ℃ and 170 ℃ was still unsatisfactory.

Furthermore, when considering a Zener type rectifying device as a rectifying device with a surge absorbing function, an important design issue is the load dump surge withstand capability, which destroys the device when a surge above the breakdown voltage of the device is applied. There is a case. It was found that further improvement of the heat dissipation characteristics of the element (smaller transient thermal characteristics) is effective for improving the breakdown resistance of the element. In particular, it is essential to improve the heat dissipation characteristics of a rectifying element having a surge absorbing function used in a vehicle AC generator.

However, the element structure of the conventional product lacks the withstand capability for a generator with a large load dump surge, and in order to improve the withstand capability, the silicon chip has been made larger and the heat sink has been made thicker. .

Also, the coefficient of linear expansion of a copper heat dissipation container with good heat dissipation is 16.7 × 10 ^-6 / ° C, which is about 6 times as large as that of silicon, 2.5 × 10 ^-6 / ° C. When soldering to a container, large thermal stress acts and causes damage. Therefore, it has a linear expansion coefficient as close as possible to silicon,
Moreover, it is necessary to select a material whose thermal conductivity is not extremely inferior to that of copper, but an appropriate material has not been known.

(Problems to be Solved by the Invention) An object of the present invention is to provide a rectifying device equipped with a heat dissipation container in which the heat dissipation characteristics and the linear expansion coefficient are more balanced than those of the conventional products, and also necessary for the surge absorbing function. Another object of the present invention is to provide a structure of a rectifying device having excellent heat dissipation characteristics at various levels.

[Structure of the Invention] (Means for Solving the Problems) The semiconductor rectifying device according to claim 1 of the present invention is particularly suitable for a device having a surge absorbing function, and is composed of copper, kovar, and copper.
On the surface of the heat dissipation container made of a layer clad material, the first main surface of the silicon chip is solder-bonded, and between the lead wire and the second main surface of the silicon chip, the same copper and kovar as in the heat dissipation container are used. It is characterized in that it has a structure in which a heat dissipation plate made of a three-layer clad material with copper is sandwiched and soldered, and the layer thickness ratio of Kovar to the total layer thickness in the three-layer clad material is 10 to 60%. The clad material having the Kovar layer thickness ratio in claim 1 includes a copper / kovar / copper thickness composition of 3: 1: 3 or 1: 2: 1. As a reference example of the present invention, the layer thickness ratio of Kovar to the total layer thickness in the three-layer clad material is 40 to
A semiconductor rectifier having a structure in which a first main surface of a silicon chip is solder-bonded to a heat dissipation container of 60% and a lead wire is directly solder-bonded to the second main surface of the silicon chip is given.
The clad material having the above Kovar layer thickness ratio in the reference example includes a copper / kovar / copper thickness ratio of 1: 2: 1.

(Operation) In the graph of FIG. 3, regarding the copper / kovar / copper three-layer clad material, the linear expansion coefficient α (left vertical axis) of the clad material with respect to the layer thickness ratio of the kovar (horizontal axis) and the heat conduction in the penetration direction. Rate λ
(Right vertical axis) is shown.

The graph of FIG. 4 shows the coefficient P (vertical axis) of the maximum principal stress acting on the chip center with respect to the Kovar layer thickness ratio (horizontal axis) when one side of the silicon chip is bonded to the clad material (solid line). Be done. The coefficient P is obtained by the following equation.

P = E ₁ t ₁ b [mn / (mn + 1)] × (α ₁ −α ₂ ) T where m = (thickness t _{2 of} clad material) / (thickness t _{1 of} silicon chip) n = (clad Longitudinal elastic modulus of material E ₂ ) / (longitudinal elastic modulus of silicon chip E ₁ ) α ₁ : coefficient of linear expansion of silicon chip α ₂ : coefficient of linear expansion of clad material T: temperature difference b: width of specimen Fig. 3 From the graph of FIG. 4 and FIG. 4, when the clad material is soldered to one main surface of the silicon chip as in the reference example, the ratio of kovar satisfying both thermal conductivity and thermal stress is 40 to 60. % Range, copper / kovar /
It can be seen that it is centered on the copper thickness composition of 1: 2: 1.

A different Kovar ratio in the range of 10 to 25%, that is, the one centering on the copper / Kovar / copper thickness composition of 3: 1: 3, has a thermal conductivity close to that of copper, but thermal stress Has a big drawback. In this case, as in claim 1 of the present invention, the thermal stress (dashed line in FIG. 4) of the heat dissipating container and the heat dissipating plate of the clad material solder-bonded to both main surfaces of the silicon chip is the Although it is about the same as the thermal stress of the chip (solid line in FIG. 4), its warpage can be eliminated, so that damage due to repeated warpage in practical use is avoided, and therefore its high heat dissipation characteristics can be utilized. The fact that the warp does not occur when the cladding material is soldered to both main surfaces of the silicon chip is not only due to the copper / kovar / copper thickness composition of 3: 1: 3 above but also of 1: 1: 1. The same applies to the case of the thing and the case of 1: 2: 1, so that the ratio of Kovar in claim 1 of the present invention can be adopted within the range of 10 to 60%.

FIG. 5 is a graph showing the temperature (horizontal axis) and the total expansion amount (vertical axis) from room temperature to that temperature for Kovar and Invar. The reason why Kovar is adopted in the three-layer clad material of the present invention is that Kovar (broken line in the same figure) is inferior to Invar (dashed line in the same figure) at a linear expansion coefficient up to 200 ° C. which is usually studied. This is because Kovar is superior to Invar in the slope of the curve above 200 ° C. From this advantage of Kovar, it is understood that Kovar's three-layer clad material is much more advantageous than copper's as well as Invar's three-layer clad material in solder joints and severe thermal shock tests. I can do it.

(Embodiment) FIG. 1 shows the structure of a rectifying element having a surge absorbing function according to the first and second embodiments of the present invention.

In the figure, the heat dissipation container 6 is made of a three-layer clad material of copper 6a, kovar 6b, and copper 6c, and the silicon chip 1 of the Zener diode is mounted on the bottom surface of the heat dissipation container 6 by the solder layer 3a. The silicon chip 1 is bonded on the upper surface thereof to the heat dissipation plate 7 of a three-layer clad material of copper 7a, kovar 7b and copper 7c by the solder layer 3b, and the other surface 7c of the heat dissipation plate 7 is joined.
Is connected to the lead wire 4 by the solder layer 3c to lead the electrode. Then, a silicone resin protective encap material 5 is filled in the concave portion of the bowl-shaped heat dissipation container 6 to cover the silicon chip 1 and integrally seal the heat dissipation container 6, the heat dissipation plate 7, and the lead wire 4. It constitutes the envelope that does.

The clad material used for the heat dissipation container 6 and the heat dissipation plate 7 bonded to both main surfaces of the silicon chip 1 of the first embodiment has a copper / kovar / copper thickness composition of 3: 1: 3 (kovar layer thickness). The ratio is 14.
6 lots (3%) were tested, and the actual value of Kovar layer thickness ratio of each lot was 10.2%, 14.3%, 14.7%, 1
It was 4.7%, 18.8%, and 24.5%.

The clad material used for the heat radiating container 6 and the heat radiating plate 7 of the second embodiment had a thickness composition of 1: 2: 1 (a Kovar layer thickness ratio of 50%), and 6 lots were tested. , The actual value of Kovar layer thickness ratio of each lot is 40.6%, 48.7%, 50.8%,
It was 51.0%, 53.7%, and 59.8%.

The surge tolerance test of the rectifying device is performed by the test circuit (C
= 80,000 μF), the capacitor peak voltage at the time of breakdown was measured. The results are shown in the bar graph in Figure 7 (for each lot).
, The target voltage level in this case is 90V as shown. The comparative examples are the conventional product using only the copper heat dissipation container shown in FIG. 7 and the element of the reference example using only the heat dissipation container of the thickness constitution 1: 2: 1 described below. is there.

As shown in FIG. 7, in the rectifying element, by disposing the clad material on both main surfaces of the silicon chip, the heat dissipation characteristics are improved as compared with the conventional product (made of copper), and in particular, the rectifying element having an excellent surge absorbing function can be obtained. I understand.

As a result of the thermal shock test, it was confirmed that the thermal stress characteristics were also excellent. The thermal shock test is performed in an atmosphere of -40 ° C.
It is a test that repeats the cycle of leaving it for 30 minutes and then leaving it in an atmosphere at 170 ° C for 30 minutes to check for defects.
The results were observed at 0 cycle and 200 cycles. In the conventional product using only the copper heat dissipation container shown in FIG. 8, the rate at which the silicon chip was damaged and the device failed was about 2% in 100 cycles.
It is 0% in cycles and 0.1% or less in 200 cycles, and the second embodiment has 100 cycles in each lot and 0% in 200 silles.
Met. The results of the above examples are due to the fact that the repeated warping of the chip disappeared during the cycle by disposing the cladding material on both main surfaces of the silicon chip.

FIG. 2 shows a structure of a reference example in which a clad material heat dissipation container is arranged on one side of a silicon chip.

In the figure, the heat dissipation container 6 is made of a three-layer clad material of copper 6a, kovar 6b and copper 6c, and the silicon chip 1 of the diode is mounted on the bottom surface of the heat dissipation container 6 by the solder layer 3a. The chip 1 is connected to the lead wire 4 by the solder layer 3b on the upper surface thereof and the electrodes are led out. In order to protect the silicon chip 1, an encapsulation material 5 of silicone resin is filled in the recess of the bowl-shaped heat dissipation container 6 to cover the silicon chip 1 and the heat dissipation container 6 and the lead wire 4. And an envelope that integrally seals and.

The clad material used in the heat dissipation container 6 of the reference example had 6 thicknesses of 1: 2: 1 (the Kovar layer thickness ratio is 50%), and 6 lots were tested. Layer thickness ratio actual value is 40.6%, 48.7%, 50.8%, 51.0%,
It was 53.7% and 59.8%.

In this reference example, as shown in FIG. 3, the thermal conductivity in the penetrating direction of the heat dissipation container clad material is about the same as that of 100% Kovar, but the thermal conductivity in the spreading direction is far better than that. Further, as shown in FIG. 4, the thermal stress exerted on the silicon chip is almost the same as that of 100% Kovar, so that the heat dissipation characteristics and the thermal conductivity characteristics are well balanced. Furthermore, as described with reference to FIG. 5, thermal stress in soldering or the like may be good. for that reason,
The results of the thermal shock test are extremely excellent. In other words, the rate at which the silicon chip is damaged and the device does not function is 2% after 100 cycles in the conventional product shown in FIG.
There were some, but the reference example was 0 in 100 cycles for each lot.
%, Less than 0.1% after 200 cycles. From the results of each lot, it was confirmed that the Kovar layer thickness ratio was in the range of 40-60%.

[Advantage of the Invention] The rectifying element using the specific clad material according to claim 1 of the present invention for the heat radiating container and the heat radiating plate is suitable for a Zener type rectifying element which requires a heat radiation characteristic particularly for a surge absorbing function. Therefore, a rectifying element having excellent heat dissipation characteristics is provided.

[Brief description of drawings]

FIG. 1 is a sectional view of a rectifying element according to claim 1 of the present invention, FIG. 2 is a sectional view of a rectifying element according to a reference example, and FIGS. 3 to 5 explain characteristics of a clad material used in the present invention. FIG. 6 is a circuit diagram of the surge withstand test device, FIG. 7 is a bar graph showing the surge withstand test result of the embodiment of the present invention,
FIG. 8 is a sectional view of a conventional rectifying element. 1 ... Silicon chip, 2,6 ... Radiation container, 3a, 3b, 3c ...
... Solder layer, 4 ... Lead wire, 5 ... Encap material,
7 ... Heat sink, 6a, 6c, 7a, 7c ... Copper layer of clad material, 6b,
7b: Kovar layer of clad material.

 ─────────────────────────────────────────────────── --Continued from the front page (56) References JP-A-49-51873 (JP, A) JP-A-52-28275 (JP, A) JP-A-63-252457 (JP, A)

Claims (1)

[Claims] 1. A semiconductor chip having a rectifying function is solder-bonded to an inner bottom of a bowl-shaped metal heat radiating container with an electrode on a first main surface of the chip, and a metal heat radiating plate is soldered to one end of a lead wire. A semiconductor rectifying device in which the semiconductor chip is soldered to the heat dissipation plate with an electrode on the second main surface of the chip and the inside of the heat dissipation container is resin-sealed, wherein the heat dissipation container and the heat dissipation plate are made of copper and kovar. A semiconductor rectifying device comprising a three-layer clad material of copper and copper and having a Kovar layer thickness ratio of 10 to 60% in the three-layer clad material.