# Patent

## Title
Heat sink arrangement for electrical apparatus

## Abstract

A printed circuit board (120) includes an insulating substrate (120a) on which conductive films (120b) are formed. Semiconductor devices (8) disposed external to the printed circuit board (120) have their leads (24a, 24b, 24c) connected to the conductive films. A flexible portion (30) is formed in the insulating substrate (120a) at a location near the location where the leads (24a, 24b, 24c) are connected to the conductive films (120b).

## Background
This invention relates to dissipation of heat from an electrical apparatus, e.g. a power supply apparatus, employing semiconductor devices.
BACKGROUND OF THE INVENTION
Some electrical apparatus, e.g. a power supply apparatus, uses power semiconductor devices as its components. Power semiconductor devices are connected to a driver printed circuit board on which a driver circuit for driving the power semiconductor devices is formed. The driver printed circuit board is connected to a control printed circuit board on which a control circuit for controlling the driver circuit is formed. The power semiconductor devices are mechanically coupled to a heat sink for dissipating heat from the semiconductor devices. In order to downsize the power supply apparatus, the control printed circuit board may be mounted to the heat sink on which the power semiconductor devices are mounted, with the driver printed circuit board mounted between the power semiconductor devices and the control printed circuit board, to thereby assemble them into a single block. If, however, rigid boards are used for the control and driver printed circuit boards, dimensional errors and/or assemblage errors of such printed circuit boards may place strain on the power semiconductor devices, causing the semiconductor devices to float up from the heat sink, which impedes normal heat dissipation and may break down the power semiconductor devices. In addition, the printed circuit boards themselves may be also strained. When such power supply apparatus is transported or removed to another place, vibrations caused by the moving may be applied to the power supply apparatus. Then, the vibrations are superposed on the strain on the power semiconductor devices and the printed circuit boards, which may lead to breakdown of the printed circuit boards and the power semiconductor devices.
JP 7-7167 U discloses use of a flexible board for connecting components mounted on a case to components mounted on a printed circuit board attached to the case.
Similar flexible boards would be used to connect the above-described power semiconductor devices to the driver printed circuit board and to connect the driver printed circuit board to the control printed circuit board. This arrangement, however, would require two flexible boards in addition to the driver and control printed circuit boards. In addition, a space for disposing the flexible boards must be secured, which impedes downsizing of the power supply apparatus.
An object of the present invention is to provide an electrical apparatus, in which electrical components are prevented from being broken down and, still, which can be small in size.
SUMMARY OF THE INVENTION
An electrical apparatus according to an embodiment of the present invention includes a first printed circuit board formed of an insulating substrate which is coated with an electrically conductive film. The first printed circuit board may be a multi-layered board or a single-layered board. An electrical component disposed external to the first printed circuit board has a rigid connector connected to the conductive film of the first printed circuit board. This connection of the connector to the conductive film may put strain to the connector, the electrical component and/or the first printed circuit board. The insulating substrate includes a flexible portion in the vicinity of the portion of the conductive film to which the electrical component is connected.
The flexible portion may be formed by thinning a portion, which is to become the flexible portion, of the insulating substrate relative to the remaining portion.
The electrical component may be a semiconductor device mounted on a heat sink. In such case, the connector is a lead of the semiconductor device. The semiconductor device may be a power semiconductor device.
The first printed circuit board may be disposed near the heat sink. In addition, a second printed circuit board may be mounted to the surface of the heat sink opposite to the surface on which the semiconductor device is mounted. The second printed circuit board is electrically and mechanically coupled to the first printed circuit board.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of an electrical apparatus according to an embodiment of the present invention.
FIG. 2 is a front view of a heat dissipating portion of the electrical apparatus shown in FIG. 1.
FIG. 3 is a side view of the heat dissipating portion shown in FIG. 2.
FIG. 4 is a cross-sectional view along a line 4-4 in FIG. 2.



DESCRIPTION OF PREFERRED EMBODIMENT OF THE INVENTION
An electrical apparatus according to an embodiment of the present invention is, for example, a power supply apparatus for use in welding or electroplating. The power supply apparatus includes, as shown in FIG. 1, an AC-to-DC converting circuit 4 for converting a three-phase commercial AC voltage, for example, applied to power supply input terminals 2a, 2b and 2c, to a DC voltage. The AC-to-DC converting circuit 4 includes, for example, a rectifying circuit and a smoothing circuit. The DC voltage from the AC-to-DC converting circuit 4 is applied to a DC-to-AC converting circuit, e.g. an inverter 6, which includes plural, e.g. six, power semiconductor devices, e.g. IGBTs 8. The IGBTs 8 are connected in a full-bridge circuit configuration. The DC voltage applied to the inverter 6 is converted therein to a high-frequency voltage, which is developed between two inverter output terminals 10a and 10b. The high-frequency voltage is voltage-transformed by a transformer (not shown), and the voltage-transformed high-frequency voltage is converted to a DC voltage by a high-frequency-to-DC converting circuit (not shown). The resulting DC voltage is applied across a load, for example, between a torch and workpiece in a welding machine, or between two electrodes for electroplating.
Control signals for controlling the respective IGBTs 8 to convert the DC voltage applied thereto to the high-frequency voltage are supplied to the respective IGBTs 8 from a driver circuit 12. A control circuit 14 gives instructions to the driver circuit 12 regarding the manner in which the IGBTs 8 should be controlled.
As shown in FIGS. 2 and 3, each of the IGBTs 8 is arranged in a chip form and mounted on a heat sink 16. Each IGBT 8 is the electrical component as referred to in the accompanying Claims.
The heat sink 16 has an IGBT mounting surface 16a of a rectangular shape, for example, as shown in FIG. 3, and also a number of fins 16b on the opposite surface. The fins 16b extend substantially perpendicularly to the mounting surface 16a. Three IGBTs 8 are disposed in a row on the mounting surface 16a, and their heat dissipating surfaces are in surface-contact with the mounting surface 16a. The three IGBTs 8 are pressed against the mounting surface 16a by means of a retainer 18a. 
The retainer 18a has three planar portions 181a contacting a larger portion of the surfaces of the three IGBTs 8 opposite to the heat dissipating surfaces thereof. The three planar portions 181a are connected together by a connecting portion 181b, which is bent, at a portion near a first side surface of the IGBTs 8, toward the mounting surface 16a of the heat sink 16. A lip portion 181c integral with the connecting portion 181b is in contact with the mounting surface 16a. The lip portions 181c is fixed to the mounting surface 16a by means of two screws 20a. The respective IGBTs 8 are screwed to the mounting surface 16a by three screws 22a extending, through the respective planar portions 181a of the retainer 18 and the IGBTs 8, into the mounting surface 16a. The remaining three IGBTs 8 are similarly mounted on the mounting surface 16a of the heat sink 16 by means of a retainer 18b and screws 20b and 22b, which are similar to the retainer 18a and the screws 20a and 22a. 
Each IGBT 8 has three leads 24a, 24b and 24c. The three leads 24a-24c of each IGBT 8 extend from a second side surface thereof, which is opposite to the first side surface, in the direction away from the retainers 18a and 18b, and are bent in a direction away from the heat sink 16. The leads 24a-24c are made of a material having high rigidity, e.g. metal. The leads 24a-24c are the connector referred to in the accompanying Claims. The leads 24a-24c are electrically and mechanically connected by, for example, soldering, to patterned conductors formed at predetermined locations on a printed circuit board 120, on which the driver circuit 12 is arranged. This eliminates the need for use of wires for electrical connections between the respective IGBTs 8 and the printed circuit board 120. The printed circuit board 120 is disposed, being spaced from and substantially in parallel with the mounting surface 16a of the heat sink 16. The printed circuit board 120 slightly overlaps the mounting surface 16a, and the remaining portion lies outside the mounting surface 16a. The printed circuit board 120 is the first printed circuit board referred to in the accompanying Claims.
The printed circuit board 120 has its portion remote from the mounting surface 16a secured to a printed circuit board 140, on which the control circuit 14 is arranged, by means of three screws 32. The driver circuit on the printed circuit board 120 is electrically connected to the control circuit 14 on the printed circuit board 140. The printed circuit board 140 is disposed, being spaced from and in parallel with the outermost fin 16b, and is secured to the outermost fin 16b by means of a plurality of spacers 26 and screws 28. Thus, the major surfaces of the printed circuit board 140 lie perpendicular to the IGBTs 8. In this manner, the heat sink 16 with the IGBTs 8 mounted thereon and the printed circuit boards 120 and 140 form one block. The printed circuit board 140 is the second printed circuit board referred to in the accompanying Claims.
Generally, the printed circuit boards 120 and 140 are formed of a rigid or hard insulating materials, e.g. a glass epoxy material, with a electrically conductive film, e.g. copper foil. Electric components are soldered to the conductive films at predetermined locations. If, therefore, the dimensional precision of the printed circuit boards 120 and 140 is low, and/or the precision of assemblage of the IGBTs 8 and printed circuits boards 120 and 140 is low, strain may be put on the IGBTs 8, which causes the IGBTs 8 to rise up from the mounting surface 16a, resulting in insufficient heat dissipation from the IGBTs 8. In some cases, strain is put on the leads 24a-24c of the IGBTs 8, causing the rigid leads 24a-24c to snap or bend.
In order to solve this problem, according to this embodiment, a flexible portion 30 is formed in the printed circuit board 120. As shown in FIG. 4, the printed circuit board 120 is a multi-layered printed circuit board formed of an epoxy glass material 120a within which a conductive pattern formed of plural, e.g. three, conductive films 120b, is arranged. The flexible portion 30 is formed by removing part of the epoxy glass material 120a from the opposite major surfaces of the epoxy glass material 120a, at a location slightly spaced in the direction away from the leads 24a-24c. The flexible portion 30 extends in the direction along which the leads 24a-24c are arranged.
The flexible portion 30 can absorb strain which may be generated, as described above, when the dimensional precision of the printed circuit boards 120 and 140 and/or the precision of assembling the IGBTs 8 and the printed circuit boards 120 and 140 are low. Then, it never happens that the contact of the IGBTs 8 with the heat sink 16 becomes defective, or that the leads 24a-24c snap or bend. Since the flexible portion 30 is formed by removing part of the insulating material of the printed circuit board 120, there is no need for preparing a separate, flexible printed circuit board for connection of the IGBTs 8 and the printed circuit board 120, in order for strain to be absorbed.
The present invention has been described as being embodied in a power supply apparatus for welders or electroplating machines. However, the present invention is not limited to them, but it can be embodied in any electrical apparatuses in which electrical components need be connected to printed circuit boards. Further, the flexible portion has been described as being formed in a multi-layered printed circuit board, but, when the printed circuit board used includes a conductive film only on one surface, the flexible portion can be formed by removing part of the insulating material from the other surface of the printed circuit board. In the described embodiment, the leads of the semiconductor devices are soldered to the printed circuit board 120, but they may be electrically and mechanically connected by screwing, caulking or the like. Furthermore, other semiconductor devices, such as bipolar transistors and FETs, than IGBTs may be used.

## Claims

1. An electrical apparatus comprising:
a first printed circuit board including an insulating substrate having first and second opposing two major surfaces, with an electrically conductive film formed inside said insulating substrate;
an electrical component external to said first printed circuit board, said electrical component having a rigid connector which extends through said first and second two opposing major surfaces and is connected to said conductive film; and
a second printed circuit board mounted at a location on a first one of said major surfaces spaced from a location on said first major surface where said electrical component is connected to said conductive film, said second printed circuit board being mounted to contact with and be perpendicular to said first major surface;
wherein a flexible portion is formed in said first printed circuit board at a location between said location where said electrical component is connected to said conductive film and said location where said second printed circuit board is mounted on said first printed circuit board;
wherein said flexible portion is formed by removing portions of said insulating substrate forming said flexible portion from said first and second major surfaces; and
wherein said flexible portion has said conductive film disposed inside said flexible portion.