Abstract:
The present invention is directed to lamination systems and methods, whereby a stack of members to be laminated is protected from the mats of the platens used to apply heat and pressure to the stack during lamination, by one or more interposer layers positioned between the stack and the platens and possibly bound to the stack.

Description:
FIELD OF THE INVENTION  
         [0001]    The field of the invention is lamination.  
         BACKGROUND OF THE INVENTION  
         [0002]    Multi-layer laminates such as interconnects and printed wiring board are sometimes damaged during the lamination process. Such damage may result in problems in subsequent processing such as circuit traces that become “shorted together” during electrolytic copper plating. Laminates with such problems must typically be either repaired or scrapped. As such, there is a continuing need for improved lamination systems and processes.  
         SUMMARY OF THE INVENTION  
         [0003]    The present invention is directed to lamination systems and methods, whereby a stack of members to be laminated is protected from the mats of the platens used to apply heat and pressure to the stack during lamination, by one or more interposer layers positioned between the stack and the platens.  
           [0004]    In one aspect of the invention, copper clad laminates are used as interposers to protect outside surfaces for a stack to be laminated from being embossed or otherwise damaged by the mats of the platens used to apply heat and pressure to the stack.  
           [0005]    In another aspect, the interposers are sufficiently thin and have a heat transfer capacity sufficiently large so as to allow the interposers to be used between a platen and a stack without preventing heat from the platen to be transferred into the stack.  
           [0006]    In yet another aspect, the interposers are sufficiently thick and/or rigid so as to prevent patterns on a platen from being transferred through the interposer to the stack.  
           [0007]    In still another aspect, a stack is bound in a manner similar to binding a book by positioning the stack between two covers/interposers, and binding the covers and the stack members together by an adhesive binding positioned along one side/edge of the stack.  
           [0008]    The systems and methods described herein are particularly applicable when vacuum laminating dry film build up materials. During such lamination using prior art devices a methods, a weave pattern from the platen mats of the vacuum laminator can transfer onto the build-up material causing an uneven, or woven, topography on the surface of the built-up layer. Because of the “weave” topography, the photoimageable dry film used to define the circuit pattern is unable to conform completely to the substrate surface. This condition results in circuit traces that become “shorted” together during the electrolytic copper plating process and must either be repaired or scrapped. The methods and devices described herein solve the problem by placing the panel to be vacuum laminated with a dry film build-up material between two pieces of clean, un-etched copper core material (one piece on the top and one piece on the bottom) to create a “sandwich”. One edge of the assembly is then secured using plating tape to prevent any of the layers from shifting, while still allowing the materials to flow during the compression stage of the vacuum lamination process.  
           [0009]    Various objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the invention, along with the accompanying drawings in which like numerals represent like components. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    [0010]FIG. 1 is a side view of a lamination system embodying the invention;  
         [0011]    [0011]FIG. 2 is an exploded side view of the stack, covers, and bindings of FIG. 1. 
     
    
     DETAILED DESCRIPTION  
       [0012]    A method of laminating a stack of members together comprises providing a stack of members to be laminated; sandwiching the stack of members between two interposers to form a protected stack; positioning the protected stack between two platens; and using the platens to apply heat and pressure to the protected stack to laminate the members of the stack together. The system of FIGS. 1 and 2 can be used to implement this method.  
         [0013]    In FIGS. 1 and 2, a lamination system  10  comprises first and second platen mats  111  and  112 , a stack to be laminated  120 , and binding and protection system (“BPS”)  130 . BPS  130  comprises interposers  131  and  132 , and binding member  135 . Interposers  131  and  132  each comprise a dielectric layer  133  sandwiched between metal layers  134 . In preferred embodiments interposers  131  and  132  are copper clad laminates with layers  134  being copper layers.  
         [0014]    It is important that the surfaces of interposers  131  and  132  that are placed in contact with surfaces  121 ′ and  122 ′ of stack members  121  and  122  be smoother than the surfaces of platen mats  111  and  112  in order to eliminate transferring any roughness or pattern of the mats onto surfaces  121 ′ and  122 ′. It is also important that the interposers  131  and  132  are sufficiently thin and have a heat transfer capacity sufficiently large so as to allow the interposers  131  and  132  to be used between platens  111  and/or  112  and stack  120  without preventing heat from the platens to be transferred into the stack.  
         [0015]    A preferred interposer is a clean, un-etched copper core comprising a 4 mil dielectric core sandwiched between two 0.5 mil thick copper layers. Such a metal clad laminate is contemplated to provide a favorable compromise between factors such as minimum thickness, heat transfer, cost, and availability. Slightly less preferred interposers comprise 0.35 mil or 0.7 mil copper layers. Other less preferred interposers may utilize metals other than copper, cores and metal layers having different thicknesses, and/or different structures such: as a single layer of either metal or dielectric material; a single layer each of metal and dielectric; or more than 3 metal and/or dielectric layers. The preferred interposer will preferably be subjected to a cleaning process prior to use to minimize the risk of transferring impurities to the stack and/or causing surface blemishes.  
         [0016]    In addition to sandwiching the stack between interposers, it is preferred that the entire package (interposers and stack) be secured along one edge using a binding member such as a heat resistant plating tape. If the entire edge is not to be bound, it is preferred that the edge be bound in at least two places. In some instances the package will be slid or otherwise moved between platens with one edge being the leading edge during such movement. In such cases it is preferred that the bound edge be the leading edge (i.e. the first edge to be moved between the platens). In less preferred embodiments, less than all of the stack members may be bound, and/or one or none of the interposers may be bound.  
         [0017]    Members  121  and  122  of stack  120  may comprise any combination of materials. However, it is contemplated that the methods and devices described herein will be particularly advantageous when stack  120  comprises a plurality of dielectric and conductive layers, with some of the conductive layers forming electrical circuits. It is contemplated that the devices and methods described herein may be most advantageously used when stack  120  comprises dry film build up materials.  
         [0018]    The actual materials and structure of platens and platen mats used are not critical. In many embodiments, mats  111  and  112  will each be made of rubber or other material coupled to a platen adapted to apply heat and pressure to a stack to be laminated.  
         [0019]    Thus, specific embodiments and applications of lamination systems and methods have been disclosed. It should be apparent, however, to those skilled in the art that many more modifications besides those already described are possible without departing from the inventive concepts herein. The inventive subject matter, therefore, is not to be restricted except in the spirit of the appended claims. Moreover, in interpreting both the specification and the claims, all terms should be interpreted in the broadest possible manner consistent with the context. In particular, the terms “comprises” and “comprising” should be interpreted as referring to elements, components, or steps in a non-exclusive manner, indicating that the referenced elements, components, or steps may be present, or utilized, or combined with other elements, components, or steps that are not expressly referenced.