GB2189343A

GB2189343A - Semi-conductor modules

Info

Publication number: GB2189343A
Application number: GB08608094A
Authority: GB
Inventors: Peter Richard Ewer; Jeffrey Robert Ellard
Original assignee: INT RECTIFIER CO Ltd; International Rectifier Corp USA
Current assignee: INT RECTIFIER CO Ltd; Infineon Technologies Americas Corp
Priority date: 1986-04-02
Filing date: 1986-04-02
Publication date: 1987-10-21
Anticipated expiration: 2006-04-02
Also published as: GB2227122A; GB9002694D0; GB8608094D0; GB2227122B; GB2189343B

Abstract

A semi-conductor element module having a housing (1,2,3) contains at least one semi-conductor element (21) having electrodes electrically connected to respective terminals (20,24) by compression assembly, the semi-conductor element and terminals being members of a plurality (15,16) contained in the housing, there being further at least one strain buffer (22), at least one electrical isolation member (25), and at least one electrically insulating compression member (19). Compression forces are applied to the stack by at least one spring means (17,18) and the module has at least two external terminals (5,6), the distance between which is adjustable, thus allowing use of elements of different heights and terminal spacings. The module is such that, in use with rated current, the junction temperature is no greater than 130 DEG C and the housing temperature is no less than 80 DEG C. The distance between the terminals is adjustable to be between 23mm or 25mm. <IMAGE>

Description

SPECIFICATION Semi-conductor modules The present invention relates to semi-conductor component modules, and is particularly but not ex clusively applicable to rectifier orthyristor modules.

It is known to provide packages or modules containing a pair of semi-conductor rectifying orthyristorelements connected in series on a basefrom which these are electrically isolated. External contacts are provided on the package to enable electrical connection to all three terminals of the series connection of two elements.

Two such packages may be externally connected together to form a full wave rectifying bridge, and similarly three such packages may be interconnected to form a three phase rectifying arrangement.

Such modules or packages are commercially available in various standard sizes and also the spacing between the external terminals has become standardized. However, unfortunately, different manufacturers adopt differing sizes and standards. Thus, manufacturers of such packages or modules are pre sentlyforced either to offer two completely separate ranges of module or must concentrate on only a single range. Both options are commercially disadvantageous.

To be more specific, one known standard thyristor module of 130A nominal rating has an overall height of 30mum and a terminal spacing of 23mm. Asecond known equivalent standard module has an overall height of 41 mm and a terminal spacing of 25mm.

When a plurality of modules of the first standard are connected together by heavy duty copper rods or the like, it is difficult if not impossible to replace a single module by another of the other standard even although its electrical properties may be perfectly adequate. Problems arise owing to the difference in height and the difference in terminal spacing.

According to one aspect of the invention, there is provided a semi-conductor element module having at least two external terminals, the distance between said terminals being adjustable.

Another problem is concerned with the internal assembly method adopted for the modules. The semiconductor elements with the module may be el ectricallyconnectedtoterminalsandothercom- ponents either by means of soldering of by means of compression bonding. Itwill be appreciated that whichever method is adopted it is necessary in high power applications for these interconnections to pass a relatively large current without appreciable voltage drop, whilst maintaining the house and junction temperatures within certain limits.

Both methods of connection havetheiradvantages and disadvantages. Whilst a soldered assembly requires fewer components, produces better thermal characteristics and simplifies the housing, as well as rendering the production of a lower assembly more easy, it has disadvantages in thattheterminalswill be more complex,furnaceop- erations are required, thermal expansion and mismatch can be expected and there are various problems with loss of yield. The selection of solder assembly is not accepted as readily by customers as is the compression bonded product.

Itwill be appreciated from theabovethat manu- facturers generally prefer to adoptthe compression bonded technique when this is feasible having regard to dimensional constraints of the finished package.

However it has previously proved impossible to provide a satisfactory compression assembled product of relatively low overall height.

According to a further aspect of the invention, there is provided a semi-conductor element module having a housing containing at least one semiconductor junction having electrodes electrically connected to respective terminals by compression assembly, the semiconductor junction and terminals forming elements of a stack contained in the housing and further comprising at least one strain buffer, at least one electrical isolation member, and at least one electrical isolation member, and at least one electrically insulation member, and at least one electrically insulating compression member, compression forces being applied to the stack by at least one spring means, the height of said stack being less than 1 5mm and the module being such that, in use with rated current, the junction temperature is no greater than 1 30 C and the housing temperature is no lessthan80'C.

Preferably, the spring means comprises a leaf or plate spring member.

Preferably, the or each isolation member consists of alumina oxide or aluminium nitride.

Preferably, the compression member consists of ceramic, e.g. aluminium oxide, or mica.

The leaf or plate spring mentioned above is preferably of lozenge shape to even out the stresses applied to the spring element.

Preferably, the strain buffer is of molybdenu m, tungsten or copper.

For a better understanding of the invention, and to show how the same may be carried into effect, reference will now be made byway of example to the accompanying drawings, in which: Figure 1 is a perspective view of a semi-conductor element module assembly in accordance with one embodiment of the invention; Figure 2 is a plan view of an upper housing portion ofthe assembly of Figure 1; Figure 3 is a longitudinal sectional view along the line Ill-Ill ofthe assembly illustrated in Figure 1; Figure4isa plan view of a lowerhousing portion of the assembly of Figure 1; Figure 5is a plan view ofa plate spring; and Figure 6is a longitudinal sectional view along section line X-X of Figure 6a of a modified embodiment.

Referring nowto Figure 1 in more detail, the illustrated module assembly comprises a base plate 1 consisting of nickel plated copper and providing two mounting holes for customer use in addition to four tapped holes for spring retaining screws, these various holes not appearing in Figure 1. Preferably, the basemembershould haveathicknessof8mmfor compatibility with commerically existing modules, but this can be reduced to 7 or 6mm if necessary to provide additional space within the assembly. Of course, when reducing its thickness in this manner it must be ensured that an unacceptable degree of bowing under stress and creep does not occur.

It may also be possible to replace the copper base buy a base of anodized aluminium in orderto improve electrical isolation properties of the module.

Mounted on the base 1, is provided a moulded case of synthetics plastics material comprising a lower part 2 and an upper part or lid 3.

In Figure 1,itmaybeclearlyseenthatthreeex- ternal contacts 4,5 and 6 extend across the upper surfaceofthe lid 3. Each contact provides an aperture for receiving a terminal screw, these apertures being elongated in the case of terminals 4 and 6 for a purpose which will be explained hereinafter.

Referring now to Figure 2, the upper surface of the lid 3 beneath the terminal members 4,5 and 6 may be seen in more detail. It may be seen that the upper surface of the lid 3 provides three rectangular recesses 7,8 and 9 along the longitudinal centre line.

Each recess contains a respective square nut for receiving a terminal screw. The two outermost nuts 10 and 11 are clearly slidable longitudinally ofthe lid by virtue of the fact that the recessesforthese nuts are elongated. The purpose of this measure will be explained hereinafter.

Figure2 illustrates three slots 12,13 and 14forreceiving the respective terminal members 4,5 and 6, which are L-shaped.

Reference will now be made to Figure 3. Inthislon- gitudinal sectional view, the individual components oftwo semi-conductors rectifier stacks 15 and 16 may be clearly seen.

Each stack is compressed in a vertical direction by means of a respective leaf spring 17 or 18. Consider ing the left hand stack 15, acompression disk 19 of aluminium oxide or mica is placed beneath the spring 17. The maximum thickness ofthis disk is 4mm, this dimension offering the best compromise between height and strength. The upper surface of the disk is domed to enablethe spring loading to be applied centrally and floatingly. This also permits the use of a flat spring which bends down under load andtherebyprovidesgreaterheightclearance eath the disk 19, is provided an upper electrical terminai 20 of 1 mm copper sheet. Beneath terminal 20, is provided a semi-conductor thyristor junction 21.

This junction is preferably of the type having a ring gate, but centre gate junctions may also be used with appropriate modification to the assembly. Beneath the semi-conductor junction 21 is provided a molybdenum disk 22 centralized by means of a washer 23 of polytetrafluoethylene. Beneath the molybdenum disk is disposed a lower electrical connection terminal 24 of 1 mm copper sheet. This lowerterminal 24 extends across to the second rectifier stack 16. Beneath the terminal 24 is located an isolation pad 25 electrically insulating the stackfrom the heat conducting base 1. This insulation pad mustensurethat electrical isolation remains effective to 2,500 volts rms. This requires a minimum thickness of 1.5mm.

This thickness is also suitable to provide adequate mechanical strength. The isolation pad is preferably of alumina oxide or aluminium nitride. The use of beryllium oxide is also possible however.

The right hand stack 16 illustrated in Figure 3 is basicallythe same as the left hand stack 15 butthe positions ofthe semi-conductor junction and the molybdenum disk are reversed.

Although not specifically illustrated in Figure 3, it will be appreciated that internal wiring interconnects external terminal member4with internal terminal 20 and that external terminal member 6 is similarly connected to the corresponding terminal in the right hand stack 16. The central external terminal member 5 is connected to the lower internal terminal 24.

It will also be appreciated that the two leaf or plate springs 17 and 18 are secured to the lower heat conducting base member 1 by a pair of screws passing through respective apertures adjacent the ends of each spring as illustrated in Figure 5.

The use of lozenge shaped springs is particularly advantageous as againstthe use of disk springs since they are less liable to relaxation.

For improved electrical isolation, the remaining space within the housing is filled with silicone rubber.

The base plate 1 must ensure notonlygood lateral heat spreading, but also must remain flat to within about20 microns during manufacturingthustoen- sure consistently low contact thermal resistance fromthesemi-conductorjunctionstothe heat sink.

Thetwohousing parts2and3areconnected together by an adhesive and similarly the lower housing part 2 is secured to the base plate 1 by means of an adhesive.

As regards the dimensions of the various components, it has already been mentioned thatthe maximum thickness ofthe ceramic compression disksl9is4mm andthatthe internal terminals are of 1 mm copper sheet. The semi-conductoriunctions are preferably of 23 to 24mm diameter. The molybdenum disks 22 are each of 1 .5mm thickness and a similar thickness is employed for the isolation pads 25. By use of plate springs 17 and 18 having a thickness of 2.5mm, it is thus possible to easily achieve an overall height of 30mm even using the compression assembly technique, the stack height being 1 Omm.

The lid 3 has an overall height of 11 mm and the total vertical height from the top of the lower housing component 2to the bottom of the base 1 is 18mm.

It has already been mentioned that the nuts 10 and 11 are slidable longitudinally and this enables the spacing of external terminal screws to the adjusted to suitvarious commercial standards. In Figure 2, both nuts 10 and 11 are illustrated in a right hand position. This is for illustration purposes only. In reality, of course, the terminal nuts 10 and 11 would normally be placed symmetrically relative to the central recess 8.

Referring now to Figure 4, which illustrates a plan viewofthe lower housing component2,the position of the fixing holes forthe plate springs 17 and 18 may be clearly observed. The left hand plate spring has fixing holes 31 and 32, and the right hand plate spring hasfixing holes 33 and 34.

Figure 5 illustrates the shape of each leaf or plate spring 17 and 18. Arrows 41 illustrate the direction of the grain flow in the material ofthe spring, which is preferably stainless steel.

It will be appreciated that the properties of the spring are extremely force between the components of the two stacks 15 and 16. Not only must the force be adequate upon manufacture, but it must be maintained over the operational lifetime of the modules.

Such springs can readily be produced by persons skilled in the art.

Itwill beappreciatedthatthemodulesdescribed and illustrated in this specification are suitable for various applications. Two such modules may be positioned side-by-side and interconnected copper connecting rods to form a bridge circuit for high power full wave rectification purposes.

Similarly,three such modules may be interconnected to provide a three phase rectifier.

It is of course already well known to form bridge circuit and rectifier circuit using modularassemblies. Unfortunately, however, the industry has not achieved a commonly accepted standard. The result is that modules of various heights and various upper terminal spacing exist. It is not possible to replace a module of one standard by a module of a differing standards having differing heights and also owing to the fact that the various standard have different spac ing between the upperterminals.

The module described in this specification is how ever able to meet all the industrial standards for the following reasons.

Firstofall, its overall height is no greaterthanthe lowest comparable module available on the market.

This is achieved in spite of the use of compression assemblytechniques rather than soldering techniques which are generallydisliked. The problem of varying terminal spacing is overcome by means of the slidable nut construction illustrated particularly in Figure 2.

When a module of greater height is to be replaced by a module according to the present invention, it is simplynecessaryto provide an auxiliary shim orspa certo bring the moduletothe desired height.

The control gates of the thyristor elements 21 are of course also connected to the external terminals such as terminals 55 of Figure3 and 4. Furtherex ternal terminals 56 are availableforconnectionto auxiliary gates, when provided.

Of course, thyristor elements 21 may be replaced by diodes, in which caseterminals 55 and 56 are unnecessary.

It will be appreciated that where the semiconductor junctions are diodes, the normal current rating is 160A nominal, whereas with thyristors the current rating is 130A nominal. The modules should be so designed that with the noted currentthejunction temperature is less than 130"C, preferably less than 1 250C, and the casing temperature is greaterthan 80 C, preferably greaterthan 85 C. Even with these restraints, and using compression assembly, it has been found possible, according to the invention,to achieve an overall stack height less than 1 5mm, in fact 1 Omm, the height of the stack being measured from the base of the leaf spring 17 or 18 to thetop surface of the base plate 1. As a result, the overall module height can be maintained less than 35mm, in fact about 30mm.

Figure 6 shows a longitudinal sectional view, (along section line X-X of Figure 6a), of a modified embodiment of semi-conductor module. In this Figure, parts and components corfesponding to those illustrated in Figures 1 to 5 are provided with the same reference numerals. Thelfollowing description will therefore be restricted to the points of difference.

Basically, each rectifier stack 15 and 16 in Figure 6 corresponds to the right hand rectifier stack illustra- ted in Figure 3. Thus, in each rectifier stack of Figure 6 the semi-conductor junction 21 is located beneath the moiybdenum disk 22 and is directly in contact with the lower copper terminal. Since both rectifier stacks are identical, however, the interconnection between the two stacks is different. Whereas in Figure 3 the two lower copperterminals are linked together to form a common lowerterminal member 24, in Figure6thelowerterminalsarenotinter- connected. Instead, the lowerterminal ofthe right hand stack 16 is electrically connected with the upper terminal of the left hand stack 1 to form a common connection terminal member 24'. The lowerterminal of the left hand stack 15 has the reference numeral 20' in Figure 6.

Figure 6 is also illustrative of the manner in which the terminal screws 10' and 11' are engaged with the slidable nuts of the outer terminals, nut 11 being shown in Section. The Figure furthermore illustrates one ofthe securing screws 31' which engages in the fixing hole31.

Also in the embodiment of Figure 6, the same dimensional restrains as discussed above in respect of Figure 3 may be achieved.

Claims

1. A semi-conductor element module having at least two external terminals, the distance between said terminals being adjustable.

2. A module according to Claim 1 wherein said distance is adjustable to be 23m m or 25m m.

3. A module according to Claim 2 or 2 wherein said distance is continuously adjustable over a range of values.

4. A module according to Claim 1,2or3wherein a third external terminal is provided, its position being adjustable.

5. A module according to any one of the preced- ing claims wherein each terminal comprises a terminal member electrically connected to an internal component, a terminal screw, and a terminal nut, the terminal screw passing through the terminal member for engagement with the nut.

6. A module according to Claim 5 wherein the nut of at least one terminal is displacabiy mounted.

7. A module according to Claim 6 wherein said nut is mounted in a recess having at least one dimension largerthan the corresponding dimension ofthe nut to permit nut displacement.

8. A semi-conductor element module having a housing containing at least one semi-conductorjunction having electrodes electrically connected to re spectiveterminals by compression assembly, the semi-conductorjunction and terminals forming el ements of a stack contained in the housing and further comprising at least one strain buffer, at least one electrical isolation member, and at least one electrically insulating compression member, compression forces being applied to the stack by at least one spring means, the height of said stack being less than 15mm and the module being such that, in use with rated current, the junction temperature is no greaterthan 1 30"C and the housing temperature is no less than 800C

9.A module according to Claim 8 wherein said spring means comprises a plate spring member.

10. A module according to Claim 8 or 9 wherein said strain buffer is of molybdenum, tungsten or copper.

11. A module according to anyone of Claims 8 to 10 wherein the or each isolation member consists of alumina oxide or aluminium nitride.

12. A module according to any one of Claims 8 to 11 wherein said compression member consists of ceramic, e.g. aluminium oxide, or mica.

13. Amodule according to anny one of Claims8 to 11 wherein said plate spring is of lozenge shape.

14. Amodule according to anyone of Claims 8to 13 wherein said stack height is less than 12mum.

15. Amoduleaccording to Claim l4whereinsaid stack height is about 1 Omm.

16. A module according to any one ofClaims8to 15 wherein the height of said housing is less than 35mm.

17. A module according to Claim 16 wherein the height of said housing is less than 32mm.

18. Amodule according to Claim 17 wherein the height of said housing is about 30mm.

19. A module according to any one of Claims 8to 18wherein at said rated currentsaid junction tem perature is less than or equal to 1 25'C.

20. Amodule according to anyone of Claims 8 to 19 wherein said housing temperature is greaterthan or equal to 85 C.

21. Amodule according to anyone of Claims stro 20 wherein said junction is a diode and said rated current is 160A nominal.

22. A module according to any one of Ciaims 8 to 21 wherein said junction is a thyristor and said rated current is 130A nominal.

23. A module according to any one of Claims 8 to 22 wherein said junction has a diameter of 23 to 24mm.

24. A plate spring of elongate lozenge shape consisiting of steel having a direction of grain flow substantially parallel to the longitudinal axis thereof.

25. Asemi-conductor element module substantially as herein before described with reference to the accompanying drawings.

26. A plate spring substantially as herein before described with reference to Figure 5 of the accompanying drawings.