Patent Publication Number: US-7582954-B1

Title: Optical leadless leadframe package

Description:
TECHNICAL FIELD 
     The present invention relates generally to the packaging of integrated circuit devices, and more particularly to the use of an optical component or window in integrated circuit packages and methods of creation thereof. 
     BACKGROUND 
     Many integrated circuit (“IC”) devices require exposure to a source of light at a point during their operational cycle. Such IC devices can include, for example, EPROMs, CCD imaging chips, and various other chips or IC devices with a light sensing component. In many such IC devices that require some sort of exposure to light, and indeed in most all IC devices, the device must generally be enclosed in a sealed environment to protect it and its associated electrical connections from damage due to exposure to the outside environment. Accordingly, numerous conventional packages for IC devices involve the formation of a window or other transparent component that enables light to reach one or more components on the IC device. 
     Early IC device packages designed to address this issue have involved the formation of a ceramic base and lid adapted to support the IC device, as well as a transparent window situated near the light sensing component. Later packages to accomplish this light providing function have included a transparent plastic or other material as the actual encapsulant for the IC device. As will be readily understood, the term “translucent” may be used in place of the terms “transparent” or “clear” for many of the items, materials and/or other light specific applications throughout this disclosure. Various references that involve providing light to a packaged IC device or component via a transparent or translucent window or other light passing channel can be found at, for example, U.S. Pat. Nos. 4,663,833; 4,766,095; 4,971,930; 5,034,800 and 7,199,438, as well as Japanese Patent No. 62-174956. 
     Where a light passage through a package is provided by using transparent material as the encapsulant for an IC device, several problems have arisen. For one thing, an encapsulant made entirely of transparent material can result in a package that allows light to reach places on the IC device where light is not desirable. For another, the production of a transparent compound to use as an encapsulant can be significantly more costly than the production of a typical silica-based encapsulant compound. Often, the cost of a transparent encapsulant compound can be roughly ten times that of a regular encapsulant compound. Another drawback is that transparent encapsulant compounds are typically produced by removing black pigment and silica from a regular encapsulant compound, which results in a clear compound that is less able to withstand stresses and thermal shock effects. As yet another drawback, many transparent encapsulant compounds are not readily marked by laser markings, which is a preferred way to mark the outside of a packaged chip. As such, packages having an entirely transparent encapsulant material are difficult or impossible to laser mark. 
     While many of the devices and techniques to provide light to an IC device via a packaging feature have generally worked well in the past, there is always a desire to provide more reliable and cost effective ways for packaging such IC devices. 
     SUMMARY 
     It is an advantage of the present invention to provide improved integrated circuit packages having optical windows or components. This can be accomplished at least in part through the use of two different types of encapsulant materials, with a stronger but opaque first encapsulant forming a substantial part of the encapsulated seal around an IC device, and a transparent second encapsulant forming a window or light tunnel in an opening the first encapsulant such that light from an outside light source is able to reach a light sensing region on the IC device. 
     It is an additional advantage of the present invention to provide such a package in a cost effective and efficient manner. This can be accomplished at least in part through the use of a stress buffer that facilitates the efficient manufacture of such an IC device with an encapsulant package having two different encapsulant materials. 
     In various embodiments, an IC device includes a die having a light sensing region disposed on a first surface, a first encapsulant formed on the die and arranged such that the light sensing region can be exposed to a light source, and a second encapsulant formed directly atop the light sensing region and adjacent to or within the first encapsulant. The first encapsulant comprises an opaque material arranged such that the light sensing region can be exposed to the light source, while the second encapsulant comprises a transparent or translucent material, such that it can transmit light therethrough from the light source to the light sensing region. The IC device can be used with leadless leadframe packages, although it can also be used with packages having other suitable conductive components. 
     In various embodiments, a stress buffer can be included as part of the IC device. The stress buffer can be disposed on the first surface of said die, and can be arranged such that the light sensing region can be exposed to the light source. The stress buffer may surround the light sensing region in some embodiments. The stress buffer can be a layer that is created at the wafer level, or can be a dam type structure that is created at the panel level. In some embodiments, the die can include one or more light sensitive areas to be shielded from the light source, and such shielding can be accomplished by the first encapsulant and/or stress buffer. In some embodiments, the first encapsulant includes one or more laser markings on an outer surface thereof. 
     In various embodiments, methods for manufacturing an integrated circuit device or package therefore are disclosed. Process steps can include creating a die having a light sensing region, forming a stress buffer on the die such that the light sensing region can be exposed to an external light source, placing a mold directly against the stress buffer, dispensing a first encapsulant over the die while said mold remains in place, removing the mold after said first encapsulant has been dispensed, and dispensing a second encapsulant into an opening in the first encapsulant left behind by the mold. As in the foregoing embodiments, the mold can be adapted to facilitate the creation of an opening above the light sensing region when an encapsulant is dispensed thereabout. The first encapsulant can comprise an opaque material, and can be dispensed such that an opening above the light sensing region is created therein due to the presence of the mold. Also, the second encapsulant can comprise a transparent or translucent material and be adapted to transmit light therethrough from the light source to the light sensing region. 
     Other apparatuses, methods, features and advantages of the invention will be or will become apparent to one with skill in the art upon examination of the following figures and detailed description. It is intended that all such additional systems, methods, features and advantages be included within this description, be within the scope of the invention, and be protected by the accompanying claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The included drawings are for illustrative purposes and serve only to provide examples of possible structures for the disclosed inventive apparatus and method for providing optical IC device packages. These drawings in no way limit any changes in form and detail that may be made to the invention by one skilled in the art without departing from the spirit and scope of the invention. 
         FIG. 1A  illustrates in top perspective view an exemplary packaged IC device. 
         FIG. 1B  illustrates in bottom perspective view the IC device of  FIG. 1A . 
         FIG. 2A  illustrates in partial side cross-sectional view an exemplary semiconductor wafer having a plurality of IC devices. 
         FIG. 2B  illustrates in partial side cross-sectional view the semiconductor wafer of  FIG. 2A  having a stress buffer material disposed thereupon. 
         FIG. 2C  illustrates in side cross-sectional view an exemplary IC device having been singulated from the wafer of  FIG. 2B  and attached and wire bonded to a panel having an attach tape according to one embodiment of the present invention. 
         FIG. 3A  illustrates in side cross-sectional view the IC device of  FIG. 2C  after the placement of a customized mold and dispensing of a first opaque encapsulant according to one embodiment of the present invention 
         FIG. 3B  illustrates in side cross-sectional view the IC device of  FIG. 3A  after the removal of the customized mold and dispensing of a second transparent encapsulant according to one embodiment of the present invention 
         FIG. 4A  illustrates in side cross-sectional view the IC device of  FIG. 3B  after the removal of the attach tape and application of laser markings to the first encapsulant according to one embodiment of the present invention. 
         FIG. 4B  illustrates in top perspective view the IC device of  FIG. 4A  according to one embodiment of the present invention. 
         FIG. 5A  illustrates in side cross-sectional view an alternative but similar IC device according to one embodiment of the present invention. 
         FIG. 5B  illustrates in top perspective view the IC device of  FIG. 5A  according to one embodiment of the present invention. 
         FIG. 6  illustrates a flowchart presenting exemplary methods of manufacturing the IC devices of  FIGS. 4A and 5A  according to various embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Exemplary applications of apparatuses and methods according to the present invention are described in this section. These examples are being provided solely to add context and aid in the understanding of the invention. It will thus be apparent to one skilled in the art that the present invention may be practiced without some or all of these specific details. In other instances, well known process steps have not been described in detail in order to avoid unnecessarily obscuring the present invention. Other applications are possible, such that the following examples should not be taken as limiting. 
     In the following detailed description, references are made to the accompanying drawings, which form a part of the description and in which are shown, by way of illustration, specific embodiments of the present invention. Although these embodiments are described in sufficient detail to enable one skilled in the art to practice the invention, it is understood that these examples are not limiting; such that other embodiments may be used, and changes may be made without departing from the spirit and scope of the invention. 
     Referring first to  FIGS. 1A and 1B , an exemplary packaged IC device is shown in top and bottom perspective views respectively. As shown, packaged IC device  10  can have a top surface  11  and a bottom surface  12 . Bottom surface  12  can include a die attach pad  13  and a plurality of contacts  14  arranged thereabout, such as in a leadless leadframe package formation, as shown. Such a leadless leadframe package can be, for example, that which is designed and manufactured by National Semiconductor Corporation of Santa Clara, Calif. Of course, other suitable leadless leadframe packages may also be used, and it will be readily understood that the present invention can be used with other types of packaging arrangements, such that its use is not limited to packages having leadless leadframes. Although the detailed description herein references leadless leadframes, such references are for purposes of illustration only, and it will be appreciated that the disclosed apparatuses and methods can be adapted for use with other packaging types and techniques. IC device  10  as shown can be substantially similar to an IC device having an optical component, such as that which is described in greater detail below. 
     Turning next to  FIG. 2A , an exemplary semiconductor wafer having a plurality of IC devices is illustrated in partial side cross-sectional view. Wafer  100  can have a plurality of dice  110  having a first surface, one or more of which may comprise one or more light sensing regions  115  and/or one or more light sensitive areas  116  that must or should be shielded from light. Such light sensing regions  115  can comprise an area on the noted first surface of the dice  110 , and/or may be light sensors atop or about the first surface, for example. Although only three dice  110  have been shown for purposes of illustration, it will be readily appreciated that wafer  100  can include dozens or even thousands of such dice, which can all be identical, or can have differing features, as may be desired. 
     Continuing on to  FIG. 2B , the semiconductor wafer of  FIG. 2A  is shown as having a stress buffer disposed thereupon, again in partial side cross-sectional view. While still at the wafer stage, a stress buffer  120  may be disposed atop dice  110 . Such a stress buffer  120  can comprise, for example, benzocyclobutene, polybenzoaxole, a polyimide, or any other suitable material adapted to absorb or otherwise account for stresses atop the first surface of the dice  110 . Stress buffer  120  can be disposed at the wafer level via, for example, screen printing, spin coating, a dry film process, or any other suitable wafer level application process for such stress buffer materials. Stress buffer  120  can be formed and arranged so as to surround the light sensor or light sensing region  115  of each die  110 , such that an outside light source will be able to provide light thereto, as will be readily appreciated. As shown, stress buffer  120  may be disposed as a layer such that one or more light sensitive areas  116  are not covered by the stress buffer  120 . Alternatively, stress buffer  120  can be created at the panel level using a “dam and fill” type approach, as will be readily understood. Such an alternative approach may require the use of different types of materials for the stress buffer. By way of example, a liquid encapsulant material having a flexural strength of 0.1 GPa and a flexural modulus of 12 GPa, such as that which is made by the Sumitomo Corporation of Tokyo, Japan, is known to work well for such “dam and fill” type purposes. Stress buffer  120  can also be designed to cover one or more of light sensitive areas  116 . 
     Moving next to  FIG. 2C , one IC device from the wafer of  FIG. 2B  is shown in side cross-sectional view as having been singulated from the wafer and attached and wire bonded to a panel. As shown, partially packaged IC device  130  can include a die  110  having one or more light sensors or light sensing regions  115 , one or more light sensitive areas  116 . Die  110  can be attached to a conductive connector element, such as leadless leadframe  133 , with attachment being made by an epoxy layer  132  or other suitable fastener. Wire bonds  131  can be used to electrically couple specific regions of the die  110  to connectors on the leadless leadframe  133 , with such usage being readily understood by those skilled in the art. A backing tape such as high temperature attach tape  134  can be used as a temporary backing to partially packaged IC device  130 , as will be readily appreciated. 
     The IC device of  FIG. 2C  is again illustrated in side cross-sectional view in subsequent process phases shown in  FIGS. 3A and 3B . In  FIG. 3A , a customized mold has been placed against the IC device, and a first opaque encapsulant has been dispensed thereabout. Partially packaged IC device  140  can be created by taking the device  130  of  FIG. 2C  and placing and holding a mold  141  directly against the stress buffer  120 . Mold  141  may be customized for this particular purpose, and can be shaped such that many or all IC devices in an entire panel may be processed in an identical or similar manner simultaneously or at a similar stage in the manufacturing process. As such, a lower protrusion as shown may exist in mold  141  for each optical IC device to be processed in the same panel, such that mold  141  can include dozens or hundreds of such customized protrusions. 
     As shown in  FIG. 3A , the lower protrusion of customized mold  141  can contact stress buffer  120  such that a cavity is created between the mold  141 , the stress buffer  120  and the light sensing region or sensor  115 , and also such that a seal is created to seal this cavity for the subsequent introduction of a first encapsulant  145 . Although the bottom surface of this lower protrusion of mold  141  is shown as being smaller than the opening formed in stress buffer  120 , it will be readily appreciated that such a bottom surface can also be larger than this stress buffer opening. In the event that the bottom surface of the lower protrusion of mold  141  is larger than the opening in the stress buffer  120 , then the lower protrusion of the mold would simply abut the upper surface of the stress buffer, rather than extend partially into it. In either situation, a cavity above the light sensing region  115  is created, which cavity is then sealed by the contact of the mold  141  against the stress buffer  120 . 
     Stress buffer  120  can be specifically designed to serve multiple purposes. For example, this stress buffer can accept the actual contact and absorb much or all of the stresses introduced by placing and holding the customized mold  141  against the partially packaged IC device, such that the die  110  and various components thereof are protected from potential damages by the use of the mold. Stress buffer  120  can also serve to work with mold  141  to create a sealed off cavity above the light sensing region  115 , such that a first opaque encapsulant  145  does not contact or cover the light sensing region when this encapsulant is dispensed thereabout. Stress buffer  120  can also be used to cover one or more light sensitive areas  116 , such that these areas are not exposed to light, regardless of the final formation or design of the first opaque encapsulant  145  and any other encapsulant or process components. Stress buffer  120  can also be designed to accomplish other objectives for the manufacture of the subject IC device and/or to function within the final IC device, as will be appreciated. 
     While customized mold  141  is held in place against stress buffer  120 , a first encapsulant  145  can be formed in the space created between the die  110  and the mold. Such an encapsulant can be any suitable plastic or other type of encapsulant typically used for encapsulating IC devices. For example, various silica-based compounds are known to work well for such encapsulating purposes, and are also known as good materials for absorbing and reducing stresses and thermal shocks to the overall packaged device. As is well known, many such encapsulants are opaque in nature, and black is a typical known color. It is preferable that the disclosed first encapsulant  145  be a good stress and thermal shock absorber, such that this first encapsulant can be any suitable opaque encapsulant that may be readily applied between the mold  141  and the die  110 , so as to encapsulate the die, wire bonds, leadframe and all other packaged components therein. 
     As shown in  FIG. 3A , first encapsulant  145  does not fill space occupied by mold  141 , which space deliberately includes a region directly above the light sensing region or sensor  115 . First encapsulant is thus formed such that an opening above this light sensing region is created therein. Although an inverted pyramid type shape is shown, it will be readily appreciated that this opening in the first encapsulant can be of any shaped desired, such as, for example, conical or cylindrical. Whichever shape of opening is desired, customized mold  141  can simply be created to result in the desired opening shape in the later formed first encapsulant  145 . As will also be readily appreciated, mold  141  can be formed of a durable material, such that it may be used repeatedly in the processing of many panels of packaged devices. 
     In  FIG. 3B , customized mold  141  has been removed and a second encapsulant  155  has been dispensed to create partially packaged IC device  150 . Since the desired package is to be an optical package, second encapsulant  155  preferably comprises a transparent material, and is dispensed in the opening created in first opaque encapsulant  145 , such that a fully encapsulated device having an optical window or light tunnel through the packaging is created. Light from an outside light source can then access the light sensor or sensing region  115  via the transparent second encapsulant  155  situated directly above this light sensor or sensing region. This second encapsulant  155  can contact the actual light sensing region  115 , since it is a transparent component and is intended to seal the device around this region. 
     Moving next to  FIG. 4A , the IC device of  FIG. 3B  has been processed further to arrive at a fully packaged IC device  160 . As will be readily appreciated, a variety of standard processing steps can be applied to the previous partially packaged IC device  150  to arrive at finished IC device  160 . For example, attach tape  134  can be removed from bottom surface  112 , the outer surface of the first encapsulant  145  can be laser marked, the IC device can be appropriately plated, and the device can be singulated from its panel, among other process steps. Laser markings  161  are shown on a top surface  111  of the overall package, and it will be readily appreciated that such laser markings are better suited for placement on the opaque material of the first encapsulant, rather than the clear material of the second encapsulant.  FIG. 4B  simply illustrates in top perspective view the IC device of  FIG. 4A . As shown, the “window” or light tunnel created by the second encapsulant within the first encapsulant can be rectangular in nature, although it will be appreciated that other shapes and formations may also be used. For example, a circular or oval shape may also work well for the intended purposes of the overall optical package. 
     As can be seen, the selective and limited use of second transparent encapsulant  155  results in an overall package having an encapsulant that is mostly opaque and relatively strong (i.e., first encapsulant  145 ), but that is conveniently transparent although relatively weaker in the desired location(s) (i.e., second encapsulant  155 ). Together, these first and second encapsulants provide an overall package that completely encapsulates the IC device contained inside, that is relatively strong compared to many optical packages, that provides the ability for an outside light source to shed light on an internal light sensor or region, and that is relatively inexpensive to manufacture. 
     Turning now to  FIGS. 5A and 5B , an alternative but similar IC device is depicted in side cross-sectional and top perspective views according to an alternative embodiment of the present invention. Fully packaged IC device  260  can be similar or even identical to IC device  160  detailed above in numerous ways. For example, the subject IC die can have a light sensor or region  215 , one or more light sensitive areas  216 , a first opaque encapsulant  245 , a second clear encapsulant  255  formed in an opening within the first encapsulant, and laser markings  261  on a top surface  211 , which is opposite a bottom surface  212 . 
     Unlike the previous fully packaged IC device, however stress buffer  220  is created so as to cover one or more light sensitive areas  216 . Again, such a stress buffer  220  can be created at the wafer level using any of a variety of wafer processing techniques, or can be created at the panel level using a dam and fill type of approach. As in the foregoing embodiments, the particular material used for the stress buffer  220  can vary, depending upon how it is applied. 
     As can be seen in  FIGS. 3A ,  4 A and  5 A, the customized mold can be designed such that the surface of its lower protrusion extends into the cavity above the light sensor, or such that it abuts the upper surface of the stress buffer directly. As will be readily appreciated, the former arrangement is reflected in the illustration of  FIG. 3A , while the latter arrangement is reflected in the illustrations of  FIGS. 4A and 5A . As seen in these last two figures, the opening in the first encapsulant (and thus the entire second encapsulant) is shaped as a result of the customized mold having abutted against the top of the stress buffer. Either arrangement is acceptable, since either arrangement accomplishes the preferable objectives that the customized mold not contact the light sensor, and that the cavity directly above the light sensor be sealed off for the application of the first encapsulant. 
       FIG. 6  illustrates a flowchart presenting exemplary methods of manufacturing the IC devices of  FIGS. 4A and 5A  according to various embodiments of the present invention. It will be readily appreciated that the methods and flowchart provided herein are merely exemplary, and that the present invention may be practiced in a wide variety of suitable ways. While the provided flowchart may be comprehensive in some respects, it will be readily understood that not every step provided is necessary, that other steps can be included, and that the order of steps might be rearranged as desired by a given manufacturer, as desired. 
     After start step  300 , a semiconductor wafer can be coated with a stress buffer layer at process step  302 . Such a wafer coating step is optional, however, and may be foregone in the event that the stress buffer is to be added at the panel level instead. After the stress buffer is added, various backgrinding, mounting and sawing processes may then be performed on the wafer at process step  304 . 
     At subsequent process step  306 , individual dice are then attached to a panel, which panel can be, for example, a leadless leadframe panel. Stress buffer dams can then be formed on the panel at process step  308 . As in the foregoing stress buffer step, the formation of stress buffer dams at the panel level is optional, and can be foregone in the event that the stress buffer was already formed at the wafer level. Wire bonding of dice to bonding pads can then be accomplished at process step  310 . 
     Detailed formation of the inventive package continues at process step  312 , as a customized mold is placed directly against various stress buffer components at the various dice on the subject panel. As noted above, this customized mold can various shapes designed to result in “openings” in an encapsulant material that is to be dispensed with the mold in place. A first opaque encapsulant is then dispensed at process step  314 , and the mold is removed thereafter at process step  316 . After the mold is removed, a second transparent encapsulant is dispensed into the openings in the first encapsulant at process step  318 . The first and second encapsulants can then be cured at process step  320 . 
     In various embodiments, the two encapsulants can be cured together. Alternatively, the first encapsulant can be cured before the second encapsulant is applied. The attach tape can be removed at process step  322 , the package can be marked with laser markings at process step  324 , and the device can be plated and singulated from the panel at process step  326 . The method then ends at end step  328 . 
     As will be appreciated, the foregoing method can be made to reflect some or all details of the stages depicted in  FIGS. 2A through 5B  above. Furthermore, steps may be performed in a different order, as may be preferred. For example, laser markings on an outer surface of the various dice may take place after plating and singulation from their respective panels. In addition, various steps may be performed at the wafer level over the panel level, or vice versa. In some embodiments, the use of various processes requiring a panel may be foregone in favor of other methods that do not require such a panel type manufacturing stage or process. 
     Although the foregoing invention has been described in detail by way of illustration and example for purposes of clarity and understanding, it will be recognized that the above described invention may be embodied in numerous other specific variations and embodiments without departing from the spirit or essential characteristics of the invention. Certain changes and modifications may be practiced, and it is understood that the invention is not to be limited by the foregoing details, but rather is to be defined by the scope of the appended claims.