Abstract:
A semiconductor package including an integrated device, the package having a front side, a back side and side walls linking the front and back sides, wherein each side wall is coated, to at least 80% of its area, with a coating material different from the material(s) of the back and front sides. A method of manufacturing a semiconductor package by providing an assembly containing an array of the packages, the assembly having thickness d 0  and being attached to a dicing tape of thickness dd, fabricating a set of first dicing streets with width w 1  and depth d 1 &lt;(d 0 +dd), filling the first dicing streets at least partially with a coating material, and fabricating, in the coating material in each first dicing street, a second dicing street with width w 2 ≦w 1  and depth d 2 ≧d 0  but &lt;(d 0 +dd).

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority of European Patent Application 14167397.0, filed May 7, 2014, the contents of which is incorporated herein by reference in its entirety. 
     FIELD OF THE INVENTION 
     The present invention relates to a semiconductor package and a method for manufacturing a semiconductor package. 
     BACKGROUND OF THE INVENTION 
     When a semiconductor device is packaged, especially in a batch process, undesired particles may arise during device dicing, e.g. by sawing or laser cutting. 
     In KR100395754 B1 for example, a pre-cutting process is performed by cutting particular units of a semiconductor package. The particular units of the semiconductor package are cut by using a dicing wheel. A cleaning and a drying process is performed to clean cut sludge caused by the pre-cutting process. A laser beam cutting process is performed by cutting the remaining thickness of the semiconductor package. 
     In such a process, contamination may arise in form of particles released from the cut surfaces or there may be thermal impact arising from the laser cutting step. 
     SUMMARY OF THE INVENTION 
     Hence, according to a first aspect of the invention, there is provided a semiconductor package, comprising an integrated device, a front side of a material A and a back side of a material B opposite to the front side. Side walls link the front side and the back side. Each side wall is coated with a coating material to at least 80% of its area, wherein the coating material is different from the material A and different from the material B. 
     The term “semiconductor package” as used herein comprises an integrated device which may comprise one or more of a die, a chip, a substrate, e.g. a glass substrate or a ceramic substrate or a semiconductor substrate, and in particular a silicon substrate. The semiconductor package may further comprise means of electrical contacting, e.g. one or more of wire bonds, through-silicon-vias, a ball grid array, a land grid array, T-contacts, a lead frame or a printed circuit board, and/or packaging, e.g. a mold or a silicon cap or a silicon interposer. The semiconductor package, and in particular its integrated device may include features such as an integrated processing circuit and/or a suspended membrane and/or a heater structure. 
     In a preferred embodiment, the semiconductor package, and in particular its integrated device comprises a sensitive element which is sensitive to one or more of humidity, temperature, gas, pressure, gas flow or differential pressure. 
     Hence, the semiconductor package may represent one or more of a humidity sensor, a temperature sensor, a gas sensor, a pressure sensor, a microphone, or a gas flow sensor. 
     Furthermore, the semiconductor package may contain additional features to support the operation of the sensitive element, e.g. a heater structure to heat the sensitive element and/or a suspended membrane to achieve thermal insulation and/or features to process the measurement signal of the sensitive element, e.g. an integrated processing circuit. 
     Material A and material B may be the same or different. They may each be combinations of materials. In one example, material A comprises mold compound and material B comprises mold compound and metal of a lead frame. In another example, material A and material B comprise silicon. 
     In a preferred embodiment, each side wall essentially is a cut surface. The term “cut surface” as used herein refers to a surface originating from a dicing process. Minor parts of the surface may still originate from a different process, e.g. etching. 
     In a preferred embodiment, the coating material seals the cut surface to reduce emission of particles related to a dicing process used to manufacture the cut surface and/or seals the cut surface to protect it. 
     Preferably, the coating material at each side wall comprises two front ends and a side face linking the front ends, wherein each side face is a cut surface. 
     In a preferred embodiment, the coating material comprises at least one of glue, encapsulant, acryl, silicone, epoxy, polyurethane or a material with less than 10% filler particles. These materials are chosen because they exhibit a low release of particles during dicing and because of their adhesive and sealing behavior. 
     In a preferred embodiment, the coating material has a width w 0  of less than 100 micrometers. The thickness has an upper limit given by miniaturization of the semiconductor package. 
     Preferably, the coating material has a width w 0  which is essential equal on all sidewalls of the diced semiconductor package. 
     In one embodiment, the coating material coated on at least one of the side walls has on a front end a positive or negative offset from the plain of the front side and/or back side of the diced semiconductor package. 
     In a preferred embodiment, the coating material coated on at least one of the side walls has at least one front end that has meniscus-like shape. 
     In one embodiment, at least one gap extends in a direction perpendicular to the side wall and is filled by a portion of the coating material. A gap in a side wall may for example arise in adhesive bonding of a silicon chip and a silicon cap. Filling the gap may serve to confine remains of dicing slurry and/or to protect the edges of a gap and/or the adhesive material which might be more sensitive to mechanical and chemical impact. 
     In one embodiment, the coating material coated on at least one of the side walls wraps around a lateral end of the front side and/or back side covering less than 20% of the area of the front side and/or back side. This may serve to protect the corresponding edges of the package and to increase adhesion of the coating material on the semiconductor package. The front or backside is not covered completely to allow access to cavities and/or openings to the inside of the package. This is especially relevant if the semiconductor package comprises a sensitive element that is sensitive to outside parameters, e.g. humidity, gas or pressure. 
     In another embodiment, the front end of the coating material coated on at least one of the side walls is covered by a lateral extension of the front side material A or by a lateral extension of the back side material B. This may serve to increase adhesion of the coating material and/or to hide it from view and/or to protect it from wear. 
     According to another aspect of the present invention, a method is provided for manufacturing a semiconductor package. A semiconductor package assembly containing an array of semiconductor packages for manufacturing a plurality of semiconductor packages is provided. Preferably, each semiconductor package comprises an integrated device. The semiconductor package assembly has a thickness d 0  and is attached to a dicing tape of thickness dd. 
     In the following, a set of first dicing streets with a width w 1  and a depth d 1 &lt;(d 0 +dd) is fabricated. 
     In the following, the set of first dicing streets is at least partially filled with a coating material. 
     In the following, in the coating material in each first dicing street of the set, a second dicing street with a width w 2 &lt;=w 1  and a depth d 2 &gt;=d 0  and d 2 &lt;(d 0 +dd) is fabricated. 
     The advantage of this method is that it allows the coating of side walls in a batch process. 
     In a preferred embodiment, the semiconductor package assembly has a front side of material A and back side of material B and the coating material is different from material A and from material B. 
     Material A and material B may be the same or different. They may each be combinations of materials. In one example, material A comprises mold compound and material B comprises mold compound and metal of a lead frame. In another example, material A and material B comprise silicon. 
     In one embodiment, the set of first dicing streets is filled with the coating material by applying the coating material in the set of first dicing streets. 
     In another embodiment, the set of first dicing streets is filled with the coating material by depositing the coating material in areas outside of but in contact with the set of first dicing streets and filling the set of first dicing streets by means of capillary force. 
     Preferably, the second dicing street in the coating material in each first dicing street of the set is fabricated in the center of each first dicing street of the set in such a way that a plurality of individual semiconductor packages having side walls that are coated by coating material of essentially equal width are formed. 
     In one embodiment, the depth of the set of first dicing streets is equal to the thickness of the semiconductor package assembly. 
     In another embodiment, the depth of the first dicing streets is smaller than the thickness of the semiconductor package assembly. 
     In one embodiment, the method for manufacturing a semiconductor package comprises a cleaning step after fabricating the first dicing streets. 
     In preferred embodiment, a curing step is performed after the application of the coating material. 
     According to another aspect of the present invention, a semiconductor package is manufactured according to above described method. 
     The described embodiments similarly pertain to the semiconductor package and the method. Synergetic effects may arise from different combinations of the embodiments although they might not be described in detail. 
     Other advantageous embodiments are listed in the dependent claims as well as in the description below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the present invention, aspects and advantages will become apparent from the following detailed description thereof. Such description makes reference to the annexed drawings, wherein the figures show: 
         FIG. 1   a ) to  c ) schematic sectional views of semiconductor packages in accordance with examples of the invention; 
         FIG. 2   a ) to  e ) schematic sectional views of diced semiconductor packages in accordance with examples of the invention; 
         FIG. 3  in its diagrams a) to e) schematic top views of steps of manufacturing a semiconductor package in accordance with an example of the invention; 
         FIG. 4  in its diagrams a) to d) schematic sectional views of steps of manufacturing a semiconductor package in accordance with an example of the invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1   a ) shows a schematic sectional view of a semiconductor package in accordance with an embodiment of the present invention. The semiconductor package has a front side  1  and back side  2 . 
     In this embodiment, a silicon die  10  which includes a sensitive element  11  is attached to a support  13 . The silicon die  10  may include features such as an integrated processing circuit and/or a suspended membrane and/or a heater structure. The support  13  may comprise means for external electrical contacting, e.g. one of a printed circuit board, a ceramic support or a lead frame. In this embodiment, the semiconductor package comprises a mold  12  which has an access opening  14  from the front side  1  to the sensitive element  11 . If the means for external electrical contacting is a lead frame, the lead frame may also be partially packaged in the mold. 
     In this embodiment, the semiconductor package has side walls  3  which are coated completely between front side  1  and back side  2  with a coating material  4  of width w 0 . The side walls  3  may be cut surfaces. Herein, cut surfaces refer to the side walls of a semiconductor package generated by dicing. The coating material  4  has two front ends  5  which are each in the plain of the front side  1  and back side  2  of the semiconductor package. 
     The coating material  4  seals the side walls  3  and may be a glue or encapsulant, e.g. comprising acryl, silicone, epoxy, polyurethane and preferentially with less than 10% filler particles. The coating material may be chosen to exhibit low particle emission if it is diced and/or to be suited as sealing material. The coating material  4  may reduce emission of particles related to a dicing process used to manufacture the cut surfaces. Such particles may arise due to the release of filling particles of mold compound which are commonly used to achieve thermal expansion matching between the mold material and silicon. 
       FIG. 1   b ) shows another embodiment of a semiconductor package in accordance with an embodiment of the present invention. In this embodiment, a silicon die  10  with an integrated sensitive element  11  is capped with a silicon cap  15  by means of an adhesive material  16 . The silicon die  10  may include features such as an integrated processing circuit and/or a suspended membrane and/or a heater structure as well as means for external contacting e.g. through silicon vias and/or metal balls. In this embodiment, the semiconductor package has side walls  3  which are coated completely between front side  1  and back side  2  with a coating material  4  of width w 0 . In this embodiment, the coating material  4  may serve to reduce environment impact on cut surfaces which may potentially be more sensitive than other surfaces. 
       FIG. 1   c ) illustrates another embodiment of a semiconductor package in accordance with an embodiment of the present invention. In this embodiment, a silicon die  10  is capped with a mold compound  11 . The silicon die  10  includes an integrated circuit and means for external contacting, e.g. through silicon vias and/or metal balls. In this embodiment, the coating material  4  may serve to reduce environment impact on cut surfaces which may potentially be more sensitive than other surfaces and it may reduce emission of particles related to a dicing process used to manufacture the cut surface. 
       FIG. 2   a ) shows another embodiment of a semiconductor package in accordance with an embodiment of the present invention. In this embodiment, the coating material  4  has a front end  5  which is to a limited extend negatively offset  17  from the plain of the back side  2  of the diced semiconductor package. 
       FIG. 2   b ) illustrates another embodiment of a semiconductor package in accordance with an embodiment of the present invention. In this embodiment, the coating material  4  has a front end  5  that has meniscus-like shape  18 . 
       FIG. 2   c ) shows another embodiment of a semiconductor package in accordance with an embodiment of the present invention. In this embodiment, a gap  19  extends in a direction perpendicular to the side wall  3  and is filled by a portion of the coating material  4 . In this embodiment, the gap  19  in the side wall  3  arises due to reduced lateral extension of the glue  16 . 
       FIG. 2   d ) illustrates another embodiment of a semiconductor package in accordance with an embodiment of the present invention. In this embodiment, the coating material  4  wraps around a lateral end  20  of the front side  1  and/or back side  2  covering less than 20% of the area of the front side  1  and/or back side  2 . The coating of the edges may serve for their protection against mechanical impact and/or wear. 
       FIG. 2   e ) shows another embodiment of a semiconductor package in accordance with an embodiment of the present invention. In this embodiment, a front end  5  of the coating material  4  is covered by a lateral extension  21  of the front side  1  material A. 
     Alternatively, a front end  5  of the coating material  4  may be covered by a lateral extension  21  of the back side  2  material B. 
       FIG. 3  illustrates in its diagrams a) to e) schematic top views of steps of manufacturing a semiconductor package in accordance with an example of the invention and  FIG. 4  in its diagrams a) to d) schematic sectional views of the respective steps. 
     In  FIGS. 3   a ) and  4   a ) a semiconductor package assembly  30  is provided. It contains an array of semiconductor packages for manufacturing a plurality of semiconductor packages. The semiconductor package assembly  30  has a thickness d 0  and is attached to a dicing tape  31  of thickness dd. 
     If one of the two sides of the semiconductor package assembly  30  is more sensitive to contaminations than the other, this side may be chosen to be attached to the dicing tape  31 . For example, if one side comprises access openings to sensitive elements, this side may be attached to the dicing tape  31 . By this means, the more sensitive side may be protected by the dicing tape  31  from particles and slurry during the following dicing steps. 
     In  FIGS. 3   b ) and  4   b ) a set of first dicing streets  32  with a width w 1  and a depth d 1 &lt;(d 0 +dd) is fabricated. The set of first dicing streets  32  is fabricated around individual semiconductor devices or groups of semiconductor devices. Dicing may be realized by sawing or laser cutting. The upper limit of the width w 1  is given by the loss of material due to the dicing process and the lower limit by a stable and reproducible process, therefore w 1  may be in a range of 30 to 500 micrometer. 
     In this embodiment, the depth d 1  of the set of first dicing streets  32  is essentially equal to the thickness d 0  of the semiconductor package assembly  30 . Herein, essentially equal means within the accuracy limits of the corresponding manufacturing process. 
     In another embodiment, the depth d 1  of set of first dicing streets  32  is smaller than the thickness d 0  of the semiconductor package assembly  30 . 
     In one embodiment, a cleaning step may be applied after fabricating the set of first dicing streets  32 . 
     In  FIGS. 3   c ) and  4   c ) the set of first dicing streets  32  are filled with a coating material  4 . The semiconductor package assembly  30  has a front side of material A and back side of material B. Material A and material B may be the same or different. They may each be combinations of materials. In one example, material A comprises mold compound and material B comprises mold compound and metal of a lead frame. In another example, material A and material B comprise silicon. 
     Preferentially, the coating material  4  is different from material A and from material B. 
     In one embodiment, the set of first dicing streets  32  is filled with the coating material  4  by applying the coating material  4  in the set of first dicing streets  32 . This may have the advantage of accurate control of the amount of coating material  4 . This process may be limited by the small width w 1  of each first dicing street of the set  32  which may lead to undesired deposition of the coating material in the vicinity of each first dicing street of the set  32  and/or by the effort and time to fill each first dicing street of the set  32 . 
     Therefore, in another embodiment, the set of first dicing streets  32  is filled with the coating material  4  by depositing the coating material  4  in areas outside of but in contact with the set of first dicing streets  32  and filling the set of first dicing streets  32  by means of capillary force. 
     In one embodiment, a curing step is performed after the application of the coating material  4 . 
     In  FIGS. 3   d ) and  4   d ) in the coating material  4  in each first dicing street of the set  32 , a second dicing street ( 34 ) with a width w 2 &lt;=w 1  and a depth d 2 &gt;=d 0  and d 2 &lt;(d 0 +dd) is fabricated. 
     In this embodiment, the second dicing street  34  in the coating material  4  in each first dicing street of the set  32  is fabricated in the center of each first dicing street of the set  32  in such a way that a plurality of individual semiconductor packages  35  having side walls  36  that are coated by coating material  4  of essentially equal width w 0  are formed. 
       FIG. 3   e ) shows in top view an example of a semiconductor package manufactured according to one embodiment of the method. 
     The semiconductor package may e.g. be released from the dicing tape by UV radiation (UV release tape). 
     It should further be noted that in any removal of material during manufacturing, the corresponding structures may be created using a chemical (wet) etching process, plasma etching process, laser cutting, mechanical milling or a combination of any of these processes, where suitable. 
     While above there are shown and described embodiments of the invention, it is to be understood that the invention is not limited thereto but may be otherwise variously embodied and practiced within the scope of the following claims.