Abstract:
A method of protecting a mold having at least one substantially planar surface provided with a plurality of mold cavities includes inserting a plurality of mandrels into respective ones of the plurality of mold cavities, depositing a layer of mold protection material onto the at least one substantially planar surface and the plurality of mandrels, and removing the plurality of mandrels from the mold substrate.

Description:
CROSS-REFERENCES TO RELATED APPLICATION 
     This application is a divisional of U.S. application Ser. No. 12/573,904 filed Oct. 6, 2009, the disclosure of which is incorporated by reference herein in its entirety. 
    
    
     BACKGROUND 
     The present invention relates to the art of molds, and more particularly, to a method of protecting a mold having a substantially planar surface provided with a plurality of mold cavities. 
     Electronic devices such as semiconductors, processors, logic chips and the like employ solder balls as an interconnection to other components. That is, the solder balls provide a communication path to and from the electronic device. In addition, the solder balls may serve as an attachment element for securing the electronic device to another component. The solder balls are formed in molds and then attached to the electronic device. Over time, and through multiple uses and associated handling, the molds become scratched either from blading of the metal into cavities formed in the mold or from normal handling. Small scratches often lead to false defects that cause confusion during inspection. Moreover, over time, small scratches develop into cracks that may lead to catastrophic mold failure. In addition, some large scratches or gouges can behave like a pathway that captures and transferring solder between mold cavities. 
     SUMMARY 
     According to an aspect of the exemplary embodiment, a method of protecting a mold having at least one substantially planar surface provided with a plurality of mold cavities includes inserting a plurality of mandrels into respective ones of the plurality of mold cavities, depositing a layer of mold protection material onto the at least one substantially planar surface and the plurality of mandrels, and removing the plurality of mandrels from the mold substrate. 
     Additional features and advantages are realized through the techniques of the present invention. Other embodiments and aspects of the invention are described in detail herein and are considered a part of the claimed invention. For a better understanding of the invention with the advantages and the features, refer to the description and to the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The forgoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is cross-sectional view of a substrate having first and second substantially planar surfaces for a mold in accordance with an exemplary embodiment; 
         FIG. 2  is a cross-sectional view of the substrate of  FIG. 1  showing a protective layer deposited on one the first substantially planar surface; 
         FIG. 3  is a cross-sectional view of the substrate of  FIG. 2  showing a photo resist layer positioned on the protective layer; 
         FIG. 4  is a cross-sectional view of the substrate of  FIG. 3  illustrating a pattern etched through the photo resist layer and the protective layer; 
         FIG. 5  is a cross-sectional view of a mold assembly  FIG. 4  showing the photo resist layer removed and a plurality of cavities etched into the substrate to form a mold having a protective layer in accordance with an exemplary embodiment; 
         FIG. 6  is a cross-sectional view of the substrate of  FIG. 3  illustrating the cavities etched through the photo resist layer and the protective layer; 
         FIG. 7  is a cross-sectional view of the substrate of  FIG. 6  showing the removal of the photo resist layer to form a mold having a protective layer in accordance with another aspect of the exemplary embodiment; 
         FIG. 8  is a cross-sectional view of a mold assembly having a plurality of cavities requiring a protective coating in accordance with another aspect of the exemplary embodiment; 
         FIG. 9  is a cross-sectional view of the mold assembly of  FIG. 8  showing mandrels inserted into the plurality of cavities; 
         FIG. 10  is a cross-sectional view of the mold assembly of  FIG. 9  illustrating a protective layer deposited over the mandrels; 
         FIG. 11  is a cross-sectional view of the mold assembly of  FIG. 10  showing the mandrels being polished even with the protective layer; and 
         FIG. 12  is a cross-sectional view of the mold assembly of  FIG. 11  showing the mandrels removed to reveal a mold assembly of  FIG. 8  having a protective layer in accordance with another aspect of the exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Mold substrates, particularly those used in connection with the formation of solder balls, get scratched either from blading of metal into mold cavities or from normal handling. Small scratches may be a nuisance or lead to false defects that create confusion during inspection. Overtime, scratches develop into cracks, which may become catastrophic failures that lead to mold breakage. In addition, large scratches or gouges can behave like a cavity, capturing and transferring solder between adjacent mold cavities. Towards that end, it is desirable to form a mold having a surface that is resistant to scratches, cracking, damage and other defects. 
     As best shown in  FIGS. 1-5 , a mold substrate constructed in accordance with an exemplary embodiment is indicated generally at  2 . Mold substrate  2  is formed preferably from borosilicate glass (BSG) and includes a main body  4  having a first substantially planar surface  6  that extends to a second substantially planar surface  8  through an intermediate portion  10 . In accordance with an exemplary embodiment, a protective layer  20  of mold protection material is deposited upon first substantially planar surface  6  as shown in  FIG. 2 . Mold protection material can take on a variety of forms such as, SiC, Diamond like carbon (DLC), Si 3 N 4 , TiCN, TiN, Al 2 O 3  and polytetraflouroethylene (PTFE). Of course, other materials having scratch resistant properties can also be used. Protective layer  20  is deposited upon first substantially planar surface  6  using a method such as chemical vapor deposition (CVD). Of course, other methods such as physical vapor deposition (PVD) can also be used to deposit the protective layer onto substrate  2 . After depositing the mold protection material onto substrate  2  forming mold protective layer  20 , a photo resist layer  30  is applied. Photo resist layer  30  takes the form of a lithographic film. After being applied, photoresist layer  30  is lithographically patterned and developed, so as to define cavity locations  31 - 33  that are etched into protective layer  20 . At this point, the photo resist layer is removed and a plurality of cavities  34 - 36  are etched into substrate  2  at the cavity locations to form a mold  40  such as indicated at  FIG. 5 . As shown, cavities  34 - 36  extend from first substantially planar surface  6  into intermediate portion  10  stopping short of the second substantially planar surface  8 . Once formed, cavities  34 - 36  can be filled with, for example, solder to form solder balls in a manner known in the art. Protective layer  20  ensures that first substantially planar surface  6  remains free from damage that can create irregularities within the solder balls formed in mold  40 . Of course it should be understood that mold  40  can be employed to form a variety of molded components and should not be considered as being limited to forming solder balls. 
     Reference will now be made to  FIGS. 6-7  in describing an alternative aspect of the exemplary embodiment. As shown in  FIG. 6 , cavities  42 - 44  defined in photoresist layer  30  are etched into both protective layer  20  into substrate  2 . Photo resist layer  30  is then removed, thus defining a mold  50  having protective layer  20  in  FIG. 7 . Once mold  50  is formed, cavities  42 - 44  are filled with solder to create solder balls in a manner similar to that described above. In a manner also similar to that described above, it should be understood that mold  50  can be employed to form a variety of molded components and should not be considered as being limited to forming solder balls. 
     Reference will now be made to  FIG. 8  in describing a method of applying a protective layer to a pre-existing mold  60 . In a manner similar to that described above, a mold  60  includes a substrate  64  formed from BSG. Substrate  64  includes a first substantially planar surface  66  that extends to a second substantially planar surface  68  through an intermediate portion  70 . Mold  60  is shown to include a plurality of cavities  80 - 82  that are configured and disposed to create, in the exemplary embodiment shown, solder balls in a manner similar to that described above. 
     Prior to applying a protective layer, each cavity  80 - 82  is filled with a corresponding sacrificial mandrel  87 - 89  deposited therein in  FIG. 9 . Sacrificial mandrels  87 - 89  are formed from a polymeric material such as, for example, a polymide. In this manner, mandrels  87 - 89  are capable of withstanding temperatures associated with depositing the protective layer onto mold  60  in a manner that will be described more fully below. As each mandrel is substantially similar, a detailed description will follow referencing mandrel  87 , with an understanding that the remaining mandrels  88  and  89  are similarly formed. 
     As best shown in  FIG. 9 , mandrel  87  includes a main body member  90  having a lower portion  92  that extends into cavity  80  and an upper portion  93  that projects above first substantially planar surface  66 . Once mandrels  87 - 89  are in place, protective layer  100  is deposited onto first substantially planar surface  6  over mandrels  87 - 89  such as shown in  FIG. 10 . That is, protective layer  100  not only covers substantially planar surface  66  but also covers exposed or upper portions  93  of mandrels  87 - 89 . In a manner similar to that described above, protective layer  100  is applied using a spin on, cure, and photoresist patterning ashing process, but could also be applied using various other processes. After applying protective layer  100 , upper portions  93  of mandrels  87 - 89 , as well as portions of protective layer  100  thereon, are polished off, thereby creating the protective layer pattern shown in  FIG. 11 , and the remaining portions of mandrels  87 - 89  coplanar therewith. Then, as shown in  FIG. 12 , mandrels  87 - 89  are removed from cavities  80 - 82  leaving behind a refurbished mold  120  having a protective layer as seen in  FIG. 12 . Mandrels  87 - 89  are removed by a chemical etch, reactive ion etching (RIE), ashing and/or some other process. 
     In addition to applying a protective layer to pre-existing molds, the present exemplary embodiments can also be employed to refurbish molds have a pre-existing protective layer. That is, over time, a protective layer on a particular mold may become worn. In such a case, the protective layer is removed and a new protective layer is applied using the method described above. That is, after removing the old protective layer and prior to applying the new protective layer, mandrels, are deposited into each of the plurality of mold cavities in a manner similar to that described above. The protective layer is then applied over the mandrels. At this point, the mandrels are polished and removed so as to form a new protective layer on a pre-existing mold. 
     At this point, it should be understood that the exemplary embodiments of the present invention provide a method for enhancing operational life of mold, particularly those used in connection with forming solder balls. The protective coating ensures that the borosilicate glass substrate remain substantially free of defects and/or cracks that may affect quality of the particles, solder balls, formed within mold cavities. At this point, it should be understood that in addition to being employed in connection with molds for creating solder balls, the present exemplary embodiments can be employed in connection with other molding operations that employ mold substrates that are prone to damage with the damage having a negative impact on a final mold product. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one ore more other features, integers, steps, operations, element components, and/or groups thereof. 
     The corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims below are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description of the present invention has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the invention. The embodiment was chosen and described in order to best explain the principles of the invention and the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated 
     The diagrams depicted herein are just one example. There may be many variations to these diagrams or the steps (or operations) described therein without departing from the spirit of the invention. For instance, the steps may be performed in a differing order or steps may be added, deleted or modified. All of these variations are considered a part of the claimed invention. 
     While the preferred embodiment to the invention had been described, it will be understood that those skilled in the art, both now and in the future, may make various improvements and enhancements which fall within the scope of the claims which follow. These claims should be construed to maintain the proper protection for the invention first described.