The present disclosure relates to electronics. Various embodiments include circuit carriers having an installation place for an electronic component, electronic circuits having such a circuit carrier, methods for producing a circuit carrier in which an installation place for an electronic component is produced, and/or methods for producing an electronic assembly in which such a circuit carrier is used.
Circuit carriers and electronic circuits are used in many products. In particular, power electronic circuits are, for example, used in rectifiers and converters. For making good thermal and electrical contact with power semiconductors in such power electronic circuits, care must be taken that their function is provided unrestrictedly. The good thermal and electrical properties with, at the same time, a low overall height must be ensured by the contact structure. In the event of a reduction in the overall height, however, the use of an insulating medium, primarily around the outer sides of the power component, is additionally required.
In particular in the case of making planar chip-top-side contacts of power semiconductors, these regions of the chip edges and the adjacent passivated power regions on the chip have to be filled with the insulating medium. For satisfactory insulation, it is necessary that this filling is carried out without bubbles. However, this represents a technical demand. The insulating material, which is also designated as an underfill material, must ensure that during the filling, gassing out from the joining zone to the outside takes place and no bubbles form in the underfill material. In particular in sintered joining zones, which are highly suitable for a thermal structure, gassing out during the filling frequently leads to bubbles. The following underfill materials, for example, are used as filling materials: epoxy resins optimized for underflow, with and without fillers.
The teachings of the present disclosure describe circuit carriers having an installation place for electronic components and an electronic circuit having such a circuit carrier in which the possibility of bubble-free filling with an underfill material is improved, methods for producing such a circuit carrier, and/or methods for producing such an electronic assembly. Bubble-free filling with underfill material is supported. For example, some embodiments include a circuit carrier (12) having an installation place (14) for an electronic component (13), characterized in that the installation place (14) has at its edge at least one recess (22) which forms a depression in the surface (27) of the circuit carrier (12), and in that a deposit (16) of a joining adjuvant is applied to the installation place (14), wherein the deposit (16) consists of a sintered material and a protuberance (23) is provided at the edge of the deposit (16).
In some embodiments, the recess (22) consists of a slot, which extends at right angles to the edge of the installation place (14).
In some embodiments, the depression is provided in an insulating layer (15) forming the surface (27) of the circuit carrier (12) and/or in a metallization (26) on the circuit carrier (12).
In some embodiments, the protuberance (23) has the form of a wedge which projects from the edge of the deposit (16).
In some embodiments, the width of the wedge corresponds exactly to the height of the deposit (16).
In some embodiments, an electronic circuit (11) having a circuit carrier (12) as described above and an electronic component (13), characterized in that the electronic component (13) is fixed to the deposit of the joining adjuvant.
In some embodiments, a gap between the circuit carrier (12) and the component (13) is filled with an underfill material (19).
As another example, some embodiments include a method for producing a circuit carrier (12), in which an installation place (14) for an electronic component (13) is produced, characterized in that at least one recess (22) is produced at the edge of the installation place (14), said recess being formed as a depression in the surface (27) of the circuit carrier (12), or surface structuring is produced.
In some embodiments, the recess (22) is produced by a material-removing method.
In some embodiments, the recess (22) or surface structuring is produced by structuring a layer on the circuit carrier (12).
In some embodiments, a deposit (16) of a joining adjuvant is applied on or to the installation place (14).
As another example, some embodiments include a method for producing an electronic assembly, characterized in that a circuit carrier (12) is produced by a method as claimed in claim 11, an electronic component (13) is fixed to the deposit (16), and a gap (18) between the circuit carrier (12) and the component (13) is filled with an underfill material (19).
In some embodiments, the underfill material (19) is introduced into the gap (18) in a region outside the at least one recess (22), e.g. exactly in the center between two recesses (22).
The exemplary embodiments explained below are embodiments of the teachings herein and do not limit the scope of those teachings. In the exemplary embodiments, the components of the embodiments that are described each represent individual features to be considered independently of one another, which each also develop the disclosure independently of one another and are therefore also to be viewed as a potential constituent part, individually or in a combination other than that shown. Furthermore, the embodiments described can also be supplemented by further features that have already been described.
In some embodiments, a circuit carrier includes an installation place which has at its edge at least one recess or surface structuring which forms a depression in the surface of the circuit carrier. Surface structuring is understood as an adaptation of the surface to the extent that this is used as a flow obstacle for the underfill material. This can be achieved, for example, by the surface being roughened, for example with a laser. The fact that the surface structuring provides a different surface means that this constitutes a flow obstacle for the underfill material. In some embodiments, this is achieved by a more difficult wettability of the structured surface as compared with the remainder of the surface of the circuit carrier or the layers located thereon. In the following text, the advantages of the teachings herein will each be explained by using the recesses. However, this is of course analogously true also when the surface structuring is used.
The introduction of a recess which is formed as a depression, allows, when filling the gap between the component and the circuit carrier that the recess remains free from underfill material for longer than the remainder of the gap between the component and the circuit carrier. In this way, there is the possibility that outgassings during the filling escape from this joining gap (gap for short below) through the depression, while the underfill material propagates in the gap. In the process, the underfill material forms a flow front. The recess is arranged at the edge of the installation place in such a way that the flow front can flow toward this gap. Therefore, the recess is only closed by the underfill material at the end, so that the recess is able to transport the outgassings to the outside until the end. The formation of bubbles may therefore be avoided.
The edge of the installation place is defined by the outer edge of the component to be installed. In other words, during the design of the installation place on the circuit carrier, it is necessary to take into account the dimensions of the component which is to be mounted. The recess then has to be provided in the circuit carrier in the region of the imaginary outer edge of the component. For example, this can be done in such a way that part of the recess lies within the installation place and part of the recess lies outside the installation place. In this way, a type of channel or “tunnel” for the outgassings is produced, while the underfill material is distributed in the gap.
In the interests of direct thermal conduction and a low overall height, the gap may be chosen to be as narrow as possible. In particular when a sintered material is used as a contact-making material, very narrow gaps can be implemented. In conventional contact deposits made of sintered material, this gap can lie, for example, in a range from 20 μm to 100 μm.
The installation places are normally rectangular or square in their basic shape, e.g., also U-shaped. In some embodiments, the recesses are arranged at the edge of the old installation place in such a way that these are located in the center between the corners of the installation place. Underfilling of the gap can then be carried out starting from the corners, so that the flow fronts move from the corners of the installation place toward the recesses and fill the recesses at the end. If, here, the flow front should reach the recess more quickly from one corner than from the other corner, the recess represents a flow obstacle, since the underfill material must overcome a resistance in order to overcome the edge of the recess, that is to say the edge of the depression forming the recess. In this way, the recess remains open for outgassing for a longer time and closes only when the flow fronts of the underfill material meet at the recess from opposite directions. The result is to achieve a bubble-free or at least largely bubble-free underfilling result.
Of course, it is also possible to provide the recesses in the corners. In this case, the filler may flow from the center of the one installation place toward the corners, if these enclose the center of the one installation place.
In some embodiments, the recess consists of a slot or a circular opening, which extends at right angles to the edge of the installation place.
In some embodiments, the recess at the edge of the installation place extends through the imaginary edge of the assembly, so that the recess can transport outgassings from the installation place to the outside. A slot which extends at right angles to the edge of the installation place can be located on the other side and this side of the edge of the installation place and therefore fulfills this object particularly well. In addition, such a slot can be produced simply, for example by micro-milling or laser machining. In some embodiments, a subtractive etching process, for example by means of photolithographic structuring, is also conceivable as a fabrication method.
In some embodiments, the depression may be provided in an insulating layer forming the surface of the circuit carrier, in particular consisting of a solder stop varnish, and/or in a metallization on the circuit carrier. If the depression, for example the slot, is produced in the surface of the circuit carrier, all the layers of the layer structure of the circuit carrier are available for its formation. The insulating layer is normally brought up to the installation place and ends at a specific distance from the installation place, in order that the latter can be reliably kept free of insulating material. If this layer consists of a solder stop varnish, for example, this is usually developed photochemically. Here, the recesses can be taken into account from the start and formed in situ with the solder stop layer with the production.
In some embodiments, the metallization on the circuit carrier is used for the production of the recess. The metallization is also applied to the circuit carrier as a layer and is structured to form contact pads and conductor tracks. During this structuring process (for example by etching technology), the depression can be produced in situ during the processing. Of course, it is also possible to provide other fabrication methods for the recess. Both in the insulating layer and in the metallization, the recesses can be formed, for example, by means of micro-milling or laser machining. These methods have the advantage of very high accuracy, so that the recesses can be produced precisely. In particular, the sharp edges of the depression which are required to stop the flow front of the underfill material can be produced excellently by these methods. In addition, it is possible also to produce recesses which reach down into the material of the circuit carrier by means of milling or laser machining. Deeper recesses have the advantage that outgassings can be transported still more reliably to the outside.
In some embodiments, a deposit of a joining adjuvant, in particular of a sintered material, may be applied to the installation place. If the joining adjuvant is already provided on the circuit carrier, this makes the mounting of the component easier. For mounting purposes, the circuit carrier is usually already provided with joining adjuvant. Here, this can be solder material which, for example, is applied as a paste by means of mask technology. If printing errors which lead to filling of the recesses occur during this process, this can be determined optically before the mounting of the components, so that a rejection or a correction of this error can be carried out in good time.
The deposit can also consist of a sintered material. This can likewise be printed from sintering paste. Here, that specified above relative to the application of solder material applies accordingly. In some embodiments, preforms (protuberances) can also be used, which can advantageously be produced particularly precisely. These are fixed in the installation place or laid on directly before the mounting of the component.
In some embodiments, the deposit may consist of sintered material, a protuberance being provided at the edge of the deposit. If the deposit consists of a sintered material, it is possible to provide protuberances which have a comparatively fine geometry. This is because the sintered deposits substantially maintain their shape during the joining (if shrinkage is disregarded), so that these fine structures are maintained. This is different in the case of solder materials, which are melted to produce the connection. Here, fine protuberances would be lost because of the surface tension of the liquid solder material.
In some embodiments, the protuberances support the outward conduction of outgassing during the filling of the gap with underfill material. Here, the protuberances are given the task of directing the underfill material in a specific direction when the latter arrives with its flow front at the protuberance, so that, for example, it is possible to prevent said underfill material from getting into regions in which bubbles can be enclosed. In some embodiments, the protuberances can also be used in such a way that the flow front is directed toward a flow obstacle such as a recess in the shape of a depression (more on this below). The recesses, which provide an edge of the depression as a flow obstacle, then lead to the flow front being stopped until the recess is also filled with underfill material at the end. Until then, the recess can be used as a channel for transporting outgassings.
However, even without the additional action of the recesses, by diverting the flow fronts or stopping the flow fronts, the protuberances can prevent underfill material which, for example, fills the gap from different corners of an installation place, from flowing together too early, and thus would prevent outgassing with the consequence of bubble formation.
If square or rectangular installation places are assumed, the protuberances can be arranged in the center between two corners in each case. This means that the likewise rectangular deposit of sintered material is likewise rectangular or square and each has the protuberance in the center between the corners.
In the sense of the disclosure, a protuberance is to be understood as a structure which projects from the edge of the deposit of sintered material and thus forms an obstacle which stops or deflects an underfill material flowing along the deposit.
In some embodiments, the protuberance has the form of a wedge which projects from the edge of the deposit. A wedge-shaped protuberance is arranged such that the wedge, so to speak, lies on its triangular surface. In other words, the wedge-shaped protuberance can be imagined as a prism with a triangular base, wherein this prism adjoins the deposit with one of its side surfaces.
In some embodiments, the width of the wedge may correspond exactly to the height of the deposit.
In some embodiments, the wedge fills the gap over its entire gap height. Since the gap width is given by the height of the sintered deposit, however, this is the case only when the width of the wedge corresponds exactly to the height of the deposit. In this way, the deflecting function of the protuberance may be used most effectively. In addition, such a protuberance which corresponds to the height of the sintered deposit can be produced most simply. Here, use is made of a mask which has a mask opening containing the protuberance, wherein the filling of this mask opening, besides the deposit of sintered material, simultaneously produces the protuberance at the same height.
Of course, the protuberance can also have geometries other than that of a wedge. These can, for example, also be cube-shaped, wherein the cube, so to speak, adjoins the side of the deposit of sintering paste. Here, too, the cube may have the same height as the deposit. In some embodiments, the protuberance having the shape of a half-cylinder, which adjoins the deposit of sintering paste with its flat side surface. Here, too, the height of this half-cylinder may correspond to the height of the deposit.
In some embodiments, the circuit carrier is formed as described above, wherein the electronic component is fixed to the deposit of the joining adjuvant.
The electronic circuit is an implementation in which the circuit carrier which has already been explained thoroughly above is used for the end product. If such an electronic assembly is underfilled with underfill material, bubble-free underfilling results can be achieved as a result, by which means the above object is achieved. The bubble-free underfill material may improve both the thermal conduction and also the electrical insulation in the electronic assembly.
In some embodiments, a gap between the circuit carrier and the component may be filled with an underfill material.
In some embodiments, at least one recess is produced at the edge of the installation place, said recess being formed as a depression in the surface of the circuit carrier. If a recess is produced, then the product produced, namely the circuit carrier, can be used to produce the electronic assembly explained above. The advantages associated herewith have already been recited and are not to be mentioned again at this point.
In some embodiments, the recess may be produced by a material-removing method, in particular by milling or drilling. As already explained, material-removing methods such as, for example, micro-milling or drilling permit particularly high accuracies. In particular, the necessary edges which form the edge of the depression can be formed with sharp edges in the recesses.
During milling, elongated recesses can be produced. Depending on whether the axis of rotation of the milling head is at right angles or parallel to the surface of the circuit carrier, the elongated recesses can have a sharp edge all round or a tapering edge at their ends. The tapering edge at the end of the recesses can be used as a flow aid in order that the recess is still filled with underfill material at the end of the underfilling process.
In some embodiments, the recess may be produced by structuring a layer, in particular by structuring an insulating layer on the circuit carrier. As already mentioned, it is also possible to produce recesses by structuring the layer. This fabrication method lies in the fact that the structuring must be carried out anyway and here no additional fabrication outlay arises for the formation of the recesses.
In some embodiments, a deposit of a joining adjuvant may be applied on or to the installation place. As already mentioned, the deposits of the joining adjuvant, in particular the sintered material, can be applied to the circuit carrier before the mounting of the electronic components. The quality of this intermediate result (before the mounting of the deposit) can then be assessed before final mounting is carried out.
In some embodiments, a circuit carrier is produced by a method as described above, wherein:
The details of the mounting method for the electronic assembly have already been explained thoroughly. In some embodiments, it is necessary to apply the deposits (possibly provided with additional protuberances) to the circuit carrier, wherein the electronic components are placed on the latter for the purpose of final mounting. The gap is then filled with the underfill material wherein, as already explained, a bubble-free underfilling result can be achieved.
In some embodiments, the underfill material may be introduced into the gap in a region outside the at least one recess, preferably exactly in the center between two recesses.
The underfill material may expand uniformly toward both sides when it is introduced in the center between two recesses. Should this not be the case, the recesses serve as a flow obstacle in order to eliminate these non-uniformities. Therefore, reliable gassing-out is easily possible. If, as already mentioned, a square or rectangular installation place is provided and the recesses are provided in the center of the side edges, then the center between the recesses is normally located in the corners (in the case of square installation places or close to the corners even in rectangular installation places).
Further details of the teachings herein will be described below by using the drawings. The same or mutually corresponding drawing elements are each provided with the same designations and will be explained repeatedly only to the extent to which differences between the individual figures result.
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If the gap 18 is filled with the solder material, then both the recess 22 and the protuberance 23 both act in their way to conduct the underfill material 19. The latter flows in each case from the corners of the component 13 (these are each located in front of and behind the sectional plane according to
This flow direction lies at right angles to the plane of the drawing. By means of the protuberance 23, this flow is then diverted to the right in the illustration according to
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11 Electronic circuit
12 Circuit carrier
13 Electronic components
14 Installation places
15 Insulating layer
16 Deposit
17 Sintered connection
18 Gap
19 Underfill material
20 Top plate
21 Further sintered connection
22 Recesses
23 Protuberances
24 Bubbles
25 Contact structures
26 Metallization
27 Surface
28 Mask openings
29 Indentations
Number | Date | Country | Kind |
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18192039.8 | Aug 2018 | EP | regional |
This application is a U.S. National Stage Application of International Application No. PCT/EP2019/072203 filed Aug. 20, 2019, which designates the United States of America, and claims priority to EP Application No. 18192039.8 filed Aug. 31, 2018, the contents of which are hereby incorporated by reference in their entirety.
Filing Document | Filing Date | Country | Kind |
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PCT/EP2019/072203 | 8/20/2019 | WO | 00 |