GB2046990A - Mounting arrangements for high power electronic components - Google Patents

Abstract

A mounting arrangement for a high power electronic component such as a thyristor 1 consists of two finned heat sinks 2, 3 which together sandwich the component between them so as to cool both of its major opposite faces, the two heat sinks being clamped together by means of pressure plates 10 which bear against the outer edges of the heat sink fins 11, 12, 13, so as to form open ended ducts 15, 16, between the pressure plates and the heat sinks. In this way the portions of the heat sinks closest to the component can be effectively cooled by means of a fluid coolant which is made to flow through the ducts. <IMAGE>

Description

SPECIFICATION Improvements in or relating to mounting arrangements for high power electronic components This invention relates to mounting arrangements for high power electronic components and is particularly applicable to arrangements in which a high power semiconductor device such as a rectifier or a thyristor, for example, is to be mounted in a manner which enables it to be cooled efficiently when it is operating. Even though semiconductor devices can be operated in an efficient manner, nevertheless when they are used to control high power levels they can dissipate a great deal of heat which must be dispersed to prevent the semi-conductor device over heating.For this reason it is customary to hold the semiconductor device in close thermal cotact with a heat sink, and for semiconductor devices which are intended to work at very high power levels it has been proposed to mount each device between a pair of heat sinks so that both sides of the semiconductor device may be cooled in a more effective manner. It is common to use a heat sink having fins so as to enhance its heat dissipation properties by thermal radiation and by bringing a very large surface area of the heat sink into contact with a fluid coolant, such as air, which flows over the surface ofthefins.When two heat sinks are used together to cool a device mounted between them, the arrangement of the fins is generally adversely affected and it has proved difficult to effectively cool by means of a fluid coolant those portions of the heat sink which are most closely adjacent to the semiconductor device which generates the heat.

The present invention seeks to provide an im proved mounting arrangement for high power electronic components in which this disadvantage is reduced.

According to this invention a mounting arrange ment for a high power electronic component in cludes two finned heat sinks arranged in operation to sandwich an electronic component between them, a pressure pad associated with each heat sink and arranged to bear against the edges of a plurality of fins forming part of the heat sink so as to form one or more opened ended ducts thereby so that, in ~operation, a fluid coolant can pass between each pressure plate and the component to be cooled, the two heat sinks being held in contact with the electronic component by fastening means linking ,both pressure pads together.

The coolant may be a liquid or it may be a gas such as air and the coolant may be forced through the ducts and over the surface of the fins under pressure or instead only convection currents may be relied upon.

Preferably at least two of the fins upon which the pressure pads bear have portions which are of a thicker section than some of the remaining fins. The thickness is related to the pressure loading applied to the component.

Preferably each heat sink has a flat surface portion which contacts the electronic component, the fins being arranged perpendicular to this surface so that they extend away from the surface on the opposite side to that of the electronic component.

Preferably means are provided for indicating when the two heat sinks exert a predetermined pressure on the electronic component which is mounted between them.

Preferably again the fastening means includes resiliently deformable means the deformation of which determines the pressure applied to the component.

Preferably again the fastening means includes elongate members which pass through the heat sinks at points arranged on a circle surrounding the electronic component. In this way the likelihood of localised stresses being generated is reduced.

Preferably the pressure pad is located between each heat sink and a respective pressure plate with a resilient member provided between each pressure pad and its pressure plate. This accommodates misalignments between the two heat sinks and also reduces the likelihood of excessive localised stresses being produced.

The invention is further described by way of example with reference to the accompanying drawings in which, Figures 1 and2 illustrate a plan view and a sectional elevation respectively of a mounting arrangement in accordance with the present invention.

Referring to the drawings, a semiconductor device, in this case a high power thyristor 1 is sandwiched between a pair of heat sinks 2 and 3.

Each heat sink 2 and 3 is provided with a flat surface portion 4 which contacts the flat outer surface of the thyristor 1. The heat sinks are formed out of a good thermally conductive material such as aluminium and are provided with thin fins 5, which extend perpendicularly away from the flat surface protions 4. The central portions of those fins nearest to the centre line 6 are of thicker section than the other fins and do not extend to the full height 8 over their entire length, but instead are provided with recessed portions so as to permit a pressure plate 9 and a pressure pad 10to be accommodated.

The pressure plate 9 is arranged to exert a pressure against the pressure pad 10, which is in contact with the upper surface of the edges of fins 11, 12, and 13. It will be seen that the space between adjacent fins 11, 12 and 13 forms a pair of ducts 15 and 16. Resilient dished washers 17 and 18 are positioned between the pressure plate 9 and the pressure pad 10 to accommodate any misalignment between the pressure plate 9 and the upper surface of the fins 11, 12 and 13 on which the pressure pad rests. The pressure applied to the thyristor is determined by the extent to which these dished washers are deformed, i.e. flattened.

As so far described the heat sink on each side of the thyristor 1 and its associated pressure pad and pressure pad are the same. The upper pressure plate 9 illustrated in Figure 2 is provided with an indicating device in the form of a washer 20 by means of which an indication is provided when a predetermined loading pressure is exceeded. In this case when the dished washers 17 and 18 are compressed to the required extent, the washer 20 forming part of the indicating device becomes free to rotate.

Prior to assembly of the mounting arrangement, the pressure pad 10 and the pressure piate 9 are clamped together by a press, with the dished washers 17 and 18 positioned between them. When the clamp force equals the pressure which in due course is to be applied to the electronic component by the mounting arrangement, the nut 21 is tightened down on the screw threaded stud 22 which forms part of the pressure pad 10 until the washer 20 is no longerfreeto rotate.

When the mounting arrangement is assembled with an electronic component, such as the thyristor 1, positioned between the heat sinks 2 and 3, the fastening studs 24, which are electrically isolated from the heat sink 3 by insulated tubes 25 and insulated cups 26 and arranged in a ring in a six studs symmetrically about the thyristor 1 as shown in Figure 1, are tightened down. They are tightened down until the washer 20 is released and is just free to rotate. At this point the thyristor 1 is subject to amounting pressure which is equal to the original clamping force applied to the pressure pad and pressure plate when the indicating device was set up.

The pressure plate 27 associated with heat sink 3 is not provided with an indicating device since equal pressures are automatically applied to both sides of the electronic component. The fins 11, 12, and 13 are thicker than the other fins since they are subject to a very large loading force, and it will be seen from Figure 1 that the fins 11 and 13 are partially shaped in section in accordance with the size of the pressure pads.

In operation, a fluid coolant, such as air, flows freely through the ducts 15 and 16 and over the fin surfaces, thereby removing heat from the heat sinks, and enabling the electronic component to be kept cool. Heat is also, of course, efficiencly radiated from the very large surface area of the fins of the heat sink.

Claims (8)

1. Amounting arrangementfora high power electronic component including two finned heat sinks arranged in operation to sandwich an electronic component between them, a pressure pad associated with each heat sink and arranged to bear against the edges of a plurality of fins forming part of the heat sink so as to form one or more open ended ducts thereby so that, in operation, a fluid coolant can pass between each pressure plate and the component to be cooled, the two heat sinks being held in contact with the electronic component by fastening means linking both pressure pads together.

2. An arrangement as claimed in claim 1 and wherein at least two of the fins upon which the pressure pads bear have portions which are of a thicker section than some of the remaining fins.

3. An arrangement as claimed in claim 1 or 2 and wherein each heat sink has a flat surface portion which contacts the electronic component, the fins being arranged perpendicular to this surface so that they extend away from the surface on the opposite side to that of the electronic component.

4. An arrangement as claimed in claim 1, 2 or 3 and wherein means are provided for indicating when the two heat sinks exert a predetermined pressure on the electronic component which is mounted between them.

5. An arrangement as claimed in any of the preceding claims and wherein the fastening means includes resiliently deformable means the deformation of which determines the pressure applied to the component.

6. An arrangement as claimed in claim 5 and wherein the fastening means includes elongate members which pass through the heat sinks at points arranged on a circle surrounding the electronic component.

7. An arrangement as claimed in claim 5 or 6 and wherein the pressure pad is located between each heat sink and a respective pressure plate with a resilient member provided between each pressure pad and its pressure plate.

8. A mounting arrangement for a high power electronic component substantialy as illustrated in and described with reference to the accompanying drawings.