Abstract:
The invention pertains to a new type of process for the manufacture of substrates with textured metalizations and holding and fastening elements for use in this process.

Description:
BACKGROUND OF THE INVENTION 
     The invention pertains to a process or method for making substrates with textured or structured metalizations. The invention also pertains to a holding and fastening element for the use in such a method. 
     The manufacture of substrates with textured or structured metalizations for the use as printed boards for electrical devices are known in a variety of models. The texturing generally takes place using a masking or etching process, for example. 
     The substrates according to the present invention are, for example, ceramic/metal substrates that in their simplest form consist of a ceramic layer that is provided with a metalization on one surface, but preferably on both surfaces, for example in the form of a metal foil applied to the surface. 
     It is known that these metalizations required for conductors, connections etc. on ceramic, e.g. on aluminum-oxide ceramic are produced by means of the so-called “DCB process” (direct copper bond technology), using metal or copper foils or metal or copper sheets forming the respective metalization that have a layer or a coating (melt-on layer) consisting of a chemical compound of the metal and a reactive gas, preferably oxygen. In this process, which is described for example in U.S. Pat. No. 3,744,120 or DE-PS 23 19 854, this layer or coating (melt-on layer) forms a eutectic system with a melting temperature under the melting temperature of the metal (e.g. copper), so that by application of the foil on the ceramic and by heating all layers these can be connected to each other, by melting on the metal or copper essentially only in the area of the melt-on layer or oxide layer. 
     This DCB technology exhibits the following processing stages: 
     Oxidation of a copper foil in such a manner that an even copper oxide layer is formed; 
     Application of the copper foil to the ceramic layer; 
     Heating of the compound to a processing temperature between approximately 1025 and 1083° C., e.g. to approx. 1071° C.; Cooling to room temperature. 
     The substrates according to the present invention are also, for example, such substrates that consist of a base and/or insulating layer made of plastic that is provided with a metalization formed by a metal foil on at least one surface area. The substrates according to the present invention are also known substrates in which a thin insulating layer, for example of plastic, is applied to one base layer made of metal, for example aluminum and which (insulating layer) bears the metalization in the form of a metal foil, for example. 
     An object of the invention is to present a new process enabling texturing in an extremely efficient nature, especially using known masking and etching technologies. 
     SUMMARY OF THE INVENTION 
     In order to attain this object, a process or method for making substrates with textured or structured metalizations is characterized in that for texturing the metalizations of at least two substrates in one process, the two substrates are fastened tightly together in a removable manner, by means of at least one holding or fastening means on one surface side of each substrate, and then, the texturing of the metalizations is performed on the other free outer surface sides of the substrates. 
     A holding or fastening element for use in such a process is characterized by being formed as a ring or plate-like body made of a sealed material, for example of an elastic or rubber-like material, whereby the body has at least one opening that is closed on its periphery and a bearing surface on each of two opposite sides encompassing the opening. 
     The process according to the present invention offers the advantage, among other things, that at least two substrates or printed boards can be textured at the same time in one process, each on only one surface (outer surface side), whereby the other surface (inner surface side) or a metalization located there is not affected. The invention offers the additional advantage that a one-sided texturing of printed boards or substrates is possible using the existing equipment normally used for two-sided texturing, so that the same equipment can be used for one-sided and two-sided texturing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is described in more detail using example embodiments in the following figures, wherein: 
     FIG. 1 shows a simplified representation in a partial cross-section of two substrates to be textured, together with a holding or fastening element; 
     FIG. 2 shows a representation similar to FIG. 1, however with substrates that are tightly connected with each other by means of the holding or fastening element; 
     FIG. 3 shows a schematic representation in top view of the array of FIG. 2; 
     FIG. 4-6 show various further steps of the process for simultaneous texturing of the two substrates held together by the holding or fastening element; 
     FIG. 7 shows an enlarged partial view in cross-section through the fastening or holding element for use in the process; 
     FIG. 8 shows a simplified partial representation of the holding or fastening element of FIG. 7 in top view; 
     FIG. 9 shows a representation similar to FIG. 7 of a further possible embodiment of the holding or fastening element; 
     FIG. 10 shows a partial representation in top view of the holding and fastening element of FIG. 9; 
     FIG. 11 shows two substrates to be textured with a simplified holding or fastening element according to a further embodiment of the invention; 
     FIG. 12 shows a simplified representation in top view of the fastening element of FIG. 11; 
     FIG. 13 shows a simplified representation in top view of a further embodiment of a fastening element; 
     FIG. 14 shows a cross-section corresponding to line  1 — 1  of FIG. 13; and 
     FIG. 15 shows a representation similar to FIG. 7 of a further possible embodiment. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In FIGS. 1-6,  1  and  2  with respect to the depicted embodiment are substrates identical in form, size and structure that in the depicted embodiment both consist of an insulating layer in the form of a ceramic layer  3  and of metalizations  4  or  5  on both surface areas of the ceramic layer  3 . 
     It is the intention of the process described in more detail below to texture both substrates  1  and  2  simultaneously, i.e. in one process, on one surface area or side, respectively, i.e. on the metalization  4 , whereby the respective metalization  5  remains unaffected. In the depicted embodiment the metalizations  4  and  5  are formed by metal foils or plates, e.g. by copper foils, that are attached to the upper surface of the ceramic layer  3 , respectively, for example using DCB technology or an active soldering process. 
     As depicted in FIG. 1, the two substrates  1  and  2  with their metalization  5  are placed on a holding or fastening element  6 . As also depicted in FIG. 3, this holding or fastening element has the form of a ring made of an air-tight and gas-tight, elastic material, in top view (FIG. 3) of a form that corresponds to the shape of the peripheral edge of the respective substrate  1  or  2 , i.e. for rectangular substrates  1  and  2  with a rectangular shape. As these figures also show, the holding or fastening element  6  also has a T-shaped cross-sectional profile that consists of a profile section  6 ′ that extends perpendicular to the plane of the ring of the holding or fastening element  7  and forms the outer edge of this ring, and of a profile section  6 ″. The latter lies with its length in the plane of the ring formed by the holding and fastening element  6  and extends from the middle of the height of the profile section  6 ′ radially inward. The profile section  6 ″ forms a ring-shaped area, on which the two substrates  1  and  2  lie with their metalization  5  on the periphery of the substrate. The profile section  6 ′ covers the substrates  1  and  2  along the periphery on the peripheral surface or face there and extends in the depicted embodiment for substrates  1  and  2  provided with a holding or fastening element  6  to the respective outer metalizations  4 . 
     As shown in FIG. 3, finger-like profile sections  6 ′″ are provided for on the profile section  6 ″ that extend into the closed space  7  formed by the holding and fastening element  6  and the substrates  1  and  2  and thus have the same thickness of the profile section  6 ″ perpendicular to the plane of the substrates  1  and  2 . The profile sections  6 ′″ thus form an additional base of the substrates  1  and  2  within the ring opening of the holding or fastening element  6  and prevent excessive tensions in the substrates due to the vacuum in the space  7 . 
     After placing the substrates  1  and  2  onto the holding or fastening element  6 , the space  7  formed between the spaced substrates is evacuated to the negative pressure P. In order to create the negative pressure P in the space  7  the array or stack consisting of the substrates  1  and  2  is brought into a chamber that evacuates to the negative pressure and then more or less immediately, i.e. in a very short period of time, for example in a period of less than 10 seconds, is ventilated to the ambient pressure Pa so that due to the sudden change in pressure the substrates  1  and  2  are pressed with their edge against the fastening element so that practically no ventilation of the space  7  to the atmosphere takes place. 
     The vacuum in the space  7  is selected such that the pressure P there after the evacuation is smaller than 80% of the ambient pressure Pa. Due to the elastic material used for the holding or fastening element  6 , a tight seal of the space  7  is ensured by the fastening element  6 , so that the substrates are securely held together during the following steps of the process. 
     In further step of the process, a layer  8  made of a photosensitive resist is applied on the two outer and thus open metalizations  4 , for example by immersing the array consisting of the two substrates  1  and  2  and the fastening element  6  in the photosensitive resist. Both photosensitive resists  8  are then exposed according to the respective desired texturing or structuring, either at the same time or one after the other. Afterwards, the exposed photosensitive resist  8  is developed in order to form the masks  9  of photosensitive resist from the metalizations  4  (FIG.  5 ). In a further process step the two-sided etching of the metalizations  4  of both substrates  1  and  2  takes place using the photosensitive masks, so that after removal of the photosensitive masks  9  the two substrates  1  and  2  are produced with the texturing on the metalizations  4 . 
     As the figures also show, the photosensitive resist  8  is applied in such a way that it also covers the space between the periphery of the respective substrate  1  and  2  and the part of the profile section  6 ′ covering this substrate on the edge, so that in a corresponding embodiment of the photo mask  9  this space is protected against the penetration of etching liquid during the etching process. 
     The separation of the substrates  1  and  2  from the fastening element  6  is effected by ventilation of the space  7 , for example by gripping the elastic fastening element  6  at a position with a profile section  6 ″″ integrated on the outer profile section  6 ′ and pulled outward so that pressure equalization with the outer environment can take place through the opening thus formed. 
     The opening can generally take place in such a way that, in order to ventilate the space  7 , the array consisting of the substrates  1  and  2  and the fastening element  6  again enters a space that is evacuated to a pressure equal to or approximately equal to the pressure P and then very slowly ventilated to the ambient pressure Pa, so that the interior space  7  is slowly ventilated without pressing the substrates  1  and  2  against the fastening element  6  and thus without breaking the seal of the substrates to the fastening element  6 . 
     In the foregoing description, it was assumed that the masks  9  are made of a photosensitive resist. Of course, other masks of an etch resistive can be used. 
     FIGS. 7 and 8 show as a further possible embodiment a fastening element  6   a,  which differs from the fastening element  6  only by an embedded metal insert  10  that, in the depicted embodiment, forms an essentially C-shaped clasp that is open in the area of the section  6 ″″. Due to the metal insert  10  the ring-shaped fastening element  6  receives an essentially solid structure that enables simpler handling, especially the connection with the substrates  1  and  2 . The metal insert  10  is completely surrounded by the material of the fastening element  6   a.    
     FIGS. 9 and 10 show in representations similar to FIGS. 6 and 7 a further possible embodiment, in which, however, instead of the metal insert  10  a reinforcement plate  11  made of a suitable material, for example of metal, is provided for and that extends in the middle plane of the ring-like fastening element  6   b  and is embedded on the edge at least in the profile section  6 ″ as well as in the profile sections  6 ′″. The plate  11  is a perforated plate with a number of openings  12  that not only improve the integration of the plate  11  in the elastic material of the profile sections  6 ″ and  6 ′″, but at the same time also create a connection between the two sides of the plate  11 , so that for the use of the fastening element  6   b  between the substrates  1  and  2  only a single space  7  is formed that is to be evacuated. In order to enable ventilation by pulling on the profile section  6 ″″, the plate  11  is provided with a notch  13  in the area of this profile section in such a way that the plate  11  is not embedded in the profile section  6 ″ with its edge. Opposite of the profile section  6 ″ an indentation  14  is provided for on the profile section  6 ″ that eases the ventilation of the space  7  by pulling on the profile section  6 ″″. 
     FIGS. 11 and 12 show as a further possible embodiment a fastening element  6   c  that consists essentially of a simple flat ring made of the elastic material, i.e. without the profile section  6 ′ and only with the profile sections  6 ″- 6 ″″. 
     FIGS. 13 and 14 show as a further embodiment a fastening element  6   d  that consists essentially of a plate made of the elastic, rubber-like material. In this plate, several continuous openings  15  are provided for that are connected on one side of the plate by groove-shaped channels  16 . On one side of the plate a heel  17  corresponding to the profile section  6 ″″ is integrated that lies adjacent to an opening  15 . In the depicted embodiments, one of the channels  16  extends to the vicinity of the heel  17 , but ends with a predefined distance before this heel or the corresponding peripheral side of the fastening element  6   d.  If used, the plate-shaped fastening element  6   d  is located between the two substrates  1  and  2 . Afterwards an evacuation of the spaces formed by the openings  15  between the two substrates  1  and  2  takes place. These spaces are connected with each other via the channels  16 . The evacuated interior spaces formed by the openings  15  and the channels  16  are sealed off from the atmosphere by the substrates  1  and  2 , so that the adjacent substrates  1  and  2  are held together by negative pressure by means of the fastening element  6   d.  After treatment, the substrates  1  and  2  can be removed from the fastening elements by pulling on the heel  17 . 
     In the above description it was assumed that the substrates  1  and  2  are both metal/ceramic substrates, especially ones in which the ceramic layer  3  is provided with a metalization  4 ,  5  on both sides that was applied on the surface in the form of a metal foil using DCB or active soldering technology. In general, other designs are conceivable, for example substrates that have a metalization on only one side, substrates whose metalization is produced by another technology, such as thick-film technology on one or two surface sides, etc. 
     FIG. 15 shows a substrate  1   a  consisting of a base layer  18  made of aluminum that is provided with a thin insulating layer  19  on one surface side on which (insulating layer) the metalization  4   a  to be textured is applied. For the texturing, the metalization  4   a  is likewise coated with the photosensitive resist  8 , from which the photosensitive mask is formed for the texturing by the later etching. The photosensitive resist  8  in this embodiment likewise covers the gap between the profile section  6 ′ and the edge of the substrate  1   a.    
     By using the process according to the present invention, especially by using a fastening element  6 ,  6   a,    6   b  with the profile section  6 ′ and the bridging of the gap between the edge of the substrate  1   a  and the area  6 ′ by the mask  9 , an unwanted effect on the base layer  18  by the etching liquid during etching is prevented. 
     The invention was described above using a sample embodiment. Of course, numerous alterations and adaptations are possible without abandoning the underlying inventive idea of the invention. 
     
       
         
               
             
               
               
               
             
           
               
                   
               
               
                 List of reference symbols 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 1, 2 
                 substrate 
               
               
                   
                 3 
                 ceramic layer 
               
               
                   
                 4, 5 
                 metalization 
               
               
                   
                 6, 6a, 6b, 6c, 6d 
                 fastening element 
               
               
                   
                 6′, 6′′, 6′′′, 6′′′′ 
                 profile section 
               
               
                   
                 7 
                 space 
               
               
                   
                 8 
                 photosensitive resist 
               
               
                   
                 9 
                 mask 
               
               
                   
                 10 
                 metal insert 
               
               
                   
                 11 
                 reinforcing plate 
               
               
                   
                 12 
                 opening 
               
               
                   
                 13 
                 notch 
               
               
                   
                 14 
                 indentation 
               
               
                   
                 15 
                 opening 
               
               
                   
                 16 
                 channel 
               
               
                   
                 17 
                 heel