Snap Fit Support Housing for a Semiconductor Power Wafer

The present invention relates to a support housing of a semiconductor power wafer, preferably for immersion in a fluorinated hydrocarbon for cooling purposes.

It is known that power diodes or thristors cooled in a chamber which contains a fluorinated hydrocarbon in the liquid state are constituted by a semiconductor wafer sandwiched between two deformable metal membranes which hold and centre the wafer in the ceramic housing which is itself pressed between two metal blocks generally made of copper and which form current inlets for the anode and the cathode.

Omitting the ceramic housing and the deformable membranes, which hinder the dissipation of heat improves the cooling of the wafer, but the blocks and the semiconductor wafer are no longer held mechanically. Therefore, the wafer is no longer mechanically centred with respect to the metal blocks and further, in the case of dismatling, the fragile semiconductor wafer has to be handled.

Supplying the triggers of conventional thyristors is also a problem. Conventional thyristors are disposed at the centre of the wafer and have been controlled, up till now, by leaf springs held inside an axial recess of the cathode block.

The leaf springs had two functions: conveying the trigger control current and pressing the trigger component of the wafer. The disadvantages of such a system are that the end of the spring scrapes the semiconductor material and may damage it subsequent to mechanical vibration, and that the pressure exerted by a leaf spring is not precise.

Preferred embodiments of the present invention mitigate these various drawbacks and generally have the following advantages: firstly, mechanical resistance is provided for the wafer between the copper blocks of the anode and of the cathode, with adequate centring of the wafer, easy handling ans storage and rapid installation in an immersed assembly; and secondly, in the case of thyristors, it improves the precision of the mechanical pressure exerted on the trigger and avoids rapid wear of the latter.

The present invention provides a support housing for a semiconductor power wafer for immersion in a fluorinated hydrocarbon, said support including said semiconductor wafer between two cylindrical metal blocks which act as a cathode and an anode, said semiconductor wafer having a diameter greater than the diameter of the cylinders of said blocks and including on the cathode side, a metal washer with a diameter substantially equal to that of said cylinders, wherein two insulating plates which have substantially polygonal outlines enclose respectively the cathode block and the anode block, each block being provided with a transversal groove and with a circlips, disposed inside said plates and in contact therewith, said plates being made integral with each other by three insulating pins which are tangential to said wafer and can be snap-fitted into three notches disposed at 120.degree. to one another on said polygonal outline.

According to one preferred embodiment, a support housing for a semiconductor power wafer for immersion in a fluorinated hydrocarbon, said support housing including between two cylindrical metal blocks which act as a cathode and an anode, said semiconductor wafer having a diameter greater than the diameters of the cylinders of said blocks, said wafer including, at its centre, a trigger component which controls the triggering of said wafer and also including, on the cathode side, a metal washer with a circular hole whose inner diameter is equal to that of said trigger component and whose outer diameter is substantially equal to that of said cylinders, said cathode block including, along its longitudinal axis, a longitudinal cylindrical bore which contains a sleeve made of insulating material, said cylindrical bore communicating with a transversal bore which is perpendicular to said longitudinal cylindrical bore, is characterized in that there are disposed inside said longitudinal bore a spherical contact piece, a spiral spring which presses said contact piece against said trigger component and a flexible conductor wire insulated from said cathode block and soldered to said contact piece.

An example of the present invention given by way of example is described with reference to the accompanying diagrammatic FIGS. 1 and 2 in which the same components illustrated in both figures bear the same reference symbols therein.

FIG. 1 is a partially cutaway longitudinal schematic view of a support housing and

FIG 2 is a partially cutaway transversal schematic view of the same housing .

As illustrated in FIG. 1, a support housing includes two cylindrical metal blocks 1 and 2 which are good conductors of heat and electricity and are made of copper, for example, and which constitute respectively, an anode terminal and a cathode terminal. A semiconductor wafer 3 whose diameter is larger than that of the blocks 1 and 2 includes a trigger component 4 of a thyristor at its centre. (Other devices, e.g. diodes, can also be mounted in such a support housing). A metal washer 5 whose diameter is substantially equal to that of the blocks 1 and 2 has a hole in its centre to allow access to the trigger component 4 and is designed to make thermal dilation compatible between the wafer 3 and the cathode copper block 2.

The cathode block 1 and the anode block 2 are placed on either side of the wafer 3 and the washer 5 by means of a support constituted by two insulating plates 6 and 7 and three pins 8,9, 10 which end in lugs made of the same insulating material. The insulating plates 6 and 7 can advantageously have a hexagonal form and are provided with notches such as 11 disposed at 120.degree. to one another. The pins 8,9, 10 are snap-fitted into the notches and are tangential to the outer circumference of the wafer 3. The insulating plates 6 and 7 are held in position on the blocks 1 and 2 by circlips 12 engaged in grooves such as 13 milled in the blocks 1 and 2. The wafer 3 is therefore centred in relation to the blocks 1 and 2. The cathode block 2 has a central recess 14 which occupies its longitudinal axis. An insulating sleeve 15 made of teflon or a like material passes therethrough. The length of the sleeve is greater than that of the cathode blocks 2 by an amount equal to the thickness of the washer 5 so as to centre it. The support housing includes mechanical means for making the blocks 1 and 2 integral with one another and can be used equally well for diodes as for power thyristors, either type of device being cooled, in operation, by being immersed in a fluorinated hydrocarbon in the liquid phase.

In the case of thyristors, the invention also relates to the auxiliary triggering system of the trigger. A transversal recess 16 perpendicular to the central recess 14 of the cathode block allows a flexible insulated wire to be installed in the cathode block 2, said wire being used to control the trigger. The wire 17 is soldered to a contact piece 18 whose end in contact with the trigger 4 is spherical. A spiral spring 19 bears against the contact piece 18 so as to provide even pressure on the trigger 4.

Such devices are applicable to railways.