Abstract:
System for attaching a die to the die pad of a lead frame incorporating a resistive heating circuit into the die pad which heats up to cure an epoxy adhesive between the die and the pad and thereby attach the die to the pad. The heating circuit also heats up to loosen the adhesive so the die can be detached from the pad for rework.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application is a continuation of application Ser. No. 09/620,182, filed Jul. 20, 2000, pending, which is a continuation of application Ser. No. 09/338,242, filed Jun. 22, 1999, now U.S. Pat. No. 6,111,220, issued Aug. 29, 2000, which is a continuation of application Ser. No. 08/711,201, filed Sep. 10, 1996, now U.S. Pat. No. 5,938,956, issued Aug. 17, 1999. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    This invention relates in general to semiconductor dice and, in particular, to devices and methods for heating adhesives and other attachment materials to package or rework semiconductor dice.  
           [0004]    2. State of the Art  
           [0005]    Semiconductor dice are small, generally rectangular integrated circuit (IC) devices cut from a semiconductor wafer, such as a silicon wafer, on which multiple IC&#39;s have been fabricated. Bare dice are typically packaged to protect them from corrosion and physical damage by attaching them to a base, such as a lead frame or a printed circuit board, with a die-attach material, such as an epoxy or polyamide resin, cured in an oven, and then encapsulated in thermosetting plastic. In some instances, bare dice are attached to a printed circuit board and enclosed by a cover that is attached to the printed circuit board with an attachment material, such as a thermoset material, that requires additional curing in an oven.  
           [0006]    This use of ovens for curing die-attach materials and attachment materials can be problematic for a number of reasons. Ovens are expensive to operate and take up precious room on the floor of a semiconductor manufacturing facility. Also, in addition to curing die-attach materials and attachment materials, ovens undesirably heat everything else on a printed circuit board or package as well, including solder joints, other adhesive joints, and other electronic devices. As a result, ovens can be destructive when sufficient care is not taken in their use. Further, because ovens cannot direct heat at individual dice or packages, they cannot be used to detach an individual die for reworking, or to detach a die cover from a package for reworking the die inside the package, without also detaching or destroying electronic devices that share a printed circuit board with the die.  
           [0007]    In an attempt to eliminate the problems associated with heating semiconductor dice in an oven, in some instances, heaters have been embedded in printed circuit boards for use in the soldering of a semiconductor device to the printed circuit board and in attachment/disassembly operations. Such arrangements are shown in U.S. Pat. Nos. 5,010,233 and 5,175,409.  
           [0008]    However, such prior art arrangements use heaters to heat large areas or the entirety of printed circuit boards or substrates, not specific localized areas of a predetermined configuration.  
           [0009]    Therefore, there is a need in the art for a device that can direct heat at a specific area of an individual die or package to cure a die-attach material or attachment material associated therewith, or to loosen a previously cured die-attach material or attachment material associated therewith for detaching and reworking the die.  
         SUMMARY OF THE INVENTION  
         [0010]    A system for attaching or removing for repair a bare die to a base, such as a lead frame, includes a heat-activated die-attach material, such as a suitable adhesive, interposed between a localized die-attach region on the base and the back surface of the die. A heating circuit, such as a thin-film resistor, integral with the base in substantial registry with the localized die-attach region generates heat in response to being electrically energized in order to activate the die-attach material. As a result, the system avoids the cumbersome use of ovens to heat the die-attach material. Instead, the system advantageously directs heat at the individual die to attach the die to the base by curing the die-attach material, or to detach the die from the base for rework by loosening the die-attach material.  
           [0011]    In another embodiment of the present invention, a system for sealing a bare die in an enclosure, such as a Chip-Scale-Package, includes a heat-activated attachment material, such as a thermoset or thermoplastic material, interposed between the enclosure&#39;s die cover and base at the interface therebetween. A heating circuit integral with either the base or the die cover in substantial registry with the interface therebetween generates heat in response to being electrically energized in order to activate the attachment material. As a result, the system advantageously directs heat at the interface between the enclosure&#39;s die cover and base to attach the die cover to the base by curing the attachment material, or to detach the die cover from the base by loosening the attachment material for repair purposes.  
           [0012]    In an additional embodiment, the previously summarized system for sealing a bare die in an enclosure includes a heat-activated, electrically resistive attachment material, such as a conductive epoxy adhesive, interposed between the die cover and the base in place of the heating circuit. In this embodiment, the attachment material itself generates heat in response to being electrically energized in order to attach or detach the die cover. 
       
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0013]    [0013]FIG. 1 is an exploded isometric view of a semiconductor die attached to a lead frame die pad using a heating circuit that is integral with the pad in accordance with the present invention.  
         [0014]    [0014]FIG. 2 is an exploded isometric view of a semiconductor die directly attached to a printed circuit board and enclosed by a die cover attached to the board using a heating circuit that is integral with the board in accordance with the present invention.  
         [0015]    [0015]FIG. 3 is an exploded isometric view of a Lead-Over-Chip type semiconductor die enclosed between a substrate board and a die cover attached to the substrate board using a heating circuit that is integral with the substrate board and/or in the die cover in accordance with the present invention.  
         [0016]    [0016]FIG. 4 is an exploded isometric view of a package with its die cover attached to its base using a heating circuit that is integral with the base in accordance with the present invention.  
         [0017]    [0017]FIG. 5 is an exploded isometric view of a package with its die cover permanently sealed and attached to its base using a heating circuit that is integral with the base in accordance with the present invention.  
         [0018]    [0018]FIG. 6 is a block diagram of an electronic system including the package of FIG. 4. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0019]    A die support member  10  of the present invention shown in FIG. 1 includes a heating circuit  12  integral with a base  14 , such as a lead frame die pad  14 . The heating circuit  12  is generally located on or near the surface of the base  14  for improved heating efficiency in a localized area of the base. Alternatively, the heating circuit  12  may be placed on the base  14  to provide a uniform heating of the entire base or predetermined portion thereof. It will be understood by those having skill in the field of this invention that any heating circuit capable of being integrated with a base will work for purposes of this invention, including resistance-connected Metal-Oxide Semiconductor (MOS) transistors connected in series, doped resistors, epitaxial-layer resistors, pinch resistors, thin-film resistors, diffused resistors, deposited resistors, plated resistors, etched resistors, etched resistors having been etched into a substrate, polysilicon resistors, and Complimentary-MOS (CMOS) well-type resistors. Also, although this embodiment of the present invention will be described with respect to a die support member having a lead frame die pad for a base, it will be understood that the present invention is applicable to any die support member having a base, including Single In-Line Memory Modules (SIMM&#39;S), Dual In-Line Memory Modules (DIMM&#39;S), etc. The base  14  may include lead frames, either conventional or Lead-Over-Chip type, a silicon substrate having a passivated surface, a glass epoxy printed circuit board, a printed circuit board including a SIMM, DIMM, or other multi-chip modules, etc. It should be understood that the present invention is not limited to the shape and configuration of the illustrated heating circuit  12  as the heating circuit  12  can include other shapes and variations.  
         [0020]    The heating circuit  12  attaches a bare semiconductor die  16 , such as a Dynamic Random Access Memory (DRAM) die, to the lead frame die pad  14  by heating and curing a die-attach material  18  on the surface of the lead frame die pad  14  in response to being energized by a supply voltage V s  or current supply.  
         [0021]    A wide variety of well-known die-attach materials will work for purposes of this invention, including polymers, such as polyamide and epoxy adhesives, eutectic materials, gold/silicon eutectic materials, eutectic solders, thermosetting materials, thermoplastic materials, conducting polyamides, conductive epoxy, and other suitable heat sealants. Of course, the heating circuit  12  can also be used to detach the bare semiconductor die  16  from the lead frame die pad  14  for purposes of reworking or replacing the bare semiconductor die  16 . Furthermore, the heating circuit  12  can also be configured or shaped to provide more heat or uniform heat to predetermined parts of the die attach material and portion of the substrate or the entire substrate through variations in the shape and size of the heating circuit  12 .  
         [0022]    Because the inventive heating circuit is associated in close proximity with a single die, the heat it generates is localized and/or concentrated and/or uniform with respect to that die. As a result, unlike conventional oven curing, the heating circuit of the present invention can attach or detach a die in the presence of neighboring electronic devices, solder joints, and adhesive joints without the excessive heating thereof.  
         [0023]    In another embodiment of the present invention shown in FIG. 2, a die support member  20  includes a heating circuit  22  integral with a base, such as a glass-epoxy printed circuit board  24 . A bare semiconductor die  26  is attached to the printed circuit board  24  using well-known Chip-On-Board (COB) or Direct Chip-Attach (DCA) methods such as die-bond/wire-bond, Tape-Automated Bonding (TAB), or Controlled-Collapse Chip Connection (C4). If desired, the bare semiconductor die  26  may include a Known-Good-Die (KGD).  
         [0024]    The heating circuit  22  attaches a die cover  28  to the printed circuit board  24  by heating and curing an attachment material  30  on the surface of the printed circuit board  24  in response to being energized by a supply voltage V s  or a current supply. A wide variety of well-known attachment materials, such as set forth hereinbefore will work for this purpose. Of course, if a thermoplastic type adhesive is used, the heating circuit  22  can also be used to detach the die cover  28  from the printed circuit board  24  for purposes of testing, reworking or replacing the bare semiconductor die  26 .  
         [0025]    It should be understood that the heating circuit  22  will work for purposes of this invention if it is incorporated into the die cover  28  rather than the printed circuit board  24 . Also, it should be understood that the printed circuit board  24  can include another heating circuit integral therewith underneath the bare semiconductor die  26  for purposes of attaching and detaching the bare semiconductor die  26  from the printed circuit board  24 . Further, it should be understood that the heating circuit  22  can be eliminated if the attachment material  30  is sufficiently conductive to act as a heating circuit itself. Well-known conductive attachment materials include eutectic solders and metal-filled epoxy and polyamide adhesives. In any event, the heating circuit  22 , whether contained on the printed circuit board  24  and/or die cover  28 , employs localized heating of the printed circuit board  24  and die cover  28  without excessive heating of other areas of the printed circuit board  24  or die cover  28 . Furthermore, the heating circuit  22  not only provides localized heat but it provides a very uniform heating of the printed circuit board  24  and/or die cover  28 . Additionally, the die cover  28  may form a hermetic seal with the printed circuit board  24 , if desired, through the use of a suitable attachment material and the heating circuit  22 .  
         [0026]    In another embodiment of the present invention shown in FIG. 3, a die support member  20  includes a heating circuit  22  integral with a base, such as a glass-epoxy printed circuit board  24 . A bare semiconductor die  26  is attached to the leads  27  of a lead frame using adhesive tape strips  27 ′ using well-known Lead-Over-Chip (LOC) technology.  
         [0027]    The heating circuit  22  attaches a die cover  28  to the printed circuit board  24  by heating and curing an attachment material  30  on the surface of the printed circuit board  24  in response to being energized by a supply voltage V s  or current supply. A wide variety of well-known attachment materials, such as set forth hereinbefore will work for this purpose. Of course, if a thermoplastic type adhesive is used, the heating circuit  22  can also be used to detach the die cover  28  from the printed circuit board  24  for purposes of testing, reworking or replacing the bare semiconductor die  26 . Any suitable adhesive may be used to hermetically attach the die cover  28  to the printed circuit board  24 .  
         [0028]    It should be understood that the heating circuit  22  will work for purposes of this invention if it is incorporated into the die cover  28 , shown in phantom as  22 ′, rather than the printed circuit board  24 . Also, it should be understood that the printed circuit board  24  can include another heating circuit integral therewith underneath the bare semiconductor die  26  for purposes of attaching and detaching the bare semiconductor die  26  from the printed circuit board  24 . Further, it should be understood that the heating circuit  22  can be eliminated if the attachment material  30  is sufficiently conductive to act as a heating circuit itself. Well-known conductive attachment materials include eutectic solders and metal-filled epoxy and polyamide adhesives. In any event, the heating circuit  22 , whether contained on the printed circuit board  24  and/or die cover  28 , employs localized heating of the printed circuit board  24  and die cover  28  without excessive heating of other areas of the printed circuit board  24  or die cover  28 .  
         [0029]    In a further embodiment of the present invention shown in FIG. 4, a die support member, such as a Thin Small Outline Package (TSOP)  40 , includes a heating circuit  42  integral with a base  44  of the TSOP  40 . A bare semiconductor die  46  is attached to a die-attach area  48  of the base  44  using well-known die-attach methods. The heating circuit  42  attaches a die cover  50  to the base  44  by heating and curing an attachment material  52  on the surface of the base  44  in response to being energized by a supply voltage V s  or current supply. Again, if a thermoplastic type adhesive is used, the heating circuit  42  can also be used to detach the die cover  50  from the base  44  for purposes of testing, reworking or replacing the bare semiconductor die  46 . Any suitable adhesive may be used to hermetically seal the die cover  50  to the base  44 , as desired. Again, the heating circuit  42  merely locally, uniformly heats up the base  44  and die cover  50  for attachment and disassembly purposes.  
         [0030]    In yet a further embodiment of the present invention shown in FIG. 5, a die support member, such as a Thin Small Outline Package (TSOP)  70 , includes a heating circuit  72  integral with a base  74  of the TSOP  70  extending therearound without any gap therein to be used to seal the base  74  to a die cover  80 . A bare semiconductor die  76  is attached to a die-attach area  78  of the base  74  using well-known die-attach methods. The heating circuit  72  attaches and seals a die cover  80  to the base  74  by heating and curing an attachment material  82  on the surface of the base  74  in response to being energized by a supply voltage V s  or current supply. If a thermoplastic type adhesive is used, the heating circuit  72  can also be used to detach the die cover  80  from the base  74  for purposes of testing, reworking or replacing the bare semiconductor die  76 . Suitable adhesives may be used to hermetically seal the die cover  80  to the base  74 . Again, the heating circuit  72  merely locally heats up the base  74  and die cover  80  for attachment and disassembly purposes.  
         [0031]    As shown in FIG. 6, the TSOP  40  of FIG. 4 can be incorporated into a memory device  60  of an electronic system  62 , such as a computer system, that includes an input device  64  and an output device  66  coupled to a processor  68 . Of course, any suitable type TSOP  40  can alternatively be incorporated into the input device  64 , the output device  66 , or the processor  68 . Alternatively, the processor  68 , or any desired type semiconductor device, may be packaged as described hereinbefore using such configurations as described hereinbefore or the like.  
         [0032]    The previously described invention provides a convenient device and method for die-attach, and for attaching a die cover, without the need for a cumbersome cure oven. The invention also provides a previously unavailable method for detaching a die or die cover for testing, reworking or replacing a die.  
         [0033]    Although the present invention has been described with reference to certain embodiments, the invention is not limited to these embodiments. For instance, the shape of the heating element of the present invention may be of any desired shape having any desired end connection arrangement to facilitate the desired sealing arrangement to form a hermetically sealed semiconductor die, if so desired. Any desired number of heating circuits may be used to heat localized areas of a substrate, semiconductor die, or die cover to facilitate attachment and disassembly for any desired purpose. Therefore, the invention is limited only by the appended claims, which include within their scope all equivalent devices or methods which operate according to the principles of the invention as described.