Abstract:
An injection molded container for storing and transporting wafers includes a base having a wafer area upon which to place a stack of a plurality of wafers. A protective wall surrounds the wafer area, and extends upward, having a first perimeter at the base and a second perimeter at a top wall extremity that is greater than the first perimeter, resulting in the wall being positioned with a draft angle to a line perpendicular to a plane of the base so as to facilitate removal of the container from an injection mold. This invention provides a plurality of wafer positioning columns, each having a surface with a line of contact rising perpendicular to the plane of the base. The lines of contact are positioned so as to restrict movement of a stack of wafers placed in the container.

Description:
[0001]     This application is related to U.S. patent application Ser. No. ______ entitled “Wafer Shipper With Orientation Control,” [Attorney Docket No. 067810-0303880] filed on the same day as this application, and which is expressly incorporated by reference herein. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention is related generally to wafer storage containers, and more particularly to an injection molded storage container with protective walls formed at a draft angle, and wafer positioning posts oriented with no draft angle.  
         [0004]     2. Description of the Prior Art  
         [0005]     Storage and shipping containers for wafers are often injection molded and have walls surrounding the wafers for protection.  FIG. 1  is an illustration of an injection molded container  10 . Using standard injection molding practices, the inside surface  12  of the container walls  14  of the container must have what is called a draft angle, such as angle  16  between a perpendicular line  18  from the plane  20  of the container base and a line  22  tangent to the wall  14  for the inside surface  12  of the container. This construction leaves the inside diameter  24  at the base plane  20  of the container smaller than the diameter  26  at the top, which is a condition that allows the container to be removed from the mold from which it is formed. A draft angle is also needed for the outside wall surface.  
         [0006]      FIG. 2  is a cross-sectional view of the container of  FIG. 1 , for more clearly showing the draft angle  16  of the inside wall surface, as well as a draft angle  17  for the outside wall surface, and for illustrating the problem with the injection molded construction when the container  10  is used to transport a stack  28  of wafers. The draft angle  16  is clearly exaggerated in  FIGS. 1 and 2  for ease of illustration. The problem with the draft angle, is that it causes a gradual increase in the space  30  between the wafers and the wall as the stack is increased in height, and thereby allowing wafer movement. The wafers can be chipped or scratched as a result of movement in the container, and generally the risk of damage to a disk in a container is proportional to the degree of movement in the container.  
       SUMMARY  
       [0007]     It is an advantage of this invention in that it provides an improved wafer storage container.  
         [0008]     It is a further advantage of this invention in that it provides a storage container for wafers that minimizes wafer movement in the container.  
         [0009]     In one embodiment of the present invention, an injection molded container for storing and transporting wafers includes a base having a wafer area upon which to place a stack of a plurality of wafer elements. The term “wafer element” will be used as a generic term to describe a wafer or a wafer mounted on a wafer frame. A protective wall surrounds the wafer area, and extends upward, having a first perimeter at the base and a second perimeter at a top wall extremity that is greater than the first perimeter, resulting in the wall being positioned with a draft angle to a line perpendicular to a plane of the base so as to facilitate removal of the container from an injection mold. This invention provides a plurality of wafer element positioning columns, each having a surface with a line of contact rising perpendicular to the plane of the base. The lines of contact are positioned so as to restrict movement of a stack of wafer elements placed in the container. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  illustrates the draft angle of a prior art injection container;  
         [0011]      FIG. 2  illustrates the potential movement of a stack of wafers in a prior art injection molded container;  
         [0012]      FIG. 3  is a simplified drawing for illustrating the present invention;  
         [0013]      FIG. 4  is a top view of  FIG. 3 ;  
         [0014]      FIG. 5  is a cross sectional view of  FIG. 3   
         [0015]      FIG. 6  is a pictorial view of a wafer storage container and cover;  
         [0016]      FIG. 7A  illustrates a stack of wafers for placement in a container;  
         [0017]      FIG. 7B  illustrates separators between wafer elements;  
         [0018]      FIG. 8  is a top view of the container of  FIG. 6 ; and  
         [0019]      FIG. 9  is a cross sectional view from  FIG. 7A  showing a method of attaching a wafer to a frame. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0020]     While the present invention will be described herein with reference to particular embodiments thereof, a latitude of modifications, various changes and substitutions are intended, and it will be appreciated that in some instances some features of the invention will be employed without a corresponding use of other features without departing from the spirit and scope of the invention as described with respect to the preferred embodiments set forth herein.  
         [0021]     The concept of the present invention is illustrated in  FIGS. 3 and 4  which are simplified drawings for use in describing the invention. A container  32  has a protective wall apparatus  34  extending upward from a base  35 . The wall apparatus can be of any configuration compatible with injection molding for providing protection to wafers placed on a wafer plane area  36 . The wall can be continuous, surrounding an enclosure  38  containing the wafer area  36  as shown, or it can be a plurality of sections. Conforming to injection molding practice, the wall or wall sections are formed with interior and exterior wall surface draft angles  40  and  41  in order to allow the container  32  to be released/ejected from the mold. The completed container  32  according to the present invention has a plurality of columns  42  positioned inside the enclosure  38  surrounded by the wall apparatus  34 . The columns  42  are configured to restrict the movement of a stack of wafer elements. The term “wafer element” will be used as a generic term to describe either a wafer or a wafer mounted on a wafer frame. In an embodiment wherein the columns are formed as an integral part of the container molding process, they are configured so as to avoid excessive resistance in the process of separating the container and mold. The areas of vertical surfaces are configured so as to be insubstantial in comparison to the surfaces having a draft angle so as to not add undue resistance to separation of the mold from the container. Each column  42  is designed with a surface  44  having a line of contact for limiting wafer movement that extends vertically upward from the plane of the wafer area  36 . The columns are configured and placed so that a vertical line of contact on each surface  44  is positioned so as to restrict movement of a stack of wafer elements  45  as shown in  FIG. 4 . As noted above, the wafer elements as defined herein can be simply a wafer, or can be a wafer attached to a wafer frame. The columns  42  are shown as round, separate posts in  FIGS. 3 and 4  for ease of illustration of the principle of the present invention, but can actually be structures of any configuration that provides the required vertical line of contact, and that facilitates ejection from a mold. The column structures can, for example, be integrally formed with the wall structure. Column cross sections, for example, can be oval, square, hexagonal, triangular, etc. The columns can each have a top surface  46  to which pressure can be applied for ejecting the container from the mold. Since there is no draft angle on the posts/columns line of contact, the distance from a wafer element to the post is the same at the bottom of a stack as it is at the top of the stack.  
         [0022]      FIG. 5  is a cross sectional view of  FIG. 3  that shows a wafer stack  47  in place in the container  32 . The view of  FIG. 5  shows the uniform/equal clearance  49  provided between the posts  42  and wafer  47 .  
         [0023]      FIG. 6  shows a particular embodiment of the present invention including a container  52  and a container cover  54 . The wafer elements in this embodiment each include a wafer frame and wafer. In this case the wafer can be either whole or diced, as will be further explained in the following. The present invention also includes containers designed according to the principles to be described, for use with wafers, without being mounted to a frame. In this case, as will be described, the wafers will have at least one orientation artifact. The wall apparatus  56  of container  52  has four sections  57 ,  59 ,  61 ,  63 . The irregular contours of the walls in this embodiment are designed to conform to the shape of wafer frames upon which wafers are attached. The irregular contour assures that all of the wafer frames are oriented the same in the container  52 , therefore making it possible for all of the wafers to also be in the same orientation. This is an alternate/optional feature. The design uses 16 columns  58 , and as shown are structures that are integrally molded with the wall structures  56 . Each of the wall sections as shown has areas  60 ,  62  and  64 , which are all molded with a draft angle, not shown, but as described in reference to  FIGS. 3 and 5 . The columns  58  all have a surface designed to provide a line of contact for restraining movement of the wafer elements. The lines of contact have a vertical orientation extending upward at a right angle relative to a base  66  defining a wafer plane upon which the stack of wafer elements are to be placed. Because the columns  58  in  FIG. 6  are molded with the wall sections, and due to the vertical/orthogonal direction of the lines of contact i.e. no draft angle on the line of contact, the columns  58  appear wider near the top of the wall structures in  FIG. 6  than at the bottom of the wall at the base  66  level. The top surfaces  67  of each column provide a substantial point of contact for application of ejector pins for pressuring the container for removal from a mold. The prongs  68  are for insertion in corresponding slots  70  in the cover  54  for securing the cover  54  over the container  52 .  
         [0024]      FIG. 7A  illustrates a stack  72  of wafer elements, wherein each wafer, such as wafer  74  is mounted on a wafer frame  76  having an irregular outline which matches a corresponding outline of the wall structure  56  in order to assure consistent alignment of the wafers in the container  52 . The stack  72  of wafer elements of  FIG. 7A  and generally for any stack, will include some form of separators between each wafer element. The separators may be for example thin disks constructed of paper or foam, and/or a carbon/carbon impregnated material. Such an arrangement using all of the above is illustrated in  FIG. 7B  wherein a container  98  has a wafer element  100  placed therein, with a carbon interleaf  102 , a foam material  104 , and a paper interleaf  106  are in position for placement on top of the wafer element  100 . A cover  108  is also shown.  
         [0025]      FIG. 8  is a top view of the container  52  of  FIGS. 6 and 7 A for showing more clearly the position of the 16 columns  58  and the shape of the wall sections  57 ,  59 ,  61  and  63 . In reference to the wafer frame  76  shown in  FIG. 7A , wall sections  57  and  63  have contour irregularities which will be referred to as orientation artifacts  78  and  79 . The frames  76  have corresponding mating irregularities which will be referred to as alignment artifacts  80  and  81 . Without at least one each of the orientation artifacts and alignment artifacts, the wafer frame could be in any one of four positions. Of course, if the wall sections and wafer frames conformed to a circular pattern, the wafer frames could have any orientation without the wall and frame mating irregularities. Although  FIGS. 7A and 8  show two orientation artifacts  78  and  79  in the walls with corresponding mating alignment artifacts  80  and  81  in the frames  76 , the present invention applies to any number of artifacts (one or more) that function to assure the orientation of the wafer frame in the container. For example, a single asymmetrical irregularity such as  79  is sufficient to assure only one position/orientation possible for a frame.  
         [0026]     The draft angle of the wall sections  60 ,  62  and  64  is evident by the line  82  indicating the inside perimeter of the wall section at the level of the bottom of the wall structure  56 . Line  84  indicates the inner perimeter of the wall section at the top of the wall, which clearly lies outside the line  82  at the bottom, and therefore indicates the draft angle. This detail is more clearly shown in the enlargened section A.  
         [0027]     Section A also shows columns  58  more clearly. Note that the top view of  FIG. 8  shows only a single line  86  passing across the line of contact i.e. the line which would contact a wafer or wafer frame. The single line indicates that the line of contact is perpendicular to the base  66 , and therefore the line of contact does not show in the top view of  FIG. 8 . In contrast, the two lines  82  and  84  indicate the draft angle of the wall sections  57 ,  59 ,  61 ,  63 .  
         [0028]      FIG. 9  is a cross sectional view of one wafer element  88 , including a wafer frame  90  in the general shape of a ring with a hole  92  there-thru into which is placed a wafer  94 .  FIG. 9  is presented in order to describe a method of attaching a wafer  94  to a frame  90 . The attachment as shown in  FIG. 9  is accomplished using an adhesive film  96 , placed with an adhesive surface in contact with a bottom surface of the frame  90  and with a bottom surface of wafer  94 . The use of tape  96  is well understood by those skilled in the art for the purpose of securing a wafer  94  within a frame  90 . The tape  96  generally covers substantially all of the bottom surface of the frame, as well as the entire bottom surface of the wafer. The tape normally used has a characteristic (example, blue color) that it does not absorb laser energy used to cut a wafer. In some applications, the tape is applied to the frame, then a wafer is placed in the hole  92  on the adhesive of the tape. A laser is then used in this particular application to cut the wafer into separate parts, i.e., the wafer is diced. The tape remains undisturbed by the cutting of the wafer. A typical thickness of the wafer frame is 0.030 inches.  
         [0029]     While the present invention has been described herein with reference to particular embodiments thereof, a latitude of modifications, various changes and substitutions are intended in the foregoing disclosure, and it will be appreciated that in some instances some features of the invention will be employed without a corresponding use of other features without departing from the spirit and scope of the invention as set forth in the appended claims.