Press-fit connections for electronic modules

A press-fit connecting element for being pressed into a first contact opening in a first connection element and into a second contact opening in a second connection element is provided. The press-fit connecting element includes an elongated base body configured to be guided through the second contact opening in the second connection element to the first contact opening in the first connection element. The press-fit connecting element further includes a first press-fit zone configured to contact-connect the first contact opening in a force-fitting manner and a second press-fit zone which is at a distance from the first press-fit zone in a longitudinal direction and configured to contact-connect the second contact opening in a force-fitting manner.

PRIORITY CLAIM

This application claims priority to German Patent Application No. 10 2010 003 367.7 filed on 26 Mar. 2010, the content of said application incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present application relates to press-fit connections for connecting electronic modules such as power semiconductor modules to printed circuit boards, supply lines and the like.

BACKGROUND

Some considerations when selecting power semiconductor modules are simple manipulability and assembly. Modern module housing designs use, for example, special press-fit technology to connect modules both to a printed circuit board and to a heat sink, for example in a single production step. Only a single screw, for example, is required for such connections. Such press-fit connections therefore provide a high-quality alternative to known soldered connections and therefore meet the requirements of modern power converter designs in a power range up to 55 kW. Such power semiconductor modules can be used in a wide variety of universal drives, variable-frequency drives, uninterruptible power supplies (UPS), inductive heating and welding systems as well as in wind power installations, solar installations and air-conditioning systems.

Module housings suitable for such press-fit technology have specially shaped, deformable press contact elements (“press-fit” pins) which are pressed into corresponding contact holes in a printed circuit board when assembling the module. The press-fit force is generated by tightening a single screw. The press contact elements in the contact holes in the printed circuit board are plastically deformed by tightening the screw. A gas-tight contact zone which is very robust with respect to environmental influences is produced.

Alternatively, modules can be pressed into printed circuit boards and fastened to the heat sink independently of the press-fit operation using screws or other means (before or after they are pressed into the printed circuit board). Power semiconductor modules have hitherto only been pressed into printed circuit boards as a whole. Other connection elements, for example low-inductance strip conductor pairs (also so-called “busbars”) are contact-connected in another manner (for example screwed).

However, before assembling the printed circuit board and module, it must be ensured that the press contact elements are not deformed. Otherwise problems may arise during assembly. Furthermore, the press contact elements on the module housing are connection elements which are geometrically relatively complicated to produce. The press-fit contacts often cannot be released and reconnected without a relatively large amount of effort on account of the remaining deformation of the contact elements on the module.

SUMMARY

The embodiments described herein enable power electronic modules to be removed after the modules are mounted on a heat sink and a busbar or a printed circuit board has been contact-connected using press-fit technology. In this case, the heat sink and the busbar or the printed circuit board remain in position and the module connections to the cooler and to the busbar or to the printed circuit board can be released so that the module can be pulled out.

According to an embodiment, a press-fit connecting element for being pressed into a first contact opening in a first connection element and into a second contact opening in a second connection element is provided. The press-fit connecting element includes an elongated base body configured to be guided through the second contact opening in the second connection element to the first contact opening in the first connection element. The press-fit connecting element also includes a first press-fit zone configured to contact-connect the first contact opening in a force-fitting manner and a second press-fit zone which is at a distance from the first press-fit zone in a longitudinal direction and configured to contact-connect the second contact opening in a force-fitting manner.

According to an embodiment, a connecting system for electronic modules includes an electronic module having at least one first connection element with at least one first contact opening, at least one external connection element with a second contact opening and at least one press-fit connecting element. The press-fit connecting element has an elongated base body configured to be guided through the second contact opening in the external connection element to the first contact opening in the first connection element of the electronic module. The press-fit connecting element also has a first press-fit zone configured to contact-connect the first contact opening in a force-fitting manner and a second press-fit zone which is at a distance from the first press-fit zone in a longitudinal direction and configured to contact-connect the second contact opening in a force-fitting manner. External connection elements may be formed, for example, by a printed circuit board or a low-inductance strip conductor pair.

DETAILED DESCRIPTION

FIG. 1adiagrammatically shows a power semiconductor module10having a plurality of press-fit pins30for contact-connection to a printed circuit board20. In the example illustrated, the module10is pressed into the printed circuit board20with the aid of a screw40and is simultaneously tightly screwed to a heat sink11. The press-fit pins30are pressed into corresponding contact holes in the printed circuit board20by the force exerted on the module10during the screwing-in operation.FIG. 1billustrates a perspective view of another module10having the press-fit pins30arranged on the module housing, but without a printed circuit board. This module is first screwed to the heat sink and can then be independently pressed into a printed circuit board. The press-fit connecting system illustrated inFIG. 1is described, inter alia, in the article by T. Stolze, M. Thoben, M. Koch, R. Severin:Reliability of pressFIT connections, in: Proceedings of PCIM Europe 2008.

FIG. 2diagrammatically shows a side view of a connecting system for electronic modules according to an embodiment for reliably electrically contact-connecting the modules. This embodiment relates to a power semiconductor module10having at least one module connection element11, e.g. a plurality of module connection elements11as shown, which are arranged on an outer side of the module housing. The connection elements11are formed, for example, from a piece of flat conductor (conductor in the form of a strip with an approximately rectangular cross section) which is guided out of the module in a manner perpendicular to the surface101of the module housing and is bent through 90° outside the module, with the result that part of the flat conductor is parallel to the housing surface101of the module10. One or more contact openings11′ (for example through-holes) are respectively provided in these sections of the module connection elements11which are parallel to the housing surface101.

A connection element outside the module may be associated with one or more module connection elements11, this connection element outside the module e.g. being a printed circuit board20as shown inFIG. 1a(such as a printed circuit card) or a further flat or strip conductor20′ (such as a busbar) and likewise having contact openings which correspond to the contact openings11′ in the module connection elements11.

A reliable electrical connection between the electronic module10and the external connection element (for example the printed circuit board20) or the external connection elements is ensured by press-fit connecting elements30which can be pressed into the contact openings in the external connection element(s). Each press-fit connecting element30is pressed into two corresponding openings.

FIG. 3illustrates an example of a press-fit connecting element30according to an embodiment. The press-fit connecting element30shown inFIG. 3comprises an elongated (in the longitudinal direction) base body33having two press-fit zones A and B which are at a distance from one another in the longitudinal direction. According to one embodiment, the maximum external dimension D1of the press-fit zone A (measured perpendicular to the longitudinal direction) is less than the maximum external dimension D2of the press-fit zone B. The base body33may also have further press-fit zones (not illustrated) at a distance from the press-fit zones A and B in the longitudinal direction.

To facilitate the operation of pressing the press-fit zones A and B into the corresponding contact openings, the press-fit connecting element30may have spring elements31,32in the region of the press-fit zones. The spring elements31,32are configured in such a manner that they are elastically and/or plastically deformed when pressed into the corresponding contact openings and exert a contact force on the inside of the contact openings. For this purpose, the spring elements31,32may have, for example, an eyelet, fork or spiral shape or any other, easily deformable geometry. As an alternative, the contact openings (for example contact openings11′ in the module connection elements11) could be elastically and/or plastically deformable. In this case, the press-fit connecting element30may have a full geometry with a square or round cross section, for example. In any case, the respective contact zone (zone A or B) and the corresponding contact opening in the respective connection element (seeFIG. 2, module connection element11and supply lead connection element20′) are matched to one another in such a manner that a reliable force-fitting connection (and consequently also reliable, low-impedance electrical contact) is ensured.

The contact zones of the press-fit connecting elements30may be very different. In addition to the slotted eyelet shape shown inFIGS. 1 and 3, the contact zones may also have other suitable shapes, for example a spiral which forms the contact zone, a star-shaped or X-shaped contact zone, etc.

The electronic module10may contain semiconductor switches, for example one or more power transistor half bridges for constructing a power converter. In this case, a reliable, low-impedance electrical connection of the load connections of the power semiconductors is desirable. In order to keep the power inductances as low as possible (and in order to thus avoid the disadvantages of high power inductances when switching high load currents), the external supply lead connection elements20′ can be in the form of parallel striplines or strip conductors (strip conductor pairs) in which the same load current respectively flows in an anti-parallel manner. In this case, the strip conductors are guided parallel to the surface101of the electronic module housing and at different distances from the housing surface101.

FIG. 4illustrates a configuration where the strip conductors20′ are guided parallel to the surface101of the electronic module housing and at different distances from the surface101. Each strip conductor20′ is associated with its own module connection element11,12,13. Connecting elements30of different lengths are provided for each strip conductor/connection element pair to compensate for the different distances between the individual strip conductors20′ and the surface101of the module housing. Those regions of the strip conductors20′ which are provided with contact openings are offset with respect to one another in the horizontal direction (that is to say in a direction running parallel to the housing surface101), with the result that a first strip conductor20′ which is further inside (that is to say closer to the module housing) does not impede the insertion of a press-fit connecting element30from a second strip conductor20′ which is further outside to the module connection element (e.g. connection element12inFIG. 4) associated with the second strip conductor20′.

FIG. 5shows an embodiment for improving the assembly of the press-fit connecting system ofFIG. 4by providing spacers40,41,42against which the respective connection elements11,12,13rest. The spacers40,41,42may be provided on the electronic module10, more precisely on the surface101of the module housing, and/or between the connection elements11,12,13,20,20′.

The spacers40,41,42form abutments for the connection elements11,12,13. The first set of spacers40are used as abutments for the module connection elements11,12,13which emerge from the surface101of the module housing in a perpendicular manner and are angled through 90° outside the module10, with the result that a limb of a connection element11,12,13runs parallel to the housing surface101. The contact openings (for example punched holes) into which the press-fit connecting elements30are pressed during assembly are also arranged in these limbs of the module connection elements11,12,13which run parallel to the housing surface101.

The first set of spacers40prevent those parts of the connection elements11,12,13which run parallel to the surface110of the electronic module10from being bent when pressing in a press-fit connecting element30, the spacers bridging the space between the surface110and the connection element11,12,13, with the result that the connection element practically rests against the module housing. In this case, the spacers40may be an integral part of the module housing. However, the spacers40are not intended to cover the contact openings (for example contact opening11′), with the result that a connecting element30can be inserted through the contact opening in question without any problems.

The second set of spacers41are used as supports for the external connection elements20,20′ or else for a printed circuit board20(e.g. seeFIG. 1). The second set of spacers41are somewhat longer than the first set of spacers40, with the result that the external connection elements20,20′ come to lie somewhat above the associated module connection elements11,13. The difference in length (measured perpendicular to the housing surface101) between the first and second set of spacers40and41corresponds approximately to the distance between the two press-fit zones A and B of an appropriate press-fit connecting element30(e.g. seeFIG. 3). If, as already illustrated inFIG. 4, a plurality of external connection elements (printed circuit boards20or strip conductors20′) are intended to be connected to the electronic module10, the connection element20′ closest to the surface101of the module housing is mounted on the second set of spacers41and the further external connection elements20′ lying above it are mounted on the respective connection element (for example strip conductor20′) lying below them via at least one third spacer42, thus resulting in a stack of connection elements and spacers (spacer41, first external connection element20′, spacer42, second external connection element20′, etc.). If appropriate, the spacers (e.g. spacer42inFIG. 5) may have through-openings through which the press-fit connecting elements30are guided in the assembled state.

Strip conductor pairs20′ which run parallel to one another at a very short distance from one another are particularly important in this context. Such strip conductor pairs20′ are at such a short distance that the inductance of the strip conductor pair is greatly reduced in comparison with individual conductors in the case of currents flowing in an anti-parallel manner. A thin insulation layer can be arranged between the two strip conductors in a strip conductor pair. The distance between two strip conductors is usually less than a row of strip conductors.

FIG. 6shows an insulation layer42′ such as a film between two strip conductors20′ (strip conductor pair) guided in a parallel manner. The insulation layer42′ can assume the function of the third spacer42shown inFIG. 5. To contact-connect the strip conductor20′ arranged on that side of the insulating layer42′ which faces away from the module10to the corresponding module connection element12, the insulating layer42,42′ has through-holes aligned with the contact openings and through which the press-fit connecting elements30′ are guided in the assembled state.

FIG. 7illustrates another embodiment of a press-fit connecting system. The system illustrated inFIG. 7is an alternative to the embodiments shown inFIGS. 5 and 6. To simplify the assembly of the electronic module10and the connection elements11,12,13,20,20′ when using at least two-layer strip conductors (strip conductor pairs), the press-fit connecting elements30may be provided, at one end, with an elongated end piece34made of an insulating material. In this case, the elongated end pieces34have similar external dimensions (transverse to the longitudinal direction) to the press-fit connecting elements30themselves, with the result that the press-fit connecting elements30can be inserted, with the end pieces34, through one or more layers of strip conductors (e.g. separated by insulating layers42′) at a different potential in order to contact-connect the lowermost strip conductor of the strip conductors20′ to a corresponding module connection element11without short-circuiting the strip conductor with the strip conductors lying above it. To ensure reliable insulation, a seal70is arranged in the space between the insulating layer42′, which separates the two strip conductors20′ in a strip conductor pair, and the corresponding press-fit connecting elements30. In one embodiment, an O-ring is used as the sealing element70.

To manipulate and simultaneously press in a plurality of press-fit connections in a simpler manner during assembly, a plurality of press-fit connecting elements30may be fastened to a carrier35, if appropriate via the end pieces34. A carrier35then carries a plurality of press-fit connecting elements30(for example all press-fit connecting elements needed to contact-connect a module connection element11), with the result that the press-fit connecting elements can be pressed in together.

In the previously described embodiments, the connection elements11,12,13of the electronic module10are guided to the outside through a surface101of the module housing. In the embodiments shown inFIGS. 8 and 9, the module connection elements are arranged directly on a substrate11on the “base” of the electronic module10and are accessible from the outside through an opening in the module housing.

InFIG. 8, the module connection elements are in the form of sleeves14into which press-fit connecting elements30can be pressed. In this case, the inner wall of the contact opening formed by a sleeve14and a corresponding press-fit zone A of the relevant press-fit connecting element form a force-fitting connection and thus also a reliable, low-impedance electrical connection. As an alternative to the sleeves shown inFIG. 8, connection elements11which are in the form of strips (e.g. see FIGS.2and4-7) and have contact openings11′ may also be directly fastened to the substrate11on the base of the module10. As illustrated inFIG. 9, the press-fit connecting elements30engage in the contact openings in the connection elements11and form a force-fitting connection.

FIG. 10shows another embodiment of the carrier element35fromFIGS. 7-9. Like the carrier element35in the embodiments shown inFIGS. 7-9, the carrier element36carries at least one press-fit connecting element30. However, at least one lever37is connected to the carrier element36. The lever37can be used to easily release again the press-fit connecting elements30which were previously pressed in. Release is affected by virtue of the lever37which is used to produce a force between the connection element11(into which the press-fit connecting elements30have been pressed) and the carrier element36. Since the press-fit connecting elements34are fastened to the carrier element, the press-fit connecting elements30are pulled out of the contact holes in the connection element.