Abstract:
In a semiconductor array having a plastic casing and a cooling portion which is at least partly not embedded in the plastic, an insulating portion is provided which is designed to slide onto the cooling portion and to provide at least partial electrical insulation of the cooling portion when slid on.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a semiconductor array having a plastic casing and a cooling portion which is at least partly not embedded in the plastic. 
     Electrical equipment is today preferably fitted with semiconductor components such as transistors or integrated circuits with the aid of automatic machinery. Semiconductor components with platic casings and suitable for clip assembly are particularly well suited for automatic fitting. 
     Power components such as power transistors which are embedded in plastic casings have, as is known, cooling plates on their undersides to cool the semiconductor component. When installing a power transistor with plastic casing and cooling plate, two cases must be distinguished: in one case the cooling plate is mounted insulated on a base, for example a chassis or cooling sheet, while in the other case the cooling plate is mounted uninsulated on a base. In the second case, the cooling plate has the same potential as the base. If a semiconductor component has to be mounted insulated on a base so that it does not assume the potential of the base, materials with good thermal conductivity and electrical insulation properties are required, and must be mounted in strips between the cooling plate and the base (cooling sheet). It is obvious that this type of mounting is not conductive to easy fitting. 
     For that reason, the method was introduced of using, in the case where a power transistor has to be mounted insulated on the base, power transistors completely embedded in plastic casings together with their cooling plates, and, in the other case where no insulation is necessary between cooling plate and cooling sheet or base on which the transistor is mounted, transistors in which the cooling plates are not surrounded by plastic at least on their undersides. 
     According to the prior art, therefore, two different plastic casings and so two different production lines are necessary, depending on the application, requiring high investment costs. 
     SUMMARY OF THE INVENTION 
     The object underlying the invention is to provide a solution that involves a substantial simplification and lower costs as compared to the prior art. According to the invention, an insulating portion is provided in a semiconductor array having plastic casing and cooling portion, said insulating portion being designed to slide into the cooling portion and, when slid on, to provide at least a partial electrical insulation of the cooling portion. 
     The word &#34;partial&#34; does not refer to the electrical insulation, which should, of course, be complete and as effective as possible, but to the surface proportion of the insulating portion. The word &#34;partial&#34; is to express that it is not the entire surface of the cooling portion that is to be insulated with the insulating portion, but, for example, only those surfaces facing the base (cooling sheet) on which the components have been mounted. 
     The invention has the advantage that the casing structure can be identical for both cases, regardless of whether the cooling portion (cooling plate) is to be mounted insulated or uninsulated on its base (cooling sheet), since, when insulation is required, only the insulating portion according to the invention has to be slid onto the cooling portion. The insulating portion according to the invention is located, unlike the previously used insulating strips, firmly on the cooling portion, which is preferably designed as a cooling plate, and its firm mounting (press fit) is in no way detrimental to automatic fitting, so that the fitting process when an insulating portion according to the invention is used is practically identical to that with a plastic casing in which not only the transistor but also the cooling plate is embedded. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be described in greater detail, by way of examples, with reference to the drawings, in which 
     FIG. 1 shows a power transistor with cooling plate and insulating portion. 
     FIG. 2 shows the power transformer with slid-on insulating portion. 
     FIG. 3 shows an integrated circuit, 
     FIG. 4 shows a power transistor with a thick insulating portion. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows a power transistor 1 with semiconductor element 2, power lines 3, connecting wires 4, plastic casing 5 comprising an electrically insulating plastic, and cooling plate 6. Cooling plate 6 is only partially embedded in the plastic 5. The plastic 5 covers only part of the upper surface of cooling plate 6 (about two thirds) and part of the lateral surfaces of cooling plate 6. The right-hand part (about one third) of cooling plate 6 is not covered by plastic at all, and this applies too to the entire underside (lower surface) of cooling plate 6. The part of cooling plate 6 not covered by plastic 5 has a hole 7 for fastening cooling plate 6 and thus power transistor 1 to a base (e.g. cooling sheet). 
     In order that the power transistor in FIG. 1 can be mounted on a base not only uninsulated but also insulated in a simple manner, a slipper-shaped or &#34;flip-flop&#34;-shaped insulating portion 8 is provided according to FIG. 1, said insulating portion being slid, as shown in FIG. 2, in a press fit onto cooling plate 6 in such a way that the entire portion of cooling plate 6 not covered by plastic is covered by the insulating portion 8 and is thereby electrically insulated. If the transistor of FIG. 2 is mounted with insulating portion 8 onto a base, such as, for example, a chassis or cooling sheet, cooling plate 6 and thus transistor 1 are electrically insulated from the base and are therefore not on the potential of the base. Insulating portion 8 is preferably designed as thin as possible to keep its thermal resistance as low as possible and for the heat from cooling plate 6 to be carried off as well as possible via insulating portion 8. It must, of course, be ensured that the insulating portion provides sufficient electrical insulation. The expression &#34;slipper-shaped&#34; or &#34;flip-flop-shaped&#34; or &#34;shoe-shaped&#34; according to FIG. 1 means that insulating portion 8 is designed in casing form to a certain extent but with one lateral surface 9 and part of surface 10 missing. Stated another way, insulating portion 8 has three lateral surfaces and two surfaces of which one (10) only partially covers the other (11). The two surfaces 10, 11 of the insulating portion are designed rectangular, and this applies to the existing lateral surfaces of insulating portion 8, too. 
     FIG. 3 differs from FIGS. 1 and 2 substantially only in that an integrated circuit 1&#39; is provided instead of power transistor 1. In other respect that are largely identical, i.e in FIG. 3 insulating portion 8 according to the invention is also provided and slid onto cooling plate 6. In contrast to the insulating portion of FIGS. 1 and 2, the two parallel lateral surfaces 12 and 13 of insulating portion 8 have a slope 14, which can, of course, also be used in the insulating portions in FIGS. 1 and 2. 
     FIG. 4 finally shows a further embodiment of the invention which differs from the other embodiments in that the upper surface 10 of insulating portion 8 is designed thicker, such that this surface is level with that surface 15 of the plastic casing facing away from cooling plate 6.