GB2094547A

GB2094547A - Stack mounted electrical components

Info

Publication number: GB2094547A
Application number: GB8107326A
Authority: GB
Original assignee: AEI Semiconductors Ltd
Current assignee: AEI Semiconductors Ltd
Priority date: 1981-03-09
Filing date: 1981-03-09
Publication date: 1982-09-15
Also published as: GB2094547B

Abstract

A stack of electrical components, such as semiconductor thyristors (1, 2) and diodes (3, 4), is divided into a number of sections, so that the clamping pressure applied within a particular section can be set independently of the clamping pressure in another section. This enables the clamping pressure to be set to its optimum level having regard to the electrical characteristics and mechanical strength of the relevant components while retaining the assembly in the form of a rigid and unitary stack. <IMAGE>

Description

SPECIFICATION A mounting arrangement for electrical components This invention relates to a mounting arrangement for electrical components and is particularly applicable to components which are required to pass very large electric currents. With such components it is important to ensure that a very good electrical contact is made, since a significant amount of heat can be generated at poor interfaces which exhibit a significant contact resistance and often heat generated within the components has to be extracted via these interfaces which must therefore provide an excellent thermal path. For these reasons high contact pressure is needed. Often a number of electrical components form a sub-assembly and it has proved convenient to mount a number of components together in a stack which can then be handled as a unified structure.This form of mounting arrangement is particularly suitable for high power semiconductor components such as transistors, diodes, thyristors and the like where it is often necessary to use a number of fairly similar components together, but the components themselves are relatively fragile and can easily be damaged by the application of excessive contact pressure and by the generation of excessive heat.

With presently known mounting arrangements, a number of components are stacked together one above the other in a linear array, with electrodes and cooling arrangements positioned between them as necessary and the whole is clamped together by means of appropriate tie rods or the like extending over the entire length of the stack -a a structure of this kind is sometimes termed "a stick stack." Such an arrangement suffers certain difficulties as the same clamping pressure is applied to all components. This means that the more fragile components can be damaged by the greater pressure needed for the highest power component or alternatively stronger (and more expensive) components must be used which are more robust then is dictated by their required power handling capabilities.

The present invention seeks to provide a mounting arrangement in which this difficulty is reduced.

According to this invention, a mounting arrangement for electrical components includes a plurality of components clamped together to form a rigid linear stack, wherein the stack is arranged in sections so that the clamping pressure within a given section can be set independently of the clamping pressure in another section.

Preferably the components are semiconductor devices. In this case it would be usual to provide electrode plates between each pair of adjacent components so as to permit electrical connection to be made, but this is not essential and in some circumstances, particularly where a number of components such as diodes are used in series so as together to provide a high voltage capability, the intervening electrode is omitted. Even though the components are clamped under high pressure to minimise interface or contact resistance, nevertheless heat can be generated at the interface and the components themselves generally generate a great deal of heat.

Accordingly, cooling members can advantageously be positioned between adjacent components so as to form an integral part of the stack.

Each section may contain a plurality of components, or only a single component, as required.

The invention is further described by way of example with reference to the accompanying drawing, in which Figure 1 illustrates a mounting arrangement which is suitable for mounting semiconductor components, and Figure 2 indicates a typical circuit configuration.

Referring to Figure 1, a stack assembly consists of four electric components, 1, 2, 3 and 4, which are all semiconductor devices. Components 1 and 2 are high power thyristors, whereas components 3 and 4 are diodes which although they are capable of passing very large currents they are of a smaller diameter and thickness and are less robust than the thyristors. Copper electrodes 5, 6, 7, 8, 9 and 10 are positioned so as to enable electrical connection to be made to both faces of the components 1 to 4, and in practice, these electrodes incorporate means for extracting heat from the stack. Typically, each electrode includes a hollow passageway through which oil can be passed, but alternatively each electrode may be ,provided with cooling fins over which air can be blown to extract the heat.

The stack is arranged in two sections 11 and 12 so that the clamping pressure applied to the thyristors 1 and 2 can be adjusted independently of the clamping pressure applied to the diodes 3 and 4. A metal reaction plate 13 (usually steel or other strong and rigid material) is positioned between the two sections 1 1 and 12 and is secured to respective pressure pads 14 and 15 by means of tie rods 16 and 17 which are held under tension. The tie rods pass through holes in the reaction plate 13 and are secured on each side by means of threaded nuts 18 and 1 9. Similarly, the other ends of the tie rods 1 6 and 1 7 are secured to respective pressure pads 14 and 15 by means of threaded nuts 20 and 21 which engage with the ends of the tie rods.The pressure pads 14 and 15 are electrically isolated from the components 1 to 4 by means of insulating plates 22 and 23, which are provided with small aperatures to allow the tie rods 1 1 and 12 to pass freely through them. In the drawing, two tie rods 16 are present and two tie rods 17 are present, although only one of each is visible. A greater or lesser number of tie rods can be provided as appropriate in view of the clamping pressure which is to be applied to the components. Insulating pads 32 and 33 are positioned on either side of the plate 13 so that it need not be at the same potential as the electrodes 7 and 8, but they can be omitted if not required.To reduce risk of electrical breakdown and arcing, each tie rod lies within a hollow closely fitting tubes 34, 35, 36, 37 of insulating material, which are sufficiently short to accommodate movement of the nuts 20,21 during adjustement of the clamping pressure.

Each pressure pad 14 and 15 contains a resiliently deformable member 24 and 25 which could conveniently take the form of one or more annular dished washers. This form of resilient member conforms as necessary to any misalignments of the plates of the insulators 22 and 23 with that of the pressure pads 14, 1 5 these may not necesarily be exactly perpendicular to the line of the tie rods - and allows the pressure to be accurately set since significant change of the effective length of the tie rods during adjustment produces moderate and controlled change in the clamping pressure. The pressure pads 14 and 15 and the members 24 arid 25 are set to the required clamp pressure prior to assembly by means of the bolts 38, 39 which comprises the dished washers.When the mounting arrangement is assembled by tightening the nuts 20, 21, previously trapped washers 40 and 41 become free when precisely the required pressure is applied to the components 1, 2, 3, 4.

Pressure indicators of this kind are more fully described in our U.K. patent 1,470,958. External electrical connections 26 and 27 are provided as necessary, depending on the nature of the electric circuit represented by the configuration of components. The structure shown corresponds to the circuit illustrated in Figure 2, but clearly many other variations are possible.

It will be appreciated that the stack forms a single unified structure which can be incorporated in larger equipment as necessary. It can be used as a module of standard size, and it would therefore often not be acceptable to provide individual and physically separate sections and in any event the long electrical paths needed to link separate sections may be quite unacceptable. An assembly as illustrated may be required to pass in excess of 1400 amps and to withstand voltages in excess of 4000 volts. The clamping force for each section can be set to the required level in accordance with the current carrying capacities and strengths of the different components. Even though the stack enables the clamping pressure applied to the two sections 16 and 17 to be independently adjusted, it can nevertheless be handled as a single unified structure for subsequent assembly in a larger equipment.

However, this form of construction possesses the incidental advantage that either section can be disassembled to replace a failed component without the need to disturb the other section.

Although only two sections are illustrated, in principle as many sections as necessary can be provided, although a slightly modified form of attachment of the tie rods must be provided if it is desired to be able to dismantle an inner section without disturbing the clamping pressure applied to outer sections.

Claims

1. A mounting arrangement for electrical components including a plurality of components clamped together to form a rigid linear stack, wherein the stack is arranged in sections so that the clamping pressure within a given section can be set independently of the clamping pressure in another section.

2. An arrangement as claimed in claim 1 and wherein the components are semiconductor devices.

3. An arrangement as claimed in claim 1 or 2 and wherein each section contains resiliently deformable means arranged to exert the clamping pressure on the component(s) within that section.

4. An arrangement as clamed in claim 3 and wherein the resiliently deformable means comprises one or more dished washers.

5. An arrangement as claimed in any of the preceding claims and wherein a common reaction plate is positioned between adjacent sections.

6. An arranqement as claimed in any of claims 3 to 5 arrd wnerein a plurailty of tie rods of independently adjustable effective length extend over each section and are coupled to said resiliently deformable'means, so as to enable the clamping pressure to be set.

7. An arrangement as claimed in claim 6 and wherein the tie rods are formed of electrically conductive material and are individually surrounded by electrically insulating sleeves.

8. A mounting arrangement for electrical components substantially as illustrated in and described with reference to Figure 1 of the accompanying drawing.

Amendments to claims filed on 27th January 1982.

Amended claims

1. A mounting arrangement for electrical components including a plurality of components clamped together to form a rigid linear stack, wherein the stack is arranged in sections so that the clamping pressure within at least one section is set at a value which differs from, and is set independently of, the clamping pressure in another section.