Patent Publication Number: US-2015076029-A1

Title: Package assembly for thin wafer shipping

Description:
FIELD OF THE INVENTION 
     The invention relates to packaging assemblies and, more particularly, to a package assembly for thin wafer shipping using force distribution plates and a method of use. 
     BACKGROUND 
     Semiconductor wafer manufacturing utilizes very sophisticated wafer processing procedures and complicated manufacturing systems. In efforts to reduce the size of the semiconductor package, manufacturers have reduced component sizes including the thickness of the wafer, itself. For example, wafer thinning can be performed by a grinding method to achieve a wafer thickness on the order of 100 microns and less. These thin wafers, though, are very fragile and brittle. Of particular concern are thinned wafers with through silicon vias (TSV), which can be about 25% as strong as non TSV wafers. For example, as the fracture strength varies with the square of wafer thickness, a force to break the thin wafers can be around 1N or less. 
     Shipping of thin wafers is thus a difficult challenge. Currently, for example, the wafers are placed into plastic containers for shipping. In known implementations, the wafers are manually placed into the containers with foam cushions on the bottom and on top and thin cleanroom paper dispersed between each wafer. Once placed into the containers, a top is placed onto the container. However using these containers and methods of insertion, the thinned wafers are subjected to an unacceptably high risk of damage. For example, when the thin wafers are flexed, whether during the packaging or shipping process, they become susceptible to micro-crack generation, which ultimately leads to wafer breakage. 
     Accordingly, there exists a need in the art to overcome the deficiencies and limitations described hereinabove. 
     SUMMARY 
     In an aspect of the invention, a package assembly comprises a container and upper and lower force distribution plates provided within the container. The upper and lower force distribution plates are positioned respectively on a top side and bottom side of the container. 
     In an aspect of the invention, a package assembly comprises: a container; a stack of wafers interposed with ESD compliant material sheets positioned within the container; and a distribution plate positioned on a top side and bottom side of the stack of wafers within the container. The distribution plates are structured to: contain the stack of wafers as a unit, allowing them to move only as a unit; and distribute forces across a surface of the stack of wafers. 
     In an aspect of the invention, a method comprises: placing a lower foam cushion or sheet in a bottom of a container; placing a lower distribution plate in the container, above the lower foam cushion or sheet; stacking a plurality of wafers and sheets interposed therebetween on the lower distribution plate; placing an upper distribution plate in the container, on top of the stack of wafers; placing an upper foam cushion or sheet on the upper distribution plate; and sealing the container. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The present invention is described in the detailed description which follows, in reference to the noted plurality of drawings by way of non-limiting examples of exemplary embodiments of the present invention. 
         FIG. 1  shows a force distribution plate in accordance with aspects of the present invention; 
         FIG. 2  shows a shipping container using the force distribution plate of  FIG. 1 , in accordance with aspects of the present invention; 
         FIG. 3  shows another variation of the shipping container using the force distribution plate of  FIG. 1 , in accordance with aspects of the present invention; and 
         FIG. 4  shows a mechanical equivalent shipping container of either  FIG. 2  or  FIG. 3 , in accordance with aspects of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     The invention relates to packaging assemblies and, more particularly, to a package assembly for thin wafer shipping using force distribution plates and a method of use. More specifically, the present invention incorporates force distribution plates within the package assembly to reduce flexing of the thin wafers while in transit. The force distribution plates are rigid plates placed below and above a stack of thin wafers in a container, thereby restricting flexure of the wafer and reducing wafer breakage. 
       FIG. 1  shows a force distribution plate in accordance with aspects of the present invention. In embodiments, the force distribution plate  10  is a reasonably flat and rigid plate sized and shaped to approximately the size (e.g., diameter) of the wafer. Accordingly, the force distribution plate  10  is sized and shaped to fit within a shipping container. The force distribution plate  10 , for example, can be standard thickness silicon wafers or some other suitable material fabricated into force distribution plates. For example, the force distribution plate  10  can be any ESD (electro-static discharge) compliant material such as metal discs, plastic discs with conductive coatings or other materials. 
     In embodiments, the force distribution plate  10  can have a thickness of about 1 mm to about 2 mm; although other dimensions are contemplated by the present invention, depending on the material used to fabricate the force distribution plate  10 . Also, the force distribution plate  10  is flat and rigid enough to prevent flexure of the wafers, during shipping. By way of example, the force distribution plate  10  is rigid enough to withstand at least 1N or more of force, to prevent flexure of the thinned wafers. It is also advantageous to minimize the weight of the force distribution plate  10 . 
       FIG. 2  shows a shipping container using the force distribution plate of  FIG. 1 , in accordance with aspects of the present invention. More specifically as shown in  FIG. 2 , two force distribution plates  10  are provided within a container  5 , on a top side and bottom side of a stack of wafers  15 . Advantageously, by using the two force distribution plates  10  it is now possible to ship upwards of 13 or more 75 micron thin wafers  15 , without damage; compared to conventional systems which were able to stack only six wafers, with the possibility of damage occurring to some of those wafers. 
     The two force distribution plates  10  advantageously distribute forces applied on the wafers over the entire surface of the wafers, thus reducing the overall force applied to any single point on the wafer. For example, vibration forces occurring during shipping as well as vertical forces applied onto the wafers during packaging and unpackaging can be distributed over the entire surface of the wafers, thereby reducing or eliminating a larger force being applied to any single point or small area on the wafer. Essentially, the two force distribution plates  10  act to contain the thin wafers  15  as a unit, allowing them to move only as a unit and distributing all forces across the wafer surface thereby reducing and eliminating any damage to the wafers. 
     Still referring to  FIG. 2 , the container  5  can be any known container currently used to ship wafers, e.g., plastic containers with a diameter of about the size of the wafers, themselves. The wafers  15  are placed in the container  5  and are separated and protected by sheets of cleanroom paper, TYVEK® (TYVEK is a trademark of DuPont Company) or other clean and ESD compliant material sheets, all of which are designated as reference numeral  20 . The ESD compliant material sheets  20  prevent rubbing and scratching of the wafers  15 . Also, foam cushions or sheets  25  can be provided on the force distribution plates  10 , on opposing sides of the stack of wafers  15 . 
       FIG. 3  shows another variation of the shipping container using the force distribution plate of  FIG. 1 , in accordance with aspects of the present invention. More specifically, two force distribution plates  10  are provided within a container  5 , on a top side and bottom side of a stack of wafers  15 , providing the advantages as described herein. The wafers  15  are placed in the container  5  and are separated and protected by sheets of cleanroom paper, TYVEK® (TYVEK is a trademark of DuPont Company) or other clean and ESD compliant material sheets  20 . Also, foam cushions or sheets  25  can be provided on the force distribution plates  10 , on opposing sides of the stack of wafers  15 . In addition, one or more perimeter cushions or sheets  25 ′ are provided about the edges or perimeter of the stack of wafers  15  to provide added protection. The one or more perimeter cushions or sheets  25 ′ prevent lateral movement of the thin wafers during shipping. Also, in this aspect of the invention, a reinforced cover  30  is provided on the upper foam cushion  20  to provide added protection during shipping. 
     As should be understood by those of skill in the art, the foam cushions or sheets  25 ′ and reinforced cover  30  can also be implemented in the embodiment of  FIG. 2 . Moreover, in any of the embodiments, it is also contemplated that the force distribution plates  10  can be provided between stacks of wafers  15 . Also, in each of the embodiments, the container  5  is assembled as follows: 
     (i) foam is placed in a bottom of the container; 
     (ii) a lower force distribution plate is provided in the container, above the foam; 
     (iii) in embodiments, side foam can provided about the perimeter of the container; 
     (iv) a plurality of wafers and sheets therebetween are stacked on the lower distribution plate (within the side foam); 
     (v) an upper force distribution plate is provided in the container, on top of the stack of wafers; 
     (vi) upper foam is placed on the upper force distribution plate; 
     (vii) in embodiments, a top cover can be placed on the upper foam; and 
     (viii) the container is sealed. 
     The wafer shipping container may then be disassembled by simply reversing the assembly process. 
       FIG. 4  shows a mechanical equivalent shipping container of either  FIG. 2  or  FIG. 3 , in accordance with aspects of the present invention. As shown in this figure, the foam sheets are represented as springs  25 ″, allowing the stack of wafers  15  bracketed by the force distribution plates  10  to move (slightly) as a unit, up and down. The force distribution plates  10  prevent the thin wafers from flexing while in the package, thus preventing damage. 
     Table 1 shows testing performed on 100 micron, 85 micron, 75 micron and 65 micron wafers. As shown in this table, each of the wafers passed all testing: downward pressure test, vibration test and drop test. 
     
       
         
           
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 Wafer 
                 Downward 
                   
                   
               
               
                 Thickness 
                 pressure 
                 Vibration 
               
               
                 (microns) 
                 Test 
                 Test 
                 Drop Test 
               
               
                   
               
             
            
               
                 100 microns  
                 Passed 
                 Passed 
                 Passed 
               
               
                 85 microns 
                 Passed 
                 Passed 
                 Passed 
               
               
                 75 microns 
                 Passed 
                 Passed 
                 Passed 
               
               
                 65 microns 
                 Passed 
                 Passed 
                 Passed 
               
               
                   
               
            
           
         
       
     
     The method(s) as described above is used in the fabrication of integrated circuit chips. The resulting integrated circuit chips can be distributed by the fabricator in raw wafer form (that is, as a single wafer that has multiple unpackaged chips), as a bare die, or in a packaged form. In the latter case the chip is mounted in a single chip package (such as a plastic carrier, with leads that are affixed to a motherboard or other higher level carrier) or in a multichip package (such as a ceramic carrier that has either or both surface interconnections or buried interconnections). In any case the chip is then integrated with other chips, discrete circuit elements, and/or other signal processing devices as part of either (a) an intermediate product, such as a motherboard, or (b) an end product. The end product can be any product that includes integrated circuit chips, ranging from toys and other low-end applications to advanced computer products having a display, a keyboard or other input device, and a central processor. 
     The descriptions of the various embodiments of the present invention have been presented for purposes of illustration, but are not intended to be exhaustive or limited to the embodiments 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 described embodiments. The terminology used herein was chosen to best explain the principles of the embodiments, the practical application or technical improvement over technologies found in the marketplace, or to enable others of ordinary skill in the art to understand the embodiments disclosed herein.