Abstract:
The print head and screen assembly of a Semi-Automatic Screen Printer is raised above its normal printing height and selective attachment of several different fixtures on the nest plate for holding the substrate in a desired position during a screen printing operation for printing gold on LTCC substrates.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is related to U.S. Ser. No. 10/718,805 entitled “Fabrication of LTCC T/R Modules With Multiple Cavities And An Integrated Ceramic Ring Frame” filed on Nov. 24, 2003 in the name of Rena Y. Jacobson et al., and to U.S. Ser. No. 10/896,174 entitled “Apparatus and Method for Side Printing On Low Temperature Co-Fired Ceramic (LTCC) Substrates” filed on Jul. 22, 2004 in the name of Rena Y. Jacobson, et al., which are assigned to the assignee of the present invention and which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to screen printing on a laminated assembly of low temperature co-fired ceramic (LTCC) material, and more particularly to a method and apparatus for screen printing gold onto fired LTCC substrates of microwave transmit/receive (T/R) modules to provide a solderable surface for side connectors, ring frames, and heat sinks that package the ceramic. 
     2. Description of Related Art 
     In forming an LTCC substrate, such as shown in related application Ser. No. 10/718,805, typically a number of LTCC tape layers are initially divided into multiple stacks of tape layers, e.g., four stacks or sections, based on a final cavity routing configuration of each stack. One of the stacks preferably comprises a set of layers for the formation of a ceramic ring frame. Each stack is then separately tack laminated, followed by cavity patterns being machined therein using a router device whereby a large number of layers are routed in a single pass, forming cavities having side walls which are relatively smooth and straight as opposed to the known prior art method of cutting individual layers with a laser, for example, which results in the formation of jagged side walls. Following cavity routing, all of the stacks are laid up on a base plate including a set of tooling pins for providing alignment of the stacks. The lay up is completed with a placement of a top mylar template followed by a copper template. The assembly is next covered with an expandable latex sheet that has been lightly coated with material for aiding the removal of the latex sheet without metal lift-off after lamination. The assembly is then placed in a lamination fixture and isostatically laminated for a specific period of time at a predetermined pressure and temperature, typically 4000-5000 psi at 72° C. for 15 minutes, resulting in a structure in the form of laminated panel. The panel is then allowed to cool, removed from the fixture where it is green cut to remove tooling holes and then fired with a designated firing profile. A plurality of mutually identical newly designed LTCC substrates for a T/R module are then diced, i.e. cut, from the panel and post fire printed as required. 
     Due to the design of conventional screen printers, e.g., the well known MPM SP-1500 printer, the printing of post-fired LTCC substrates incorporating the above noted design was limited to a certain range of the overall thickness of the substrate or board. For instance, the allowable thickness of the substrates were limited to less than 1″ maximum. Substrates with a thickness greater than 1″ were not able to access the print position inside of the standard screen printing machine due to the fact that the printer head was in the way. 
     Accordingly, screen printing LTCC substrates in the post-fired condition require a certain type of unique fixturing of the substrate on a screen printer for accurate and consistent placement of the printed pattern. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide an apparatus for performing screen printing on an LTCC substrate in the post-fired condition. 
     It is another object of the present invention to provide an assembly for performing screen printing on an LTCC substrate using standard screen printers. 
     These and other objects are achieved in the present invention by an improved apparatus and method for screen printing gold on LTCC substrates by a modification of an MPM SP-1500 Semi-Automatic Screen Printer by raising the print head and screen assembly above its normal printing height and selective attachment of several different fixtures on the nest plate for holding the substrate in a desired position during a screen printing operation. 
     In one aspect of the invention there is provided an apparatus for enabling printing on ceramic material including low temperature co-fired ceramic material, comprising: screen-printing apparatus for applying a predetermined pattern of metallization to a surface of ceramic material and including a fixture support plate which is movable under a print head having a screen-printing assembly and having a first separation distance between the fixture support plate and the print head during a screen-printing operation; a modification of said screen-printing apparatus whereby the print head is raised above the fixture support plate so as to provide a second separation distance greater than said first separation distance during a printing operation; and a fixture located on a surface of the fixture support plate for holding said ceramic material in a selected orientation during a screen-printing operation. 
     In another aspect of the invention there is provided an apparatus for enabling printing on ceramic material, including low temperature co-fired ceramic (LTCC) material, comprising: a fixture located on a support member moved under a print head during a printing operation, said fixture includes a base plate for attachment to said support plate of the screen printing apparatus, an intermediate body member on said base plate, a top plate on said intermediate body member, and a slot in the top plate extending into the body for holding said ceramic material; and wherein said ceramic material comprises a laminate assembly includes top, bottom and side surfaces and said fixture includes a slot for holding said laminate assembly so as to enable printing of said pattern of metallization on said side surface. 
     In a further aspect of the invention there is apparatus for enabling printing on ceramic material, including low temperature co-fired ceramic (LTCC) material, comprising: a fixture located on a support member moved under a print head during a printing operation, said fixture includes a base plate for attachment to said support plate of the screen printing apparatus, a body member on said base plate including a recessed shelf in a top surface thereof for holding said ceramic material; and wherein said ceramic material comprises a laminate assembly which includes top, bottom and side surfaces and said recessed shelf holding said laminate assembly so as to enable printing of said pattern of metallization on selectively said top and bottom surfaces of the laminate assembly. 
     And still further there is provided an apparatus for enabling printing on ceramic material, including low temperature co-fired ceramic (LTCC) material, comprising: a fixture located on a support member moved under a print head during a printing operation, said fixture includes a base plate for attachment to said support plate of the screen printing apparatus, an intermediate body member on said base plate, a top plate on said intermediate body member, and a vertical bore through said base plate, said body member, and said top plate and being connected to a vacuum source for holding said ceramic material in place on the top plate; and wherein said ceramic material comprises green ceramic tape and said green ceramic tape being held in place on the top plate so as to enable printing of said pattern of metallization thereon. 
     Further scope of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be noted, however, that the detailed description and specific examples, while indicating the preferred method of the invention, are provided by way of illustrations only, since various changes, alterations and modifications coming within the spirit and scope of the invention will become apparent to those skilled in the art from the following detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will become more fully understood when considered in conjunction with the accompanying drawings, which are provided by way of illustration and thus are not meant to be considered in a limiting sense, and wherein: 
         FIG. 1  is a front elevational view of a standard MPM SP-1500 screen printer; 
         FIG. 2  is a perspective view further illustrative of the screen printer shown in  FIG. 1 ; 
         FIG. 3  is a perspective view of a frame assembly including 3 in. spacer members used to raise the print head and screen of the screen printer shown in  FIG. 1 ; 
         FIG. 4  is a side elevational view of the frame assembly shown in  FIG. 3  installed in the screen printer shown in  FIG. 1 ; 
         FIGS. 5 ,  6  and  7  are illustrative of three different fixtures which can be mounted on the nest plate of the screen printer shown in  FIG. 2 ; 
         FIG. 8  is a perspective view of the fixture shown in  FIG. 5  mounted on the nest plate; 
         FIG. 9  is a partial view of the fixture shown in  FIG. 5  illustrating two clamp assemblies used to position a substrate inserted vertically in the top of the fixture shown in  FIG. 5 ; 
         FIG. 10  is further illustrative of the fixture shown in  FIG. 5  mounted on the nest plate; and 
         FIG. 11  is a perspective view of the fixture shown in  FIG. 6  mounted on the nest plate. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings, and more particularly to  FIGS. 1 and 2 , shown thereat is a well known MPM SP-1500 semi-automatic screen printer  10  which includes, among other things, a generally rectangular bed  12 , a workholder nest plate  14  which is mounted on rails  16  and  18  supported by a frame assembly  20 . The nest plate  14  is adapted to be moved forwardly and rearwardly by a motor  22  and connecting rod  24 . The nest plate  14  shown in  FIG. 1  is fitted with a porous vacuum plate  26  which is moved under a print head  28  having a screen assembly  30  including a squeegee head when lowered during a printing operation. Reference numeral  32  denotes a control console for the printer. 
     In a desire to use the MPM SP-1500 printer  10  for screen printing on a substrate such as shown in related application Ser. No. 10/718,805 referenced above, it was noted that the height of the substrate when stood on its end, for example, would not clear the bottom surface of the printer head  28 . In order to overcome the height problem of the substrate in relation to the printer head  28 , the first step taken in the subject invention was to raise the height of the screen assembly  30  in its lowered position 3 in. above the nest plate  14  as shown in  FIG. 4 . This is achieved by modifying the frame assembly  20  shown in  FIGS. 1 and 2  to a frame assembly  20 ′ such as shown in  FIG. 3 . The frame assembly  20 ′ is similar to the frame assembly  20  except for four upwardly facing 3 in. spacer elements  34 ,  36 ,  38  and  40  located in a generally rectangular arrangement on the rear portion of a pair of elongated side members  42  and  44  and a spacer element  43  located on the cross member  43 . Cross members  41 ,  43  and  45  are secured to the side members  42  and  44  in the same manner as in the conventional frame  20  of  FIG. 1 . 
     With the print head  28  and screen assembly  30  now raised 3 in. by virtue of the frame assembly  20 ′ shown in  FIG. 3 , the present invention is used in connection with three separate screen printing fixtures as shown in  FIGS. 5 ,  6  and  7 , and which are attachable to the printer nest plate  14 . The fixture shown in  FIG. 5  and identified by reference numeral  46 , is utilized for holding parts, e.g., an LTCC substrate, vertically for side printing while the fixture shown in  FIG. 6  and identified by reference numeral  48  is designed to hold parts horizontally on a recessed shelf for printing on the top and bottom surfaces of a substrate. The fixture shown in  FIG. 7  and identified by reference numeral  50  comprises a fixture for screen printing layers of LTCC green tape. All three fixtures  46 ,  48  and  50  are fabricated in resin so as to allow for inexpensive and also speedy manufacturing. 
     Considering now the details of the side print fixture  46  shown in  FIG. 5 , and which is additionally disclosed in  FIGS. 8 ,  9  and  10 , fixture  46  includes a base plate  52  which can be bolted to the nest plate  14  as shown in  FIG. 8 . An intermediate body member  54  on the base plate  52  forms a pedestal upon which is located a top plate  56  including an aperture  58  for a vertical slot  60 , shown in  FIG. 9 , and extending down into the body member  54  so that an LTCC substrate  62  can be inserted vertically therein for printing on the top side surface  64  thereof when contacted by a squeegee head, not shown, which forms part of the print screen assembly  30 . The substrate  62  is fully enclosed in the resin fixture  46  and is held in position by a vertical locating clamp assembly  66  and a horizontal locating clamp assembly  68 . As shown in  FIG. 9 , the clamp assembly  66  includes a substrate engaging member  70  which contacts the bottom surface  71  of the substrate  62  and a threaded bolt member  72  located behind the slot  58  in the recess  74 , as shown in  FIG. 5 , which is adapted to move the member  70  vertically so that the top surface  64  of the substrate  62  projects slightly above the top surface  57  of the top plate  56 . The horizontal locating clamp  68  likewise includes a substrate engaging member  76  which is moved horizontally by means of a threaded bolt  78  and acts to firmly hold the substrate  62  in place in the fixture slot  60 . 
     With respect to the second fixture  48  shown in  FIG. 6 , it also includes a base plate  80  which can be attached to the nest plate  14 . On the base plate  80  is located a generally rectangular pedestal  82  having a recessed shelf  84  formed on the top surface  86 .  FIG. 6  shows an LTCC substrate  62  located on the shelf  84 . A single clamp assembly  88  including a pressure plate member  89  is adapted to contact a side edge of the substrate  62  located in the recess of the shelf  84  and can be moved inwardly by means of a threaded screw  90  as needed. A pair of guide pins  92  and  94  project through the pedestal  82  so that the pressure plate  88  moves so as to exert balanced pressure against the substrate  62  when positioned on the recessed shelf  84 . 
     Accordingly, the top and bottom as well as side surfaces of a substrate  62  can be printed on demand. 
       FIG. 11  discloses the third fixture  48  mounted on the nest plate  14  in the same manner that the fixture  46  is bolted onto nest plate  14  as shown in  FIG. 10 . The third fixture  50  as shown in  FIG. 7  is used when there is a requirement to print green ceramic tape layers at the 3 in. elevated height as shown for the fixtures  46  and  48 . The fixture  50  includes a vertical bore  102  which extends through the top plate  100 , the pedestal  98 , and the base plate  96  for coupling to a vacuum source, not shown, which is required to hold thin layers of tape in place on the top surface  104  when placed thereon. The top surface  104  also includes a generally rectangular recess  106  surrounding the bore  102  so as to receive an O-ring for additionally holding the tape layers in place on the fixture  50 . 
     The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.