Abstract:
A method of producing a package ( 30 ) for a semiconductor die (or chip) including a semiconductor die ( 20 ) having one or more bond pads on the top surface for providing terminals for one or more sensors ( 22 ) in the upper surface and a die carrier ( 32 ) including an opening ( 34 ) and one or more external terminals. The semiconductor die ( 20 ) upper surface is fixed on the die carrier ( 32 ) and each bond pad is coupled to a portion of the external terminals exposed at the die carrier ( 32 ) lower surface, for example, with weld points ( 42 ). A sealing ring ( 44,46 ) encapsulates the interface zone ( 40 ) and a coating material ( 48 ) encapsulates the die carrier ( 32 ) lower surface and a lower surface of the semiconductor die ( 20 ).

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is the National Stage of International Application No. PCT/FR00/02367 filed on Aug. 24, 2000, which is based upon and claims priority from prior French Patent Application No. 9911024 filed Sep. 2, 1999, the entire disclosure of which in herein incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to packaging semiconductor dies and more particularly to a method for packaging a semiconductor die containing one or more sensors and to a package resulting in particular from this method. 
     2. Description of Related Art 
     Without limiting the scope of the present invention, the background of the present invention is described in connection with the packaging of semiconductor dies containing one or more optical sensors, which can be any sensors designed to detect any spectrum of light, including infrared. Accordingly, the present invention is applicable to the packaging of any semiconductor die containing one or more sensors, such as fingerprint sensors, where conventional packaging techniques and materials reduce the effectiveness of the sensors. 
     Semiconductor dies or integrated circuits containing optical sensors, unlike most semiconductor dies, must be packaged in such a way as to allow light to contact the optical sensors and motion sensors, but still protect these sensors from environmental contamination. This is also true for infrared sensors, such as those used in integrated circuit fingerprint sensors. As a result, the performance and sensitivity of optical and other sensors can be significantly diminished by contaminants and moisture introduced during the packaging process, or by contaminants, air bubbles, irregularities and deformities in the packaging material itself. 
     In addition, some packages for semiconductor dies containing sensors utilize a transparent plastic resin or epoxy resin. 
     The use of a transparent plastic resin or epoxy resin, however, introduces additional problems. First, the most commonly used agents to facilitate the molding of the package and increase the package&#39;s reliability cannot be used. Second, these transparent materials are harder to handle and clean out of the molds. Third, these materials are more expensive and require lengthy cure times (2 to 3 times that of a normal package). 
     Accordingly, there is a need for a method for packaging semiconductor dies containing one or more sensors that is durable, economical, efficient and effective. More specifically, the package should not significantly interfere with sensor performance while simultaneously protecting the sensors from foreign materials and contaminants. 
     SUMMARY OF THE INVENTION 
     The subject of the present invention is first of all a method for packaging a semiconductor die which comprises the steps of attaching a surface of a semiconductor die to a surface of a die carrier having external lead bonds or terminals, such that this die carrier does not extend in front of one or more sensors provided on the top surface of the semiconductor die and one or more bond pads on the top surface of the semiconductor die are coupled to one or more of the bond pads of said die carrier in an annular interface area formed between the top surface of the semiconductor die and a surface of said die carrier; encapsulating said interface area with a sealing ring; and encapsulating the bottom surface of the die carrier and a bottom surface of the semiconductor die with a packaging material. 
     According to an alternative embodiment of the invention, the method comprises the steps of: attaching a top surface of a semiconductor die to a bottom surface of a die carrier such that one or more sensors within the top surface of the semiconductor die are disposed below a first opening in the die carrier that is larger than the one or more sensors but smaller than the semiconductor die and an interface area is formed between said die and said die carrier where the top surface of the semiconductor die extends beyond the first opening in the die carrier and one or more bond pads on the top surface of the semiconductor die are coupled to one or more of the exterior terminals on the bottom surface of the die carrier; curing the semiconductor die attached to the die carrier; encapsulating the interface area with a sealing ring; curing the sealing ring; encapsulating the bottom surface of the die carrier and a bottom surface of the semiconductor die with a packaging material; and curing the packaging material. 
     According to the invention, the method may advantageously comprise the steps of: encapsulating an exterior portion of the interface area with a first sealing ring; curing the first sealing ring; encapsulating the bottom surface of the die carrier and a bottom surface of the semiconductor die with a packaging material; curing the packaging material; encapsulating an interior portion of the interface area with a second sealing ring; and curing the second sealing ring. 
     According to another alternative embodiment of the invention, the method comprises the steps of: attaching a bottom surface of a semiconductor die to a top surface of a recessed area of a pre-printed frame, the recessed area being larger than the semiconductor die, the semiconductor die having one or more bond pads on a top surface for providing terminals to one or more sensors within the top surface, and the pre-printed frame having one or more wire leads; curing the semiconductor die attached to the pre-printed frame; forming a dam to surround the recessed area to prevent a packaging material from entering the recessed area; curing the dam; forming wire bonds to couple each bond pad to a portion of one of the wire leads that is near the recessed area; encapsulating the wire bonds with a sealing ring; curing the sealing material; encapsulating the bottom surface of the pre-printed frame with the packaging material; and curing the packaging material. 
     According to the invention, the method may advantageously further comprise a step of applying a protective coating over the one or more sensors of the semiconductor die. 
     According to the invention, the method may advantageously furthermore comprise attaching a cap having a second opening larger than the sensors of the semiconductor die, the cap being attached to the top surface of the die carrier; and substantially encapsulating the cap with the packaging material. 
     Another subject of the invention is a semiconductor die package comprising a semiconductor die having one or more bond pads on a top surface for providing terminals to one or more sensors, in particular optical sensors, within the top surface; a die carrier which does not extend in front of said sensors and which has one or more bond pads comprising bond terminals and having external lead bonds, the bond pads of said die carrier and the bond pads of said die determining between them an annular interface area and being coupled in this area; a sealing ring encapsulating said interface area; and a packaging material encapsulating the bottom surface of the die carrier and a bottom surface of the semiconductor die. 
     According to the invention, the package may advantageously comprise a die carrier having a first opening larger than the one or more sensors but smaller than the semiconductor die and one or more external terminals; the top surface of the semiconductor die attached to the bottom surface of the die carrier such that the one or more sensors are disposed below the first opening and an interface area is formed where the top surface of the semiconductor die extends beyond the first opening in the die carrier and each bond pad is coupled to a portion of one of the external terminals that is exposed on the bottom surface of the die carrier; a sealing ring encapsulating the interface area; and a packaging material encapsulating the bottom surface of the die carrier and a bottom surface of the semiconductor die. 
     According to the invention, the sealing ring may advantageously comprise a first external sealing ring and a second internal sealing ring. 
     According to the invention, each bond pad is coupled to one of the external pads on the bottom surface of the die carrier by a solder bump. 
     According to the invention, the die carrier may advantageously comprise a substrate and each external terminal comprises a bond pad formed on a top surface of the substrate. 
     According to the invention, the die carrier may advantageously comprise a pre-printed frame and each external terminal comprises a wire lead. 
     According to the invention, the package may advantageously comprise a pre-printed frame having a recessed area which is larger than the semiconductor die and one or more wire leads, a bottom surface of the semiconductor die being attached to a top surface of the recessed area of the pre-printed frame; a wire bond coupling each bond pad to a portion of one of the external terminals near the recessed area; a dam surrounding the recessed area to prevent packaging material from entering the recessed area; a sealing material encapsulating each wire bond; and a package material encapsulating the bottom surface of the pre-printed frame. 
     According to the invention, the package may advantageously furthermore comprise a cap having a second opening similar in size to the first opening, the cap being attached to the top surface of the pre-printed wire frame and the packaging material substantially encapsulating said cap. 
     According to the invention, said sealing ring and/or said packaging material may advantageously comprise a thixotropic epoxy-based material. 
     According to the invention, the one or more sensors are covered with a protective layer. 
     According to the invention, the package may advantageously furthermore comprise a transparent encapsulation material in the first opening and on the top surface of the semiconductor die. 
     According to the invention, the package may advantageously furthermore comprise a lens disposed above the one or more sensors. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and further advantages of the invention may be better understood by referring to the following description in conjunction with the appended drawings, in which: 
     FIGS. 1A-1C depict a top view of a semiconductor die having one or more sensors in accordance with the present invention; 
     FIG. 2 depicts a top view of a package for a semiconductor die having one or more sensors in accordance with a first embodiment of the present invention; 
     FIG. 3 depicts a cross sectional view of the package depicted in FIG. 2 in accordance with the first embodiment of the present invention; 
     FIGS. 4A-4D depict, in cross sectional views, the method of producing the package depicted in FIGS. 2 and 3 in accordance with the first embodiment of the present invention; 
     FIGS. 5A-5F depict, in cross sectional views, the method of producing a package for a semiconductor die having one or more sensors in accordance with a second embodiment of the present invention; and 
     FIGS. 6A-6F depict, in cross sectional views, the method of producing a package for a semiconductor die having one or more sensors in accordance with a third embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     While the making and using of various embodiments of the present invention are discussed in detail below, it should be appreciated that the present invention provides many applicable inventive concepts which can be embodied in a wide variety of specific contexts. The specific embodiments discussed herein are merely illustrative of specific ways to make and use the invention and do not limit the scope of the invention. 
     The descriptions of the figures to follow discuss methods of packaging semiconductor dies containing sensors whose functionality and reliability depend on the fundamental characteristics of light traveling to or from the device. In addition, the packaging methods described below are equally applicable to other types of sensors, such as fingerprint sensors. The discussion centers around general flip chip or wire bonded attachments, but is not intended to limit the scope of the invention to these configurations, since the method of packaging may be used for any chip attachment configuration. Moreover, lenses and other focusing or filtering elements can be easily added to the packages described below. 
     Turning now to FIG. 1A, a top view of a semiconductor die  20  having a quad bond pad row arrangement is depicted and will now be described. The semiconductor die  20  has a sensor area  22 , which contains one or more sensors (not shown), and one or more bond pads  24 . The one or more sensors (not shown) are typically optical sensors or sensors designed to detect any spectrum of light, including infrared. The one or more sensors (not shown) may also be fingerprint sensors or some other type of non-optical sensor. The sensor area  22 , however, may also contain additional circuitry (not shown), such as control, memory, processing or other non-sensing circuits. The bond pads  24  are located between the sensor area  22  and the perimeter of the semiconductor die  20 , and provide terminals to the one or more sensors (not shown) contained in the sensor area  22 . The bond pads  24  may be arranged in a quad bond pad row arrangement (FIG.  1 A), dual bond pad row arrangement  26  (FIG.  1 B), or a single bond pad row arrangement  28  (FIG.  1 C). In any case, the number and configuration of the bond pads  24  on the semiconductor die  20  may vary and are not limited by FIGS. 1A,  1 B and  1 C. 
     Now referring to FIG. 2, a top view of a package for a semiconductor die containing one or more sensors in accordance with a first embodiment of the present invention is denoted generally as  30  and will now be described. The package  30  comprises a semiconductor die  20  attached to a die carrier or substrate  32 . The semiconductor die  20  has one or more bond pads  24  on the top surface in a quad bond pad row arrangement. As previously mentioned in reference to FIGS. 1A,  1 B and  1 C, the number and configuration of the bond pads  24  can vary. The substrate  32  has an opening  34 , which is larger than the sensor area  22 , but smaller than the semiconductor die  20  and the one or more bond pads  24 . The opening  34  extends all the way through the substrate  32 . 
     The top surface of the semiconductor die  20  is attached to the bottom surface of the substrate  32  so that the sensor area  22  is disposed below the opening  34  and an interface area  40  (FIG. 3) is formed where the top surface of the semiconductor die  20  extends beyond the opening  34  in the substrate  32  and each bond pad  24  is coupled to one of the external terminals  36  with a solder bump  42  (FIG.  3 ). 
     Now referring to FIG. 3, a cross-sectional view of the package depicted in FIG. 2 is shown. As previously described, the package  30  comprises a semiconductor die  20  attached to a substrate  32 . The semiconductor die  20  has a sensor area  22 , which is preferably covered with a protective layer  38 . The substrate  32  has an opening  34 , which is larger than the sensor area  22 , but smaller than the semiconductor die  20  and the one or more bond pads  24  (FIG.  2 ). The opening  34  extends all the way through the substrate  32 . 
     The top surface of the semiconductor die  20  is attached to the bottom surface of the substrate  32  so that the sensor area  22  is disposed below the opening  34  and an annular interface area  40  is formed where the top surface of the semiconductor die  20  extends beyond the opening  34  in the substrate  32  and each bond pad  24  is coupled to one of the external terminals  36  with a solder bump  42 . The external terminals  36  are strategically placed over the top surface of the substrate  32  to provide a physical connection to the bond pads  24  once the solder bumps  42  are re-flowed. 
     The interface area  40  is encapsulated with a sealing ring, which may be applied in a two stage process to form a first sealing ring  44  and a second sealing ring  46 . The single sealing ring configuration may be used when the solder bumps  42  can be encapsulated while maintaining the required thermal cycle/shock performance, such as in low cost situations where lower reliability is acceptable. The two sealing ring configuration, however, provides increased reliability. The first sealing ring  44  provides good mechanical definition of the exposed sensor area  22  that results in mechanical accuracy, repeatability and reproducibility. The second sealing ring  46  provides higher reliability in terms of thermal cycle/shock performance and prevents failure mechanisms caused by cracked solder bumps  42  due to excessive stress induced by differences in the thermal coefficient of expansion of the first sealing ring  44 , packaging material  48 , and the substrate  32 . Either way, the sealing rings  44  and  46  prevent any packaging material  48  from getting into the sensor area  22 . 
     The first sealing ring  44  encapsulates the exterior portion of the interface area  40 , whereas the second sealing ring  46  encapsulates the interior portion of the interface area  40 . The first sealing ring  44  preferably comprises a high-purity, thixotropic epoxy-based non-flowing retaining dam material having a high glass transition temperature with a low coefficient of thermal expansion and an excellent thermal shock/cycle performance. The second sealing ring  46  preferably comprises a high-purity, high-flow underfilling material having a low coefficient of thermal expansion and an excellent thermal shock/cycle performance. If only one sealing ring is used, it should comprise a high-purity, thixotropic epoxy-based non-flowing retaining dam material having a high glass transition temperature with a low coefficient of thermal expansion and an excellent thermal shock/cycle performance. 
     The bottom surface of the substrate  32  and the bottom surface of the semiconductor die  20  are encapsulated with a packaging material  48 . The packaging material  48  preferably comprises a high-purity, thixotropic epoxy-based encapsulant material having a low coefficient of thermal expansion and an excellent thermal shock/cycle performance. 
     Now referring to FIGS. 4A-4D, the method of manufacturing the package depicted in FIGS. 2 and 3 will be described. As will be readily appreciated by those skilled in the art, some of the steps described below may be modified or combined into a single step to produce an equivalent device. Accordingly, the present invention is not strictly limited by the order described or depicted in the following figures. 
     Step One (FIG. 4A) 
     The top surface of the semiconductor die  20  is attached to the bottom surface of the die carrier or substrate  32  such that the sensor area  22  containing the one or more sensors within the top surface of the semiconductor die  20  is disposed below the opening  34  in the substrate  32 . The opening  34  is larger than the sensor area  22 , but is smaller than the semiconductor die  20 . An annular interface area  40  (FIG. 3) is formed where the top surface of the semiconductor die  20  extends beyond the opening  34  in the substrate  32 . Each bond pad  24  (FIG. 2) is coupled to one of the external terminals  36  (FIG. 2) that are exposed on the bottom surface of the substrate  32  with a solder bump  42 . The assembly (substrate  32  and semiconductor die  20 ) is then cured. 
     Step Two (FIG. 4B) 
     The exterior portion  50  of the interface area  40  (FIG. 3) is encapsulated with the first sealing ring  44 . The first sealing ring is then cured. 
     Step Three (FIG. 4C) 
     The bottom surface of the substrate  32  and the bottom surface of the semiconductor die  20  are encapsulated with a packaging material  48 . The packaging material  48  is then cured. 
     Step Four (FIG. 4D) 
     The interior portion  52  of the interface area  40  (FIG. 3) is encapsulated with a second sealing ring  46 . The second sealing ring is then cured. Note that the first and second sealing rings  44  and  46  can be combined into a single sealing ring that encapsulates the interface area  40  (FIG.  3 ), thus eliminating step four. 
     Step Five (FIG. 3) 
     The protective layer  38  is formed on top of the sensor area  22  and the external terminals  36  are formed. A lens or filter may also be installed in or above the opening  34  (FIGS.  2  and  4 A). The package is then preferably cleaned. 
     Now referring to FIGS. 5A-5F, the method of manufacturing a package in accordance with a second embodiment of the present invention will be described. In this embodiment, a pre-printed frame  60  is used as the die carrier, rather than the substrate  32  in FIGS. 2-4D. Pre-printed frames  60  are well known by those skilled in the art and typically contain one or more etched and stamped wire leads (not shown) and frame alignment holes (not shown). 
     Step One (FIG. 5A) 
     The top surface of the semiconductor die  20  is attached to the bottom surface of the die carrier or pre-printed frame  60  such that the sensor area  22  containing the one or more sensors within the top surface of the semiconductor die  20  is disposed below the first opening  34  in the pre-printed frame  60 . The first opening  34  is larger than the sensor area  22 , but is smaller than the semiconductor die  20 . An annular interface area  66  (FIG. 5D) is formed where the top surface of the semiconductor die  20  extends beyond the opening  34  in the preprinted frame  60 . Each bond pad  24 FIGS. 1A,  1 B or  1 C) is coupled to one of the external terminals or wire leads  74  (FIG. 5F) that are exposed on the bottom surface of the pre-printed frame  60  with a solder bump  42 . The assembly (pre-printed frame  60  and semiconductor die  20 ) is then cured. 
     Step Two (FIG. 5B) 
     The exterior portion  62  of the interface area  66  (FIG. 5D) is encapsulated with the first sealing ring  44 . The first sealing ring is then cured. 
     Step Three (FIG. 5C) 
     The interior portion  64  of the interface area  66  (FIG. 5D) is encapsulated with a second sealing ring  46 . The second sealing ring is then cured. Note that the first and second sealing rings  44  and  46  can be combined into a single sealing ring that encapsulates the interface area  66  (FIG.  5 D), thus eliminating step three. 
     Step Four (FIG. 5D) 
     A cap  68  is attached to the top surface of the pre-printed frame  60  with an adhesive  70 , such as a polymide adhesive. The cap  68  has a second opening  72  similar in size to the first opening  34  in the pre-printed frame  60 . The cap  68  adds mechanical strength and stability to the package. The assembly is then cured. 
     Step Five (FIG. 5E) 
     The bottom surface of the pre-printed frame  60  and the bottom surface of the semiconductor die  20  are encapsulated and the cap  68  is substantially encapsulated with a packaging material  48 . The packaging material  48  is then cured. 
     Step Six (FIG. 5E) 
     The protective layer  38  is formed on top of the sensor area  22  and the external terminals or wire leads  74  are trimmed and formed. A lens or filter may also be installed in or above the first opening  34  or second opening  72  (FIG.  5 D). The package is then preferably cured. 
     Now referring to FIGS. 6A-6F, the method of manufacturing a package in accordance with a third embodiment of the present invention will be described. In this embodiment, like FIGS. 5A-5F, a pre-printed frame  80  is used as the die carrier. This pre-printed frame  80 , however, does not have a first opening  34  (FIG.  5 D). Instead, the pre-printed frame  80  has a recessed area  82  that is larger than the semiconductor die  20 . This arrangement provides a low-profile package. 
     Step One (FIG. 6A) 
     The bottom surface of the semiconductor die  20  is attached to the top surface of the recessed area  82  of the pre-printed frame  80  with an adhesive  84 , such as a polymide adhesive. The assembly (pre-printed frame  80  and semiconductor die  20 ) is then cured. 
     Steps Two and Three (FIG. 6B) 
     A dam  86  is formed to surround the recessed area  82  and prevent the packaging material  48  (FIG. 6E) from entering the recessed area  82  and the semiconductor die  20 . The dam is then cured. Wire bonds  88  are formed to couple each bond pad  24  (FIGS. 1A,  1 B and  1 C) to a portion of one of the wire leads  98  (FIG. 6F) that is near the recessed area  82 . Wire bonding is well known to those skilled in the art. 
     Step Four (FIG. 6C) 
     A cap  90  is attached to the top surface of the pre-printed frame  80  with an adhesive  84 , such as a polymide adhesive. The cap  90  has an opening  92  above the portion of each of the exterior terminals  94  that is near the recessed area  82 , the dam  86  surrounding the recessed area  82 , and the recessed area  82 . The cap  68  adds mechanical strength and stability to the package. The assembly is then cured. 
     Step Five (FIG. 6D) 
     The wire bonds  88  are encapsulated with a sealing material  96 . The sealing material  96  is then cured. 
     Step Six (FIG. 6E) 
     The bottom surface of the pre-printed frame  80 , the dam  86  and the recessed area  82  are encapsulated and the cap  90  is substantially encapsulated with a packaging material  48 . The packaging material  48  is then cured. 
     Step Six (FIG. 6F) 
     The protective layer  38  is formed on top of the sensor area  22  and the external terminals or wire leads  98  are trimmed and formed. A lens or filter may also be installed in or above the opening  92  (FIG.  6 C). The package is then preferably cleaned. 
     Although preferred embodiments of the invention have been described in detail, it will be understood by those skilled in the art that various modifications can be made therein without departing from the spirit and scope of the invention as set forth in the appended claims.