Abstract:
Consistent with an example embodiment, there is a semiconductor device, having a topside surface and an underside surface, the semiconductor device comprises an active device of an area defined on the topside surface, the topside surface having a first area. A protective material is on to the underside surface of the semiconductor device, the protective material has an area greater than the first area. A laminating film attaches the protective material to the underside surface. The protective material serves to protect the semiconductor device from mechanical damage during handling and assembly onto a product&#39;s printed circuit board.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/717,594 filed on Oct. 23, 2012 and is incorporated by reference in its entirety. 
     
    
     FIELD OF INVENTION 
       [0002]    The embodiments of the present invention relate to semiconductor device packaging and, more particularly, to WLCSP packaging having modifications that protect the semiconductor die from handling damage so as to enhance the manufacturability and quality of products. 
       BACKGROUND 
       [0003]    The electronics industry continues to rely upon advances in semiconductor technology to realize higher-function devices in more compact areas. For many applications realizing higher-functioning devices requires integrating a large number of electronic devices into a single silicon wafer. As the number of electronic devices per given area of the silicon wafer increases, the manufacturing process becomes more difficult. 
         [0004]    The packaging of an IC device is increasingly playing a role in its ultimate performance. For example, in mobile devices (i.e., mobile phones, tablet computers, laptop computers, remote controls, etc), WLCSP components are used in their assembly. WLCSP components save valuable space in the mobile device. After assembly, in some example processes, customers encapsulate these WLCSP devices by injection molding or casing. This manual post-processing of the WLCSP may result in device damage. Consequently, the customer may prefer to have the WLCSP product surrounded by non-brittle material, which prevents damage to the die itself, before receiving the product for assembly in to his mobile device. 
         [0005]    There is a need for a WLCSP assembly process which can address the challenges raised by the needs of mobile applications. 
       SUMMARY 
       [0006]    The present disclosure has been found useful in the packaging of semi-conductor devices which find their way into portable electronic devices. In particular, WLCSP products which are furnished as unpackaged die to manufacturers of mobile devices, who in turn encapsulate these devices directly onto a printed circuit board (in an effort to conserve valuable space in the mobile device) may subject these unpackaged die to rough handling. The handling may result in cracking or other latent damage which may not show up until the mobile device reaches the end user. 
         [0007]    The user laminates a protective material on the underside of a wafer having device die. Through processing the unpackaged die are protected on their undersides with a oversized protective cover which absorbs the shocks of manual handling during assembly of the mobile device. The process can also be used for chip-scale packaging (CSP) with or without solder balls. 
         [0008]    In an example embodiment, there is a method for assembling a wafer level chip scale processed (WLCSP) wafer, the wafer having a topside surface and an underside surface, a plurality of device die on the topside surface. The method comprises back grinding, to a first thickness, the underside surface the wafer. Mounted onto a first sheet of dicing foil is the underside of the wafer; the wafer is sawed to a depth of the first thickness. The dicing foil is stretched and space is made between each one of the plurality device die. The plurality of spaced device die is remounted on the topside surface onto a second sheet of dicing foil. A layer of protection material of a second thickness is laminated onto the undersides of the plurality of spaced device die. To a depth of the second thickness, there is a sawing through the protection material between each of the plurality of spaced device die. Each of the plurality of spaced device die has a protective layer on the underside, the protective layer has an area greater than the area of each one of the plurality of device die. 
         [0009]    In another embodiment, there is a semiconductor device, having a topside surface and an underside surface. The semiconductor device comprises, an active device of an area defined on the topside surface, the topside surface having a first area. A protective material is on to the underside surface of the semiconductor device, the protective material has an area greater than first area. A laminating film attaches the protective material to the underside surface. 
         [0010]    The above summaries of the present disclosure are not intended to represent each disclosed embodiment, or every aspect, of the present invention. Other aspects and example embodiments are provided in the figures and the detailed description that follow. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    The invention may be more completely understood in consideration of the following detailed description of various embodiments of the invention in connection with the accompanying drawings, in which: 
           [0012]      FIG. 1  is a flow diagram of an embodiment according to the disclosure; 
           [0013]      FIG. 2  depicts an embodiment according to the present disclosure as it protects the WLCSP device; 
           [0014]      FIGS. 3A-3H  illustrate the assembly of an example WLCSP device according an embodiment according to the disclosure; 
           [0015]      FIG. 4A  illustrates a finished device assembled with plastic foil according to an embodiment of the present disclosure; and 
           [0016]      FIG. 4B  illustrates a finished device assembled with a metal foil according to an embodiment of the present disclosure. 
       
    
    
       [0017]    While the invention is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the intention is not to limit the invention to the particular embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims. 
       DETAILED DESCRIPTION 
       [0018]    The disclosed embodiments have been found useful in preventing damage to the Wafer Level Chip-Scale Product (WLCSP) devices during their assembly. The process provides mechanical protection to the silicon device by mounting the device onto a protective material larger than the device die dimensions; the protective material forms a boundary on the device underside that keeps assembly tooling from directly contacting the silicon device, thus avoiding chipping and other damage. Such a process may be integrated into the customary back-end assembly. 
         [0019]    In an example embodiment, the user takes a wafer substrate having devices. The wafer undergoes electrical tests (e.g., E-sort) to sort out non-functioning devices; other processes may forego E-sort and cull out non-functioning devices after packaging. The user laminates the WLCSP wafer of a thickness onto a grinding foil. The backside of the WLSCP wafer is ground down to a thinner thickness. The thinned WLCSP wafer is mounted dicing foil and the grinding foil is removed. The WLSCP wafer is diced. The dicing foil is stretched to separate the device die. The device die are mounted on their contact side onto another film surface. Backsides of device die are laminated with a foil of either metal or plastic. After backside lamination, the protected device die are separated. 
         [0020]    Refer to  FIG. 1 . In an example embodiment according to the present disclosure, a wafer having undergone electrical testing is mounted on a grinding foil  100 . Back grinding of the wafer underside thins out the wafer  110 . The wafer is mounted on a flexible film/dicing foil; the grinding foil is removed  120 . The WLCSP wafer is diced (e.g, sawed) to define the individual WLCSP devices  130 . The dicing foil is stretched so that the WLCSP device die are separated  140 . The separated device die are remounted, on the ball bond side, onto another mounting foil  150 . Upon the backside of the separated device die, lamination is applied  160 . 
         [0021]    The stretched wafer with separated device die is remounted onto a second dicing foil  170 . The device die are sawn apart (e.g., “singulated”). The singulated product is removed from the sawing tape; product is placed into appropriated tray (i.e., JEDEC approved, etc.)  190  or may be spooled onto carrier tape for tape and reel packaging applications. Depending upon device type, devices undergo and optional final electrical testing, packing, and shipping to end user  195 . 
         [0022]    Refer to  FIG. 2 . In an example embodiment, an assembly  200  includes an silicon device  210  of a thickness T 1 . A protection angle α and the silicon thickness T 1  define the stand-off distance T 3  of the protection material. For example, to protect a device die of thickness, T 1 =150 μm, against an impact by a tool  5  with a 20 degree impact angle, a stand-off of about 55 μm is appropriate. Generalized, the stand-off distance is: 
         [0000]      T 3 =tan αT 1   (1)
 
         [0023]    The total thickness, T 2  of the protective material  220  and glue  215  is determined by materials used. The amount of standoff would be achieved by the stretching of the dicing foil  140  to separate out the WLCSP die a prescribed amount, remounting the separated WLCSP die on the contact pad side  150 , then laminating the backside protection thereon  160 . For example, a pre-grinding thickness, T 0  of an eight-inch wafer (20.3 2cm) is about 725 μm, for a six-inch wafer (15.24 cm). Note that this technique may be applied to wafer substrates of any size and may be useful for twelve-inch (30.48 cm) substrates. Further, devices using balls, bumps, pads, etc. benefit from the protective material. In an example process, a WLCSP is ground to a thickness of about 400 μm with a ball bond side of about 200 μm. It is desirable to achieve a minimum wafer thickness, T 1 ; however, it is limited by the technical ability to thin down wafers with 200 μm bumps. Thickness, T 1  in an example process may be in the range of about 150 μm to about 250 μm. 
         [0024]    The protective material  220  laminated with a glue  215 , to the underside of the silicon  210  may be plastic of metal. The plastic material may be made of, but not necessarily limited to, KAPTON®, PTFE (polytetrafluoroethylene), molding compound, etc. KAPTON is the brand name of the polyimide film (i.e., poly-oxydiphenylene-pyromellitimide) manufactured by the E.I. du Pont de Nemours and Company. The protective material  220  and glue  215  used for the lamination must withstand a temperature range of about 200° C. to 300° C. usually encountered in the reflow process for WLCSP device assembly. Metal protective material  220  may be of, but not necessarily limited to, stainless steel, copper, and copper alloys; these metals are similar to those used in the manufacturing of lead frames. 
         [0025]    Refer to  FIGS. 3A-3H . In an example WLCSP wafer  200  with active devices  320 , ball bonds  340  connect to the active regions of devices,  FIG. 3A . In this example, each potential device will have four ball bonds. The WLCSP wafer  320  is mounted on the ball bond side to a grinding foil  310 . Referring to  FIGS. 3B-3E , the backside  330  is ground down to a defined thickness (from an initial wafer thickness T 0  to a final wafer thickness T f ). The thinned wafer  300  is mounted on a flexible film/dicing foil  335  on its backside  330 . Apparatus  360  (e.g., a tooling jig in the manufacturing equipment) keeps the flexible film  335  and attached thinned wafer  300  in tension ( FIG. 3C ). Referring to  FIG. 3D , the thinned wafer  300  is sliced with a wafer saw  10  or equivalent, resulting in separate devices  325  with ball bonds  345 . In the apparatus  360 , the flexible film  335  is stretched separating device die  325  farther apart. Refer to  FIGS. 3E-3H . After stretching, the flexible film  335  the device die  325  are remounted onto another film  355  on the ball bond  345  side which is in another apparatus  362 . With a glue  370 , backside protection  365  is applied to the undersides  330  of the remounted device die  325 . 
         [0026]    Refer to  FIG. 3G . Upon the backside protection  365 , the device die are remounted onto a sawing tape  375 , the sawing tape  375  mounted on apparatus  363 . Refer to  FIG. 3H . Wafer saw  15  clears the space between device die  325  and cuts through the backside protection film  365  so that the now-protected devices  325  may be separated into single devices. 
         [0027]    Refer to  FIG. 4A . In an example embodiment, on device die  410 , having ball bonds  420 , the backside protection  440  may be a polymer, plastic material combined with the glue layer  430 . The device  410  has been back-ground to a thickness T 1 . The protective backside protection  440  and glue layer  430  would be at a thickness T 2 . The total allowable thickness for the device die&#39;s application is the sum of T 1  and T 2 . 
         [0028]    Refer to  FIG. 4B . In another example embodiment, on device die  415 , having ball bonds  425 , backside protection  445  may be metallic material. Metals may include copper or steel, but are not necessarily limited to those. The device  415  is back-ground to a thickness T 1 ′. The protective backside protection  445  and glue layer  435  would be at a thickness T 2 ′. Also, the metal protective backside protection  445  would likely be thinner than the plastic backside protection  440 . As with  FIG. 2 , the total allowable thickness for the device die&#39;s application is the sum of T 1 ′ and T 2 ′. It is possible in a particular application using two or more device die, to have one product die protected with a polymer material and another product die protected with a metallic material; the overall thickness of each product may be the same, however, so as to accommodate a fixed height within the system application. 
         [0029]    The embodiments discussed, protect both the underside and sidewall of the WLCSP device against mechanical impacts from subsequent handling during assembly (i.e., tweezers, pipettes, vacuum wands, etc.). The thickness of the material and the T 3  standoff distance determine the degree of protection. 
         [0030]    In the example embodiment of a plastic/coating, the coating should be as thick as possible to minimize the effective silicon thickness and by the degree of exposure (to sources of mechanical damage) of the side wall area of the sensitive silicon. A relative small stand-off distance T 3  should be enough to securely protect the chip itself against mechanical impacts. 
         [0031]    Numerous other embodiments of the invention will be apparent to persons skilled in the art without departing from the spirit and scope of the invention as defined in the appended claims.