Abstract:
An integrated circuit (IC) device comprising: 1) an integrated circuit (IC) die having a first surface, a second surface opposite the first surface, and sidewalls extending between the first surface and the second surface; and 2) an integrated circuit (IC) package for supporting the IC die, wherein the IC package is attached to at least one of the sidewalls of the IC die such that at least a portion of the IC die first surface and at least a portion of the IC die second surface are exposed.

Description:
TECHNICAL FIELD OF THE INVENTION  
         [0001]    The present invention is generally directed to integrated circuit (IC) packages and, more specifically, to an IC device which exposes the upper and lower surfaces of the integrated circuit die.  
         BACKGROUND OF THE INVENTION  
         [0002]    The size of integrated circuit (IC) packages continues to decrease even as the complexity and level of circuit integration in the IC packages continue to increase. This is particularly true in the case of system-on-a-chip (SoC) devices, in which most, if not all, of an electronic appliance is integrated onto a single integrated circuit die. Thus, relatively complex devices, such as cell phones, network interface cards (NICs), communication buses, and the like, are now being implemented as a single integrated circuit or perhaps only several integrated circuits.  
           [0003]    Many integrated circuit (IC) devices do not encapsulate the entire IC chip in a protective package. For example, an IC sensor chip used in a fingerprint reader is a Touch-chip™ device (produced by STMicroelectronics, Inc.) that uses a sensor array to read a fingerprint. In order to work properly, the sensor array must be at least partially exposed in order to receive the finger of a user. Other types of IC packages that expose the surface of the integrated circuit are chemical and pressure sensors. Optical sensors may be covered by a lens element. Light sensitive elements on the surface of the IC die are left exposed in order to detect light. More generally, it is useful in many applications to leave at least a portion of the surface of an IC die exposed so that test points on the IC die may be probed. Alternatively, it may be useful to leave a portion of the IC die surface exposed so that an end-user of the IC device may incorporate the IC package into a larger system by forming electrical connections to points on the surface of the IC die selected by the end-user, rather than the manufacturer of the IC package.  
           [0004]    For these types of devices, it is necessary to package the IC die in such a way that the edges and wires of the IC die are protected, but the sensor array and/or test points on the surface or the IC die remain completely exposed. The packaging is usually accomplished using some kind of molding process. However, this process is made more difficult by the need to prevent molding flash from forming on the IC sensor and by the need to compensate for variation in die thickness and die tilt. The exposed IC sensor surface is brittle and must be handled carefully to prevent it from shattering during the manufacturing process and in the field.  
           [0005]    Also, these sensors are generally integrated into a hand-held device, such as a mobile phone to check fingerprints, a portable glucose meter to check the composition of body fluids, or a web-cam to take a picture. The packaging of these sensors has to be very efficient, to make the sensor very adaptable for integration into a hand-held system using a conventional surface mount (soldering) process. The smallest possible package is the silicon sensor itself, without the packaging. However, this is not compatible with the surface mounting process. Standard packages, such as Dual-in-Line package (DIP) or Quad Flat Pack (QPF), increase the mounting areas because of their leads. Other packages, such as BGA, add an excessive amount of additional thickness to the sensor.  
           [0006]    Therefore, there is a need in the art for improving the packaging of an IC sensor that contains at least a partially exposed integrated circuit die surface.  
         SUMMARY OF THE INVENTION  
         [0007]    To address the above-discussed deficiencies of the prior art, it is a primary object of an advantageous embodiment of the present invention to provide an integrated circuit (IC) device comprising: 1) an integrated circuit (IC) die having a first surface, a second surface opposite the first surface, and sidewalls extending between the first surface and the second surface; and 2) an integrated circuit (IC) package for supporting the IC die, wherein the IC package is attached to at least one of the sidewalls of the IC die such that at least a portion of the IC die first surface and at least a portion of the IC die second surface are exposed.  
           [0008]    According to one embodiment of the present invention, the IC package has a first surface and a second surface opposite the IC package first surface, and wherein the IC package second surface lies in substantially the same plane as the IC die second surface.  
           [0009]    According to another embodiment of the present invention, a first portion of the IC package is attached to and covers at least part of a peripheral portion of the IC die first surface.  
           [0010]    According to still another embodiment of the present invention, the IC package encases at least one electrical connection extending between a contact pad on the peripheral portion of the IC die first surface and a contact pad disposed on the IC package second surface.  
           [0011]    According to yet another embodiment of the present invention, an exposed surface of the contact pad disposed on the IC package second surface lies in substantially the same plane as IC die second surface.  
           [0012]    According to a further embodiment of the present invention, an exposed surface of the contact pad disposed on the IC package second surface is recessed in an indentation in the IC package second surface.  
           [0013]    According to a still further embodiment of the present invention, substantially all of the IC die second surface is exposed.  
           [0014]    According to a yet further embodiment of the present invention, the IC die second surface is suitable for attachment to a heat sink.  
           [0015]    In one embodiment of the present invention, the IC die second surface is suitable for attachment to a ground plane contact of a printed circuit board.  
           [0016]    In another embodiment of the present invention, at least one of the IC die first surface and the IC die second surface have exposed test points thereon.  
           [0017]    The foregoing has outlined rather broadly the features and technical advantages of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features and advantages of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art should appreciate that they may readily use the conception and the specific embodiment disclosed as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the invention in its broadest form.  
           [0018]    Before undertaking the DETAILED DESCRIPTION OF THE INVENTION below, it may be advantageous to set forth definitions of certain words and phrases used throughout this patent document: the terms “include” and “comprise,” as well as derivatives thereof, mean inclusion without limitation; the term “or,” is inclusive, meaning and/or; the phrases “associated with” and “associated therewith,” as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like; and the term “controller” means any device, system or part thereof that controls at least one operation, such a device may be implemented in hardware, firmware or software, or some combination of at least two of the same. In particular, a controller may comprise a data processor and an associated memory that stores instructions that may be executed by the data processor. It should be noted that the functionality associated with any particular controller may be centralized or distributed, whether locally or remotely. Definitions for certain words and phrases are provided throughout this patent document, those of ordinary skill in the art should understand that in many, if not most instances, such definitions apply to prior, as well as future uses of such defined words and phrases.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]    For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, wherein like numbers designate like objects, and in which:  
         [0020]    [0020]FIG. 1A is a cross-sectional view of an apparatus for fabricating an integrated circuit (IC) device according to the principles of the present invention;  
         [0021]    [0021]FIG. 1B is a cross-sectional view of the finished integrated circuit (IC) device fabricated by the apparatus illustrated in FIG. 1A above;  
         [0022]    [0022]FIG. 1C is a side view of finished integrated circuit (IC) devices mounted on a printed circuit board (PCB);  
         [0023]    [0023]FIG. 2A is a bottom view of the finished integrated circuit (IC) device fabricated by the apparatus illustrated in FIG. 1A above;  
         [0024]    [0024]FIG. 2B is a top view of the finished integrated circuit (IC) device fabricated by the apparatus illustrated in FIG. 1A above;  
         [0025]    [0025]FIG. 3 is an enlarged cross-sectional view of an exemplary electrical connection in the integrated circuit (IC) package illustrated in FIG. 1B according to one embodiment of the present invention;  
         [0026]    [0026]FIG. 4 is an enlarged cross-sectional view of an exemplary electrical connection in the integrated circuit (IC) package illustrated in FIG. 1B according to another embodiment of the present invention;  
         [0027]    [0027]FIG. 5 is an enlarged cross-sectional view of an exemplary electrical connection in the integrated circuit (IC) package illustrated in FIG. 1B according to still another embodiment of the present invention;  
         [0028]    [0028]FIG. 6 is an enlarged cross-sectional view of an exemplary electrical connection in the integrated circuit (IC) package illustrated in FIG. 1B according to still another embodiment of the present invention;  
         [0029]    [0029]FIG. 7 is an enlarged cross-sectional view of an exemplary electrical connection in the integrated circuit (IC) package illustrated in FIG. 1B according to still another embodiment of the present invention; and  
         [0030]    [0030]FIG. 8 is an enlarged cross-sectional view of an exemplary electrical connection within the integrated circuit (IC) package in FIG. 1B according to still another embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0031]    [0031]FIGS. 1 through 8, discussed below, and the various embodiments used to describe the principles of the present invention in this patent document are by way of illustration only and should not be construed in any way to limit the scope of the invention. Those skilled in the art will understand that the principles of the present invention may be implemented in any suitably arranged integrated circuit device.  
         [0032]    It should be noted that the sizes and thicknesses of objects in FIGS.  1 - 6  are not to scale. FIGS.  1 - 6  are primarily intended to show the relative positions of objects. Furthermore, the terms “upper surface” and “lower surface” are used for convenience with respect to the device positions shown in FIGS.  1 - 6 . However, the terms “upper surface” and “lower surface” should not be construed as absolute terms so as to limit the scope of the present invention. Those skilled in the art will understand that the devices shown in FIG. 1- 6  may be inverted or tilted on one side, thereby altering the meaning of upper surface and lower surface. More generally, the terms “first surface” and “second surface” may be used to distinguish between opposing sides of an IC die, and IC package, or another device.  
         [0033]    [0033]FIG. 1A is a cross-sectional view of an apparatus for fabricating integrated circuit (IC) device  190  according to the principles of the present invention. IC device  190  comprises integrated circuit (IC) package  150 , which supports and protects integrated circuit (IC) die  105 . IC die  105  has exposed upper and lower surfaces according to the principles of the present invention. Conventional molding techniques may be used to fabricate IC package  150 .  
         [0034]    Initially, IC die  105  is temporarily mounted on carrier  110  using a die attach compound. Electrical connections, generally designated as item  115  in FIG. 1A, are added between contacts on the surface of IC die  105  and the surface of carrier  110 . Electrical connections  115  are discussed below in greater detail.  
         [0035]    Carrier  110  may be made from a variety of materials, including paper, polymer film, metal on printed circuit board (PCB), or the like. Much of the surface area of carrier  110  exhibits low adhesion to the molding compound used to make the body of IC package  150  and to the die attach compound.  
         [0036]    The body of IC package  150  is made by means of mold block  125 , movable insert block  130  and spring  135 . The lower surfaces of mold block  125  and movable block  130  are separated from the upper surfaces of IC die  105  and carrier  110  by soft film  120 , which provides a layer of cushioning protection. Soft film  120  may initially be sealed against the lower surfaces of mold block  125  and movable block  130  by means of vacuum pressure.  
         [0037]    Once soft film  120  is in place on the lower surfaces of mold block  125  and movable block  130 , mold block  125  and movable block  130  are pressed down against IC die  105  and carrier  110 , thereby forming cavity  140 . Carrier  110  is supported on its lower surface  110  by a bottom mold block (not shown) or other supporting surface (not shown). Soft film  120  forms a seal against the surfaces of IC die  105  and carrier  110 , preventing the molding compound from leaking out of cavity  140  or from contacting the portion of the upper surface of IC die  105  that is to be left exposed.  
         [0038]    After the molding compound is injected into cavity  140  are allowed to harden, soft film  120 , mold block  125 , and movable block  130  are removed and carrier  110  is removed from the bottom surfaces of IC die  105  and IC package  150 , thereby producing the final product. FIG. 1B is a cross-sectional view of finished integrated circuit (IC) device  190 , fabricated by the apparatus and method described above in FIG. 1A. Electrical connections  115  within IC package  150  are omitted for the purpose of simplicity in explaining FIG. 1B.  
         [0039]    As FIG. 1B illustrates, upper surface  105   a  and lower surface  105   b  of IC die  105  are now exposed. The molding compound that forms IC package  150  bonds to side surface  105   c  of IC die  105  and to the outer periphery (i.e. peripheral portion) of upper surface  105   a  of IC die  105 . Lower surface  150   b  of IC package  150  lies in substantially the same plane as lower surface  105   b  of IC die  105 . Inner sidewall  150   c,  outer sidewall  150   d,  and upper surface  150   a  of IC package  150  form a tub-like structure around upper surface  105   a  of IC die  105 .  
         [0040]    [0040]FIG. 1C is a side view of finished integrated circuit (IC) devices  190 A and  190 B mounted on printed circuit board (PCB)  199 . The reduced package thickness gives IC devices  190 A and  190 B a reduced profile. Additionally, the direct contact between lower surface  105   b  and the surface of PCB  199  provides superior heat dissipation and grounding.  
         [0041]    [0041]FIG. 2A is a bottom view of finished integrated circuit (IC) device  190  fabricated by the apparatus illustrated in FIG. 1A above. Lower surfaces  200  of electrical connections  115  are visible at various points on lower surface  150   b  of IC package  150 . All of lower surface  105   b  of IC die  105  is exposed.  
         [0042]    [0042]FIG. 2B is a top view of finished integrated circuit (IC) device  190  fabricated by the apparatus illustrated in FIG. 1A above. Outer sidewall  150   d,  inner sidewall  150   c,  and upper surface  150   a  of IC package  150  are visible. Only a portion of upper surface  105   a  of IC die  105  is exposed.  
         [0043]    Since upper surface  105   a  and lower surface  105   b  of IC die  105  are exposed, it is possible to use IC device  190  as, for example, an optical sensor if upper surface  105   a  or lower surface  105   b  contains light sensitive elements. Alternatively, IC device  190  may be used as a touch sensor if a touch array is disposed on upper surface  105   a  of IC die  105 . Also, test points on upper surface  105   a  and lower surface  105   b  of IC die  105  now may be probed, or an end-user may solder additional wire leads to points on upper surface  105   a  and lower surface  105   b  of IC die  105 .  
         [0044]    Furthermore, a heat sink and/or a metal ground plane device may be attached directly to lower surface  105   b  of IC die  105 . This is a particularly advantageous feature of the present invention. As shown in FIG. 1C, a large number of IC devices (e.g.,  190 A,  190 B) constructed similarly to IC device  190  may be mounted directly on printed circuit board (PCB)  199 , which contains exposed ground contacts and heat sinks. Such a configuration would have a narrow profile and the IC devices could be tightly packed together.  
         [0045]    [0045]FIG. 3 is an enlarged cross-sectional view of exemplary electrical connection  115  in integrated circuit (IC) package  150  in FIG. 1B according to one embodiment of the present invention. The enlarged view extends from boundary A 1  to boundary A 2  in FIG. 1B. Carrier  110  is still in place.  
         [0046]    Electrical connection  115  may use any conventional wire bonding technique to create a connection between a contact point on upper surface  105   a  of IC die  105  and an external contact pad on the lower surface  105   b  of IC package  150 . In an exemplary embodiment, electrical connection  115  may use a stitch and ball technique to form metal ball  305 , metal ball  310 , wire  315 , and metal pad  320 . Metal pad  320  is temporarily affixed to carrier  110  by any known technique, including an applique applied to film, selective plating, and the like. When the mold compound is injected, the mold compound surrounds metal ball  305 , metal ball  310 , and wire  315  and locks them in placed when the mold compound hardens.  
         [0047]    It is noted that metal pad  320  may either remain in place in IC package  150  when carrier  110  is removed or may be pulled out of IC package  150  when carrier  110  is removed. These two different configurations may be selected by controlling the relative strengths of the mechanical, chemical or metallurgical joining forces between:  
         [0048]    1) metal pad  320  and the molding compound of IC package  150 , and/or between metal pad  320  and ball  310 ; and  
         [0049]    2) the interface between the lower surface of metal pad  320  and the upper surface of carrier  110 .  
         [0050]    [0050]FIG. 4 is an enlarged cross-sectional view of exemplary electrical connection  115  within integrated circuit (IC) package  150  according to another embodiment of the present invention. If the interface between metal pad  320  and the molding compound of IC package  150  is stronger than the interface between the lower surface of metal pad  320  and the upper surface of carrier  110 , metal pad  320  remains inside IC package  150  when carrier  110  is removed. The bottom surfaces of metal pads  320  then becomes the lower surfaces  200  shown in FIG. 2A. Conventional method can then be used to create solder ball  400  on the lower surface of metal pad  320 .  
         [0051]    The relative adhesion strength between these interfaces may be controlled by varying the wirebonding parameters (e.g., force, energy, and time), and by varying the type and amount of plating on metal pad  320 , as is generally known in the art.  
         [0052]    [0052]FIG. 5 is an enlarged cross-sectional view of exemplary electrical connection  115  within integrated circuit (IC) package  150  according to still another embodiment of the present invention. If the interface between the lower surface of metal pad  320  and the upper surface of carrier  110  is stronger than the interface between metal pad  320  and the molding compound of IC package  150 , metal pad  320  is pulled out of IC package  150  when carrier  100  is removed. This leaves an indentation in lower surface  150   b  of IC package  150 . The lower surfaces of metal balls  310  then becomes the lower surfaces  200  shown in FIG. 2A. Conventional method can then be used to create solder ball  500  on the lower surface of metal pad  320 .  
         [0053]    [0053]FIG. 6 is an enlarged cross-sectional view of an exemplary electrical connection in the integrated circuit (IC) package illustrated in FIG. 1B according to still another embodiment of the present invention. FIG. 6 differs from FIG. 3 in that the shape of metal pad  320  has been modified and metal ball  310  has been omitted. Metal ball  310  is not strictly required, so wire  315  is bonded directly to the upper surface of metal pad  620 . Metal pad  320  has been replaced by metal pad  620 , which has a trapezoidal cross-sectional area. The trapezoidal cross-sectional area makes it easier for metal pad  620  to be pulled out of IC package  150  by carrier  110 , if so desired.  
         [0054]    [0054]FIG. 7 is an enlarged cross-sectional view of an exemplary electrical connection in the integrated circuit (IC) package illustrated in FIG. 1B according to still another embodiment of the present invention. FIG. 7 differs from FIG. 6 in that metal pad  720  has been inverted. Metal pad  720  has a trapezoidal cross-sectional area similar to metal pad  320 . However, since the wider base of the trapezoid is now within IC package  150 , the hardened molding compound prevents metal pad  720  from being pulled out when carrier  110  is removed.  
         [0055]    [0055]FIG. 8 is an enlarged cross-sectional view of exemplary electrical connection  115  within integrated circuit (IC) package  150  according to still another embodiment of the present invention. In FIG. 8, intermediate substrate (or interposer)  805  is used to form electrical connections. Carrier  110  holds intermediate substrate  805  in place while wire  315  is soldered to contact pad  810  and during the molding process. After carrier  110  is removed, the lower surface of intermediate substrate  805  is exposed, including contact pad  815 . The lower surface of intermediate substrate  805  lies in substantially the same plane as lower surface  105 b of IC die  105 .  
         [0056]    Intermediate substrate  805  may be any one of several standard packaging designs, including organic laminate (PC board), polyimide tape, or ceramic. Internally, intermediate substrate  805  contains conductive paths (typical metal) on one or more conduction layers that connect contact pad  810  and contact pad  815  by through hole, metal vias, and the like. Contact pad  815  may receive a solder ball as explained above in FIG. 4.  
         [0057]    Although the present invention has been described in detail, those skilled in the art should understand that they can make various changes, substitutions and alterations herein without departing from the spirit and scope of the invention in its broadest form.