DETAILED DESCRIPTION OF THE INVENTION

[0021] Embodiments of the present invention will be hereinafter described with reference to the accompanying drawings. It should be understood that these illustrations are not to be taken as actual views of any specific apparatus or method of the present invention, but are merely exemplary, idealized representations employed to more clearly and fully depict the present invention than might otherwise be possible. Additionally, elements and features common between the drawing figures retain the same numerical designation.

[0022] A method and apparatus of a first embodiment of the present invention are shown in FIGS. 1 ( a )- 1 ( d ). FIG. 1 ( a ) depicts a simplified, exploded perspective view of a semiconductor die 110 and a superimposed interposer substrate 130 prior to being mutually attached. The semiconductor die 110 may include a semiconductor substrate comprising a singulated semiconductor die or a plurality of unsingulated dice (also known in the art as a “partial wafer”). The semiconductor substrate may comprise, for example and not by way of limitation, silicon, gallium arsenide, indium phosphide or other semiconductor material known in the art. The semiconductor substrate may be severed from a larger substrate such as, for example and not by way of limitation, a silicon wafer or another substrate such as silicon-on-insulator (SOI), silicon-on-glass (SOG), etc. The semiconductor die 110 includes an active surface 112 and a back side 114 , the active surface 112 including a plurality of bond pads 116 p bearing electrically conductive bumps 116 b. The bond pads 116 p may be centrally located as shown in FIG. 1 ( a ) in one or more rows, or may be peripherally located along one or more edges of active surface 112 , as known in the art. In addition, other bond pad arrangements may be easily accommodated.

[0023] Bumps 116 b preferably comprise, but are not limited to, conductive pillars, columns, or balls. The material of conductive bumps 116 b may include, but is not limited to, any known suitable metals or alloys thereof, such as lead, tin, copper, silver or gold. Conductive or conductor-filled polymers may also be employed, although gold and PbSn solder bumps are currently preferred. The bumps 116 b may be of uniform characteristics throughout or include, for example, a core of a first material (including a nonconductive material) having one or more conductive layers of other materials thereon. The bumps 116 b, depending upon the material or materials employed therefor, may be formed using an evaporation process, a C4 process, electroplating, electroless plating, laser bonding, or any other process as known to one of ordinary skill in the art.

[0024] The interposer substrate 130 may be a flexible dielectric tape or a ribbon type laminate structure having a first surface 132 and a second surface 134 , the second surface 134 including electrical contacts thereon in the form of ball pads 135 . The ball pads 135 may be formed of any suitable conductive material such as gold or tin/lead solder, the material being selected for compatibility with that of discrete conductive elements to be subsequently formed thereon. The interposer substrate 130 comprises a first portion 136 and a second, laterally offset portion 138 spaced from first portion 136 by spacer portion 140 defined between fold lines 142 . Both first portion 136 and second portion 138 may have ball pads 135 .

[0025] The interposer substrate 130 may be formed from any known substrate materials and is preferably formed of, by way of example, a laminated polymer material and, more specifically, a polyimide or other thermoset polymer film. In a preferred embodiment, the interposer substrate 130 may be ultra-thin with any suitable thickness, but preferably in the range between about 70 um and about 90 um.

[0026] FIG. 1 ( a ) also illustrates a cut-out from the interposer substrate 130 depicting the internal electrical interconnection or trace routings therein over one of the dielectric films thereof, the other being partially removed for clarity. In particular, the ball pads 135 on the second surface 134 of the interposer substrate 130 interconnect through conductive traces 144 to corresponding bond posts 143 exposed on the first surface 132 of first portion 136 . Each bond post 143 is electrically connected and rerouted by way of a corresponding trace 144 to two corresponding ball pads 135 on the second surface 134 of the carrier substrate 130 , one on first portion 136 and one on second portion 138 . Traces 144 may be formed by masking and etching a conductive film, such as copper, on one of the dielectric films, by printing using conductive ink, or otherwise as known in the art. Bond posts 143 are formed of a conductive material compatible for bonding with bumps 116 . Although actually sandwiched between the two dielectric films of interposer substrate 130 , traces 144 are shown partially revealed from the side in FIGS. 1 ( b ) and 1 ( c ) and partially in broken lines to better illustrate their extensions from bond posts 143 to ball pads 135 .

[0027] FIG. 1 ( b ) is a simplified cross-sectional view of the semiconductor die 110 mounted to the first portion 132 of interposer substrate 130 . In particular, the bumps 116 on the active surface 112 of the dies 110 are bonded to the bond posts 143 on the first surface 132 of the first attach portion 136 of the carrier substrate 130 . The interposer substrate's first portion 136 is thus directly facing the active surface 112 of the semiconductor die 110 so that the second portion 138 of the interposer substrate 130 is unattached and extends freely laterally from the first portions 13 . The post-to-bump bonding is preferably accomplished by means of, but is not limited to, an anisotropic conductive film (ACF), an anisotropic conductive paste (ACP), a thermal compression (TC) bonding process or a thermosonic (TS) bonding process.

[0028] A dielectric filler material 146 , commonly termed an “underfill” material, may be disposed in the gap 148 between active surface 112 and first surface 132 of first portion 136 . Such may be particularly desirable if TC or TS bonding is employed, whereas ACF or ACP may be applied across the entire interface between active surface 112 and first surface 132 . The methods employed to apply the filler material 146 to the gap 148 may include, but are not limited to, gravity dispensing, pressure injecting, combinations of pressure and vacuum to draw the material 146 into gap 148 and other suitable techniques known in the For example, filling the gap 148 may be accomplished by applying the filler material 146 from a dispenser, approximate either one side or two adjacent sides of the die 110 . The filler material 146 maybe self-curing through a chemical reaction, or a cure accelerated by heat, ultraviolet light or other radiation, or other suitable means in order to form a solid mass bonded to active surface 112 and first surface 132 of first portion 136 .

[0029] FIG. 1 ( c ) is a simplified cross-sectional view of the semiconductor die 110 mounted by active surface 112 to the interposer substrate 130 and having an adhesive material 152 on the back side 114 . The adhesive material 152 may be applied to back side 114 of the semiconductor die 110 subsequent to attaching the interposer substrate 130 to the die's active surface 112 or may be applied to overly the back surface 114 at the wafer level or after dicing the wafer into individual or multiple semiconductor die/dice and before attachment to interposer substrate 130 . The adhesive material 152 applied may be a double-sided adhesive tape, the outer layer of adhesive facing away from back side 114 being covered with a protective layer until adherence is required.

[0030] FIG. 1 ( d ) is a simplified cross-sectional view of the interposer substrate 130 mounted to both the active surface 112 and the back side 114 of the semiconductor die 110 . After the die 110 and first portion 136 of the interposer substrate 130 are mounted and the adhesive material 152 has been applied to the back side 114 of the semiconductor die 110 , the flexible interposer substrate 130 is folded along fold lines 142 and wrapped around a side 154 of the semiconductor die 110 (as shown by the arrow in FIG. 1 ( d )) so that the extended second portion 138 of interposer substrate 130 may be adhesively attached to the back side 114 of the semiconductor die 110 via the adhesive material 152 with the spacer portion 140 of interposer substrate 130 lying over side 154 of semiconductor die 110 . In this manner, the first portion 136 and the second portion 138 of the interposer substrate 130 are respectively attached to the active surface 112 and the back side 114 of the semiconductor die 110 to provide a wrapped die 160 . In this manner, the interposer substrate 130 sandwiches the semiconductor die 110 to substantially overlie the active surface 112 , back side 114 and edge 154 . Wrapped die 160 includes a first and a second outside surface 162 and 164 , respectively, each outside surface 162 and 164 comprising second surface of interposer substrate 130 and exhibiting an array of ball pads 135 thereon.

[0031] As shown in FIGS. 1 ( e ) and 1 ( f ), discrete conductive elements 172 may be applied to or formed on either the first outside surface 162 ( FIG. 1 ( e )) and/or the second outside surface 164 ( FIG. 1 ( f )) of the wrapped die 160 to complete chip scale package 170 . The discrete conductive elements 172 are arranged in a two-dimensional array, commonly known as a ball grid array or BGA, corresponding to the array pattern of ball pads 135 to which conductive elements 172 are bonded so as to provide external electrical connections (I/Os) for the wrapped die 160 . The array may comprise rows and columns of conductive elements 172 , one or more concentric circles or rectangles of bumps, and may be highly populated as illustrated herein or comprise an open array with fewer elements and large pitch (spacing) between the discrete conductive elements 172 . The conductive elements 172 may comprise balls, bumps, pillars, columns or other suitable structures. The conductive elements may include, but are not limited to, any known conductive metal or alloys thereof, such as lead, tin, copper, silver, or gold as well as conductive or conductor-filled polymers. The conductive elements 172 may include a core of a first material (including non-conductive materials having one or more conductive layers thereon).

[0032] As shown in FIG. 1 ( g ), the chip scale package 170 with conductive elements 172 attached thereto may then be mounted to a carrier substrate such as a printed circuit board (PCB) 182 or any other substrate or other higher level packaging, such as an interposer or another semiconductor die, the conductive elements 172 providing mechanical and electrical connections to terminal pads (not shown) of the other substrate. The conductive elements 172 provide a standoff between the wrapped die 160 and, for example, PCB 182 . The chip scale package 170 may thus be bonded to terminal pads or trace ends of the PCB 182 by, for example, reflowing (in the case of solder) or curing (in the case of conductive or conductor-filled polymers) to form an electronic assembly as known in the art.

[0033] Once the chip scale package 170 is mounted to the PCB 182 via the conductive elements 172 , a dielectric filler material 184 may then be optionally be provided therebetween as known in the art for enhanced securement of chip scale package 170 and to preclude shorting between conductive elements 172 .

[0034] In addition, a nonconductive layer or film 186 may optionally be applied to overlie the outside surface 162 or 164 of the wrapped die 160 having no conductive elements 172 thereon. The insulating layer or film 186 prevents electrical shorting between exposed, laterally adjacent ball pads 135 which, for clarity, are not shown in FIG. 1 ( g ) as they are covered by film 186 . This insulating layer or film 186 may be applied subsequent to, or preferably prior to, mounting the wrapped die 160 to the PCB 182 .

[0035] It will be appreciated by those of ordinary skill in the art that the above described first embodiment of the chip scale package of the present invention provides an extremely thin package offering the flexibility of bumping either the active surface or back side of a semiconductor die. Thus, a so-called “mirror” die (i.e., a die having a mirror image I/O array to another, similar die) may be easily formed without retooling. It is further appreciated that the minimized height of the chip scale package of the present invention is accomplished by easily manipulating a preformed, ultra thin, flexible interposer substrate to provide the wrapped die rather than through complex and expensive alterations in the die fabrication process. The present invention may be used to provide a robust chip scale package with a minimized height or thickness of as little as 0.85 mm. The present invention may substantially prevent potential damage to the semiconductor die during handling, assembly with a carrier substrate and testing of the resulting assembly, such as a memory module. During operation, the present invention may substantially protect the semiconductor die from environmental concerns since the interposer substrate is wrapped around both the active surface and back side of the die.

[0036] FIGS. 2 ( a ) and 2 ( b ) show simplified cross-sectional views of multiple CSP's of the present invention as a stacked assembly. The stacking is accomplished by mounting the conductive elements 172 of one BGA die to corresponding ball pads 135 on the first or second outside surface 162 and 164 of a wrapped die 160 of chip scale package 170 . Multiple chip scale packages 170 may be stacked in a similar manner to significantly multiply the integrated circuit density, the bottom chip scale package 170 being mounted to a PCB or any other carrier substrate or higher level packaging. FIGS. 2 ( a ) and 2 ( b ) depict stacking the chip scale packages 170 in different orientations corresponding to the different orientations shown and described in association with FIGS. 1 ( e ) and 1 ( f ), respectively. It will be appreciated that different types of dice may be stacked, for example a logic die on a memory die, or an SRAM die on a DRAM die. Alternatively, a plurality of memory dice may be stacked to effectively provide a virtual, single stack memory “module” of enhanced memory capacity or memory and logic dice may be stacked on a microprocessor die to provide a chip scale computer. Further, another BGA die of different design may be stacked on a chip scale package of the present invention and bonded to exposed ball pads thereon.

[0037] The decision of proceeding to bump the first or second outside surface 162 , 164 of the wrapped die 160 may be made just prior to adding the conductive elements 172 to complete the chip scale package 170 , providing additional flexibility in the planning and production of the chip scale package 170 of the present invention. Furthermore, should the orientation of the wrapped die 160 need to be reversed or flipped, this may easily be achieved by removing the conductive balls 172 from ball pads 135 on one surface of the wrapped die 160 and adding the conductive balls 172 to the ball pads 135 on the opposite surface of the wrapped die 160 .

[0038] A method and apparatus of a second embodiment of the present invention is shown in FIGS. 3 ( a )- 3 ( e ). The second embodiment of the present invention is similar to the first embodiment in major aspects, the second embodiment including an additional semiconductor die.

[0039] As shown in the simplified cross-sectional view in FIG. 3 ( a ), the second embodiment includes a first and second dice 110 a and 110 b. The first and second dice 110 a and 110 b each include an active surface 112 and a back side 114 respectively and each may include conductive bumps such as (for example) solder bumps or gold stub bumps 116 b formed on or attached to bond pads 116 p on the active surfaces 112 thereof As in the first embodiment, the bond pads 116 p may be formed in an arrangement such as one or more rows centrally located on the active surfaces 112 or, alternatively arranged along a periphery thereof

[0040] FIG. 3 ( b ) is a simplified cross-sectional view of the first and second dice 110 a and 110 b attached to an interposer substrate 230 . The first and second dice 110 may be attached to first portion 236 of interposer substrate 230 employing the same processes as discussed with respect to the first embodiment, either simultaneously or sequentially. Interposer substrate 230 is structured in a similar manner to that of interposer substrate 130 , being a laminate of two dielectric films having conductive traces 144 extending therebetween. However, conductive traces 144 of interposer substrate 230 extend from metallization pads 242 to an array of conductive through vias 235 extending from a first surface 232 of interposer substrate 230 to a second, opposing surface 234 .

[0041] As shown in FIG. 3 ( c ) and 3 ( d ), the arrangement of the second embodiment provides for the second portion 238 of the carrier substrate 230 , being freely extended laterally from first portion 238 and separated therefrom by spacer portion 240 as shown in FIG. 3 ( b ), to fold or wrap around either a side 154 of the first die 110 a ( FIG. 3 ( c )) or a side 154 of the second die 110 b ( FIG. 3 ( d )). Prior to folding the carrier substrate 230 , a non-conductive adhesive material 252 , such as Hitachi DF-400, Hitachi HM-122 and Lintec LE-5000X, may be applied to the back side 114 of the first or second die 110 a and 110 b to which second portion 238 is to be adhered. The non-conductive adhesive material 252 may be applied at any time prior to folding the carrier substrate 230 to be attached thereon, which may include applying the adhesive on the back sides 114 at the wafer level or subsequent to dicing the wafer. Thus, the second portion 238 of the carrier substrate 230 may fold around and be adhesively attached to either the back side 114 of the first die 110 a or the back side 114 of the second die 110 b, to form a stacked die assembly 260 .

[0042] An array of discrete conductive elements 172 may then be applied to the side of stacked die assembly 260 on the exposed outside surface 262 a FIG. 3 ( c )) or 262 b ( FIG. 3 ( d ) of the carrier substrate 230 to form a multi-die chip scale package 270 . Specifically, the discrete 172 conductive elements are applied to or formed on exposed surfaces of through vias 235 of the interposer substrate 230 , the exposed surfaces on the via ends comprising ball pads as in the first embodiment described above. The conductive elements 172 may be of any suitable configuration and material or materials, as previously described above. The conductive filling of the through vias 235 may be selected to be compatible with the conductive material of discrete conductive elements 172 or the exposed surfaces of the through vias 235 may be plated for better bonding with the conductive elements 172 , as well known in the art. Furthermore, as shown in FIG. 3 ( e ), a dielectric or insulating layer or film 186 may optionally be applied to the exposed back side of the first or second die 110 a or 110 b, depending upon which die is not covered with second portion 238 of interposer substrate 230 . This insulating layer 186 may also be optionally provided at the wafer level or after the wafer is diced into individual semiconductor die. The insulating layer 186 may be provided to overlie the chip scale package 270 as a covering for physical protection of the die and to reduce the potential for shorting of the assembly in use. If the covered die is of a type wherein the back side is voltage biased, the use of insulating layer 186 is particularly desirable.

[0043] As depicted in FIG. 3 ( e ), the chip scale package 270 may be attached to terminal pads or other conductive structures of a carrier substrate such as PCB 182 or any other higher level packaging by the array of discrete conductive elements 172 . The manner of attachment is dependent upon the type of discrete conductive elements 172 employed, as described above. Also, in a similar manner to that described in the previous embodiment, the discrete conductive elements 172 provide a standoff between the stacked die assembly 260 and the PCB 182 , into which a dielectric filler material may be introduced as well known in the art.

[0044] Thus, it is apparent that the second embodiment of the chip scale package of the present invention encompasses a novel and unobvious method and apparatus and provides the capability to fabricate an ultra thin, stacked multiple die, chip scale package of no more than approximately 1.0 mm in height. Further, the option of attaching the second portion 238 of the interposer substrate 230 to the back side of either the first or second die 110 a Or 110 b may be determined just prior to actually attachment thereof, providing additional flexibility in the planning, production and in-line balancing of the chip-scale package of the present invention. As with the first embodiment, the dual attachment capability facilitates the fabrication of mirror-image packages.

[0045] In FIGS. 4 ( a )- 4 ( b ), a variant of the second embodiment is illustrated. Previously identified components and features are identified by the same reference numerals. This variant is similar to the second embodiment except that the interposer substrate 330 is extended in length and comprises a first portion 336 , first spacer portion 340 a and two second portions 338 a and 338 b separated by a second spacer portion 340 b. With this configuration, the second portions 338 a and 338 b may be wrapped about the back sides 114 of both the first die 110 a and the second die 110 b by folding the two second portions 338 a and 338 b about the side 154 of one of the dice 110 , covering that side 154 with the first spacer portion 340 a, securing second portion 338 a on the back side 114 of the one of the dice 110 , then covering the two adjacent sides 154 of the dice 110 on the other side of the assembly with second spacer portion 340 b and securing second portion 338 b to the back side 114 of the other die 110 to form a stacked die assembly 360 . Both second portions 338 a and 338 b may include an array of ball pads 135 to which traces 144 (not shown) extend from contact points with the bond pads of the dice 110 . This variant of the second embodiment thus provides both an upper outside surface 362 and a lower outside surface 364 , on which discrete conductive elements 172 may be placed in an array corresponding to the pattern of ball pads 135 . As in the second embodiment, the stacked die assembly 360 with discrete conductive elements 172 forming a chip scale package 370 may then be attached to terminal pads or other contacts of a carrier substrate such as a printed circuit board 182 or any other higher level packaging. However, in this variant of the second embodiment, the chip scale package 370 may be stacked with one or more other chip scale packages bearing 370 discrete conductive elements 172 since the interposer substrate 330 wraps around both the upper and bottom outside surface 362 and 364 , to enable electrical connection with another stacked die assembly 360 . It will also be readily appreciated by those of ordinary skill in the art that another flip-chip type die or a stacked die assembly of different design may be connected to a stacked die assembly, and that dice with different functions may be combined into a stacked die assembly or connected thereto. Thus, this variant of the second embodiment provides even further advantages of increasing integrated circuit density.

[0046] It will be understood and appreciated by those of ordinary skill in the art that a die having a first arrangement of bond pads on an active surface thereof (for example, a central row), may be combined into a dual die assembly with a second, different arrangement of bond pads (for example, two peripheral rows on opposing edges of the active surface) through appropriate configuring of the interposer substrate contacts and traces. Further, different die generations, i.e., one or more “shrinks” of a basic design, may be combined into an assembly.

[0047] While the present invention has been disclosed in terms of a certain preferred embodiments and alternatives thereof, those of ordinary skill in the art will recognize and appreciate that the invention is not so limited. Additions, deletions and modifications to the disclosed embodiments may be effected without departing from the scope of the invention as claimed herein. Similarly, features from one embodiment may be combined with those of another while remaining within the scope of the invention.