Abstract:
A printed circuit board (PCB) has a first, structured metalization arranged on its top side and at least one second metalization arranged below the first metalization in a vertical direction, parallel to the first metalization and insulated therefrom. Also on the PCB top side is a bare semiconductor chip having contact electrodes connected by bonding wires to corresponding contact pads of the first metalization on the PCB top side. A first portion of the contact electrodes and corresponding contact pads carry high voltage during operation. All high-voltage-carrying contact pads are conductively connected to the second metalization via plated-through holes. An insulation layer completely covers the chip and a delimited region of the PCB around the chip, and all high-voltage-carrying contact pads and the plated-through holes are completely covered by the insulation layer. A second portion of the contact electrodes and corresponding contact pads are under low voltages during operation.

Description:
PRIORITY CLAIM 
       [0001]    This application claims priority to German Patent Application No. 10 2013 219 780.2, filed on 30 Sep. 2013, the content of said German application incorporated herein by reference in its entirety. 
       TECHNICAL FIELD 
       [0002]    The invention relates to the field of power semiconductor modules, their construction and manufacturing methods. 
       BACKGROUND 
       [0003]    Modern power semiconductor modules comprise not only power electronic semiconductor components (in particular power semiconductor switches), but also integrated circuits (ICs) as important components. The latter are used e.g. for switching power semiconductor switches or for measuring currents or temperatures. In this context, the term “intelligent power semiconductor modules” (“intelligent power module”, for short: IPM) is often employed. Such IPMs typically comprise, in addition to the power electronics, the required driver circuits (gate drivers) and the like. The operating voltages customary in power semiconductor modules can be in the range of from hundreds of volts to a few kilovolts. These high voltages are present directly at some external contacts (high-voltage contacts) of the ICs (e.g. of the gate drivers), for which reason these IC units require effective insulation. Depending on the application and standards associated therewith, it is thus necessary to maintain spacings between the high-voltage contacts of the ICs and current-carrying parts at low potential (so-called air clearances and creepage paths), such that sufficient insulation is ensured. Insulating a plurality of IC units supplied with high voltage from one another likewise requires specific spacings relative to one another. If a plurality of such ICs are arranged on a printed circuit board (printed circuit card), these lateral spacings of the units on the printed circuit board provide for a large area requirement. The endeavor to obtain ever more compact modules demands a reduction of the area of the printed circuit board. 
         [0004]    One possibility for ensuring the required area of the printed circuit board with the insulation remaining the same (i.e. with the creepage path remaining the same) consists in replacing the conventional SMD (SMD=surface mounted device) IC packages by packages having a smaller pitch (pitch=spacing of connection legs) or a BGA (BGA=ball grid array). 
         [0005]    However, this method requires an additional insulation layer with which these chip packages have to be coated, which results in an additional work step. Moreover, the production of an insulation layer below the ICs can be realized only with high outlay. The area gained by these methods on the printed circuit board in comparison with the initial situation is only minimal and is therefore at odds with the significantly greater outlay of the insulation requirements (additional insulation layer). 
       SUMMARY 
       [0006]    A power semiconductor module is provided that has a reduced space requirement with the same functionality, and a corresponding production method. 
         [0007]    One aspect of the invention relates to a power semiconductor module. In accordance with one example of the invention, the power semiconductor module comprises a printed circuit board having a first, structured metalization arranged on a top side of the printed circuit board and having at least one second metalization, which is arranged below the first metalization in a vertical direction, parallel to said first metalization and is insulated therefrom. Arranged on the top side of the printed circuit board there is at least one bare semiconductor chip having a plurality of contact electrodes, which are in turn connected by means of bonding wires to corresponding contact pads of the first metalization on the top side of the printed circuit board. A first portion of the contact electrodes and of the corresponding contact pads carry high voltage during operation. All high-voltage-carrying contact pads are conductively connected to the second metalization via plated-through holes. An insulation layer completely covers the chip and a delimited region of the printed circuit board around the chip, wherein all high-voltage-carrying contact pads and the plated-through holes are completely covered by the insulation layer. A second portion of the contact electrodes and of the corresponding contact pads are under low voltages during operation. 
         [0008]    A second aspect of the invention relates to a method for producing a power semiconductor module. In accordance with one example of the invention, the method comprises providing a printed circuit board having a top side and an underside, wherein structured metalizations are arranged on the top side and underside, and providing at least one bare semiconductor chip arranged on the top side of the printed circuit board and having a plurality of contact electrodes, which are connected by means of bonding wires to corresponding contact pads of the structured metalization on the top side of the printed circuit board. A first portion of the contact electrodes and of the corresponding contact pads carry high voltage during operation, and all high-voltage-carrying contact pads are conductively connected via plated-through holes to the structured metalization on the underside in an inner layer. An insulation layer is applied such that it completely covers the chip and a delimited region of the printed circuit board around the chip, wherein all high-voltage-carrying contact pads and the plated-through holes are completely covered by the insulation layer. 
         [0009]    Those skilled in the art will recognize additional features and advantages upon reading the following detailed description, and upon viewing the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The invention is explained in greater detail below on the basis of examples illustrated in the drawings. The figures illustrated in the drawings are not necessarily true to scale, nor should they be understood as restrictive with regard to the invention. Rather, importance is attached to elucidating the principle underlying the invention. In the drawings, identical reference signs designate identical components or signals having an identical or similar meaning. 
           [0011]      FIG. 1A  shows, in a longitudinal sectional illustration, one exemplary embodiment of a power semiconductor module comprising a power semiconductor substrate and a control printed circuit board; 
           [0012]      FIG. 1B  shows, in a longitudinal sectional illustration, a further exemplary embodiment of a power semiconductor module comprising a power semiconductor substrate and a control printed circuit board; 
           [0013]      FIG. 2  shows one example of the control printed circuit board with a plurality of semiconductor chips arranged thereon using standard SMD technology with a package in a plan view; 
           [0014]      FIG. 3  illustrates the space saving in comparison with the example from  FIG. 2 , which is achieved by the use of a control printed circuit board with bare driver IC and additional insulation; 
           [0015]      FIG. 4A  shows a cross section through a part of the control printed circuit board with standard SMD drivers in accordance with  FIG. 2  (horizontal insulation clearance); 
           [0016]      FIG. 4B  shows a cross section through a part of the control printed circuit board in accordance with  FIG. 3  (insulation in the vertical direction through the printed circuit board); and 
           [0017]      FIG. 5  shows one exemplary embodiment of a printed circuit board with a plurality of layers in a cross-sectional illustration. 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    In the following detailed description, reference is made to the accompanying figures illustrating specific exemplary embodiments for elucidation purposes. It goes without saying that the features of the different exemplary embodiments described herein can be combined with one another, unless indicated otherwise. 
         [0019]      FIG. 1A  shows a cross section through a power semiconductor module  1  in accordance with one example of the invention. The specific configuration of the control printed circuit board  10  makes it possible to integrate both the power electronics components and the control electronics into a compact package (e.g. an “EasyPACK® 2B” from Infineon), which hereto could only accommodate power electronics components (without a control printed circuit board). The printed circuit board  10  and the power semiconductor substrate  5  are arranged one above the other in the example illustrated in  FIG. 1 . In this case, the module  1  comprises the printed circuit board  10  with electronics components fitted thereon, which are explained further below with reference to subsequent figures, and also a power semiconductor substrate  5 , which can be arranged on a heat sink  7 . The power semiconductor substrate  5  has a structured metalization  12  at its top side  5   o,  wherein the top side is that side of the substrate which faces the printed circuit board  10 . Various power semiconductor components  6  (e.g. IGBTs or diodes) can be arranged on the power semiconductor substrate  5 . 
         [0020]    The power semiconductor substrate  5  can be, in particular, a DCB substrate (DCB=direct copper bonded), a DAB substrate (DAB=direct aluminum bonded), or an AMB substrate (AMB=active metal braze), which have an insulating carrier composed of ceramic. A further power electronics substrate is the so-called IMS (IMS=insulated metal substrate), in which a metallic carrier is insulated from the metalization by a thin insulation layer. A metalization is arranged on both sides of the carrier (insulated metal or ceramic). The top-side metalization (top side  5   o ) is structured and therefore has conductor tracks, soldering pads and bonding pads and the like. The underside metalization (underside  5   u ) is usually over the whole area. In contrast to the power semiconductor substrate, the printed circuit board  10  does not comprise a ceramic carrier, but rather comprises a base material customary for printed circuit boards (PCBs), such as e.g. FR1 to FR5, wherein FR4 and FR5 (both glass-fiber-reinforced epoxy resin) are very often used. 
         [0021]    Furthermore, contact pins  18  are fitted (e.g. by means of connection elements  19 ) on the top side  5   o  of the power semiconductor substrate  5 , wherein, with the module package closed, contact is made with the electronics in the module by means of such contact pins. For this reason, the contact pins project from the top side of the package and serve as external load terminals (“power terminals”) of the module  1 . The contact pins  18  can be led through the printed circuit board  10 , for which purpose corresponding holes are provided in the printed circuit board. If an electrically conductive contact between the contact pin  18  and the printed circuit board metalization is desired, the hole can be metallized and the contact pin  18  can be in electrical contact with said metalization in this case. The hole is then designated as contact hole  17 . If a nonconductive feedthrough of the contact pin  18  through the printed circuit board  10  is required, the hole is configured such that it is insulating, rather than metalized. The hole is then designated as through hole  16 . Besides the contact pins  18  fitted to the power semiconductor substrate  5 , contact pins  18 ′ can likewise be fitted on the printed circuit board  10  by means of connection elements  19 ′, which contact pins can likewise project from the closed module. In this case, the contact pins can be configured such that they all project by the same distance outside the module. Two voltage regions thus exist in the module, a high-voltage region  40  and a low-voltage region  41 . The voltage regions  40  and  41  are separated from one another—as indicated by a dash-dotted line in  FIG. 1A . This separation becomes possible by virtue of an insulation layer  30 , which will be described in detail later. 
         [0022]    The advantage of the arrangement of the (driver) printed circuit board  10  in the manner illustrated in  FIG. 1A  is that the module package can be equipped very densely without external changes. It thus becomes possible to incorporate a control printed circuit board into a small module package which hitherto had space only for power semiconductor substrates (wherein the control printed circuit board was connected to the module externally). For the mechanical stabilization of the construction, a reinforcer plate can optionally also be inserted between power semiconductor substrate  5  and printed circuit board  10 . The top side of the module package can be formed by a package cover, through which the contact pins are led. The cover can additionally have an opening, through which potting compound (e.g. a silicone gel) can be filled into the finished module in order to cover possibly exposed components on the power semiconductor substrate  5 . The potting compound also serves to increase the insulation strength. 
         [0023]      FIG. 1B  shows a cross section through a power semiconductor module  1  in accordance with a further exemplary embodiment of the invention, which is constructed analogously to that in  FIG. 1A . The difference here, however, is that all high-voltage-carrying parts of the printed circuit board  10  are coated with the insulation layer, as a result of which there are no longer any exposed high-voltage-carrying parts on the top side  10   o  of the printed circuit board  10 . As a result, the high-voltage region  40  is restricted to the underside  10   u  of the printed circuit board  10 , as a result of which high- and low-voltage regions are separated or insulated from one another by the printed circuit board itself. Horizontal insulation clearances then need no longer be complied with on the top side of the printed circuit board. 
         [0024]    Specific examples of the configuration of the printed circuit board are described in greater detail below. In this respect,  FIG. 2  illustrates an exemplary embodiment of a known solution (in plan view) in which semiconductor chips  25  with package  25  are arranged on a printed circuit board  10  (PCB). In this case, the semiconductor chips  25  are arranged in a package (chip package), for example of the SOIC-16 type (SOIC denotes “small outline IC” and designates an SMD package form). The electrical connection contacts  26  (also called pins or terminals) of the chips project from the chip package and are soldered to the top-side metalization of the printed circuit board  10 . High voltage is present at these contacts in part, for which reason an effective insulation is required. In the exemplary embodiment, the insulation is achieved by virtue of the ICs being arranged on the printed circuit board at a correspondingly sufficient lateral insulation distance D INS  from one another. This lateral insulation distance avoids excessively high creepage currents. The required minimum distances and the package sizes of the chips  25  thus define for the printed circuit board  10  a minimum size which must be present in order to maintain the lateral insulation distances of the ICs. Furthermore, optional semiconductor components  6  (e.g. diodes) are illustrated schematically. 
         [0025]      FIG. 3  shows a plan view of the top side  100  of the printed circuit board  10  in accordance with one example of the invention. In this case, the conventional chips with package  25  are replaced by bare chips  20  (also called “bare die”). The chips  20  have bonding pads  22 , which are connected by means of bonding wires  14  to corresponding contact pads  23  on the structured metalization  11  on the top side of the printed circuit board  10 . In addition, further optional semiconductor components can be arranged on the printed circuit board  10 . The bare chips  20  have significantly smaller dimensions than the chip packages of the chips  25  from  FIG. 1 . However, the use of “bare dies” requires a different solution for ensuring the insulation. 
         [0026]    The required insulation is provided by an insulation layer  30 , which completely encloses both the complete bare chip  20  and the contact-connection thereof comprising the contact electrodes  22 , contact pads  23 , bonding wires  14  and vias  13  (see  FIG. 4B ). The insulation layer  30  extends over a delimited region  31  around the bare chip  20  and is produced for example by means of a “dam and fill” method known per se. The totality of this insulation and the chip with the contact-connection thereof is designated as “insulated semiconductor chip”  21 . The insulation layer  30  is practically an encapsulation of the chip and the contact-connection thereof. A “bare die” encapsulated in this way is significantly more compact than the packages (e.g. SOP or SSOP-Package) of the semiconductor chips in  FIG. 1 . As a result, it is possible to significantly reduce the size of the printed circuit board with insulation clearances between the encapsulated semiconductor chips  21  remaining the same, since the space-consuming chip packages are no longer necessary. 
         [0027]      FIGS. 4A and 4B  illustrate sectional views of the examples from  FIG. 2  and  FIG. 3 , respectively. In this case,  FIG. 4A  shows the printed circuit board  10  having a top side  10   o  and an underside  10   u,  wherein the top side  100  and/or the underside  10   u  have/has a structured metalization  12 . On the top side  10   o  there is applied at least one chip with package  25 , the electrical contacts  26  of which are electrically conductively connected to the printed circuit board  10 . Besides the chip with package  25 , optional further semiconductor components  6  (e.g. diodes) can be applied on the top side  100 . Optional semiconductor components  6  can likewise be applied on the underside  10   u  of the printed circuit board  10 . The chip with package  25  on the top side  100  of the printed circuit board  10  can be electrically conductively connected to the underside  10   u  by means of a via  13 . Since high voltage is present at a portion of the electrical contacts  26  of the chip with package  25  (on the right-hand side of the chip in the exemplary embodiment) and it is not insulated, a high-voltage region  40  arises and no contacts with low voltage are permitted to lie within said high-voltage region. Said high-voltage region  40  is illustrated in a hatched manner in  FIG. 4A . The chip with package  25  is supplied with high voltage in this case from the underside  10   u  of the printed circuit board  10  through the via  13 , for which reason the underside  10   u  is likewise part of the high-voltage region  40 . Disposed in relation thereto is the low-voltage region  41 , which is situated at the electrical contacts  6  with low voltage. Said low-voltage region  41  is illustrated with a wavy pattern in  FIG. 4A . It is necessary for the two voltage regions to be effectively separated in order to avoid creepage currents or short circuits. The solution to this consists in a certain distance D INS  (cf.  FIG. 2 ) between the chips with package  25 , which results in large printed circuit board sizes. 
         [0028]      FIG. 4B  shows a longitudinal section with respect to the plan view from  FIG. 3 , but with more details.  FIG. 4B  shows the printed circuit board  10  having a top side  10   o  and an underside  10   u.  Both the top side  10   o  and the underside  10   u  can have a structured metalization  12 . At least one bare chip  20  is arranged on the top side  10   o.  The chip  20  has one or a plurality of bonding pads  22  electrically connected to corresponding contact pads  23 , situated on the printed circuit board  10 , by means of bonding wires  14 . All high-voltage-carrying contact pads  23  are electrically connected to the structured metalization  12  of the underside  10   u  of the printed circuit board  10  by vias  13 . In the case of multilayer printed circuit boards, the potential can also be passed to an intermediate layer instead of to the underside (cf.  FIG. 5 ). Further semiconductor components  6  can be arranged both on the top side  10   o  and on the underside  10   u  of the printed circuit board  10 . For the insulation of the “bare die”  20 , an insulation layer  30  is applied to a delimited region  31  comprising the bare chip  20  and the contact-connection thereof (i.e. the contact electrodes  22 , the contact pads  23 , the bonding wires  14  and the vias  13  used). All high-voltage-carrying parts of the insulated chip  21  are thus encapsulated by the insulation layer. 
         [0029]    The voltage regions as already mentioned in the case of  FIG. 4A  are now manifested differently. As a result of the insulation with the insulation layer  30 , there are no exposed high-voltage-carrying parts located on the entire top side  10   o  of the printed circuit board  10 , as a result of which the high-voltage region  40  is restricted to the underside  10   u  of the printed circuit board  10  (if appropriate, to an intermediate layer in the case of multilayer printed circuit boards). The entire top side  10   o  of the printed circuit board  10  can thus be assigned to the low-voltage region  41  since all high-voltage-carrying parts are encapsulated. The lateral insulation distance for separating the voltage regions which is required in the exemplary embodiment in  FIG. 4A  is therefore no longer necessary in the exemplary embodiment in  FIG. 4B . Instead, the printed circuit board  10  itself forms the insulating or separating medium of the voltage regions, which overall permits a significantly more compact design. 
         [0030]    Like  FIG. 4B  already,  FIG. 5  shows the printed circuit board  10  in lateral cross section. In this exemplary embodiment, the printed circuit board comprises a so-called multilayer printed circuit board, which has three metalization layers in the present case. The printed circuit board  10  therefore has a first layer  11   a  composed of printed circuit board basic material (e.g. FR4) and a second layer  11   b,  which likewise consists of the printed circuit board basic material. The two layers  11   a  and  11   b  are connected by means of a (structured) metalization layer  10   z.  Three metalization layers (top side, inside, underside) are thus available in total. The printed circuit board  10  can also comprise more than three layers. The through contact from the top side  10   o  of the printed circuit board  10  to the underside  10   u  thereof or to an inner layer  10   z  is effected by vias  13 , as in the previous exemplary embodiments. As also already in  FIGS. 4A and 4B , the insulation layer encompasses the entire bare semiconductor chip  20  and the contact-connection thereof and the via(s)  13  used therefor, such that no high-voltage-carrying components without encapsulation are exposed on the top side  10   o  of the printed circuit board  10 . 
         [0031]    Spatially relative terms such as “under”, “below”, “lower”, “over”, “upper” and the like, are used for ease of description to explain the positioning of one element relative to a second element. These terms are intended to encompass different orientations of the package in addition to different orientations than those depicted in the figures. Further, terms such as “first”, “second”, and the like, are also used to describe various elements, regions, sections, etc. and are also not intended to be limiting. Like terms refer to like elements throughout the description. 
         [0032]    As used herein, the terms “having”, “containing”, “including”, “comprising” and the like are open-ended terms that indicate the presence of stated elements or features, but do not preclude additional elements or features. The articles “a”, “an” and “the” are intended to include the plural as well as the singular, unless the context clearly indicates otherwise. 
         [0033]    With the above range of variations and applications in mind, it should be understood that the present invention is not limited by the foregoing description, nor is it limited by the accompanying drawings. Instead, the present invention is limited only by the following claims and their legal equivalents.