JP-2026075113-A - Circuit boards and power devices

Abstract

[Problem] To provide a circuit board with high thermal conductivity and excellent thermal cycle resistance, and a power device using the same. [Solution] The device comprises a ceramic substrate made of a material mainly composed of silicon nitride, a bonding layer formed on one main surface of the ceramic substrate, and a conductive layer bonded to the ceramic substrate via the bonding layer, wherein the distance from the interface between the ceramic substrate and the bonding layer is 10 μm or less, and the maximum equivalent circular diameter of the Kirkendal voids present in the conductive layer is 2 μm or less. [Selection Diagram] Figure 1

Inventors

• 猪飼 良仁
• 茂木 淳
• 光岡 健

Assignees

• 日本特殊陶業株式会社

Dates

Publication Date

20260507

Application Date

20260227

Priority Date

20240426

Claims (6)

1. A ceramic substrate made of a material mainly composed of silicon nitride, A bonding layer formed on one main surface of the ceramic substrate, The system comprises a conductive layer bonded to the ceramic substrate via the bonding layer, The distance from the interface between the ceramic substrate and the bonding layer is 10 μm or less, and the maximum equivalent circular diameter of the voids present in the conductive layer is 2 μm or less. A circuit board characterized by the fact that no cracks of 1 mm or more occur when a thermal cycle test is performed 500 times, with each cycle consisting of maintaining the board at -40°C for 5 minutes, maintaining it at 220°C for 5 minutes, and then cooling it to -40°C.
2. The circuit board according to claim 1, characterized in that the void is a Kirkendal void.
3. The circuit board according to claim 2, characterized in that the distance from the interface is within 10 μm, and the proportion of the area occupied by the Kirkendal void within the conductor layer in a cross-section perpendicular to the plane direction is 10% or less.
4. The circuit board according to any one of claims 1 to 3, characterized in that the thickness of the bonding layer is 3 μm or less.
5. The aforementioned conductive layer is mainly composed of Cu, The circuit board according to any one of claims 1 to 3, characterized in that the bonding layer contains at least Ti.
6. A circuit board according to any one of claims 1 to 3, A power device characterized by comprising a power semiconductor mounted on the aforementioned conductive layer.

Description

This invention relates to a circuit board composed of a ceramic substrate mainly composed of silicon nitride, and a power device using the same. Traditionally, silicon nitride has attracted attention as an insulating heat dissipation substrate for inverter power modules installed in EVs (Electric Vehicles) and HVs (Hybrid Vehicles) due to its high thermal conductivity and strength. While aluminum nitride has been widely used as such an insulating heat dissipation substrate material, in the case of high-current power modules such as those used in EVs, temperatures can reach around 250°C. The difference in thermal expansion between the substrate and the bonded metal, such as copper, generates significant thermal stress, and the low-strength aluminum nitride can develop cracks and fractures. Therefore, although its thermal conductivity is inferior to aluminum nitride, silicon nitride, which has high thermal conductivity among general insulating ceramics and even higher strength, is increasingly being adopted. The bonding of the silicon nitride heat dissipation substrate to the conductive layer is generally performed by brazing, using a metal-containing brazing material as an intermediary. Patent Document 1 discloses a ceramic circuit board that has high bonding strength and excellent heat cycle resistance, with the aim of improving the operational reliability of electronic devices and having excellent heat dissipation. This ceramic circuit board is a ceramic circuit board in which both main surfaces of the ceramic substrate and a metal plate are bonded via a silver-copper brazing layer, and the silver-copper brazing layer consists of 75 to 98 parts by mass of silver powder and 2 to 25 parts by mass of copper powder, totaling 100 parts by mass, with a graphite powder content of 0.1 to 5.0 parts by mass and a content of at least one active metal selected from titanium, zirconium, hafnium, niobium, tantalum, vanadium, and tin of 0.5 to 10 parts by mass, and the specific surface area of the graphite powder is 5 to 100 m² /g. Japanese Patent Publication No. 2014-118310 This is a cross-sectional view of a circuit board according to an embodiment of the present invention.This flowchart shows the manufacturing procedure for the circuit board according to this embodiment.This flowchart shows the manufacturing procedure for silicon nitride sintered bodies.This figure shows the results of the thermal cycling test.This is a cross-sectional view showing an example of a power device according to an embodiment of the present invention. The inventors focused on the fact that voids (Kirkendal voids) are generated depending on the bonding conditions due to the difference in diffusion rates between Cu and Ti. They discovered that by controlling the size and content of these voids, it is possible to avoid the decrease in thermal conductivity, crack propagation, and thermal cycling performance caused by these voids, leading to the present invention. In other words, a circuit board according to one aspect of the present invention comprises a ceramic substrate made of a material mainly composed of silicon nitride, a bonding layer formed on one main surface of the ceramic substrate, and a conductor layer bonded to the ceramic substrate via the bonding layer, characterized in that the distance from the interface between the ceramic substrate and the bonding layer is 10 μm or less, and the maximum equivalent circular diameter of voids present in the conductor layer is 2 μm or less. This configuration allows the inventors to avoid a decrease in thermal conductivity and crack propagation even in the presence of voids, thereby maintaining high thermal conductivity and thermal cycling resistance. Embodiments of the present invention will be described in detail below with reference to the drawings. In this embodiment, Kirkendal voids are shown as voids. However, the voids are not limited to Kirkendal voids. [composition] Figure 1 is a cross-sectional view of a circuit board according to an embodiment of the present invention. In this embodiment, a ceramic substrate (Si 3N 4) and a conductor layer (Cu) are joined by a bonding layer (Ti-containing). As shown by the arrow on one side of Figure 1, Kirkendal voids are generated in the conductor layer due to the difference in diffusion rates between Cu and Ti. The bonding strength between the ceramic substrate and the conductor layer increases with higher bonding temperatures and longer heating times, but more Kirkendal voids are generated. On the other hand, the lower the bonding temperature and the shorter the heating time, the less likely Kirkendal voids are to be generated, but the bonding strength decreases. Therefore, by controlling the generation of Kirkendal voids according to the bonding temperature and time, it is possible to realize a circuit board with high thermal conductivity and excellent thermal cycle resistance. In this embodiment, as indicated by the arrows on both sides of Figu