Abstract:
An electronic component includes at least one semiconductor chip. The semiconductor chip is attached on a first side of a wiring board or a leadframe. The wiring board is provided with interconnect structures at least on a second side. The first side of the wiring board, with the semiconductor chip located on it, is completely enclosed by a package. The package is provided with a cooling element, which is an integral part of the package. The invention also relates to a method for producing the electronic component.

Description:
BACKGROUND OF THE INVENTION 
   Field of the Invention 
   The invention relates to an electronic component and a method for producing the electronic component. 
   Considerable power losses during operation and the associated development of heat in some electronic components with semiconductor chips often require them to include cooling devices. The cooling devices are generally passive heat sinks that are connected to the electronic components during or after their production. In standard packages with supporting elements on the wiring board or the leadframe (BGAs, Ball Grid Arrays), restricted space prevents the mounting or fitting of a cooling element in particularly compact packages. Examples of such compact packages are those termed Fine Pitch BGAs. The heat dissipation in such compact packages can occur, for example, by adapting the thermal ambient conditions, i.e. by a suitable construction of the printed circuit board. Heat dissipation can occur in specially constructed carrier substrates: for example, carrier substrates having an increased number of thermal apertures under the semiconductor chip. Finally, enlarging can prevent thermal problems. 
   SUMMARY OF THE INVENTION 
   It is accordingly an object of the invention to provide an electronic component and a method for producing the electronic component that overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and that avoids the disadvantages of the prior art and provide an electronic device with at least one semiconductor chip, the device having a very compact package and adequate cooling. 
   With the foregoing and other objects in view, there is provided, in accordance with the invention, an electronic component. The electronic component includes a semiconductor chip, a wiring board, a package, and a cooling element. The semiconductor chip has an active front side with semiconductor structures and a passive rear side without semiconductor structures. The wiring board has a first side attached to the semiconductor chip and has interconnect structures at least on a second side facing away from the semiconductor chip. The package completely encloses the first side of the wiring board. The cooling element is integrated into the package. 
   In other words, an electronic component has at least one semiconductor chip with an active front side with semiconductor structures and a passive rear side without semiconductor structures. The active front side or the passive rear side attaches onto a first side of a wiring board or a leadframe. The wiring board or leadframe includes interconnect structures at least on a second side, opposing the semiconductor chip. Moreover, a package encloses the first side of the wiring board, with the semiconductor chip located on it. According to the invention, the package includes a cooling element, which is an integral part of the package. 
   Integrally connecting the cooling element to the package allows the electronic component to be shrunk because power loss occurring during operation can be effectively dissipated. Not fitting the cooling element on the wiring board frees additional surface area for establishing bonding connections. A further advantage is the consequently obtained flexibility in the construction of the electronic component. If, for example, it is found during the development process of the semiconductor chip that the power losses arising during operation are less than originally calculated, it is readily possible simply to dispense with the cooling element and produce the component package without such a cooling element. This means that the construction of the carrier substrate or wiring board or leadframe does not have to be changed. 
   It is also advantageous that already existing processing processes scarcely have to be changed because the invention can be used with minimal modifications on many existing package assembly lines. With the aid of the cooling elements, the electronic components can consequently be produced with smaller packages of a thermal resistance that could otherwise only be achieved with larger packages. 
   In one embodiment of the invention, the cooling element is formed as a metal plate. The high thermal conductivity of the metal increases heat dissipation. If appropriate, the metal plate may be provided with further passive or active cooling devices that could be connected to the cooling element with heat conducting paste. A further advantage of the cooling device including a metal plate is its shielding property. The shielding property protects the cooling element from disturbing electromagnetic influences. 
   A further embodiment provides that the cooling element covers at least the entire upper surface area of the package. In this embodiment, the cooling element has particularly good shielding properties. Moreover, the embodiment optimizes dissipation of power loss in the form of heat. 
   In the case of one embodiment according to the invention, the cooling element has clearances, in which the package engages. This ensures a firm and unreleasable connection between the cooling element and the package. Moreover, this connection provides a good heat transfer contact between the package and the cooling element. 
   In accordance with a further embodiment, the clearances have a funnel-shaped cross-section, with the funnel becoming wider toward the top. The clearances preferably have an angular or round contour. Such a formation makes close and unreleasable interlocking possible between the package and the cooling element, which moreover can be produced relatively easily and consequently at low cost. 
   In an embodiment of the invention, the clearances have a diameter ranging from three to fifteen percent (3–15%) of a side length of the cooling element. Such a clearance creates a good ratio between the optimum mechanical connection and the most effective possible heat dissipation. With clearances that are too small, there would be the risk of a connection between the package and the cooling element that is too weak. With clearances that are too large, the heat-dissipating capability is reduced from the lower effective cooling area. 
   One embodiment of the invention provides that the clearances are etched. This allows even the smallest clearances to be produced in almost any desired contour in a very exact way. Etching also has the advantage that even large batches of cooling elements that are later divided can be provided with clearances in one operation. 
   An alternative embodiment of the invention provides that the clearances are made by laser drilling or by punching, whereby very exact and dimensionally accurate clearances can be produced. Laser drilling is particularly suitable for smaller batches, whereas punching is also suitable for very large numbers of units at very high throughput rates. 
   In the case of one embodiment according to the invention, the clearances create a form-locking connection to the package in the form of a dovetail connection, which provides a very stable connection between the cooling element and the package. A form-locking connection is one that connects two elements together due to the shape of the elements themselves, as opposed to a force-locking connection, which locks the elements together by force external to the elements. 
   According to one embodiment of the invention, the package is formed from a plastic. The insulating properties of plastics are particularly well suited for enclosing the semiconductor chip. Moreover, plastics can be processed very easily by the injection-molding process. The cooling element can be encapsulated with the plastic in one operation without significant problems. 
   In an embodiment of the invention, the cooling element has a matrix structure. Each semiconductor chip is covered by one surface-area portion. Separating joints subdivide neighboring surface-area portions. In this way, a common cooling element can be used to cover even relatively large surface areas of a number of electronic components, which, if appropriate, are then subsequently separated individually. In this case, the sawing track regions for dividing the subassemblies run along the separating joints of the cooling element. This matrix structure permits particularly efficient and low-cost production. 
   With the objects of the invention in view, there is also provided a method for producing an electronic component. The first step of the method is providing a wiring board. The next step is applying semiconductor chips to the wiring board. The next step is bonding the semiconductor chips to the wiring board. The next step is applying a package to the semiconductor chip and the wiring board. The next step is integrally connecting a cooling element to the package. 
   In other words, the method according to the invention for producing an electronic component according to one of the embodiments described above can have at least the following method steps. Semiconductor chips are applied to a wiring board or a leadframe and connected to the latter and soldering or bonding connections are subsequently established between the semiconductor chips and the wiring board. After that, a package and a cooling element connected to it are applied to the semiconductor chip and the wiring board, the cooling element being integrally connected to the package. 
   This method according to the invention for producing the electronic component makes it possible to provide an integrated cooling element in a particular simple and low-cost way, allowing particularly compact forms of the package to be realized. 
   One embodiment of the method according to the invention provides that a number of semiconductor chips are applied to a wiring board. In this way, relatively large components can be provided in one operation with a cooling element, which in this case expediently has a matrix structure. 
   In the case of one embodiment according to the invention, the wiring board is separated into individual electronic components after the package and the cooling elements have been applied. This makes it possible for relatively large matrix units to be initially produced and then subsequently separated individually into smaller electronic components. 
   According to one embodiment of the invention, the package is produced from plastic by transfer molding. The cooling element is attached to an upper mold part or a lower mold part of a mold and separated from the latter after the molding process. The method makes allows an integrated package with a cooling element to be produced easily and quickly. The cooling element is in this case placed into the mold and can, if appropriate, rest loosely in the upper or lower part of the package. An advantageous variant may be that of keeping the cooling element in its place by vacuum suction devices. These include suction lines in the upper or lower part of the package, against which the cooling element lies with an intermediate film layer, which serves for sealing. 
   One embodiment of the method according to the invention provides that sawing track regions on the wiring board are disposed congruently with separating joints in the cooling element. In this way, during the individual separation it is not necessary to cut through the cooling element but only through narrow webs. 
   A further alternative embodiment of the method according to the invention provides that the cooling element has a frame, which is connected to cooling areas by thin webs, is placed in the mold and is clamped between the upper mold part and lower mold part. Thereby, further fixings of the cooling element in the mold can be dispensed. Examples of further fixings include self-adhesive films, attachment by vacuum suction, or the like. The surrounding frame can either remain on the electronic component and be used for further mechanical handling, or else it may be advantageous to cut off the frame together with its thin webs from the cooling element after removal from the mold, in order to keep the package as compact as possible. 
   Other features which are considered as characteristic for the invention are set forth in the appended claims. 
   Although the invention is illustrated and described herein as embodied in an electronic component and a method for producing the electronic component, it is nevertheless not intended to be limited to the details shown, since 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. 
   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 
       FIG. 1  is a diagrammatic sectional view showing an electronic component with a cooling element according to the invention; 
       FIG. 2  is a sectional view showing a variant of the electronic component according  FIG. 1 ; 
       FIG. 3  is a plan view of a cooling element in matrix form; 
       FIG. 4  is a sectional view showing a mold with placed-in components for producing an electronic component; 
       FIG. 5  is a sectional view showing an alternative variant of the mold according to  FIG. 4 ; 
       FIG. 6  is a sectional view showing a further alternative variant of the mold according to  FIGS. 4 and 5 ; and 
       FIG. 7  is a plan view showing the cooling element according to  FIG. 6 . 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring now to the figures of the drawings in detail and first, particularly to  FIG. 1  thereof, there is shown an electronic component according to the invention, which is provided with a cooling element  20 . A wiring board  4 , which is provided on its first side (upper side)  5  with a multiplicity of contact terminal areas  12 , can be seen. Soldering connections  14  mount a semiconductor chip  2  on the contact terminal areas  12 . If appropriate, the semiconductor chip  2  also may be connected to the wiring board  4  by bonding connections not shown here. The contact terminal areas  12  on the first side  5  of the wiring board  4  are respectively connected to contact areas  8  on a second side  6  (underside), on which a contact bump, for example in the form of a solder ball or the like, is located in each case. These solder balls are suitable for making possible what is known as flip-chip mounting of the electronic component. 
   The soldering connections  14  between the electrical terminals of the active side of the semiconductor chip  2  and the contact terminal areas  12  of the wiring board  4  are enclosed by an insulating layer  16 , which may for example include a layer of insulating plastic. The first side  5  of the wiring board  4  and the entire semiconductor chip  2  are surrounded by a package  18 , which preferably includes a plastic. The plastic is applied by an injection-molding process (known as transfer molding). The package  18  covers the semiconductor chip  2  and is in turn covered on its upper surface area by a cooling element  20  in the form of a metal plate. The cooling element  20  forms a form-locking connection with the package  18  by engaging pins  24  in clearances  22 , and is consequently an integral part of the package  18 . 
   As can be seen from  FIGS. 1 and 2 , the clearances  22  are formed in the represented cross section in a funnel-shaped manner, the funnel becoming wider toward the top, i.e. away from the package. The pins  24 , which are formed during the injection-molding process of the package  18 , engage in the clearances  22  and form with the latter in each case a kind of dovetail connection. The cooling element  20  consequently rests flat on the package  18 . As a result, the cooling element  20  dissipates the heat produced by power losses during the operation of the semiconductor chip  2  of the electronic component. 
     FIG. 2  shows in a schematic cross-sectional representation a variant of the electronic component according to  FIG. 1 . The same parts as in  FIG. 1  are provided with the same reference numerals and are not explained again. In this embodiment, the cooling element  20  is made somewhat thicker in the central portion of its surface area, so that it reaches almost as far as the semiconductor chip  2  and is not separated from the latter by the upper surface area of the package  18  of plastic. Rather, between the cooling element  20  and the passive rear side of the semiconductor chip  2  there is a connecting layer  21 , which provides an adhesive bond and best possible heat transfer between the semiconductor chip  2  and the cooling element  20 . The remaining details of this embodiment that can be seen correspond to the representation according to  FIG. 1 . 
     FIG. 3  shows in a schematic plan view a cooling element  20  by way of example, which has a number of surface-area portions  27 , which are in each case separated by separating joints  26  in the form of elongate apertures. In the exemplary embodiment shown, two surface-area portions  27  are in each case disposed in pairs next to one another and are separated by separating joints  26 . Any number of pairs of surface-area portions  27  may be disposed next to one another in the length. Each surface-area portion  27  is provided for forming a cooling element  20  for a semiconductor chip  2 . The cooling element  20  constructed in the form of a matrix can be individually separated after mounting on the semiconductor chip  2  together with the wiring board. The separating joints  26  in this case expediently lie congruently over the sawing track regions of the carrier substrate. It is similarly possible, however, to mount a matrix of cooling elements  20  on a number of semiconductor chips  2 , which form a common electronic component. 
   The clearances  22  are disposed in each case in the form of a four-cornered ring on a surface-area portion  27 , with five clearances  22  respectively lying on each side of a surface-area portion  27 . In the exemplary embodiment represented, the clearances  22  are made square in each case. However, round or oval contours or contours of some other shape are also similarly possible. The clearances  22  expediently have a diameter that corresponds approximately to three to fifteen percent (3%–15%) of a side length of a surface-area portion  27 . In this way, they are large enough to provide, with the pins  24  engaging in them, a secure connection to the package  18 . On the other hand, they are small enough to leave sufficient cooling area of the cooling element  20  and not to impair the heat-dissipating properties of the latter. 
   The clearances  22  may be etched, punched, formed by laser drilling, or formed in some other suitable way. Etching has the advantage that very exact holes with precisely the desired funnel angles can be formed even in the case of relatively large batches. 
     FIGS. 4 to 6  respectively show in schematic cross-sectional representations a mold  32  with placed-in components for producing an electronic component according to the invention. In this case, a wiring board  4  with semiconductor chips  2  mounted on it is respectively placed on the lower mold part  36  ( FIGS. 4 and 6 ) or on the upper mold part  34  ( FIG. 5 ) of a mold  32  and is firmly clamped between the upper mold part  34  and lower mold part  36 . 
   In the exemplary embodiment according to  FIG. 4 , an adhesive film  38  is attached to the upper mold part  34 , formed in a hollow-shaped manner, and the cooling element  20  is attached on the film. The thin adhesive film  38  is preferably formed as a single-sided adhesive film. The adhesive film  38  can be easily removed again from the upper side of the cooling element  20  after the injection-molding process. In the upper mold part  34 , there can be seen a number of apertures  40 . The apertures  40  are provided for the attachment by vacuum suction of the optionally single-sided adhesive film  38 . In this way, the film  38  with the cooling element  20  adhesively bonded to it can be reliably held at its intended position while the liquid plastic is injected into the mold  32 . After removal from the mold, an electronic component with a cooling element  20  integrally connected to the package  18  is obtained. 
     FIG. 5  shows an alternative variant of the mold  32 , in which not only the wiring board  4  but also the film  38  is clamped between the lower mold part  36  and upper mold part  34 . The film  38  in this case covers the entire curvature of the lower mold part  36  formed in a hollow-shaped manner. In this embodiment, the upper mold part  34  is formed in a planar manner. The cooling element  20  is applied to the planar surface-area portion of the lower mold part  36  and held by the film  38 . 
     FIG. 6  is a further embodiment of the mold  32  with the wiring board  4  placed in it and semiconductor chips  2  mounted on the wiring board. In this case, the wiring board  4 , the film  38 , and the cooling element  20  are clamped between the upper mold part  34  and lower mold part  36  of the mold  32 . As in the embodiment according to  FIG. 4 , it is also the case in this embodiment according to  FIG. 6  that the lower mold part  36  with the wiring board  4  resting on it is made planar and the lower mold part with the film  38  adhesively bonded to it is made curved. 
   As can best be seen from the plan view of  FIG. 7 , an alternative embodiment of the cooling element  20  has a peripheral edge  28  that is connected to the surface-area portions  27  via a number of webs  30 . In the exemplary embodiment shown, four surface-area portions  27  are respectively grouped together as a square and respectively separated from one another by separating joints  26 . Respectively provided at each corner of this matrix of four, there is a web  30 . The web leads to the frame  28  at an angle of about forty-five degrees (45°) in relation to the side edge of the matrix. The frame  28  is respectively kept at a constant distance from the matrix of four of the surface-area portions  27 . 
   The edge  28  serves for the clamping between the upper mold part  34  and lower mold part  36 , as can be seen in  FIG. 7 . The webs  30  represent the connection to the actual cooling element  20  and are partly encapsulated by the plastic. As can be seen from  FIG. 6 , the webs  30  follow the curved contour of the upper mold part  34 , so that the cooling element  20  according to  FIG. 7  has altogether a roof-like contour. The frame  28  in this case forms the base area; the webs  30  lead obliquely upward, so that the surface-area portions  27  attached to them form an elevated surface area with respect to the frame  28 . For example, this contour may be formed by punching and thermoforming. 
   In the embodiment of  FIG. 7 , the matrix of four of the surface-area portions  27  is adjoined by a further matrix of four, which is attached to the common frame  28 . This relatively large cooling element  20  can either be connected to a package  18  of an electronic component in a single processing step or be separated in advance into individual parts. However, the separation may also take place after the encapsulation of relatively large subassemblies of electronic components, which are subsequently and individually separated. In this case, the separating joints  26  expediently come to lie over sawing track regions between neighboring electronic components.