Abstract:
The invention relates to a method for the selective surface treatment of a planar workpiece, whereby, on at least one of two metallic surface sides, two similar workpieces are detachably connected to eah other at least in a partial region, on teh first surface side thereof, such as to be sealed to the outside.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The invention relates to a process for the selective surface treatment of board-shaped components.  
         [0002]     Known in the art is the manufacture of printed circuit boards for electrical and electronic circuits using a board-shaped base material, which in the simplest case consists of an insulating layer that is provided on its two surfaces with a metal layer, for example, with a copper layer. The latter is then structured with known masking and etching technology, so that the required strip conductors, connections, contact surfaces, etc. are retained.  
         [0003]     Also known in the art is the manufacture of so-called DCB substrates, which consist essentially of a ceramic layer, for example, a layer of aluminum oxide ceramic, which is provided on its two surfaces with metallization in the form of a metal or copper foil, which then is structured by means of the masking and etching technology. The metal or copper foil is applied with an active soldering process or the known direct bonding process, which is described in US-PS 37 44 120 or DE-PS 23 19 854.  
         [0004]     In many cases with board-shaped components with metallic surfaces, for example, printed circuit boards or substrates, it is also necessary, preferably after the structuring of the metallizations, to carry out selective surface treatment, which in the simplest case means that on only one of the two surfaces of the component, at least one metallic layer or several metallic layers are applied one after the other, for example a metal surface of copper is followed by a layer of nickel and on top of that possibly a further layer of gold, e.g. for producing the best possible electric contact or a strip conductor (also for high-frequency circuits) with the lowest possible resistance.  
         [0005]     An object of the invention is to present a process that enables the selective surface treatment of board-shaped components with especially simple means.  
       SUMMARY OF THE INVENTION  
       [0006]     The process according to the invention enables the selective surface treatment in an especially simple manner, without complex processing steps and without the use of additional production aids for covering or masking such surfaces on which the surface treatment should not take place.  
         [0007]     “Components” according to the present invention are, in general, board-shaped components with a metallic surface on two opposing surface sides, but preferably printed circuit boards.  
         [0008]     “Surface treatment” according to the invention is in particular the application of at least one metallic layer, for example by means of galvanic and/or chemical plating. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]     The invention is described in more detail below based on the drawings and sample embodiments:  
         [0010]      FIG. 1  shows a schematic representation in cross section of a DCB single substrate manufactured using the process according to the invention;  
         [0011]      FIG. 2  shows a schematic representation in top view of a DCB multiple substrate manufactured using the process according to the invention;  
         [0012]      FIG. 3  shows, in different positions, process steps for the manufacture of the substrate in  FIG. 1 ; and  
         [0013]      FIG. 4  shows a simplified representation in cross section of a vacuum base plate for use in the process in  FIG. 3 .  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0014]     In the drawings,  1  generally designates a DCB single substrate, which includes of a ceramic layer  2  (for example of an aluminum oxide ceramic), a metallization  3  provided on the top side of the ceramic layer  2  and a metallization  4  provided on the bottom side of the ceramic layer  2 . Both metallizations  3  and  4  are formed by a copper foil, which is connected on the surface with the ceramic layer  2  by means DCB technology. The metallization  3  is structured so that it forms a plurality of electrically separate strip conductors and/or contact surfaces and/or connections of an electric circuit, which accommodates electric components not depicted that are connected with the contact surfaces or strip conductors. On the top side facing away from the ceramic layer  2  the structured metallization  3  is surface-treated, namely in the manner that by means of chemical plating a nickel layer  5  and on top of this a gold layer  6  is applied, the thicknesses of which however are exaggerated in the depiction in  FIG. 1 .  
         [0015]     The bottom metallization  4  of the DCB single substrate  1  in the depicted embodiment is structured so that this metallization ends at a distance from the edge of the square or rectangular ceramic layer  2 . One surface treatment does not have the metallization  4 .  
         [0016]     The DCB single substrate is produced in a multiple printed panel, i.e. a DCB multiple substrate  7  is manufactured according to  FIG. 2  with a plurality of single substrates  1  in rows and columns parallel to the edges, i.e. is structured corresponding to these single substrates  1  on the top and bottom of the ceramic layer of the DCB multiple substrate. On the top forming the surface-treated metallization  3  of the later single substrate  1 , the DCB multiple substrate  7  is provided along the edges with additional metal edges or studs  8  and  9  formed by structuring of the respective copper foil to prevent unwanted breaking of the multiple substrate  7  into the single substrates  1  after etching or lasering of the multiple substrate  7 , i.e. after placing the break lines  10  between the single substrates  1 , namely during further handling of the multiple substrate  7 , for example when equipping the single substrates with the electric components, etc. Such metallized metal studs  8  and  9  or metallized edge areas, which prevent unwanted breaking of the multiple substrate  7 , are described e.g. in DE 43 19 944 A1.  
         [0017]     The surface treatment of the metallizations  3  takes place by a corresponding treatment of the multiple substrate  7  and in any case before separating the multiple substrate  7  into the single substrates  1 .  
         [0018]      FIG. 3  shows a schematic depiction of various steps for manufacturing the multiple substrate  7  with the selective surface treatment only of the metallizations  3 , but not of the metallizations  4 .  
         [0019]     First, the copper foils  3 ′ and  4 ′ forming the metallizations  3  and  4  are applied corresponding to position a) by means of DCB technology to both surfaces of the ceramic layer  2  of the multiple substrate  7 . In further processing steps, the copper foils  3 ′ and  4 ′ are structured for example by means of the usual masking and etching technology, in order to form the metallizations  3  and  4  of the single substrates  1  corresponding to position b) and at the same time also the metal (copper) studs  8  and  9  along the edges of the multiple substrate  7  on the top of the multiple substrate  7  or the ceramic layer  2 . Such metal or copper studs are missing on the bottom of the ceramic layer  2  with the structured metallizations  4  of the single substrates  1 .  
         [0020]     As  FIG. 2  shows, the studs  8  extend over the entire length of the respective edge of the multiple substrate  7 , while the studs  9  end at a certain distance from the studs  8 , so that in the space formed between the stud  8  and  9  a break line  10  can also be placed parallel to the adjacent stud  8  for example by means of lasering, namely such that this break line  11  extends over the entire width of the multiple substrate  7 .  
         [0021]     The structuring of the copper foils  3 ′ and  4 ′ is followed in a further processing step by the selective surface treatment only of the metallizations  3 , but not of the metallizations  4 . For this purpose, two multiple substrates  7  are connected with each other tightly but detachably by means of a connecting element  12  with their bottom side accommodating the metallizations  4 , namely such that the metallizations  4  are fully covered toward the outside by the connecting element  12 . In the depicted embodiment the connecting element  12  has a frame-like design and extends along the edge of the bottom of the multiple substrate  7 , namely where the outer metal studs  8  and  9  are located on the top of the respective multiple substrate  7 . The connecting element  12  is connected tightly but detachably with the bottoms of the two multiple substrates  7  in a suitable manner, for example by means of a sealing or connecting mass, which makes it possible to detach the multiple substrate  7  from the connecting element  12 .  
         [0022]     The fact that the metal studs  8  and  9  are missing on the bottom of the multiple substrate  7  on the edge and especially on the transitions between the adjacent metal studs  8  and  9  achieves a full-surface and tight connection between the bottom of the ceramic layer  2  of each multiple substrate  7  and a connecting element  12 . The metallizations  4 , for which no surface treatment is provided, are therefore located in the space enclosed tightly by the connecting element  12  and the ceramic layers  2  of the two multiple substrates  7 , as depicted in position c) of  FIG. 3 , so that the subsequent surface treatment takes place only on the exposed metallizations  3 . In principle, a selective surface treatment of only the metallizations  3  and of the metal studs  8  and  9  would be conceivable by masking the metallizations  4  on the bottom accordingly before the surface treatment. However, the advantage of the process described above over such a procedure is, for example, that the application of additional masking before the selective surface treatment and the removal of this masking after the selective surface treatment and the ensuing additional costs for material and disposal are eliminated; in addition, there are no soiled baths due to the components or coating required for masking in connection with the surface treatment.  
         [0023]     It was assumed above that for the selective surface treatment of the metallizations  3 , the two multiple substrates  7  are connected with each other by means of the frame-like connecting element  12 , using an adhesive and sealing mass.  FIG. 4  shows a simplified depiction of a vacuum base plate  13 , which can be used for connecting two multiple substrates  7  on their bottom sides during the selective surface treatment of the metallizations  3 . The plate  13 , the edge dimensions of which correspond to the edge dimensions of the multiple substrate  7  or of the ceramic layer  2  of this multiple substrate, in the depicted embodiment is symmetrical to a middle plane extending parallel to the surfaces of this plate  13 , namely with several chambers  13 ′, which are open toward the two surfaces, and with several studs  14  between the chambers  13 ′. The studs  14  are designed in partial areas with a low height and in partial areas with a greater height and form in these partial areas of greater height contact or support surfaces  15  for the bottom of the two multiple substrates  7 , which are connected with each other by means of the base plate  13 . By means of the narrower design of the studs  14  in partial areas the chambers  13 ′ are connected with each other. Along the edge, the base plate  13  forms a self-contained frame section  16 , on which a wraparound seal  17  is located on the top and on the bottom along the edge of the base plate  13 . On the frame section  16  there is furthermore at least one connector  18  provided with a shut-off valve and which leads into one of the chambers  13 ′ and which can be connected or is connected to a vacuum source not depicted.  
         [0024]     For the selective surface treatment, the two multiple substrates  7  are placed with their bottom on one side of the vacuum base plate  13 , so that the wraparound seal  17  there bears against the bottom of the ceramic layer  2  of a multiple substrate  7 , namely along the edge of this multiple substrate where the metal studs  8  and  9  are located on the top. By applying a vacuum to the base plate  13  or the chambers  13 ′ enclosed by the ceramic layers  2  by means of the connector  18 , the multiple substrates  7  are fixed on the base plate  13 , so that for example after closing the valve of the connector  18 , the selective surface treatment of the multiple substrates  7  on the metallizations  3  can then take place.  
         [0025]     In principle it is of course also possible to maintain the vacuum connection to the base plate  13  during the selective surface treatment. The shut-off of the connection  18  after evacuation of the chambers  13 ′ and before the selective surface treatment ensures, however, that in the event of a faulty seal between the single substrates  7  and the base plate  13 , no medium used for the surface treatment can enter the vacuum source.  
         [0026]     It was assumed above that the process achieves a selective surface treatment of metallizations on DCB substrates. Of course, the process is also suitable for the selective surface treatment of metallizations of other substrates, which for example can be used as printed circuit boards for electric circuits, e.g. of substrates that have an insulating layer made of ceramic or of another insulating material, for example of plastic, however not using the DCB technology. Furthermore, the described process is also generally suitable for the selective surface processing of metal layers or components that for example are to be provided with one or more layers e.g. of metal on only one surface.  
         [0027]     In principle it is of course also possible that the processing steps for the selective surface treatment be repeated, i.e. at least two times, namely for example in the embodiments described in the drawings such that in a first phase, the selective surface treatment of the metallizations  3  takes place, as described above, and then in a second phase, in which then two multiple substrates  7  for example are detachably connected by means of the connecting element  12  on their tops in order to seal the latter, the selective surface treatment of the metallizations  4  takes place. Analogous to this, the selective surface treatment is possible in several phases also with other substrates and components.  
         [0028]     Furthermore, it was assumed above that the structured metallizations  3  are produced by means of masking and etching technology. It is, of course, also possible to apply these metallizations  3  to the respective insulating layer, e.g. ceramic layer, already in structured form.  
       REFERENCE LIST  
       [0000]    
       
           1  DCB single substrate  
           2  ceramic layer  
           3 ,  4  metallization  
           3 ′,  4 ′ copper foil  
           5 ,  6  surface layer  
           7  multiple substrate  
           8 ,  9  metal stud  
           10 ,  11  breaking line  
           12  connecting element  
           13  vacuum base plate  
           13 ′ chamber  
           14  stud  
           15  contact surface  
           16  frame section  
           17  wraparound seal  
           18  connection