Abstract:
Improvements in a single and dual stage wafer cushion is disclosed where the wafer cushion can use an edge hinge as a single first stage cushion and a second mid span hinge for the dual stage wafer cushion. This dual stage design gives two distinctly different cushioning forces as opposed to using a single stage design where the force is linear with the amount of compression that is being applied to the outer surfaces of the wafer cushion. The outside edge of the ring provides the greatest expansion such that only the outer edge of the ring makes contact with the outer edge of a wafer. The wafer cushion is a material that flexes and absorbs shocks before the shock is transferred to the wafer stack. The material minimizes debris or contaminants from embedding into the wafer cushion and also prevents sheading of material from the wafer cushion.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    Not Applicable 
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not Applicable 
       THE NAMES OF THE PARTIES TO A JOINT RESEARCH AGREEMENT 
       [0003]    Not Applicable 
       INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC 
       [0004]    Not Applicable 
       BACKGROUND OF THE INVENTION 
       [0005]    1. Field of the Invention 
         [0006]    This invention relates to improvements in a cushioning device for cushioning a stack of semiconductor wafers within a wafer transportation container. More particularly, the present cushioning device is a formed or folded ring with compound bends and surfaces that provide variable amounts of cushioning as the compound bends and surfaces engage. 
         [0007]    2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98 
         [0008]    When semiconductor wafers are placed within a transportation container the stack of wafers are either loose or are compressed against the opposing houses. In either case, transportation of the semiconductor wafers can cause abrasion to some or all of the stacked wafers. Some patents have been filed using separator sheets, pads or foam rings to cushion the outer semiconductor wafers and absorb shock and movement as the semiconductor wafers are being transported. 
         [0009]    Limiting radial movement becomes an important issue when shipping to prevent abrasion of the prime wafer surface, which may or may not contain circuitry. This is also true for bumped wafers that may or may not be stacked on spacer rings where the rings must only touch the periphery of the wafer and not shift radially into the areas containing the solder bumps. The Wafer Cushioning Rings ability to protect semiconductor wafers is enhanced when using a wafer container that reduces radial wafer shift. 
         [0010]    If a rigid spacer is used the spacer can cause harm to the wafers and may not provide sufficient grip on the wafers to prevent movement. If a foam spacer is used the foam spacers are susceptible to damage and aging. Several products and patents have been filed that disclose these features. Exemplary examples of patents covering these products are disclosed herein. 
         [0011]    U.S. Pat. No. 3,392,824 issued Jul. 16, 1968 to S. F. Flynn and U.S. Pat. No. 5,366,079 issued Oct. 22, 1994 to Chih-Ching Lin et al., both disclose packaging system for cushioning circuit wafer where the cushioning system is a Bellville type platter or a platter with flexed legs that extend from the center of the platter. While these patents disclose a cushioning system for wafers the cushions slide radially on the outer surface of the wafers as the spacers are crushed within the transportation housing. This can cause damage to the wafers. 
         [0012]    U.S. Pat. No. 6,926,150 issued Aug. 9, 2005 to Gonzlo Amador et al., and U.S. Pat. No. 7,530,462 issued May 12, 2009 to Toshitsugu Yajima et al., both disclose a wafer cushion using a rigid disk space. These patents are more related to spacers between the semiconductor wafers rather that providing cushioning and gap filling. In a number of cases these spacers are supplemented with foam pads located either across the entire surface of the wafer or on just the outer edges of the wafer. 
         [0013]    U.S. Pat. No. 7,425,362 issued Sep. 16, 2008 to James R. Thomas et al and U.S. Pat. No. 7,611,766 issued to Masahiko Fuyumuro on Nov. 3, 2009 discloses a wavy pad where the high and low parts of the pad fill the space between the wafers and the transportation housing. These pads are made from a variety of materials from plastic to paper and are fabricated in variable profiles to accommodate the space between the wafers and transportation housing. 
         [0014]    U.S. Pat. No. 6,926,150 issued Aug. 9, 2005 to Gonzalo Amador et al., U.S. Pat. No. 7,316,312 issued Jan. 8, 2008 to Pei-Liang Chiu and U.S. Patent Application Number 2002/0144927 to Ray G. Brooks et al that published on Oct. 10, 2002 discloses a foam pad or ring to cushion the wafers within the packaging. The amount of force that is applied by a foam pad can be a significant variable as the foam ages. Foams can also be a cause of contamination as the foam cell structure breaks down. Foam particles can also be a contaminant that interferes with the doping of semiconductor wafers. In some cases the foam makes contact with the entire surface of the wafers and can cause deformation of the wafer(s). 
         [0015]    What is needed is a cushioning ring that has a variable amount of cushioning to accommodate the minor variation on the top and bottom of a stack of semiconductor wafers. The pending design provides this solution with a single and dual stage wafer cushion. 
       BRIEF SUMMARY OF THE INVENTION 
       [0016]    It is an object of the single and dual stage wafer cushion to operate with a wafer carrier where the cushion can be placed on both the bottom of the wafer carrier and on the top of wafers that are placed within the carrier. The cushion expands and collapses to accommodate variations in wafer thicknesses and variation in carrier housings. While the variation in wafer thickness on an individual wafer may be small, when the variations are accumulated the gap can be larger than desired. The cushioning provides minimal forces on the wafers and the housing to make the housing easy to open and further limit movement of the wafers within the wafer carrier. 
         [0017]    It is an object of the single and dual stage wafer cushion to be manufactured to fit within the housing of a wafer carrier. The shape of the cushion is a folded ring where the fold is open on the outside diameter. The outside edge of the ring provides the greatest expansion such that only the outer edge of the ring makes contact with the outer edge of the wafer. This minimizes the contact area with wafer and places any axial load on the outer edge surface of the wafer where a wafer typically is placed on a separator disk to minimize damage to the inner surface of the wafers and minimize flexing of the center of the wafer(s). 
         [0018]    It is another object of the single and dual stage wafer cushion to be made of a material where it can flex and absorb any shocks before the shock is transferred to the wafer stack. The material can be molded, thermoformed, cast or vulcanized. 
         [0019]    It is another object of the single and dual stage wafer cushion to be made with a cross section shape having only half a “V” where the ring would be attached by bonding or clipping to the top and or bottom cover such that the cover provides the limiting function of the missing half of the “V”. This design would be capable of having a single or dual stage version. This design allows single or multiple arms or “V rings” to be stacked to take up excess space inside the box. 
         [0020]    It is another object of the single and dual stage wafer cushion to be made from a non-absorbent material. This prevents debris or contaminants from embedding into the wafer cushion and also prevent sheading of material from the wafer cushion. 
         [0021]    It is still another object of the single and dual stage wafer cushion to use both an edge hinge as a single first stage hinge and a second mid span hinge for the dual stage wafer. This dual stage design gives two distinctly different cushioning forces as opposed to using a single stage design where the force is liner with the amount of compression that is being applied to the outer surfaces of the wafer cushion. 
         [0022]    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 SEVERAL VIEWS OF THE DRAWING(S) 
         [0023]      FIG. 1  shows an isometric view of a single and dual stage wafer cushion. 
           [0024]      FIG. 2  shows an isometric sectional view of the single and dual stage wafer cushion. 
           [0025]      FIG. 3  shows an isometric sectional view of the single and dual stage wafer cushion in a second preferred embodiment. 
           [0026]      FIG. 4  shows an isometric sectional view of the single and dual stage wafer cushion in a third preferred embodiment. 
           [0027]      FIG. 5  shows an isometric view of the single and dual stage wafer cushion on a stack of semiconductor wafers without the top housing of the wafer shipper installed. 
           [0028]      FIG. 6  shows an isometric view of the single and dual stage wafer cushion on a stack of semiconductor wafers with the top housing of the wafer shipper installed. 
           [0029]      FIG. 7  shows a side sectional view of the single and dual stage wafer cushion with the wafer cushion in an uncompressed condition. 
           [0030]      FIG. 8  shows a side sectional view of the single and dual stage wafer cushion with the wafer cushion initially compressed. 
           [0031]      FIG. 9  shows a side sectional view of the single and dual stage wafer cushion with the wafer cushion partially compressed. 
           [0032]      FIG. 10  shows a side sectional view of the single and dual stage wafer cushion with the wafer cushion more fully compressed. 
           [0033]      FIG. 11  shows an isometric sectional view of the single and dual stage wafer cushion in a fourth preferred embodiment. 
           [0034]      FIG. 12  shows an isometric view of the single and dual stage wafer cushion from the fourth preferred embodiment bonded to the bottom housing without wafers installed upon the wafer cushion. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0035]      FIG. 1  shows an isometric view of a single and dual stage wafer cushion  20  and  FIG. 2  shows an isometric sectional view of the single and dual stage wafer cushion. The single and dual stage wafer cushion  20  from  FIG. 1  shows essentially a ring shaped cushion where the inside of the wafer cushion  20  is open. In the preferred embodiment two single and dual stage wafer cushions  20  are placed on a stack of semiconductor wafers  40  as shown in  FIG. 2 . The stack of semiconductor wafers in this figure include spacer rings  50  is placed between each semiconductor wafer  40 . The spacers  50  allow for stacking of “Bumped” wafers substrates with tiny solder balls used for electrical interconnection to the final product or external circuitry. Bumped wafer stacks are normally used with solid height, non-adjustable spacer rings  50  between the wafers to prevent the solder balls (bumps) from being damaged by contact with adjacent substrates  40 . 
         [0036]    This first preferred embodiment is a ring designed with a dual spring rate or variable spring rate. The dual stage version  20  has one spring rate for easy loading and closing of the shipper top cover (not shown), whereas the second stage of the spring provides a stiffer spring rate to absorb energy if the shipper is dropped or mishandled, thus protecting the wafer stack or substrate stack. 
         [0037]    With the cushion configured as a “V Ring” the cross section is shaped like a “V” to provide a spring or cushioning for the wafers. This design lends itself to the injection molding process, vulcanization or other manufacturing methods with the V shaped cross section. The tip  23  of the V provides the point of contact to the wafer and the shipping container. There is also a case where multiple stacking “V rings” can be used to take up excess space inside the wafer shipping container. One advantage of the “V” shape is that it allows the ring to only contact a small zone  23  and  34  on the wafer  40  near the perimeter. 
         [0038]    For bumped wafers, there is normally a 3 mm wide exclusion zone for circuitry or solder bumps that extends inward from the perimeter of the wafer. Our preferred embodiment has a slightly raised zone with radius at the point of wafer contact, but it does not have to have this feature. The slightly raised area at the tip of the “V” allows additional clearance for any solder bumps that are near the “keep out” zone.  FIG. 2  shows a two separate wafer cushions with a lower cushion placed into the wafer carrier  21  under all of the wafers  40 . The outside diameter edge  23  of the lower cushion is sized to fit within the wafer carrier  21  with the lower bottom surface  22  supported on the bottom of the wafer carrier  21  support. 
         [0039]    The weight of the wafers  40  and support rings  50  at least partially load the lower wafer cushion whereby at least partially compressing the lower cushion such that the first stage or inside diameter  30  hinge  31  of the wafer cushion at least partially compress the wafer cushion. It should be noted from  FIG. 2  that when the first stage is compressed a second cushion gap is still visible both inside and outside of the middle surface  32 .  FIG. 2  further shows that when the first stage has made contact only the outer diameter edge  34  makes contact with the outer edge of the semiconductor wafer  40  and the remaining inner diameter surfaces of the wafer cushion “float” above the semiconductor wafer without making contact with the surface of the semiconductor wafer(s). When the top housing (not shown) of the wafer carrier is installed the top housing compresses the top surface  35  of the upper wafer cushion and loads the lower wafer cushion whereby providing even cushion between the top and the bottom wafer cushion. 
         [0040]      FIG. 3  shows an isometric sectional view of the single and dual stage wafer cushion in a second preferred embodiment. In this embodiment the wafer cushion  20  has an inner lip  60  that provides additional strength for the hinge  65  and also provides a gripping surface for easier removal of the wafer cushion  20 . The outside diameter  64  is sufficiently sized to center the wafer cushion within a wafer carrier. The top  61  and bottom surface  62  of the wafer cushion  20  has a slight radial curve to maintain contact with just the outer edge top or bottom surface of a semiconductor wafer. It is further contemplated that a portion  66  of the cushion can be broken, serrated or formed to create multiple finger portions that independently flex from the inside diameter hinge  65 . In the embodiment shown the void areas  66  exists through both the upper and lower lips or arms but could also be formed to exist only through one leg of the cushion whereby leaving the other leg continuous. At the first stage of compression the inside outer surfaces  64  of the wafer cushion come in contact and leave an air gap from the inside hinge area  65  to the outer surfaces to provide the second stage of cushioning. 
         [0041]      FIG. 4  shows an isometric sectional view of the single and dual stage wafer cushion  20  in a third preferred embodiment. This third preferred embodiment will be briefly described in this figure and described in more detail in  FIGS. 5 to 10 . This embodiment has a plurality of flexible arms that extend from the inside diameter hinge area  70  and  75 . The extreme upper and lower surfaces  71  make contact with the outer upper and lower surfaces of a semiconductor wafer when the wafer cushion is installed in a wafer carrier. The extreme outer diameters(s)  73  are sufficiently sized to fit within a wafer carrier and provide little or no movement within the wafer carrier. The wafer cushion is shown in an expanded and in a first stage compressed stage in  FIGS. 5 and 6  within a wafer carrier. 
         [0042]      FIG. 5  shows an isometric view of the single and dual stage wafer cushion on a stack of semiconductor wafers without the top housing of the wafer shipper installed and  FIG. 6  shows an isometric view of the single and dual stage wafer cushion on a stack of semiconductor wafers with the top housing of the wafer shipper installed. From  FIGS. 5  and  6  the lower cushion is compressed with the lower lip  22  in contact with the bottom housing  21  and the upper lip  23  in contact with the lowest semiconductor wafer  40 . The stack of semiconductor wafers  40  are each separated with a wafer separator  50  placed between each semiconductor wafer  40 . In  FIG. 5  the upper wafer cushion is shown uncompressed where the first or single stage of cushion is not compressed and the middle of the extended arms are not in contact at mid span  76  and  77 . The bottom surface of the wafer cushion at  72  is in contact with the outer top surface of the top semiconductor wafer  40 . The tangent arched top surface of the wafer cushion  71  provides generally just a linear point contact with the semiconductor wafer  40  and the top  25  or bottom  21  housing. The outer edge  74  and  78  of the cushion approximates the outside diameter of the semiconductor wafers  40 . 
         [0043]    When the top housing  25  is lowered onto the wafer cushion the arms will move closer together as they hinge from the inner radius  70 . When the housings  21  and  25  are secured the top housing will push upon the outer edge  26  of the top wafer cushion and the central portion  77  of the arms will make contact and form the first stage of cushion. 
         [0044]      FIG. 7  shows a side sectional view of the single and dual stage wafer cushion with the wafer cushion in an uncompressed condition,  FIG. 8  shows a side sectional view of the single and dual stage wafer cushion with the wafer cushion initially compressed,  FIG. 9  shows a side sectional view of the single and dual stage wafer cushion with the wafer cushion partially compressed and  FIG. 10  shows a side sectional view of the single and dual stage wafer cushion with the wafer cushion more fully compressed. Starting with  FIG. 7  the wafer cushion  20  is in a natural uncompressed condition without any forces  100  and  101  causing the cushion to compress. The hinge  70  and  75  creates a curve to keep the arms on an open “U” or “V” configuration. The top  71  and bottom surfaces  72  of the wafer cushion are at the greatest dimension. The outer lip  74  and  78  are essentially the same dimension, but it is contemplated that they can exist at different radii as well. The central  76  and  77  or second (dual) stage of the arms open and not in contact. 
         [0045]    In  FIG. 8  forces  100  and  101  cause the arms to compress and the interior area begins to compress. Both the end  70 ,  73  and the mid-section elbow, profile or hinges  76  and  77  flex as the force increases until the inner surfaces of the arms make contact as shown in  FIG. 9 . The force  100  and  101  creates a first load or spring constant profile. 
         [0046]    At this stage the resisting spring force to provide a cushion changes because the length of the lever arms has been shortened. In the embodiment shown the contact between the arm segments is approximately at mid span, but it is contemplated that the central contact can take place at any point in the span of the arms to yield a different cushion force profile. The profile shown in  FIG. 9  represents the condition where the housings are closed and in a normal shipping mode. Additional applied force between the forces shown in  FIGS. 9 and 10   100 / 101  verses  102 / 103  provides a second load or spring constant that is different from the load or spring constant as applied from  FIGS. 7 to 9 . The spring constant can be linear stepped or non-linear based upon the shape, angles and constant or variable thicknesses of the hinge and or leg section(s). 
         [0047]      FIG. 10  shows a shock load condition that might occur when the wafer carrier is dropped or bumped. The forces  102  and  103  continue to push on the extreme ends of the arms. The outer lengths of the arms are in compression along their length(s). It should be noted that even at this loading an air gap  79  still provides some further cushioning and the inside on the cushion still provides a space for clearance of components that may be placed on the semiconductor wafers. 
         [0048]      FIG. 11  shows an isometric sectional view of the single and dual stage wafer cushion  29  in a fourth preferred embodiment and  FIG. 12  shows an isometric view of the single and dual stage wafer cushion from the fourth preferred embodiment bonded to the bottom housing without wafers installed upon the wafer cushion. 
         [0049]    “Single Sided Ring”—One version of the cushioning ring  29  described above is a ring with a cross section shape having only half a “V” where the ring would be attached, (bonded or clipped) to the top or bottom cover such that the cover provides the limiting function of the missing half of the “V”. This design would be capable of having a single or dual stage version. This design allows multiple “V rings” to be stacked to take up excess space inside the box. The bottom of this cushion  90  can be bonded to the lower housing  21  (or  25 ). While this single sided ring has only one arm the arm has a similar configuration with an inside hinge area  91  and  92 , a mid-span elbow  93  to form a division between the first and second stage of the cushion. The outer edge  95  is sized to provide clearance of the housing  21  wall to provide free movement and flexing. The top edge of the wafer cushion  96  is configured to make contact with just the outer edge of the wafer separator or the semiconductor wafer (not shown). The lower radii  94  provide additional shock cushioning when the wafer stack flattens the majority of the wafer cushion  29 . 
         [0050]    In the preferred embodiment the wafer cushion is made from a compliant material having a hardness of shore D of between 10 and 70 but other hardness are contemplated based upon the material that is being cushioned and the stack height/weight that is being cushioned. It is also contemplated that the upper and lower wafer cushions being used in a wafer shipper can have different properties and configurations based upon the weight or the fact that the semiconductor wafers exist above or below the wafer cushions. The profile from the central hinge to the outer contact points can be curved, or have variable cross section, or multiple steps, profiles, elbows or bends to achieve non-linear cushion forces or multiple stage wafer cushions. 
         [0051]    Thus, specific embodiments of a single and dual stage wafer cushion have been disclosed. It should be apparent, however, to those skilled in the art that many more modifications besides those 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.