Abstract:
An interface unit and a printed circuit board configuration includes at least two interface units for linking conventional commercially available packages of integrated circuits on a printed circuit board in a more flexible and compact way, which allows compact high-performance electronic circuits to be produced on a small surface area and with low development expenditure.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    Field of the Invention  
           [0002]    The invention relates to the problem of mounting packages that hold integrated semiconductor chips on an electronic printed circuit board.  
           [0003]    Electronic circuits that cannot be fabricated entirely on a single semiconductor chip as an integrated microelectronic circuit include electronic and microelectronic components that are disposed on a printed circuit board as a carrier and are connected to one another by interconnects running on the printed circuit board. The electronic components are, for example, passive components such as resistors or capacitors; more complex components, on the other hand, are produced as microelectronic integrated semiconductor circuits that are held in a package with external terminals and are mounted on the printed circuit board. When there are a large number of electronic circuits, a number of such packaged microelectronic semiconductor circuits are disposed on one printed circuit board. For instance, memory modules or other complex circuits, such as, for example, embedded DRAMs, always have a number of microelectronic semiconductor chips disposed on the printed circuit board.  
           [0004]    In view of progressive miniaturization, both of the electronic circuit and of the microelectronic integrated circuits themselves, with every circuit to be developed there newly arises the problem of configuring the individual elements of the circuit as compactly as possible. Furthermore, a newly developed circuit is intended to perform as well as possible and be as versatile as possible, which is best achieved by a large part of the electrical operations being executed by the microelectronic integrated semiconductor circuits.  
           [0005]    A new integrated semiconductor chip cannot be independently produced for every electric circuit to be developed. It is rather the case that, for reasons of cost, the further technical development of semiconductor chips is proceeding independently of the further development of macroscopic electronic circuits, realized, for instance, on printed circuit boards. Therefore, to perform complex tasks by way of circuit engineering, as many commercially available semiconductor chips as possible are disposed on a printed circuit board. The desire for great versatility and performance capability of the electronic circuit, with at the same time compactness of the printed circuit board, leads to the necessity for as many integrated memory chips as possible to be disposed in a confined space next to one another on the printed circuit board.  
           [0006]    Every newly developed configuration of commercially available semiconductor memory chips on a printed circuit board has great effects on the routing of the interconnects on the printed circuit board and requires corresponding expenditure to be invested in the construction of the interconnect routing. At the same time, there are always specifications to be observed regarding the length of typically several hundred interconnects, regarding the thicknesses of the interconnects and regarding the distances between different components. These specifications, compliance with which is required for the technical functional capability of an electronic circuit, greatly restrict the possibilities for the configuration of the electronic and microelectronic components on the printed circuit board. The microelectronic semiconductor chips in particular, which are always held in a package that typically has several dozen to several hundred contact terminals disposed in rows, are difficult to integrate in a circuit layout due to the prescribed configuration of their external terminals.  
           [0007]    In particular, in the case of circuits to be newly developed that are sold in small numbers, and, therefore, only allow limited expenditure on construction, the difficulty of integrating microelectronic semiconductor chips represents a particular hurdle.  
         SUMMARY OF THE INVENTION  
         [0008]    It is accordingly an object of the invention to provide a connection of packaged integrated memory chips to a printed circuit board that overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and that facilitates the integration of a number of microelectronic semiconductor chips in an electronic circuit to be disposed on a printed circuit board, and, in particular, to dispose integrated semiconductor chips on a single printed circuit board, specifically, in relatively large numbers and, at the same time, in a confined space.  
           [0009]    With the foregoing and other objects in view, there is provided, in accordance with the invention, an interface unit for an electronic circuit, the interface unit including an interface body having first electrical contacts for electrically and mechanically connecting the interface body to the printed circuit board, second electrical contacts for electrically and mechanically connecting the interface body to at least one package with an integrated semiconductor chip, and the first electrical contacts electrically connected to the second electrical contacts.  
           [0010]    According to the invention, an interface unit that is disposed between the printed circuit board and one or more packaged semiconductor chips and can be connected to both is proposed. With the aid of such an interface unit, more versatile and flexible electrical-mechanical connections can be established between microelectronic integrated semiconductor chips and a printed circuit board.  
           [0011]    Conventionally, every integrated, packaged semiconductor chip is electrically and mechanically connected directly to the printed circuit board through the contacts of its package. With the interface units according to the invention, an intermediate level is introduced into such a connection, making it possible for the packaged semiconductor chips to be adapted both to changing contact configurations of the printed circuit board and to different electrical operating parameters on the part of the electronic circuit produced on the printed circuit board. This significantly increases the flexibility of the circuit construction; circuit layouts that were previously technically unfeasible are no longer hindered by the specified configuration of commercially available circuit packages, but, instead, can be realized both by the construction of the interface units according to the invention and by their configuration on the printed circuit board. The invention makes a much more varied integration of integrated semiconductor chips possible in large numbers in a confined space on electronic printed circuit boards and lowers the expenditure and costs for the production of electronic circuits.  
           [0012]    In accordance with another feature of the invention, the second electrical contacts are formed at the same time as second mechanical connecting device. The interface unit must be connected to the packages of the integrated semiconductor chips; this connection must be produced mechanically and electrically. It keeps costs down if mechanical connections are configured simultaneously as electrical connections, and vice-versa. Many electrical contacts—generally at least several dozen—are required between an interface unit and a packaged integrated semiconductor chip in order to link the integrated semiconductor circuit to the electronic circuit surrounding it. If these electrical contacts, already high in number, are used at the same time for the mechanical connection of the interface unit to an integrated semiconductor chip, there is no need for otherwise required separate mechanical connecting device. The interface unit and the package of the integrated semiconductor chip can, therefore, be configured more simply.  
           [0013]    In accordance with another feature of the invention, the first electrical contacts are pin contacts.  
           [0014]    In accordance with a further feature of the invention, the second electrical contacts of the interface unit are formed as elements for a mechanical plug-in connection. A plug-in connection between integrated semiconductor chips and interface units makes simple, low-cost and rapid mounting possible. Such a connection is advantageous even when the integrated semiconductor chips are later to be separated from the printed circuit board.  
           [0015]    In accordance with an added feature of the invention, the second electrical contacts are sockets for pin contacts. Because integrated semiconductor chips have to be attached on the upper side of the interface units according to the invention, facing away from the printed circuit board, it is advantageous to be on the safe side with regard to possible damage if the contacts of the interface units are themselves configured as a contact socket, i.e., as a concave depression in the upper side of the interface unit, into which contact pins of the integrated semiconductor chips can be inserted. In such a case, those contact terminals of the interface unit that are not connected to corresponding pins are protected against mechanical or electrical damage.  
           [0016]    With regard to the first connecting device, which establishes the connection of the interface unit with respect to the electronic printed circuit board, in accordance with an additional feature of the invention, they are also formed as elements for a mechanical plug-in connection. By contrast with a packaged integrated semiconductor chip with a definitively specified configuration of the contact terminals, the printed circuit board offers more possibilities with regard to different types of mounting on account of its larger surface area. In any event, a mechanically secure connection between the interface unit and the electronic printed circuit board is required. In addition, however, the large surface area of a printed circuit board also offers the possibility, in principle, of providing on sides of the printed circuit board additional connecting elements for various alternative configurations of the interface unit on it. A plug-in connection in which the interface units are inserted perpendicularly into the printed circuit board would offer the advantage that no lateral misalignments can occur, which under some circumstances would lead to damage to the semiconductor chips to be inserted thereabove in a second level. Even in those cases in which interfaces or the integrated semiconductor chips are to be quite frequently unplugged and plugged in again or exchanged when there is a defect, the plug-in connection is an appropriate mechanical type of connection.  
           [0017]    In accordance with yet another feature of the invention, the second electrical contacts of the interface unit are disposed such that the interface unit can be simultaneously connected to in each case a proportionate number of contacts of at least two packages of integrated semiconductor chips. Such an embodiment allows even much more versatile connection possibilities between integrated semiconductor chips and an electronic printed circuit board. Definitively specified configurations of contact terminals of a semiconductor package can not only be connected to geometries of contact terminals on the printed circuit board, in that the interface unit respectively carries a single semiconductor chip and is merely used as an adapter for different configurations of the board contacts; rather, the configuration of the interface unit as a connecting element between the printed circuit board and at least two semiconductor chips makes it possible for these semiconductor chips to be linked as a network over the printed circuit board to one another and to the latter. In such a case, the second electrical contacts are disposed on the interface unit such that they are disposed in a concentrated manner in at least two different regions—preferably of the upper side—of the interface unit and, consequently, make it possible for contact to be made respectively with an integrated semiconductor chip of each region of a concentrated number of contacts. This allows a number of semiconductor chips to be simultaneously connected by a single interface unit, it generally being necessary for each semiconductor chip to be connected to a number of interface units, i.e., at least two.  
           [0018]    In such a case, a number of interface units and a number of semiconductor chips are used on the printed circuit board. For example,  50  percent of the contacts of a package of a semiconductor chip may be connected to a first interface unit according to the invention, whereas the remaining contacts of the package are connected to a second interface unit of identical construction. Such a configuration makes bridge-like configurations possible, in which the packaged semiconductor chips are connected to the printed circuit board by at least two interface units each. In addition, any other forms are conceivable, for instance, cross-shaped interface units, which respectively make contact with half of two rows of contacts neighboring one another of a semiconductor package.  
           [0019]    In accordance with yet a further feature of the invention, the interface unit is of a rectangular form and the second electrical contacts are disposed on two mutually parallel sides of the interface unit such that the interface unit can be connected on each side to in each case a package of an integrated semiconductor chip. In such a case, two interface units respectively serve as “bridge piers” for a semiconductor chip to be attached to them.  
           [0020]    In accordance with yet an added feature of the invention, the first connecting device is disposed on two other, mutually parallel sides of the interface unit. In such a case, the electrical connection between the interface units and the printed circuit board—for example, by bonding wires—is produced laterally of the two remaining edges of the rectangular interface unit. As such, the contacts of the integrated semiconductor chips may also be led to contact terminals disposed further away on the printed circuit board. Alternatively, these first electrical contacts may also at the same time be formed as mechanical connecting elements with respect to the printed circuit board, taking up only little surface area under the two remaining side edges of the interface unit.  
           [0021]    In the simplest case, the interface unit according to the invention merely establishes a mechanical and electrical connection between one printed circuit board and integrated semiconductor chips. On the other hand, one development provides that the interface unit has an electronic circuit that connects the first and the second electrical contacts to one another. Such a switching electronic circuit between the printed circuit board and the semiconductor chips makes possible a still more flexible electrical adaptation of the two parts to each other than by electrical resistances realized just by lengths of interconnects. Furthermore, a still more complex and, at the same time, compact overall circuit can be realized in this way.  
           [0022]    In accordance with yet an additional feature of the invention, the first electrical contacts form a ball-grid array. In such a case, the electrical contacts are formed on the underside of the interface unit to produce spherical solder pads, which are disposed in the form of rows or a matrix, i.e., an array.  
           [0023]    Alternatively, the first electrical contacts may be flip-chip contacts. In such a case, the solder points of the printed circuit board and of the interface unit are connected to another without lengthy contact pins in between.  
           [0024]    With regard to the connections with respect to the integrated semiconductor chips, in accordance with again another feature of the invention, second electrical contacts are formed for connecting to Thin Small Outline Packages (TSOPs). These packages are standardized and available with different numbers of contacts. Adaptation and configuration of the second electrical contacts of the interface unit according to the invention with respect to such commercially available semiconductor packages makes it possible for integrated semiconductor chips to be integrated into outer electronic circuits at particularly low cost.  
           [0025]    With the objects of the invention in view, there is also provided an electronic circuit configuration, including an electronic printed circuit board, at least one package with an integrated semiconductor chip, at least two interface units, each of the units individually mechanically and electrically connected to the printed circuit board, individually mechanically and electrically connected to the at least one package, and each having an interface body with a first connecting device mechanically connecting the interface body to the printed circuit board, a second connecting device mechanically connecting the interface body to the at least one package, first electrical contacts electrically connecting the interface body to the printed circuit board, second electrical contacts electrically connecting the interface body to the at least one package, and the first electrical contacts electrically connected to the second electrical contacts.  
           [0026]    Such a configuration integrates integrated semiconductor chips into a more complex electronic circuit in a simple, versatile and low-cost manner and allows novel configurations of semiconductor chips that cannot be realized by conventional methods to be produced on a semiconductor board.  
           [0027]    A first embodiment of this circuit configuration provides that the interface units are disposed at equal distances in relation to one another in the form of rows on the printed circuit board and the packages of the integrated semiconductor chips are connected in a bridge-like manner to two neighboring interface units in each case. The forming of many such bridge constructions on one and the same printed circuit board, in particular, makes an especially compact configuration of the semiconductor chips possible, largely independently of the routing of the interconnects of the printed circuit board, and additionally increases many times over the performance capability of the electronic circuits formed in this way.  
           [0028]    In accordance with again a further feature of the invention, the interface units and the packages of the integrated semiconductor chips are disposed in the form of a matrix on the printed circuit board. In such an embodiment, the greatest possible flexibility is achieved, in that integrated semiconductor chips are linked in a matrix-like manner above the actual plane of the printed circuit board.  
           [0029]    In accordance with a concomitant feature of the invention, the circuit configuration according to the invention is preferably a memory module, in which the packages carry integrated DRAM memory chips. Specifically memory chips such as dynamic random-access memories are often interconnected in high numbers in order to increase the capacity of a memory beyond the degree of integration currently achieved in the case of the individual integrated semiconductor circuit.  
           [0030]    Other features that are considered as characteristic for the invention are set forth in the appended claims.  
           [0031]    Although the invention is illustrated and described herein as embodied in a connection of packaged integrated memory chips to a printed circuit board, it is, nevertheless, not intended to be limited to the details shown because various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.  
           [0032]    The construction and method of operation of the invention, however, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0033]    [0033]FIG. 1 is a perspective view of an interface unit according to the invention for connecting to a printed circuit board and to at least one package of an integrated semiconductor chip;  
         [0034]    [0034]FIG. 2 is a fragmentary, diagrammatic, cross-sectional view of a circuit configuration according to the invention; and  
         [0035]    [0035]FIG. 3 is a plan view of two different embodiments of a circuit configuration according to the invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0036]    Referring now to the figures of the drawings in detail and first, particularly to FIG. 1 thereof, there is shown perspective view of an interface unit  20  according to the invention. The interface unit  20  is of a rectangular form, viewed from above, and has on its underside, in the vicinity of two side faces  24 , a first connecting device or means  11 , which is formed here as pin-shaped plug-in connecting elements  11  and can be inserted into corresponding sockets of a printed circuit board  10 . On the upper side, the interface unit  20  has a large number of second connecting terminals or means  21  for mechanically connecting the interface unit  20  to one or two packages  30  of integrated semiconductor chips. If only a single semiconductor package  30  is connected to the interface unit, it is centrally plugged onto the interface unit  20  depicted. The interface unit  20  may, however, also be connected to a number of semiconductor packages, for example, two, in that their contacts are respectively inserted into a row of the terminals  21  represented on the interface unit. By such a configuration, the interface unit according to the invention switches between different contact configurations of the printed circuit board and the packages to be disposed thereupon of the integrated semiconductor chips. These can be disposed much more flexibly, depending on the configuration of the interface units and their configuration on the printed circuit board, than if they are connected directly to the printed circuit board  10 .  
         [0037]    In FIG. 1, the first connecting device  11 , the contact pins  11 , are simultaneously also suitable for establishing the electrical connection  12  with respect to the printed circuit board. For such a purpose, they must be produced from an electrically conductive material. As an alternative thereto, the first electrical contacts may also be formed as solder contact points  12 , which are electrically connected to the printed circuit board after the mechanical attachment of the interface unit on the printed circuit board by the bonding wires  14  represented.  
         [0038]    The mechanical and electrical connection between the interface unit  20  and the semiconductor package(s) to be attached thereover can be formed in the same way. In the simplest case, plug-in contact sockets  21  are recessed into the interface units. As a second connecting device  21 , they establish the mechanical and electrical connection with respect to the semiconductor chips. If these second connecting devices are not connected to corresponding contacts of the semiconductor chips, they are protected against mechanical or electrical damage as contacts recessed into the interface unit.  
         [0039]    Schematically represented in the center of the upper side of the interface unit is an electronic circuit  28 , which connects the first electrical contacts  11  to the second electrical contacts  21 . If no electronic circuit  28  is provided, the contacts  11  and  21  are connected to one another by interconnects in or on the interface unit.  
         [0040]    From the second contacts  21 , there preferably extends laterally of the faces  23 , above the interface unit  20 , in each case a semiconductor package  30 , which is, in turn, connected at its opposite ends to the printed circuit board  10  through a further interface unit  20 .  
         [0041]    The semiconductor configuration obtained in this way on a printed circuit board is represented in FIG. 2. On the printed circuit board  10  there are a number of interface units  20  disposed equidistantly in a row, over which packages  30  with integrated semiconductor chips  31 , preferably, with memory chips such as, for example, DRAMs  31 , are disposed in a bridge-like manner.  
         [0042]    In FIG. 2, various embodiments of the connection of the interface units  20  to the printed circuit board  10  and the semiconductor packages  30  are depicted in a combined manner. The interface unit  20  on the extreme right in FIG. 2 is linked both to the printed circuit board  10  and to the semiconductor packages  30  disposed above it, mechanically by plug-in connections  11  and  21 , respectively, and electrically by additional electrical contacts  12 ,  22 , to be precise by bonding connections  12 ,  22 . The interface unit  20  represented in the middle is mechanically and electrically connected to the printed circuit board  10  by contacts  11 , which may be either a ball-grid array, i.e., a configuration of contacts with solder balls at the contact end, or flip-chip contacts. The middle interface unit  20  is connected to the semiconductor packages  30  mechanically by plug-in connections  21  and electrically by additional bonding connections  22 . The left interface unit is electrically and mechanically connected to the printed circuit board  10  and to the semiconductor packages  30  with the aid of plug-in connections  11 ,  12 . A single plug-in connection  25 , for example, with respect to a semiconductor package, includes a socket  26  recessed into the interface unit  20  and a pin contact  27  of the semiconductor package  30  to be inserted therein.  
         [0043]    In the case of the configuration represented in FIG. 2, the interface units  20  according to the invention are disposed in a row on the printed circuit board and, together with the semiconductor chips  31  held in packages  30 , form the printed circuit board configuration  40  according to the invention.  
         [0044]    [0044]FIG. 3 shows such a printed circuit board configuration  40  in two different embodiments. In the right-hand half of the printed circuit board  10 , two bridge constructions  41  including interface units  20  and semiconductor packages  30  are represented. With them, a large number of integrated semiconductor chips can be loaded in rows close together over large regions on the surface area of the printed circuit board.  
         [0045]    A still more complex linkage is made possible by the printed circuit board configuration represented on the left in FIG. 3, in which the interface units  20  and the packages  30  of the integrated semiconductor chips  31  are linked in a matrix-like manner to form a network  42  of chips. In the network configuration  42  represented, each interface unit  20  is connected to up to four semiconductor packages  30 , and vice-versa.  
         [0046]    In the case of both embodiments, electronic subcircuits  29  present on the interface units  20  can link a number of integrated semiconductor chips  30  to one another. If there is no independent electronic circuit  28  provided on an interface unit, only first terminals  11 ,  12  and second terminals  21 ,  22  are connected to one another by lines  29 .  
         [0047]    The mounting technologies represented in FIG. 3 and corresponding mounting technologies, within the knowledge of one having ordinary skill in the art, for the attachment of semiconductor packages  30  on printed circuit boards  10  with the aid of the interface units according to the invention make it possible for integrated circuits to be linked to printed circuit boards and also directly to one another in the manner of a modular system.  
         [0048]    The separation according to the invention of the integrated circuits to be applied to a printed circuit board  10  into a circuit chip—for instance, with a memory circuit such as a DRAM—and a structurally separate data interface  20  allows the integrated circuits to be interconnected more flexibly than previously. The interface units can be produced in series as standardized interfaces and linked with commercially available semiconductor packages to form larger switching networks.  
         [0049]    Preferred applications of the present invention are memory modules that are, for example, to be connected to TSOPs or other packages. A configuration of the integrated semiconductor memories on a printed circuit board in the manner of a matrix or in rows, for example, allows the packing density to be increased to a degree that is only reached by the further development of the integrated semiconductor memories themselves some years later, after much longer technical development work.