Semiconductor device

A semiconductor device includes semiconductor elements and a multilayer substrate including an insulating plate and a circuit board on which the semiconductor elements are arranged that is arranged on the front surface of the insulating plate. The semiconductor device also includes a printed circuit board that is arranged facing a principal surface of the multilayer substrate and in which through holes are formed, as well as conductive posts that are inserted through the through holes and are electrically connected to the semiconductor elements via bonding materials. Furthermore, the semiconductor device includes fuses that are formed between the interior walls of the through holes and the outer peripheral surfaces of the conductive posts, are electrically connected to the printed circuit board via the conductive posts, and melt at a first temperature.

BACKGROUND OF THE INVENTION

Technical Field

The present invention relates to a semiconductor device.

Background Art

Semiconductor devices that include power semiconductor elements are used in power converters and as switching devices. In such semiconductor devices, semiconductor elements such as insulated-gate bipolar transistors (IGBTs) and power metal-oxide-semiconductor field-effect transistors (MOSFETs) are connected together such that the overall semiconductor device can function as a switching device, for example.

One such type of semiconductor device includes: a multilayer substrate including an insulating plate in which a circuit board is formed on the front surface and a metal plate is formed on the rear surface; and semiconductor elements that are formed on the circuit board with solder interposed therebetween. The semiconductor elements are electrically connected to one another and to the circuit board via wires made of aluminum or the like (see Patent Document 1, for example).

In this type of semiconductor device, if an overcurrent starts to flow due to short-circuits or the like in the semiconductor elements, the wires melt and thus function as fuses against the overcurrent, thereby making it possible to prevent heat generation, damage, and the like due to the overcurrent.

However, semiconductor devices that include power semiconductor elements and have a structure in which instead of wires, conductive posts, for example, are arranged in through holes in a conductive supporting member (such as a printed circuit board) such that the semiconductor elements are electrically connected to one another and to the circuit board via the conductive posts have also been proposed (see Patent Document 2, for example).

RELATED ART DOCUMENTS

Patent Documents

SUMMARY OF THE INVENTION

However, semiconductor devices in which conductive posts formed in a conductive supporting member are used as the connection structures are more prone to heat generation, damage, and the like due to overcurrent because none of the structures melt when overcurrent flows.

Moreover, in order to prevent this heat generation, damage, and the like, it is necessary to form separate circuits or the like that function as fuses against overcurrent. However, giving the semiconductor device this functionality results in an increase in costs due to the need to provide additional regions in which to form the required circuits or the like, for example.

The present invention was made in view of these problems and aims to provide a semiconductor device that includes fuse functionality. Accordingly, the present invention is directed to a scheme that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.

To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, in one aspect, the present disclosure provides a semiconductor device, including: a semiconductor element; a multilayer substrate including an insulating plate, and one or more circuit boards on a front surface of the insulating plate, the semiconductor element being disposed in a prescribed area on one of the one or more circuit boards; a printed circuit board positioned to face a principal surface, including the one or more circuit boards, of the multilayer substrate and in which a first through hole is formed at a position opposite to the semiconductor element; a first conductive post inserted into the first through hole and electrically connected to the semiconductor element via a bonding material; and a first fuse member disposed between an interior wall surface of the first through hole and an outer peripheral surface of the first conductive post and electrically connected to the first conductive post and to the printed circuit board, a melting temperature of the first fuse member being a first temperature.

The technology disclosed herein makes it possible to prevent heat generation, damage, and the like due to overcurrent in a semiconductor device, thereby making it possible to prevent decreases in the reliability of the semiconductor device. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory, and are intended to provide further explanation of the invention as claimed.

DETAILED DESCRIPTION OF EMBODIMENTS

Next, an embodiment will be described below with reference to figures.

First, the exterior of a semiconductor device according to the embodiment will be described with reference toFIG. 1.

FIG. 1is an exterior view of a semiconductor device according to an embodiment.

As illustrated inFIG. 1, a semiconductor device100includes a molded body formed by molding a resin material such as an epoxy resin. In this semiconductor device100, through holes2for inserting screws are formed in the left and right ends inFIG. 1, and insulating walls3that have a U-shape when viewed in a plan view are formed surrounding the through holes2.

Furthermore, in the semiconductor device100, external connection terminals4A,4B, and4C and control terminals5A and5B that protrude upwards are respectively formed along both the front and rear edge sides of the upper surface between the left and right insulating walls3.

Next, the configuration of the semiconductor device100will be described with reference toFIG. 2.

FIG. 2is a side see-through view of the semiconductor device according to the embodiment.

Note that inFIG. 2, the connection structures that connect conductive posts130to semiconductor elements121and122and to a circuit board112bare illustrated in a simplified manner (all of these components will be described later). These connection structures will be described in more detail with reference toFIG. 3.

The semiconductor device100includes the semiconductor elements121and122, a multilayer substrate110on which the semiconductor elements121and122are arranged, and a printed circuit board140arranged facing the multilayer substrate110.

The semiconductor elements121are power semiconductor elements such as IGBTs (or power MOSFETs). The semiconductor elements122are free wheeling diodes (FWDs).

The multilayer substrate110includes an insulating plate111, circuit boards112aand112bformed on the front surface of the insulating plate111, and a metal plate113formed on the rear surface of the insulating plate111.

The insulating plate111is made of a ceramic with good thermal conductivity such as alumina.

The circuit boards112aand112bare made of copper plates with a thickness of approximately 0.3 mm to 1 mm, for example. Moreover, the circuit board112ahas a pattern for mounting the semiconductor elements121and122and is connected to the external connection terminals4A and4C. Furthermore, the circuit board112bis arranged at a prescribed distance away from the circuit board112a, has a pattern for connecting to the conductive posts (described later), and is connected to the external connection terminals4B.

The metal plate113has a thickness of approximately 0.3 mm to 1 mm, is made of a metal such as copper that exhibits high heat dissipation, for example, and is formed over the entire rear surface of the insulating plate111.

In the printed circuit board140, through holes are formed in prescribed positions, and the conductive posts130are inserted through these through holes. Conductive patterns that form current paths for primary circuits, gate wiring patterns that are connected to gate electrodes of the semiconductor elements121via the conductive posts130, and emitter auxiliary terminal wires are formed on both surfaces of the printed circuit board140. The gate wiring patterns are connected to terminal connection patterns that are connected to the control terminals5B.

Furthermore, the external connection terminals4A,4B, and4C are inserted through the printed circuit board140without making contact therewith.

In this way, the desired circuit configurations can be achieved using the multilayer substrate110, the semiconductor elements121and122, and the printed circuit board140in which the conductive posts130are formed.

Next, the connection structures that connect the semiconductor elements121and122to the conductive posts130that are inserted through the through holes in the printed circuit board140will be described in more detail with reference toFIG. 3.

FIG. 3is an enlarged cross-sectional view of the main components of the semiconductor device according to the embodiment.

InFIG. 3, the main components of the semiconductor device100in a cross section taken along the lengthwise direction of the conductive posts130are enlarged and illustrated in more detail. Moreover, in order to simplify the description, the components illustrated inFIG. 3are not necessarily illustrated exactly to scale relative to in the actual semiconductor device100.

As described above, the semiconductor device100includes the multilayer substrate110, the semiconductor elements121and122, the printed circuit board140, and conductive posts131,132, and133(these will be referred to collectively as “the conductive posts130”), and all of these components are sealed within a sealing resin160.

The semiconductor elements121and122are arranged on the circuit board112aof the multilayer substrate110with solder121aand122ainterposed therebetween.

Moreover, the semiconductor device121is thicker than the semiconductor device122and generates more heat, for example.

The printed circuit board140has through holes141,142, and143formed therein and is arranged facing the circuit boards112aand112bof the multilayer substrate110. Moreover, the diameter of the through holes141,142, and143is greater than or equal to approximately 2.1 mm and less than or equal to approximately 4.5 mm, for example.

The conductive posts131,132, and133are respectively inserted through the through holes141,142, and143, and the bottom ends of the conductive posts are respectively bonded to the semiconductor elements121and122and the circuit board112bvia bonding materials131a,132a, and133asuch as solder. Moreover, the diameter of the conductive posts131,132, and133is greater than or equal to approximately 0.1 mm and less than or equal to approximately 0.5 mm, for example.

Furthermore, fuses141aand142a(first fuses) and fuses143a(second fuses) are respectively formed between the interior walls of the through holes141,142, and143and the outer peripheral surfaces of the conductive posts131,132, and133. The thickness of the fuses141a,142a, and143a(in the radial direction) is greater than or equal to approximately 1 mm and less than or equal to approximately 2 mm, for example.

The fuses141a,142a, and143aelectrically connect the conductive posts131,132, and133to the printed circuit board140and are made of a conductive metal material. Moreover, the fuses141aand142aare made of a material that melts at a first temperature, while the fuses143aare made of a material that melts at a second temperature that is lower than the first temperature, as will be described in more detail next. The first temperature of the fuses141aand142aand the second temperature of the fuses143amust at least be greater than the temperatures of the conductive posts131,132, and133, respectively, when the semiconductor elements121and122of the semiconductor device100are operating at the maximum operating temperature of 175° C. (these temperatures are approximately 100° C. to 175° C. for the conductive posts131and132that are bonded to the semiconductor elements121and122and approximately 50° C. to 100° C. for the conductive posts133that are bonded to the circuit board112b, for example). Meanwhile, the first temperature of the fuses141aand142aand the second temperature of the fuses143aare also less than or equal to the temperatures that occur when the semiconductor device100generates excess heat due to overcurrent (these temperatures are approximately 180° C. to 690° C. for the conductive posts131and132that are bonded to the semiconductor elements121and122and approximately 150° C. to 500° C. for the conductive posts133that are bonded to the circuit board112b, for example).

The sealing resin160includes metal reservoirs161a,162a, and163aconstituted by spatial regions that have openings that cover the through holes141,142, and143(from the upper side inFIG. 3) and that include the upper ends of the conductive posts131,132, and133. These metal reservoirs161a,162a, and163acan be formed by placing hollow resin cylinders that have openings just in one end over the upper ends of the conductive posts131,132, and133such that the through holes141,142, and143are covered by those openings, and then filling in and curing the sealing resin160, for example. In this way, the metal reservoirs161a,162a, and163aare formed within the sealing resin160.

Similarly, the sealing resin160includes metal reservoirs161b,162b, and163bconstituted by spatial regions that have openings that cover the through holes141,142, and143(from the bottom side inFIG. 3) and that include the conductive posts131,132, and133. These metal reservoirs161b,162b, and163bcan be formed by inserting the conductive posts131,132, and133through the bottom surfaces of hollow resin cylinders that have openings just in one end such that the through holes141,142, and143are covered by those openings, and then filling in and curing the sealing resin160, for example. In this way, the metal reservoirs161b,162b, and163bare formed within the sealing resin160.

The metal reservoirs161a,162a,163a,161b,162b, and163bhave a cylindrical shape, for example. However, as long as the through holes141,142, and143are covered (from both the lower and upper sides) by the openings, the metal reservoirs161a,162a,163a,161b,162b, and163bare not limited to having a cylindrical shape and may instead have a prismatic shape, a circular cone shape, or a polygonal cone shape.

Moreover, for the metal reservoirs161a,162a,163a,161b,162b, and163b, any configuration in which at least one of the upper metal reservoirs161a,162a, and163aand the lower metal reservoirs161b,162b, and163b(that is, upper and lower as illustrated inFIG. 3) are formed for the conductive posts131,132, and133is possible. Furthermore, a single overall metal reservoir may be respectively formed for each of the groups of the conductive posts131,132, and133.

Next, a state in which overcurrent begins to flow while the semiconductor device100configured as described above is operating will be described with reference toFIGS. 4A and 4B.

FIGS. 4A and 4Bare drawings for explaining the fuse functionality of the semiconductor device according to the embodiment.

FIGS. 4A and 4Bare enlarged views of a region around the semiconductor element121, for example, in the semiconductor device100, and here the state of the conductive posts131that are bonded to the semiconductor element121will be described as an example.

FIG. 4Aillustrates a normal operating state of the semiconductor device100, andFIG. 4Billustrates a state is which overcurrent is flowing in the semiconductor device100.

As described above, the first temperature of the fuses141ais greater than the normal operating temperature of the semiconductor device100but less than or equal to the temperature of the semiconductor device100when overcurrent occurs. Therefore, as illustrated inFIG. 4A, while a normal current is flowing through the semiconductor device100, the fuses141ado not melt even if heated and remain arranged between the conductive posts131and the through holes141, thereby maintaining an electrical connection between the conductive posts131and the printed circuit board140.

Meanwhile, when overcurrent occurs in the semiconductor device100and this overcurrent passes through the conductive posts131, the overcurrent also passes through the fuses141aand causes heat to be generated. When the temperature of the fuses141abecomes greater than the first temperature due to this heat generation, the fuses141amelt.

As illustrated inFIG. 4B, the melted fuses141aflow into and are collected in the metal reservoirs161b, for example. When this happens, the electrical connections between the conductive posts131and the printed circuit board140are severed, thereby preventing overcurrent from flowing between the conductive posts131and the printed circuit board140. In this way, the fuses141aformed between the through holes141and the conductive posts131provide a fuse functionality against overcurrent.

The description above applies not only to the conductive posts131but also to the fuses142aand143afor the conductive posts132and133when overcurrent occurs.

As described above, the semiconductor device100includes the semiconductor elements121and122and the multilayer substrate110including the insulating plate111and the circuit board112aon which the semiconductor elements121and122are arranged that is arranged on the front surface of the insulating plate111. The semiconductor device100also includes the printed circuit board140that is arranged facing the principal surface of the multilayer substrate110and in which the through holes141and142are formed, as well as the conductive posts131and132that are inserted through the through holes141and142and are electrically connected to the semiconductor elements121and122via the bonding materials131aand132a. Furthermore, the semiconductor device100includes the fuses141aand142athat are formed between the interior walls of the through holes141and142and the outer peripheral surfaces of the conductive posts131and132, are electrically connected to the printed circuit board140via the conductive posts131and132, and melt at a first temperature.

Meanwhile, the semiconductor device100also includes the conductive posts133that are inserted through the through holes143and are electrically connected to the circuit board112bvia the bonding materials133a. The semiconductor device100also includes the fuses143athat are formed between the interior walls of the through holes143and the outer peripheral surfaces of the conductive posts133, are electrically connected to the printed circuit board140via the conductive posts133, and melt at a second temperature that is lower than the first temperature.

When overcurrent occurs in this semiconductor device100, that overcurrent flows through the fuses141a,142a, and143a, thereby causing the fuses141a,142a, and143ato melt. This severs the electrical connections between the conductive posts131,132, and133and the printed circuit board140, thereby preventing overcurrent from flowing therebetween. Therefore, the semiconductor device100makes it possible to reduce cost increases as well as prevent damage or the like due to overcurrent without having to form separate circuits that have fuse functionality, thereby making it possible to reduce decreases in the reliability of the device.

In the semiconductor device100, the semiconductor elements121and122reach a higher temperature than the circuit board112b(on which no semiconductor elements are arranged). In other words, the conductive posts131and132that are respectively bonded to the semiconductor elements121and122will generally reach higher temperatures than the conductive posts133that are bonded to the circuit board112b. Therefore, the first temperature of the fuses141aand142afor the conductive posts131and132that are bonded to the semiconductor elements121and122is set to a higher value than the second temperature of the fuses143aof the conductive posts133that are only bonded to the circuit board112b. This makes it possible to ensure that the fuses141a,142a, and143athat are arranged between the interior walls of the through holes141,142, and143and the outer peripheral surfaces of the conductive posts131,132, and133only exhibit fuse functionality for the appropriate levels of overcurrent.

Next, the fuses141a,142a, and143aof the semiconductor device100will be described with reference toFIGS. 5A and 5B.

FIGS. 5A and 5Bare top views of a fuse of the semiconductor device according to the embodiment.

Here, the fuse141aillustrated inFIG. 5Awill be described as an example.

FIG. 5Ais a top view of the fuse141a, andFIG. 5Bis a top view of another fuse.

As illustrated inFIG. 5A, the fuse141adescribed in the present embodiment is formed around the entire gap between the conductive post131and the through hole141.

Meanwhile, inFIG. 5B, a substantially cross-shaped fuse241athat is centered about the conductive post131is arranged between the conductive post131and the through hole141. Here, the fuse241ais made of a material with lower electrical resistivity than the conductive post131, and this fuse241agenerates heat due to electrical resistance when overcurrent flows therethrough. When conductive post131is made of copper, for example, the fuse241ais made of a tin solder or the like. InFIG. 5B, the fuse241ais only partially formed in the through hole141in order to ensure that the fuse241awill melt more reliably due to the heat generated by electrical resistance when overcurrent occurs. This also increases the current density of the current that flows through the fuse241a, thereby resulting in generation of more heat due to electrical resistance.

Moreover, inFIG. 5B, the fuse241ais formed in a substantially cross-shaped shape that is divided into four portions. However, the fuse241amay instead be divided into less than four portions or more than four portions and may also be formed in any other shape that allows current to flow (such as a ball shape or a cylinder shape).