DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT

[0030] In the following detailed description, reference is made to the accompanying drawings that show, by way of illustration, specific embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention. It is to be understood that the various embodiments of the invention, although different, are not necessarily mutually exclusive. For example, a particular feature, structure, or characteristic described herein, in connection with one embodiment, may be implemented within other embodiments without departing from the spirit and scope of the invention. In addition, it is to be understood that the location or arrangement of individual elements within each disclosed embodiment may be modified without departing from the spirit and scope of the invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined only by the appended claims, appropriately interpreted, along with the full range of equivalents to which the claims are entitled. In the drawings, like numerals refer to the same or similar functionality throughout the several views.

[0031] FIGS. 1 - 7 illustrate a method of fabricating a microelectronic device assembly according to the present invention. FIG. 1 illustrates a first microelectronic die 102 (such as a microprocessor, a chipset, a memory device, an ASIC, and the like) attached by a back surface 104 thereof to a substrate 112 (such as an interposer, a motherboard, a back surface of another microelectronic dice, or the like) by a first layer of adhesive 114 . As shown in FIGS. 1 and 2 , a plurality of bond pads 116 is disposed on an active surface 106 of the first microelectronic die 102 . The first microelectronic die bond pads 116 are generally placed near edges 120 of the first microelectronic die active surface 106 . The first microelectronic die 102 is electrically connected to the substrate 112 by attaching a first plurality of bond wires 118 between the first microelectronic die bond pads 116 and a corresponding first plurality of lands 122 on a surface 124 of the substrate 112 .

[0032] As shown in FIGS. 3 and 4 , a plurality of adhesive globules 126 is disposed, such as by dispensing with a needle, on the first microelectronic die active surface 106 in position where they will not interfere with the first plurality of wire bonds or the first microelectronic die bond pads 116 . The adhesive globules may be epoxies, urethane, polyurethane, silicone elastomers, and the like. Preferably, the adhesive globules comprise an adhesive paste having a viscosity of between about 10,000 and 20,000 cps at 5 rpm with thixotropy of between about 5 and 10. Adhesives having such properties may include various Dexter Hysol Epoxy adhesives, available from Locite Americas, Windsor Locks, Conn., USA, and various silicone based adhesives, such as Dow Corning 7920, available from Dow Corning, Midland, Mich., USA. Although FIG. 5 illustrates five adhesive globules 126 , it is understood that the present invention is not so limited. Any number of globules may be used, which may be dependent on the type and viscosity of the adhesive material used.

[0033] A second microelectronic die 132 is attached to the first microelectronic die 102 by contacting a back surface 134 of the second microelectronic die 132 with the adhesive globules 126 , which form adhesive pillars or standoffs 138 , as shown in FIG. 5 . The viscosity of the material used for the adhesive standoffs 138 holds the second microelectronic die 132 away from the first plurality of bond wires 118 (even after subsequent curing of adhesive standoffs 138 ).

[0034] As shown in FIGS. 5 and 6 , the second microelectronic die 132 includes a plurality of bond pads 142 disposed on an active surface 136 thereof, which are generally placed near edges 140 of the second microelectronic die active surface 136 . After curing the adhesive standoffs 138 , the second microelectronic die 132 is electrically connected to the substrate 112 by attaching a second plurality of bond wires 144 between the second microelectronic die bond pads 142 and a corresponding second plurality of lands 146 on the substrate surface 124 , as shown in FIG. 7 . The curing of the adhesive standoffs 138 has a lower CTE affect on the microelectronic dice than a single layer of adhesive material, because the contact area of the CTE mismatched materials is smaller. The first plurality of substrate lands 122 and the second plurality of substrates lands 146 are generally connected to conductive traces (not shown) that are in contact with external electrical connection devices, such as solder ball or pins (not shown), which may connect to external electrical devices (not shown).

[0035] Although FIGS. 1 - 7 show an embodiment wherein the first microelectronic die 102 is approximately the same size as the second microelectronic die 132 , the present invention is not so limited. For illustration purposes, FIG. 8 shows an embodiment wherein a second microelectronic die 132 ′ is smaller in at least one dimension from said first microelectronic die 102 and FIG. 9 shows an embodiment wherein a second microelectronic die 132 ″ is larger in at least one dimension from said first microelectronic die 102 .

[0036] Furthermore, although FIGS. 1 - 7 shown an embodiment having two microelectronic dice (the first microelectronic die 102 and the second microelectronic die 132 ), the present invention is not so limited, as any number of microelectronic dice may be stacked using the present invention. For illustration purposes, FIG. 10 shows an embodiment having three microelectronic dice wherein a third microelectronic die 152 is stacked on the second microelectronic die 132 . The process of stacking the third microelectronic die 152 is the same as stacking the second microelectronic die 132 , as discussed above. A second plurality of adhesive globules is disposed on the second microelectronic die active surface 136 in positions where they will not interfere with the second plurality of wire bonds 144 or the second microelectronic die bond pads 142 . The third microelectronic die 152 is attached to the second microelectronic die 132 by contacting a back surface 154 of the third microelectronic die 152 with the adhesive globules, which form adhesive standoffs 158 , as shown in FIG. 10 . The third microelectronic die 152 includes a plurality of bond pads 162 disposed on an active surface 166 thereof, which are generally placed near the edges 160 of the third microelectronic die active surface 156 . After curing the adhesive standoffs 158 , the third microelectronic die 152 is electrically connected to the substrate 112 by attaching a third plurality of bond wires 164 between the third microelectronic die bond pads 162 and a corresponding third plurality of lands 166 on the substrate surface 124 .

[0037] After the stacking of the microelectronic dice, an encapsulation material 174 (such as a filled epoxy material, a silicon elastomer, or the like) is disposed to cover the first microelectronic die 102 and the second microelectronic die 132 to form a microelectronic package 170 , as shown in FIG. 11 . For illustration purposes, the stacked assembly shown in FIG. 7 is encapsulated in FIG. 11 . As shown in FIG. 11 and as will be understood by those skilled in the art, the encapsulation material 174 flows between the first microelectronic die 102 and the second microelectronic die 132 , and between at least two of the adhesive standoffs 138 . The encapsulation material 174 between the first microelectronic die 102 and the second microelectronic die 132 greatly reduces or eliminates the affect of the CTE mismatch between the adhesive standoffs 138 and the first microelectronic die 102 and the second microelectronic die 132 , because hardness of the encapsulation material 174 after curing reduces or eliminates the movement of the microelectronic dice. Furthermore, the reduced volume of adhesive material in the adhesive standoffs 138 , compared to a single thick adhesive layer, reduces or eliminates problem induced by moisture absorption.

[0038] It is, of course, understood that the first microelectronic die 102 could also be a flip-chip, as known in the art, wherein the active surface 106 is electrically connected to the substrate 112 through a plurality of solder balls 176 with an underfill material 178 disposed between the first microelectronic die 102 and the substrate 112 , as shown in FIG. 12 . The standoffs 138 extend between the first microelectronic die back surface 104 and the second microelectronic die back surface 134 .

[0039] The microelectronic packages formed by the present invention, such as microelectronic package 170 of FIG. 11 , may be used in a computer system 180 , as shown in FIG. 13 . The computer system 180 may comprise a motherboard 182 with the microelectronic package 170 attached thereto, within a chassis 184 . The motherboard 182 may be attached to various peripheral devices including a keyboard 186 , a mouse 188 , and a monitor 190 .

[0040] Of course, the current invention is not limited to the use of an adhesive material to form the pillars. As shown in FIG. 14 , the standoffs 192 may comprise solid structures or plugs. As shown in FIG. 15 , the standoffs 192 may include a core 194 , such as a tape material, plastic, and the like (preferably an elastomeric material, such as Dexter Propriety Pliable Organics Spacer, available from Locite Americas, Windsor Locks, Conn., USA), having a first adhesive surface 196 to attach to the second microelectronic die back surface 134 and a second adhesive surface 198 to attach to the first microelectronic die active surface 106 . As will be understood by those skilled in the art, the placement of the standoffs 192 occurs in place of the disposition of the adhesive globules 126 , as shown in FIGS. 3 and 4 , and the method of fabrication remains the same. FIG. 16 illustrates the assembly of FIG. 14 having the encapsulation material 174 disposed thereon. As will be understood by those skilled in the art, the encapsulation material 174 flows between the first microelectronic die 102 and the second microelectronic die 132 , and between at least two of the standoffs 192 .

[0041] It is further understood that for the embodiments illustrate in FIGS. 1 - 13 , the adhesive used to from the standoffs need not necessary be globules. Rather the adhesive may be formed, such as by stenciling, from wet or dry adhesives to form the standoffs 190 shown in FIG. 17 . Stencilable adhesive materials may include include various silicone based adhesives, such as Dow Corning 6910, 7910, and 7920, available from Dow Corning, Midland, Mich., USA. Furthermore, as shown in FIGS. 18 a - d , the cross sectional shape or the standoffs 190 may be any appropriate shape including circular (element 190 in FIG. 18 a ), square (element 190 ′ in FIG. 18 b ), rectangular (element 190 ″ in FIG. 18 c ), and triangular (element 190 ′″ in FIG. 18 d ). Such shapes can be achieved with stencil shapes for wet materials, or cut or punched out for dry materials. It is, of course, understood that such cross sectional shapes also apply to the embodiments discussed and illustrated with regard to FIGS. 14 - 16 .

[0042] Having thus described in detail embodiments of the present invention, it is understood that the invention defined by the appended claims is not to be limited by particular details set forth in the above description, as many apparent variations thereof are possible without departing from the spirit or scope thereof.