Patent Publication Number: US-2021168943-A1

Title: Method for manufacturing a conductor structural element and conductor structural element

Description:
TECHNICAL SUBJECT AREA 
     The present invention relates to a method for manufacturing a conductor structural element and to a conductor structural element. 
     DESCRIPTION OF THE PRIOR ART 
     Various component mounting techniques are known from the prior art, which are also suitable for structures with embedded components/power semiconductors. The mounted components are embedded in a dielectric layer (prepreg layer). Such a method is known, for example, from WO 2011/079918 A2, which discloses a conductor structural element in which a component is inserted into a dielectric layer and connected to a conductor pattern structure, which is essentially flush with the surface. To make contact with the component, bump-type elements or copper pillars which protrude from the copper layer are provided, as is also known from DE 696 35 603 T2, for example. 
     DE 10 2016 206 607 A1 discloses electronic components with contacting elements designed as copper pillars. 
     SUMMARY OF THE INVENTION 
     Based on the above, according to the invention a method for manufacturing a conductor structural element having the features as disclosed herein is proposed, as well as a conductor structural element having the features as disclosed herein. 
     The basic idea of the invention is to provide a mounting area which is formed as a left out space or recess on an electrically conductive base layer of a conductor structural element. The left out space is achieved by applying, in particular by electroplating, an electrically conductive layer which defines a recess, the shape, size and arrangement of which is chosen in such a way that it can accommodate at least one corresponding contacting element of an electronic component to be mounted. The application of the electrically conductive layer is implemented, for example, as mentioned above, by electroplating/galvanic deposition, but can also be implemented by other application processes, such as e.g. 3D printing or other processes familiar to the person skilled in the art. 
     Further advantages and embodiments of the invention are described in the the description and the enclosed drawing. 
     It goes without saying that the aforementioned features and those yet to be explained below can be applied not only in the corresponding specified combination, but also in other combinations or in isolation without departing from the scope of the present invention. 
     The invention is shown in the drawing highly schematically (and not true to scale) by reference to an exemplary embodiment and is described in detail in the following text with reference to the drawing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a plan view of an embodiment of a mounting area according to the invention. 
         FIG. 2  shows a plan view of a further embodiment of a mounting area according to the invention. 
         FIG. 3  shows the mounting area of  FIG. 2  with a registration mark which is also applied thereon. 
         FIGS. 4 to 8  illustrate a sequence of a method according to the invention. 
         FIG. 9  shows a plan view of the mounting area produced according to the invention according to the viewing direction IX of  FIG. 8 . 
         FIGS. 10 to 12  show further method steps according to the invention. 
         FIG. 13  shows a view from the mounting side of a conductor structural element according to the invention directly before the mounting of an electronic component. 
     
    
    
     DETAILED DESCRIPTION 
     Identical and similar features represented in the individual figures are indicated by the same reference signs. 
       FIG. 1  shows an example of an electrically conductive layer  13  (e.g. a copper layer) applied to an electrically conductive base layer  12 , e.g. a copper film, according to the invention. The electrically conductive layer  13  can be produced, for example, by electroplating. In the electrically conductive layer  13  there is a mounting structure  14 . The mounting structure  14  comprises, in particular, a mounting area  16  formed by leaving out a space in the electrically conductive layer  13 . The left out space can be circular, for example, as shown in the embodiment of  FIG. 1 . The left out space can in principle have any shape, and it falls within the skilled person&#39;s knowledge to determine a suitable shape. A circular left out space is recommended in order to make the component mounting process as simple as possible. 
     The term plating is to be understood as the application of metal layers, in particular copper layers (copper plating), to a base layer or an existing layer structure, as is commonly known in circuit board technology. In particular, within the scope of the present invention, this includes the application of metallic pattern structures (referred to in the industry as pattern plating). 
     The mounting structure  14  can also comprise a conductor track  18 , as shown, which is also formed in the plated-on layer  13 . The conductor track  18  is conductively connected to a section  15  of the mounting structure  14 . The section  15  surrounds the mounting area  16  and defines it. In the exemplary embodiment shown, the section  15  is formed as a circular ring which is connected integrally to the conductor track  18  and is widened compared to the latter (i.e. an outer diameter D of the circular ring  15  is greater than a width b of the conductor track  18 ). In the exemplary embodiment shown, an internal diameter d of the circular ring  15  (corresponding to the diameter of the mounting area  16 ) is also larger than the width b of the conductor track  18 . The section  15  may have any other desired shape. 
       FIG. 2  shows a further exemplary embodiment of a mounting structure  14  produced according to the invention by plating onto an electrically conductive base layer  12 , for example a copper film. In this exemplary embodiment, the left out mounting area  16  is formed as a circular recess in the conductor track  18 . This means that the diameter d of the mounting area  16  is approximately equal to or less than the width b of the conductor track  18 . Alternatively (not shown), the diameter of the mounting area can also be slightly larger than the width of the conductor track (in which case it is no longer a single-piece structure, but two separate regions). 
       FIG. 3  shows the exemplary embodiment of  FIG. 2  with a registration mark  20  which is additionally plated onto the base layer  12 . The registration mark  20  can be designed as a circular disc, as shown. However, it can also have other suitable shapes. The placement of the registration mark  20  can be positionally defined in relation to the mounting area  16 . The application of a registration mark  20  is of course not limited to the exemplary embodiment of  FIG. 2 , but can also be provided in the exemplary embodiment of  FIG. 1  and in any other possible design. The registration mark  20  is used by a placement robot in a known manner to align the intended placement of the mounting area  16  to the registration mark  20 . 
     By reference to the following figures the method for manufacturing a conductor structural element according to the invention will now be described. 
     Firstly, an electrically conductive base layer  12 , in particular a copper layer/copper film, is provided, onto which an electrically conductive structured layer  13 , in particular of copper, is applied by means of pattern plating or other suitable application methods. The layer  13  applied in this way is designed such that it forms a left out or recessed mounting area  16 . As illustrated in  FIGS. 1 to 3 , the structured layer  13  can also comprise a conductor track  18  or at least a conductor track section, by means of which a section  15  of the electrically conductive layer  13  at least partially surrounding the mounting area  16  (for the case in which a diameter of the mounting area  16  is larger than the width of the conductor track) and defining the same, is contacted (see also  FIG. 6 ). 
     In addition, at least one electronic component  40  is provided. The electronic component can be, for example, a power semiconductor, a logic chip, an ASIC, etc. The electronic component  40  comprises a component body  42 , on which contacting elements  44  are provided (see  FIG. 4 ). The contacting elements can be constructed in particular as copper columns or copper bumps (known to the person skilled in the art by the term “copper pillar”). Other contacting means, such as e.g. solder coatings at the end of the copper pillars, are of course also possible. Solder in the context of the invention can mean classical solders based on Sn alloys, but also so-called diffusion solders (Au/Sn, AgSn . . . ), etc., which are completely converted into an intermetallic phase after the soldering process. The contacting elements  44  (as illustrated in  FIG. 5 ) may be coated with an adhesion promoter  46 , for example in the form of a brown-etched structure. Other forms of the adhesion promoter are familiar to the person skilled in the art. 
     In a next step, the at least one mounting structure  14  is mounted with one (or possibly more) component(s)  40 , as illustrated in  FIG. 6 . In the case of the exemplary embodiment shown, two mounting structures  15  are shown, each with one mounting area  16 , into which an electronic component  40  with two contacting elements  44  is inserted. The mounting areas  16  are formed in such a way that the respective diameter d of the mounting areas essentially corresponds to an external diameter D′ of the contact elements  44  to be inserted, in such a way as to allow an insertion/mounting with an exact fit. To secure the contacting elements  44  in the recesses forming the mounting areas  16 , suitable joining means can be provided in the region of the contact surface, e.g. adhesives (particularly fast-curing adhesives, e.g. epoxy adhesives) or solder, or similar. The contacting elements  44  of the electronic component  40  and or the connecting agent can be heated directly before the component mounting, so that a better and faster joint is produced during the mounting process due to the heating. If solders are used, the soldering can be carried out during the component mounting by means of a heated placement head. Alternatively, the mounting can be performed at room temperature and the soldering can be carried out in a subsequent reflow soldering process. 
     If necessary, the mounted component can be stabilized after assembly by means of “underfilling”. In this process, the gap between the component  40  and the surface  12  is filled with an insulation material applied in liquid form and then cured. 
     Then, layers of electrically insulating material  30  (such as prepreg material) are applied around and on the mounted component  40  and the resulting layer structure can be laminated with a cover layer  32  if required. Due to the lamination/compression process the resin contained in the electrically insulating material is liquefied and after curing forms a resin layer/dielectric layer  30  surrounding the mounted component  40  and the mounting structures  14  (see  FIG. 7 ). If necessary, the assembled structure can be subjected to an adhesive promotion process once again. For example, the cover layer is a copper layer, e.g. as a copper film. 
     Finally, the base layer material (base copper) is removed either in the region of the contacts or completely, depending on the nature of the subsequent connection technique, i.e. the contacting elements  44  are exposed from the side of the base layer  12 , as illustrated in the drawing of  FIG. 8 . The reference sign  24  indicates the location of such an exposed recess in the base layer  12 , so that the contacts  44  are freely accessible.  FIG. 9  shows a plan view of such an exposed contact  44  seen from a viewing direction IX marked with an arrow in  FIG. 8 . In  FIG. 9 , the reference sign  26  indicates the connection means (adhesive/solder). The exposure of the contacts, i.e. the removal of the base copper material in the region of the contacting elements  44 , is carried out in a manner that is generally known to the person skilled in the art. 
     The contacts are then cleaned (for example, by laser, chemically or using a plasma), after which a conducting layer  28  is deposited (see  FIG. 10 ). The conducting layer  28  can be applied either selectively (as in the region of the exposed contacting element (reference sign  44  and/or  26  and/or  15 ; see  FIG. 9 )) or over the whole surface (in addition to the region of the exposed contacting element  44  on the base layer  12  also, preferably over the conductor track  18 ). A copper layer/electrically conductive layer is then galvanically deposited on this conductive layer and on the exposed copper contacts.  FIG. 10  shows a selective application to the left-hand contact element  44  in the drawing and a whole-surface application to the right-hand contacting element  44  in the diagram. This drawing is only intended for illustrative purposes, in reality, in each embodiment a decision on a form of the conductive layer plating will be made. Selective application of the conductive layer can be carried out, for example, by means of a conductive polymer (DMSE), while whole-surface application can be carried out, for example, by chemical deposition of copper. 
     Alternatively, the base layer  12  can be removed essentially completely. The contacting elements  44 ,  46  can then be connected to the conductive layer  13  (i.e. the layer sections or conductor tracks forming the recesses that receive the contacting elements) by means of a selectively operating application method (laser induced forward transfer method or metal sputtering with mask, 3D printing etc.). 
     As shown in  FIG. 11 , as an alternative to achieving a greater mechanical robustness of the layer, parts of the base copper  12  and parts of the plated-on layer  13  and the contacting element  44  can be removed, e.g. by laser ablation. The recesses  24  thus generated are then filled up by selective or whole-surface plating (see reference sign  28  in  FIG. 12 ). Greater removal and higher plating increases the reliability of the conductive structure. The metal layer  28  is applied e.g. by galvanic deposition or by additive copper application using laser application methods (laser-induced forward transfer). In this process, copper is transferred from a substrate to the object to be coated by laser bombardment. The resulting outer layer thus produced can then be structured. 
       FIG. 13  shows a plan view of a detail of a component side of a conductor structural element  10  according to the invention, directly before the component mounting. The base copper  12 , which is now exposed again after the removal (stripping) of the temporarily applied photoresist, and the copper structures that have been plated on, are now visible. In addition to the already described conductor track  18  and the mounting area  16  formed therein (see  FIG. 2 ), these comprise a connection point  22  for contacting and a structured copper track  23 , which is essentially rectangular in shape and surrounds a rectangular area  34  into which the conductor track  18  with the mounting area  16  protrudes. Alternatively, a design with a combined mounting and contact area ( 16 ,  34 ) can also be implemented. 
     In addition to the conductor structural element  10 , an electronic component  40  to be mounted is also shown in top view. The electronic component  40  has a footprint congruent with the rectangular area  34  and is fitted with a contacting element  44 , which, when the component  40  is inserted into the rectangular area  34 , comes to rest in the left out or recessed mounting area  16  exactly as described above. A metallized area  46  (which can be a source contact) of the component  40  is positioned in the rectangular area  34 . 
     Furthermore, also conceivable is a combination in which the contacting element  44  is contacted by means of the method according to the invention, while the area  46  is contacted conventionally after the process of embedding, i.e. with laser vias and through-contacts, for example. In principle, however, both contacts allow the application of the method according to the invention. 
     With the procedure according to the invention, the mounting rate can be significantly increased compared to conventional methods, e.g. thermal bonding, since the precise-fitting design of the contacting elements and mounting area allows highly accurate component mounting. The use of fast-curing connection means enables the mounted component to be quickly fixed in position, so that further processing is possible sooner. The copper pillars described as contacting elements can be implemented very precisely and in small dimensions, and the mounting can accordingly be carried out with high positional accuracy. 
     A conductor structural element according to the invention can be treated as a semi-finished product and then integrated into a printed circuit board, but it can also be formed as a stand-alone printed circuit board.