Abstract:
A structure and method for protecting encapsulated semiconductor integrated microcircuit dice during shipping. The structure secures the position of the encapsulated die or dice atop an EMR-penetrable element using an adhesive layer, the stickiness, adhesiveness or coefficient of friction of which is alterable by exposure to EMR of a predetermined wavelength range, such as ultraviolet light. Once the structure reaches its destination, prior to removal of the packaged dice, the adhesive layer is exposed to EMR, such as ultraviolet light, through the element. This exposure reduces the stickiness, adhesiveness, or coefficient of friction of the adhesive to facilitate encapsulated die removal. The EMR-sensitive adhesive does not leave contaminating silicon residue on the removed encapsulated die.

Description:
TECHNICAL FIELD 
     This invention relates to semiconductor integrated microcircuit manufacturing and more particularly to temporarily packaging encapsulated integrated circuit dice for shipping. 
     BACKGROUND ART 
     Semiconductor integrated circuit chips are typically constructed en masse on a single wafer or other substrate of silicon or other semiconductor material. After the circuits are created, the wafers or substrates are split up, or “singulated”, into individual integrated circuit chips or dice. Typically, each die is then individually encapsulated into integrated circuit packages which are capable of being attached to printed circuit boards. Encapsulated dice are often sold or transferred to other manufacturing sites. The encapsulated dice must therefore be shipped through the mail or by other freight means to destinations which can be cities, states or even countries apart. Freight travel often involves subjecting articles so transported to a harsh, contaminant-laden environment in terms of dirt and dust, as well as mechanical shock and vibration. This environment requires that the encapsulated dice be temporarily packaged to protect them from such exposure. 
     Over the years, the electronic industry has developed packages called carrier tapes which temporarily contain the dies during shipping. In general, carrier tapes that are used to transport components from a component manufacturer to a different manufacturer that assembles the components into new products are well known. For example, in the field of electronic circuit assembly, electronic components are often carried from a supply of such components to a specific location on a circuit board for attachment thereto. The components may be of several different types, including surface mount components. Particular examples include memory chips, integrated circuit chips, resistors, connectors, dual in-line processors, capacitors, gate arrays, etc. Such components are typically affixed to a circuit board that may later be incorporated into an electronic device. 
     Rather than manually affixing each individual electronic component to a circuit board, the electronics industry makes extensive use of robotic placement machines, sometimes known as “pick-and-place” machines, which grasp a component at a specific location (the supply) and place it at another specific location (the circuit board). To ensure the sustained operation of the robotic placement machine, a continuous supply of electronic components must be furnished to the machine. 
     One way to provide a continuous supply of electronic components to a desired location is to use a carrier tape. Conventional carrier tapes generally comprise an elongated plastic strip (often referred to as the carrier) that has a series of identical pockets formed at predetermined, uniformly spaced intervals along the length of the strip. The pockets are designed to receive an electronic component. A continuous cover (often referred to as a cover tape) is applied over the elongated strip to retain the components in the pockets. The carrier tape is fed to the robotic placement machine that strips the continuous cover tape from the carrier and removes the components from the pockets and places them onto the circuit board. 
     A need exists for packaging and methods for inexpensively protecting encapsulated dice during shipping from contamination and damage, as well as facilitating removal of the encapsulated dice from packaging upon reaching their destination. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention provides a structure having an ultraviolet (UV) light or other electromagnetic radiation (EMR) transmissive or penetrable plate upon which has been placed a layer of UV light or other EMR-sensitive adhesive for securing the position of the encapsulated die or dice during shipping. The adhesive is sensitive to selected, predetermined wavelengths of EMR in that its adhesiveness, stickiness or coefficient of friction is alterable by exposing the adhesive to such selected wavelengths of EMR, such as UV light. Upon arrival of the structure at its destination, the adhesive is subjected to an EMR source emitting such radiation within the selected wavelengths, thereby reducing its adhesiveness, and allowing for less powerful pickup of the encapsulated dice during removal. The present invention may be embodied in the form of a tape-and-reel transport system for encapsulated dice. 
     According to one aspect of the invention, provided is a method method for loading, carrying and dispensing encapsulated semiconductor dice, comprising: 
     adhering a plurality of encapsulated dice in spaced relationship along an elongated tape element; 
     winding said elongated tape element on a reel; 
     unwinding said elongated tape element; 
     exposing said adhered singulated dice to EMR within a predetermined wavelength range and reducing the adherence of said adhered encapsulated dice to said tape element responsive to said EMR exposure. 
     Another aspect of the present invention provides a flexible carrier tape for storage and delivery of encapsulated die by an advancement mechanism, the carrier tape comprising: 
     a strip portion having a plurality of aligned pockets for carrying the encapsulated die, the pockets being spaced along the strip portion and having a bottom and opening through a top surface thereof; and, 
     an electromagnetic radiation sensitive material disposed on the bottom of the pockets for affixing the encapsulated die thereto. 
     Other objects and aspects of the present invention will become readily apparent to those skilled in this art from the following detailed description. The embodiments shown and described provide illustration of the best mode contemplated for carrying out the invention. The invention is capable of modifications in various obvious respects, all without departing from the invention. Accordingly, the drawings are to be regarded as illustrative in nature, and not as restrictive. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic side sectional elevation of a tape-and-reel encapsulated die transport assembly and associated EMR chamber according to the invention; 
     FIGS. 2A and 2B are schematic top views of two encapsulated die-support tapes of different design employing EMR-sensitive adhesives in different patterns; 
     FIG. 3 is an enlarged side sectional view of an encapsulated die-support tape including encapsulated die containment cavities; and 
     FIG. 4 is a transverse cross-sectional view of an encapsulated die-support tape defining a continuous channel for receiving dice therein. 
     FIG. 5 is a block diagram of the steps necessary for shipping encapsulated dice packaged in carrier tape according to the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 depicts a tape-and-reel transport assembly  200 , herein illustrated with reel  202  feeding a continuous carrier tape  204  bearing a plurality of encapsulated dice  206  secured by EMR-sensitive adhesive segments  208  over ENR-penetrable windows  210  (elements  206 ,  208  and  210  shown enlarged for clarity) in carrier tape  204  into an EMR chamber  220  to effect release of the encapsulated dice  206  through sequential exposure to an EMR source  222  within chamber  220 . Carrier tape  204  comprises a material which is penetrable by (i.e., transmits) ultraviolet (UV) light, such as substantially clear plastic, glass or polycarbonate. EMR source  222  is preferably placed below and aimed upwardly through carrier tape  204  as it passes through EMR chamber  220 . EMR source  222  may be continuously activated, intermittently activated responsive to the presence of a carrier tape-adhered encapsulated die thereover, or continuously activated but shielded by a shutter structure until such time as a carrier tape-adhered encapsulated die is disposed thereover. Upon arrival of the tape and reel at its destination, the UV-sensitive adhesive is subjected to a UV light of sufficient intensity. The exposure reduces the coefficient of friction of the adhesive and the encapsulated die can then be easily removed through vacuum pick-up means. Reel  202  carrying a tape  204  bearing encapsulated dice  206  adhered thereto and wound around reel  202  would typically be disposed for transport in a case  300  as known in the art, or at least in an EMR-opaque antistatic bag  302  (both shown in reduced size in FIG.  11 ). In this embodiment, UV-sensitive adhesives and a UV EMR source are employed. In this embodiment, the adhesive layer is formed using ultraviolet sensitive tape (UV tape) of the type which is currently used to hold IC wafers firmly in place during the singulation process. UV tape typically comprises a layer of ultraviolet curable, pressure sensitive adhesive such as acrylic attached to a UV-penetrable polyvinyl chloride backing. 
     UV tape is currently available from suppliers such as Kanematsu USA, Inc., of New York, N.Y. under the brand name Furukawa UV Tape; Uniglobe Kisco Co., of Santa Clara, Calif., under the brand name Bando Dicing Tape; and others. Although UV-sensitive adhesive tape is the preferred adhesive, other EMR-sensitive adhesives such as glues and gels may be used in place of the UV tape without departing from the invention. 
     In general, any means for containing the dice may be used without departing from the invention so long as those means allow for the penetration of electromagnetic radiation which will reduce the coefficient of friction of the adhesive layer. 
     The pre-exposure stickiness, level of adhesion or coefficient of friction of the UV-sensitive adhesive should generally be strong enough to securely hold the encapsulated dice during the rigors of shipping, and be weak enough after exposure and curing to allow for vacuum pick-up. The adhesive should not contain a significant concentration of any undesirable compounds which would result in contamination of the encapsulated die or dice. 
     Although UV light is used in the preferred embodiment, other types of electro-magnetic radiation may be used so long as the plate portion is penetrable by it, and the adhesive layer is sensitive to it. For the commercially available UV-sensitive adhesive tape disclosed above and for most clear plastic, glass or polycarbonate, UV light having a wavelength of between 250 and 350 nanometers has been found to be adequate. UV sensitive adhesives by different manufacturers are responsive to different but largely overlapping wavelength ranges, and the invention may thus be practiced effectively with such different adhesives using a wide-spectrum UV source. 
     FIGS. 2A and 2B depict several variations in the structure of carrier tape  204  according to the invention. FIG. 2A illustrates a carrier tape  204   a  having indexing holes  240  at equal intervals along each lateral edge thereof for precise, controlled movement of tape  204   a  by indexing pins or sprockets as known in the art, such feature being conventional. As tape handling equipment for TAB (tape automated bonding) operations is conventionally most often designed to handle either 35 mm or 70 mm wide tape (depending upon packaged die size), it is contemplated, although not required, that the present invention might be practiced with tapes of those widths so as to facilitate use of existing equipment. Tape  204   a  may be substantially comprised of a flexible, EMR-opaque metallic or non-metallic (such as synthetic resin) material, and includes EMR-transmissive segments  242  formed therein or placed over apertures formed therein at encapsulated die placement locations  244 . Segments  242  carry an EMR-sensitive adhesive patch  246  on their upper, or carrier, surfaces. Encapsulated dice  206  are then placed on adhesive patches  246 , adhering thereto until they are subsequently released by selective EMR exposure, as previously described. After adherence of encapsulated dice  206 , tape  204   a  is then wound about a reel  202  for transport, reel  202  then being typically placed in reel case  300  or an EMR-opaque anti-static bag  302 . Segments  242  and adhesive patches  246  may be embodied in several ways. For example, segment  242  may comprise an adhesive-coated tape as previously mentioned. Alternatively, adhesive  246  may comprise dots, crosses or X&#39;s of adhesive applied through a stencil or by a printing head, or sprayed, onto segments  242 . 
     FIG. 2B depicts a carrier tape  204   b  comprised of two robust, mutually parallel edge strips  260  containing indexing holes  240 , with a continuous intervening encapsulated die support strip  262  of EMR-transmissive material disposed therebetween. The entire tape  204   b  or only encapsulated die support strip  262  may be formed of EMR-transmissive material, as desired or required. The edge strips  260  may be of greater thickness than encapsulated die support strip  262  to eliminate stretching of tape  204   b,  and to facilitate the use of a thinner, and thus more EMR-transmissive segment for encapsulated die support strip  262 . Further, edge strips  260  may extend above the upper surface of support strip  262  so as to provide a recessed channel for containing and protecting encapsulated dice  206  when tape  204   b  is wound on reel  202 . If desired, transversely-extending brace members  263  may extend between edge strips  260  to stabilize the encapsulated die support areas and reduce the tendency of carrier tape  204   b  to flex when the encapsulated dice adhered thereto are retrieved. An EMR-sensitive adhesive may be applied to encapsulated die support strip  262  in the manner described with respect to FIG. 2A, or, as depicted, may comprise a single continuous adhesive strip  264  or two mutually parallel adhesive strips  266  (shown in broken lines). 
     FIG. 3 depicts an enlarged side sectional view of a segment of a tape  204   c,  depicting encapsulated die containment cavities  270  having EMR-penetrable bottoms  272  for carrying and enclosing encapsulated dice  206  adhered to EMR-sensitive adhesive material  274 . When wound on a reel  202 , cavities  270  will protect encapsulated dice  206  on tape  204   c  against damage and contamination. It should be noted that conventional tape structures employing cavities typically require a lid or shutter over the mouth of each cavity to prevent the enclosed encapsulated die from falling out, which requirement is eliminated by the present invention. 
     FIG. 4 depicts a transverse cross-sectional view of a tape  204   d  defined by a central channel-shaped member  280 , at least the bottom  282  of which is comprised in whole or in segments of an EMR-transmissive material. Longitudinally-spaced dots or segments or a continuous strip or strips of EMR-sensitive adhesive material  284  are applied to bottom  282  inside channel shaped member  280 . Packaged dice  206  are carried on adhesive material  284 , protected within the confines of channel-shaped member  280 . Lateral flanges  286  extend transversely to tape  204   d  along the length thereof, and may be placed at the upper, midportion or lower extents of the channel sidewalls  288  as shown in broken lines. Flanges  286  may include apertures for engagement by tape-handling mechanisms. 
     FIG. 5 shows exemplary process steps for transporting or shipping an encapsulated die according to the invention. The process begins with placing  61  the encapsulated die on an unexposed UV-sensitive layer of adhesive such as UV tape attached to the upper surface of a substantially transparent portion of a bed. The term “substantially transparent” in this specification means that the portion is capable of passing through UV light with a satisfactorily low amount of attenuation. The next step involves enclosing  62  the encapsulated die within the tape and sending  63  the tape to its destination. During transport, the tape should not be irradiated by any UV light source. This is usually accomplished by placing the wound carrier tape within an opaque antistatic bag. Upon arrival, there are the steps of: exposing  64  a portion of the tape existing between the encapsulated die and the substantially transparent portion of the bed to electromagnetic radiation in the form of ultraviolet light; opening  65  the tape (if a cover is used); and removing  66  the encapsulated die from the tape. The exposing step may occur before or after the opening step. 
     While the preferred embodiments of the invention have been described, additions, deletions and modifications may be made to those illustrated, features of different embodiments combined, and other embodiments devised, without departing from the spirit of the invention and the scope of the appended claims.