# Patent

## Title
Substrate-less stackable package with wire-bond interconnect

## Abstract

A method for making a microelectronic unit includes forming a plurality of wire bonds on a first surface in the form of a conductive bonding surface of a structure comprising a patternable metallic element. The wire bonds are formed having bases joined to the first surface and end surfaces remote from the first surface. The wire bonds have edge surfaces extending between the bases and the end surfaces. The method also includes forming a dielectric encapsulation layer over a portion of the first surface of the conductive layer and over portions of the wire bonds such that unencapsulated portions of the wire bonds are defined by end surfaces or portions of the edge surfaces that are uncovered by the encapsulation layer. The metallic element is patterned to form first conductive elements beneath the wire bonds and insulated from one another by portions of the encapsulation layer.

## Background
BACKGROUND OF THE INVENTION
Microelectronic devices such as semiconductor chips typically require many input and output connections to other electronic components. The input and output contacts of a semiconductor chip or other comparable device are generally disposed in grid-like patterns that substantially cover a surface of the device (commonly referred to as an “area array”) or in elongated rows which may extend parallel to and adjacent each edge of the device's front surface, or in the center of the front surface. Typically, devices such as chips must be physically mounted on a substrate such as a printed circuit board, and the contacts of the device must be electrically connected to electrically conductive features of the circuit board.
Semiconductor chips are commonly provided in packages that facilitate handling of the chip during manufacture and during mounting of the chip on an external substrate such as a circuit board or other circuit panel. For example, many semiconductor chips are provided in packages suitable for surface mounting. Numerous packages of this general type have been proposed for various applications. Most commonly, such packages include a dielectric element, commonly referred to as a “chip carrier” with terminals formed as plated or etched metallic structures on the dielectric. These terminals typically are connected to the contacts of the chip itself by features such as thin traces extending along the chip carrier itself and by fine leads or wires extending between the contacts of the chip and the terminals or traces. In a surface mounting operation, the package is placed onto a circuit board so that each terminal on the package is aligned with a corresponding contact pad on the circuit board. Solder or other bonding material is provided between the terminals and the contact pads. The package can be permanently bonded in place by heating the assembly so as to melt or “reflow” the solder or otherwise activate the bonding material.
Many packages include solder masses in the form of solder balls, typically about 0.1 mm and about 0.8 mm (5 and 30 mils) in diameter, attached to the terminals of the package. A package having an array of solder balls projecting from its bottom surface is commonly referred to as a ball grid array or “BGA” package. Other packages, referred to as land grid array or “LGA” packages are secured to the substrate by thin layers or lands formed from solder. Packages of this type can be quite compact. Certain packages, commonly referred to as “chip scale packages,” occupy an area of the circuit board equal to, or only slightly larger than, the area of the device incorporated in the package. This is advantageous in that it reduces the overall size of the assembly and permits the use of short interconnections between various devices on the substrate, which in turn limits signal propagation time between devices and thus facilitates operation of the assembly at high speeds.
Packaged semiconductor chips are often provided in “stacked” arrangements, wherein one package is provided, for example, on a circuit board, and another package is mounted on top of the first package. These arrangements can allow a number of different chips to be mounted within a single footprint on a circuit board and can further facilitate high-speed operation by providing a short interconnection between packages. Often, this interconnect distance is only slightly larger than the thickness of the chip itself. For interconnection to be achieved within a stack of chip packages, it is necessary to provide structures for mechanical and electrical connection on both sides of each package (except for the topmost package). This has been done, for example, by providing contact pads or lands on both sides of the substrate to which the chip is mounted, the pads being connected through the substrate by conductive vias or the like. Solder balls or the like have been used to bridge the gap between the contacts on the top of a lower substrate to the contacts on the bottom of the next higher substrate. The solder balls must be higher than the height of the chip in order to connect the contacts. Examples of stacked chip arrangements and interconnect structures are provided in U.S. Patent App. Pub. No. 2010/0232129 (“the '129 Publication”), the disclosure of which is incorporated by reference herein in its entirety.
Despite all of the above-described advances in the art, still further improvements in making and testing microelectronic packages would be desirable.
BRIEF SUMMARY OF THE INVENTION
An aspect of the present disclosure relates to a method for making a microelectronic unit. The method includes forming a plurality of wire bonds on a first surface in the form of a conductive bonding surface of a structure comprising a patternable metallic element. The wire bonds are formed having bases joined to the first surface and end surfaces remote from the bases and remote from the first surface. The wire bonds further have edge surfaces extending between the bases and the end surfaces. The method also includes forming a dielectric encapsulation layer over at least a portion of the first surface of the conductive layer and over portions of the wire bonds such that unencapsulated portions of the wire bonds are defined by at least one of the end surface or a portion of the edge surface thereof that is uncovered by the encapsulation layer. Then, the metallic element is selectively patterned to form first conductive elements insulated from one another by at least portions of the encapsulation layer. At least some of the wire bonds are disposed atop the first conductive elements.
A microelectronic element can be included in the structure and electrically connected with the conductive layer when the step of removing portions of the conductive layer is performed. The step of forming the dielectric encapsulation layer can be carried out with the microelectronic element electrically connected with the conductive layer and such that the encapsulation layer at least partially covers at least one surface thereof. At least some of the first conductive elements can be electrically connected between respective ones of the wire bonds and the microelectronic element.
An example of the method can further include the step of forming a redistribution layer over the second surface of the encapsulation layer. The redistribution layer can include conductive contacts displaced in at least one lateral direction from the unexposed portions of the wire bonds.
At least some of the wire bonds can be formed such that the end surfaces thereof are displaced in one or more lateral directions from the bases thereof. In an example, the bases of the wire bonds can be arranged in a first pattern having a first minimum pitch and the unencapsulated portions of the wire bonds can be arranged in a pattern having a second minimum pitch that is greater than the first minimum pitch. Alternatively, the bases can be arranged in a first pattern having a first minimum pitch and the unencapsulated portions of the wire bonds can be arranged in a pattern having a second minimum pitch that is less than the first minimum pitch.
The method can further include forming second conductive elements overlying the second surface of the dielectric layer. At least some of the second conductive elements can be connected with respective ones of at least some of the unencapsulated portions of the wire bonds.
The step of selectively removing portions of the conductive layer can include forming at least some first conductive elements as contact pads to which bases of wire bonds that are not electrically connected with other elements of the unit are electrically connected.
The method can further include the step of thinning the unit by one of grinding or polishing. In an example, the encapsulation layer can be formed having an initial thickness such that the end surfaces of the wire bonds are substantially covered, and the step of thinning the unit can include removing a portion of the encapsulation layer such that the end surfaces become unencapsulated by the encapsulation layer.
The step of forming the encapsulation layer can include dispensing an encapsulant onto the first surface of the conductive layer and at least edge surfaces of the wire bonds. Further, the step of forming the encapsulation layer can include molding an encapsulant in contact with the conductive layer, at least edge surfaces of the wire bonds, and at least surface of the microelectronic element.
The method can further include removing a carrier from a surface of the conductive layer opposite the wire bonds prior to performing the step of selectively removing portions of the conductive layer.
In an embodiment, the conductive layer can have a thickness of less than 20 microns.
Another aspect of the present disclosure relates to a method for making a microelectronic package. The method can include forming a plurality of wire bonds on a first surface of a conductive layer of an in process unit. The in-process unit has at least one microelectronic element joined thereto that is electrically connected with portions thereof. The wire bonds are formed having bases joined to the first surface and end surfaces remote from the bases and remote from the first surface. The wire bonds further have edge surfaces extending between the bases and the end surfaces. The method also includes forming a dielectric encapsulation layer over at least a portion of the first surface of the conductive layer, over at least a portion of the at least one microelectronic element, and over portions of the wire bonds such that unencapsulated portions of the wire bonds are defined by at least one of the end surface or a portion of the edge surface thereof that is uncovered by the encapsulation layer. Portions of the conductive layer are selectively removed to form first conductive elements thereof. At least some of the first conductive elements are electrically connected with at least some of the wire bonds, and at least some of the first conductive elements include at least some of the portions of the conductive layer with which the microelectronic element is electrically connected.
Another aspect of the present disclosure relates to a method for making a microelectronic unit. The method includes forming a plurality of wire bonds on a first surface that is a conductive bonding surface of structure comprising a patternable metallic element. The wire bonds have bases joined to the first surface and end surfaces remote from the bases and remote from the first surface. The wire bonds further have edge surfaces extending between the bases and the end surfaces. When forming the wire bonds, the conductive layer includes a plurality of regions attached to one another at at least some edges thereof. The method also includes forming a dielectric encapsulation layer over at least a portion of the first surface of the conductive layer and over portions of the wire bonds, such that unencapsulated portions of the wire bonds are defined by at least one of the end surface or a portion of the edge surface thereof that is uncovered by the encapsulation layer, wherein when performing the step of selectively removing portions of the encapsulation layer, a plurality of microelectronic elements are joined to the conductive layer, in the form of an in-process unit having at least one microelectronic element electrically connected with each of at least some of the regions of the conductive layer. The metallic element is then selectively patterned to form first conductive elements insulated from one another by at least portions of the encapsulation layer. At least some of the wire bonds are disposed atop the first conductive elements. The in-process unit is then severed into a plurality of microelectronic units, each including the first conductive elements of a region of the conductive layer and the at least one microelectronic element electrically connected therewith.
Another aspect of the present disclosure relates to a method for making a microelectronic assembly. The method includes making a first microelectronic package, including forming a plurality of wire bonds on a first surface of a conductive layer of an in process unit. The in-process unit has at least one microelectronic element joined thereto and electrically connected with portions thereof. The wire bonds are formed having bases joined to the first surface and end surfaces remote from the bases and remote from the first surface. The wire bonds further have edge surfaces extending between the bases and the end surfaces. Forming the first microelectronic package also includes forming a dielectric encapsulation layer over at least a portion of the first surface of the conductive layer, over at least a portion of the at least one microelectronic element, and over portions of the wire bonds such that unencapsulated portions of the wire bonds are defined by at least one of the end surface or a portion of the edge surface thereof that is uncovered by the encapsulation layer. Portions of the conductive layer are then selectively removed to form first conductive elements thereof. At least some of the first conductive elements are electrically connected with at least some of the wire bonds and at least some of the first conductive elements include at least some of the portions of the conductive layer with which the microelectronic element is electrically connected. The method also includes joining the first microelectronic package with a second microelectronic package overlying the second surface of the encapsulation layer of the first package. The second microelectronic package includes a plurality of contacts exposed at a first surface thereof. Joining the first microelectronic package with the second microelectronic package includes electrically connecting the unencapsulated portions of the wire bonds of the first microelectronic package with the contacts of the second microelectronic package.
Another aspect of the present disclosure relates to a microelectronic package including at least one microelectronic element. The package further includes first electrically conductive elements including terminals exposed at a mounting surface of the package. At least some of the first conductive elements are electrically connected to the at least one microelectronic element through vias integrally formed with the first conductive elements. The package further includes wire bonds having bases joined to respective ones of the conductive elements and adjacent the first surface of the dielectric encapsulation layer and end surfaces remote from the bases. Each wire bond defines an edge surface extending between the base and the end surface thereof. The package also includes a dielectric encapsulation layer having a first surface and a second surface remote from the first surface. At least a portion of the first surface is exposed at the mounting surface of the package. The dielectric encapsulation layer fills spaces between the wire bonds such that the wire bonds are separated from one another by the encapsulation layer. Unencapsulated portions of the wire bonds are defined by at least portions of the end surfaces of the wire bonds that are uncovered by the encapsulation layer at the second surface thereof.
At least some of the unencapsulated portions of the wire bonds can be displaced in at least one lateral direction from the respective bases thereof.
The package can further include a second microelectronic element. In an example the first microelectronic element can include contacts exposed at a front face thereof that are disposed toward the first surface of the dielectric layer, and the second microelectronic element can include contacts exposed at a front face thereof that is disposed toward the second surface of the dielectric layer. In such an example, the package can further include second conductive elements exposed at the second surface of the encapsulation layer. At least some of the second conductive elements can be connected between respective ones of the contacts of the second microelectronic element and respective ones of the unencapsulated wire bond portions. The first and second microelectronic elements can be electrically connected by at least one wire bond that is electrically connected with at least one contact of the first microelectronic element and at least one contact of the second microelectronic element. Alternatively, the second microelectronic element can be connected with one of the second conductive elements by a wire bond joined between one of the contacts of the second microelectronic element and a respective one of the second microelectronic elements. In another example, the first and second microelectronic elements can be electrically connected by a wire bond joined to a contact of the second microelectronic element and a respective one of the conductive elements exposed at the first surface of the encapsulation layer.
A microelectronic assembly can include a first microelectronic package as described above and a second microelectronic package that includes a microelectronic element and terminals exposed at a surface of the second microelectronic package. The terminals can be electrically connected with the microelectronic element. Further, the second microelectronic package can overlie the first microelectronic package and can be bonded thereto with the terminals thereof electrically connected to at least some of the unencapsulated portions of the wire bonds of the first microelectronic package.
A system can include a microelectronic package, as described above and one or more electronic components.



BRIEF DESCRIPTION OF THE DRAWINGS
Various embodiments of the present invention will be now described with reference to the appended drawings. It is appreciated that these drawings depict only some embodiments of the invention and are therefore not to be considered limiting of its scope.
FIG. 1 shows a top schematic view of an in-process unit that can be processed to form a microelectronic package by steps according to a method of the present disclosure;
FIG. 2 shows a side elevation view of the in-process unit of FIG. 1;
FIG. 3 shows a top view of the in-process unit of FIG. 1 in a further process step of the method;
FIG. 4 shows a side elevation view of the in-process unit of FIG. 3;
FIG. 5 shows a detail view of a portion of the in-process unit of FIG. 4 as indicated by area A;
FIG. 6 shows a top view of the in-process unit of FIG. 1 in a further process step of the method;
FIG. 7 shows a side elevation view of the in-process unit of FIG. 6;
FIG. 8 shows a detail view of a portion of the in-process unit of FIG. 7 as indicated by area B;
FIG. 9 shows a side elevation view of a microelectronic package that can result the method;
FIG. 10 shows a detail view of the package of FIG. 9 as indicted by area C;
FIG. 11 shows the detail view of FIG. 10 after a further optional process step of the method;
FIG. 12 shows a side view of the package of FIG. 9 in a further optional process step of the method;
FIG. 13 shows a detail view of a portion of the package of FIG. 11 as indicated by area D;
FIG. 14 shows an alternative in-process unit that can be processed to form a microelectronic package by steps according to variation of a method of the present disclosure;
FIG. 15 shows a detail view of a portion of the in-process unit of FIG. 13 as indicated by area E;
FIG. 16 shows a side elevation view of a microelectronic package that can result the method variation;
FIG. 17 shows a detail view of a portion of the package of FIG. 16 after a further optional process step of the method variation;
FIG. 18 shows an alternative microelectronic package;
FIG. 19 shows a detail view of a portion of the package of FIG. 18 as indicated by area F;
FIG. 20 shows a further alternative microelectronic package;
FIG. 21 shows a detail view of a portion of the package of FIG. 19 as indicated by area G;
FIG. 22 shows a further alternative microelectronic package;
FIG. 23 shows a further alternative microelectronic package; and
FIG. 24 shows an example of a microelectronic assembly that can include one or more packages according to various embodiments shown herein.



DETAILED DESCRIPTION
Turning now to the figures, where similar numeric references are used to indicate similar features, there is shown in FIG. 9 a microelectronic unit or package 10 according to an embodiment of the disclosure, for which FIGS. 1-8 show various stages of formation of the microelectronic package according to a method in another embodiment of the disclosure. The embodiment of FIG. 9 is a microelectronic package 10 in the form of a packaged microelectronic element such as a semiconductor chip assembly that is used in computer or other electronic applications.
The microelectronic package 10 of FIG. 9 includes a microelectronic element 22. The microelectronic package 10 can be embedded within an encapsulation layer 42 or may be contacted by the encapsulation layer at one or more surfaces thereof, e.g., a font or rear surface or an edge surface extending between the front and rear surfaces. The encapsulation layer 42 has a thickness extending from a first surface 43, and a second surface 44. The first and second surfaces can be at least partially exposed at respective first and second mounting surfaces 11 and 12 of the packages 10. Such a thickness can be at least equal to a thickness of the microelectronic element 22, itself. As seen in FIG. 9, encapsulation layer 42 can further extend outwardly from the microelectronic element 22 in lateral directions, as shown in the plan-view of FIG. 5. A plurality of wire bonds 32 are also embedded within encapsulation layer and extend between end surfaces 35 and 38 that are respectively uncovered by the encapsulation layer and which may be flush (e.g., co-planar) with surfaces 43 and 44. For purposes of this discussion, the first surface 43 may be described as being positioned opposite or remote from second surface 44. Such a description, as well as any other description of the relative position of elements used herein that refers to a vertical or horizontal position of such elements is made for illustrative purposes only to correspond with the position of the elements within the Figures, and is not limiting.
Microelectronic element 22 can be a semiconductor chip or another comparable device having a plurality of active or passive circuit elements therein or both active and passive circuit elements which may be in the form of an integrated or passives on a chip (“IPOC”), among others. In the embodiment of FIG. 9, microelectronic element 22 has at least portions of edge and rear surfaces contacted (e.g., covered by) encapsulation layer 42. The microelectronic element 22 may be positioned such that its contacts 24 are adjacent the first mounting surface 11 of the package. Further, in such an arrangement, contacts 24 are connected with conductive elements 28 that extend along first surface 43 of encapsulation layer 42 to electrically connect with wire bonds 32 at end surfaces 35, thereof, which can be defined by bases 34 of the respective wire bonds 32. Such bases 34 can be an artifact of the process used to form wire bonds 32, and can be in the shape of such bases 34 as formed by ball bonding, as shown, or by wedge bonding, stitch bonding or the like. In other embodiments, such as that shown in FIG. 15, bases 34 can be partially or fully removed during fabrication, such as by a thinning process of grinding, lapping, polishing, or other suitable technique. Such thinning or other process can also reduce the height of the wire bonds 32 such that end surfaces 35 are defined as extremities of the wire bonds 32 that were above the bases 34. In an embodiment, the microelectronic contacts 24 can be electrically connected with conductive elements 28 by conductive (e.g., metalized) vias 24 that include vias deposited onto the contacts 24 of the microelectronic element such as by plating, sputtering, or vapor deposition of one or more metals, such as one or more of copper, nickel, chromium, aluminum, gold, titanium, tungsten, cobalt, or one or more alloys thereof, without limitation. In one example, conductive elements can be formed by depositing a liquid conductive matrix material having metallic and non-metallic components, and thereafter curing the deposited conductive matrix material. For example, a conductive matrix material can be deposited and used such as described in commonly owned U.S. application Ser. No. 13/158,797, the disclosure of which is incorporated by reference herein.
Conductive elements 28 can include respective “contacts” or “pads” that can be exposed at the second surface 45 of encapsulation layer 42. As used in the present description, when an electrically conductive element is described as being “exposed at” the surface of another element having dielectric structure, it indicates that the electrically conductive structure is available for contact with a theoretical point moving in a direction perpendicular to the surface of the dielectric structure toward the surface of the dielectric structure from outside the dielectric structure. Thus, a terminal or other conductive structure that is exposed at a surface of a dielectric structure may project from such surface; may be flush with such surface; or may be recessed relative to such surface and exposed through a hole or depression in the dielectric. In one example, the conductive elements 28 can be flat, thin elements that are exposed at first surface 43 of encapsulation layer 42. Conductive elements 28 can have any suitable shape and in some cases can be circular. Conductive elements 28 may be electrically interconnected with one another, to microelectronic element 22, or both, by traces 31. Conductive elements 28 can also be formed along front surface 26 of microelectronic element 22.
As shown in FIGS. 11 and 12, additional conductive elements 28 can be exposed at a second surface 44 of encapsulation layer 42. Such conductive elements 29 can overlie and electrically connect with end surfaces 38 of wire bonds 32. In other variations, such conductive elements can include pads 28 that are displaced in at least one lateral direction along surface 44 from a corresponding wire bond, to which they can be connected at an end surface 34 thereof by a trace 30.
Wire bonds 32 can be joined to at least some of the conductive elements 28, such as on the faces 30 thereof. Wire bonds 32 can be joined at a base 34 thereof to the conductive elements 28 and can extend to an end 36 remote, i.e. opposite, from the respective bases 34 and from first surface 43. The ends 36 of wire bonds 32 can be characterized as being “free” in that they are not electrically connected or otherwise joined to microelectronic element 22 or any other conductive features within microelectronic package 10 that are, in turn, connected to microelectronic element 22. In other words, free ends 36 are available for electronic connection, either directly or indirectly as through a conductive element 28 or other features discussed herein, to a conductive feature external to package 10. The fact that ends 36 held in a predetermined position by, for example, encapsulant layer 42 or otherwise joined or electrically connected to another conductive feature does not mean that they are not “free” as described herein, so long as any such feature is not electrically connected to microelectronic element 22. Conversely, bases 34 may not be free as they can be either directly or indirectly electrically connected to microelectronic element 22, as described herein. As shown in FIG. 9, bases 34 can be rounded in shape, extending outward from an edge surface of wire bond 32 defined between base 34 and end 36. The particular size and shape of base 34 can vary according to the type of material used to form wire bond 32, the desired strength of the connection between wire bond 32 and conductive element 28, or the particular process used to form wire bond 32. Exemplary methods for making wire bonds 28 are described in U.S. Pat. No. 7,391,121 to Otremba, in U.S. Pat. App. Pub. No. 2005/0095835 (describing a wedge-bonding procedure that can be considered a form of wire bonding), and in commonly-assigned U.S. patent application Ser. Nos. 13/462,158; 13/404,408; 13/405,108; 13/405,125; and 13/404,458, the disclosures of which are incorporated herein by reference in their entireties.
Wire bonds 32 are formed by bonding a metal wire made of copper, gold, nickel, solder, aluminum, or metal alloy, among others, at a surface thereof and performing on or more other steps so as to form a wire bond having a base and an uncapsulated surface remote, e.g., opposite, therefrom with a length of the wire extending therebetween. Additionally, wire bonds 32 can be made from combinations of materials, such as from a core of a conductive material, such as copper or aluminum, for example, with a coating applied over the core. The coating can be of a second conductive material, such as aluminum, nickel, platinum, or palladium, among others. Alternatively, the coating can be of an insulating material, such as an insulating jacket. In an embodiment, the wire used to form wire bonds 32 can have a thickness, i.e., in a dimension transverse to the wire's length, of between about 15 μm and 150 μm. In general, wire bonds 32 can be formed on a metal bonding surface, i.e. a first metal bonding surface of a structure using a wire bond tool. In other embodiments, including those in which wedge bonding is used, such as described below, wire bonds 32 can have a thickness of up to about 500 μm. A leading end of a wire segment is heated and pressed against the receiving surface to which the wire segment bonds, typically forming a ball or ball-like base 34 joined to the surface of the conductive element 28. The desired length of the wire segment to form the wire bond is drawn out of the bonding tool, which can then sever or cut the wire bond at the desired length. Wedge bonding, which can be used to form wire bonds of aluminum, for example, is a process in which the heated portion of the wire is dragged across the receiving surface to form a wedge that lies generally parallel to the surface. The wedge-bonded wire bond can then be bent upward, if necessary, and extended to the desired length or position before cutting. In a particular embodiment, the wire used to form a wire bond can be cylindrical in cross-section. Otherwise, the wire fed from the tool to form a wire bond or wedge-bonded wire bond may have a polygonal cross-section such as rectangular or trapezoidal, for example.
The free end 36 of wire bond 32 can define respective end surfaces 38. End surface 38 can form at least a part of a contact in a pattern such as a grid or an array formed by respective end surfaces 38 of a plurality of wire bonds 32. FIGS. 5 and 6 show an exemplary pattern for such an array of contacts formed by end surfaces 38. Such an array can be formed in an area array configuration, variations of which could be implemented using the structures described herein. In a variation of that shown, there need not be end surfaces of a wire bond at every position of the grid or array pattern in FIG. 5. Such an array can be used to electrically and mechanically connect the microelectronic package 10 to another microelectronic structure, such as to a printed circuit board (“PCB”), or to other packaged microelectronic elements, an example of which is shown in FIG. 23. In such a stacked arrangement, wire bonds 32 and conductive elements 28 can carry multiple electronic signals therethrough, each having a different signal potential to allow for different signals to be processed by different microelectronic elements in a single stack. The grid or array pattern in which end surfaces 38 are disposed at certain positions that can be disposed at positions thereof that are the same as or different than the grid or array pattern in which bases 34 are disposed. In the example shown in FIG. 9, where wire bonds 32 are generally vertically arranged, such arrays may be identical. In other arrangement, such as that shown in FIG. 22 can include wire bonds 532 that are angled with respect to surface 45 of encapsulation layer 42 such that the array of end surface 38 has a greater pitch than that of bases 34. An inverse of such an arrangement is also possible. Further, as discussed above, conductive elements 28 can be laterally displaced from end surfaces 35 or 38 to which they are electrically connected by traces 31. This arrangement can also provide for different pitches over surfaces 43 and 44 or other different arrangements of contacts.
As shown in FIG. 23 such a package 10 can be arranged in a stack with other similar packages or the like. While FIG. 23 shows two such microelectronic packages 10, three, four or even more can be arranged in such a stack, which can also be assembled with a circuit panel 90 with solder masses 52 joining conductive element 28 to panel contacts 92. Solder masses 52 can also be used to interconnect the microelectronic assemblies in such a stack, such as by electronically and mechanically attaching end surfaces 38 to conductive elements 28 or connecting conductive elements 28 to other conductive elements 28.
Encapsulation layer 42 serves to protect the other elements within microelectronic package 10, particularly wire bonds 32. This allows for a more robust structure that is less likely to be damaged by testing thereof or during transportation or assembly to other microelectronic structures. Encapsulation layer 42 can be formed from a dielectric material with insulating properties such as that described in U.S. Patent App. Pub. No. 2010/0232129, which is incorporated by reference herein in its entirety.
As discussed above, FIG. 22 shows an embodiment of microelectronic assembly 510 having wire bonds 532 with ends 536 that are not positioned directly above the respective bases 534 thereof. That is, considering first surface 514 of substrate 512 as extending in two lateral directions, so as to substantially define a plane, end 536 or at least one of the wire bonds 532 is displaced in at least one of these lateral directions from a corresponding lateral position of base 534. As shown in FIG. 22, wire bonds 532 can be substantially straight along the longitudinal axis thereof, as in the embodiment of FIG. 9, with the longitudinal axis being angled at an angle 546 with respect to second surface 545 of encapsulation layer 542. Although the cross-sectional view of FIG. 5 only shows the angle 546 through a first plane perpendicular to first surface 514, wire bond 532 can also be angled with respect to first surface 514 in another plane perpendicular to both that first plane and to second surface 545. Such an angle can be substantially equal to or different than angle 546. That is the displacement of end 536 relative to base 534 can be in two lateral directions and can be by the same or a different distance in each of those directions.
In an embodiment, various ones of wire bonds 532 can be displaced in different directions and by different amounts throughout the assembly 510. Such an arrangement allows for assembly 510 to have an array that is configured differently on the level of surface 544 compared to on the level of surface 545. For example, an array can cover a smaller overall area or have a smaller pitch on surface 544 than at the second surface 545 level. Further, some wire bonds 532 can have ends 536 that are positioned above microelectronic element 522 to accommodate a stacked arrangement of packaged microelectronic elements of different sizes. In another embodiment, wire bonds can achieve this lateral displacement by including curved portions therein. Such curved portions can be formed in an additional step during the wire bond formation process and can occur, for example, while the wire portion is being drawn out to the desired length. This step can be carried out using available wire-bonding equipment, which can include the use of a single machine. Such curved portions can take on a variety of shapes, as needed, to achieve the desired positions of the ends of the wire bonds. For example, curved portions can be formed as S-curves of various shapes. Examples of this are described further in [refer to earlier BVA case].
FIGS. 1-8 show a microelectronic package 10 in various steps of a fabrication method thereof. FIGS. 1 and 2 show microelectronic package 10 at a step where microelectronic element 22 has been bonded to a structure comprising a patternable metallic element 28′. The structure may include or consist of a metallic or other electrically a conductive material layer extending in first and second transverse directions 15,17 to define a general shape of package 10, as can be seen in the plan view of FIG. 1. Microelectronic element 22 can be assembled, e.g., bonded, to the conductive material layer 28′ using an adhesive layer or polymeric material which is not fully cured. In some embodiments, the structure may include a support layer or device, e.g., a carrier to support the conductive material layer 28′ during at least some steps during fabrication. Such a support layer can be removed after formation of the encapsulation layer 42.
FIGS. 2 and 3 show microelectronic package 10 having wire bonds 32 joined at predetermined locations on surface 30′ of conductive material layer 28′. As discussed, wire bonds 32 can be applied by heating an end of a wire segment to soften the end such that it forms a deposition bond to conductive element 28 when pressed thereto, forming base 34. The wire is then drawn out away from conductive element 28 and manipulated, if desired, in a specified shape before being severed to form end 36 and end surface 38 of wire bond 32. Alternatively, wire bonds 32 can be formed from, for example, an aluminum wire by wedge bonding. Wedge bonding is formed by heating a portion of the wire adjacent the end thereof and dragging it along the conductive element 28 with pressure applied thereto. Such a process is described further in U.S. Pat. No. 7,391,121, the disclosure of which is hereby incorporated by reference herein in its entirety, and in previously-referenced U.S. patent application Ser. No. 13/402,158.
In FIG. 5-7 encapsulation layer 42 has been added to microelectronic package 10 by being applied over surface 30′ of conductive material layer 28′, extending upwardly therefrom and along edge surfaces 37 of wire bonds 32. Encapsulation layer 42 can also extend along at least a portion of microelectronic element 22, including over at least one of the front face, rear face, or edge surface thereof. In other examples, the encapsulation layer 42 can be formed such that it does not contact any portions of microelectronic element 22, such as by being laterally spaced away therefrom. Encapsulation layer 42 can be formed by depositing an encapsulant, e.g., a resin over the stage of microelectronic package 10 shown in FIG. 4. In one example, this can be done by placing package 10 in an appropriately configured mold having a cavity in the desired shape of the encapsulation layer 42 that can receive package 10. Such a mold and the method of forming an encapsulation layer therewith can be as shown and described in U.S. Pat. App. Pub. No 2010/0232129, the disclosure of which is incorporated by reference herein it its entirety. Alternatively, encapsulation layer 42 can be prefabricated to the desired shape from an at least partially compliant material. In this configuration, compliant properties of the dielectric material allow encapsulation layer 42 to be pressed into position over wire bonds 32 and microelectronic element 22. In such a step, wire bonds 32 penetrate into the compliant material forming respective holes therein, along which encapsulation layer 42 contacts edge surfaces 37. Further, microelectronic element 22 may deform the compliant material so that it can be received therein. The compliant dielectric material can be compressed to expose end surfaces 38 on outer surface 44. Alternatively, any excess compliant dielectric material can be removed from encapsulation layer to form a surface 44 on which ends surfaces 38 of wire bonds 32 are uncovered.
In an example, the encapsulation layer 42 can be formed such that, initially, surface 44 thereof is spaced above end surfaces 38 of wire bonds 32. To expose the end surfaces 38, the portion of encapsulation layer 42 that is above end surfaces can be removed, exposing a new surface 44 that is substantially flush with end surfaces 38, as shown in FIG. 7. In a further alternative, encapsulation layer 42 can be formed such that surface 44 is already substantially flush with end surfaces 38 or such that surface 44 is positioned below end surfaces 38. Removal, if necessary, of a portion of encapsulation layer 42 can be achieved by grinding, dry etching, laser etching, wet etching, lapping, or the like. If desired, a portion of the ends 36 of wire bonds 32 can also be removed in the same, or an additional, step to achieve substantially planar end surface 38 that are substantially flush with surface 44. In a particular example, the encapsulation can be applied over the microelectronic element 22, wire bonds 34, and patternable conductive element 28′ without using a mold and excess encapsulant can be removed after the application thereof to expose the end surfaces of the wire bonds, e.g., but polishing or one or more of the above methods.
After formation of dielectric layer 42, conductive material layer 28′ can be patterned, by chemical or mechanical etching (such as laser etching or the like), to make conductive elements 28 and/or traces 31 by removing portions of conductive material layer 28′ and leaving the portions thereof in the desired locations and form of the desired conductive elements 28 or traces 31. This can be done to make selective interconnections between wire bonds 32 and contacts 24 of microelectronic element 22 or to form conductive elements 28 displaced from respective wire bonds 32 with which they can be connected by traces 31. In some embodiments, conductive vias 25 can be formed to connect traces 31 or conductive features 28 in the form of pads with the microelectronic contacts 24.
As shown in FIG. 10, the package 10 can then be thinned to planarize surface 44 and end surfaces 38 of wire bonds 32. This can include exposing a surface of microelectronic element 22 on surface 44, which can also include thinning of microelectronic element 22 itself. Additionally or alternatively, conductive features 28 and/or traces 31 can be formed over surface 44, as described above. This can be done by depositing or joining a conductive layer over surface 44 and then patterning the layer to form such conductive elements 28 and traces 31.
FIGS. 15 and 16 show a microelectronic package 110 that is similar in construction to that shown in FIG. 9 but with microelectronic element 110 in a “face-up” arrangement. In such an arrangement, microelectronic contacts 124 are disposed toward surface 144 of encapsulation layer 142. Further, microelectronic element 122 can connect with the pattern of wire bonds 132 by conductive features 128 and traces 131 that are exposed at surface 144. As shown in FIGS. 15 and 16, such traces 131 and conductive elements 128 can connect with microelectronic contacts 124 by metalized vias 125 that extend from surface 144 to the contacts 124.
As illustrated in FIG. 15, the routing achieved by traces 131 and conductive elements 128 exposed on surface 144 can be the only routing in package 110, with surface 45 being ground down to remove conductive material layer 128′ (FIG. 14), which can also remove further encapsulation material, bases 134, and all or a portion of the attachment layer 120. Alternatively, as shown in FIG. 16 electrically conductive routing elements can also be included on surface 145 that can be for purposes or redistribution of wettable contacts in the array over surface 145. In other examples, a designated wire bond can connect with the microelectronic element 122 by routing over surface 144, which can, in turn connect with other wire bonds by routing over surface 145 that is connected with such designated wire bonds.
FIGS. 13 and 14 show microelectronic package 110 in process steps that can lead to either of the completed packages 110 shown in FIGS. 15 and 16. Specifically, FIGS. 13 and 14 show package 110 with microelectronic element 122 bonded, face-up, on conductive material layer 128′. Similarly, wire bonds 132 have been joined to surface 30′ of conductive material layer 28′ and formed according to any one of the processes described above. Further, encapsulation layer 142 has been deposited over exposed portions of surface 130′ and over wire bonds 132 and microelectronic element 122, according to any of the various processes described above. Routing circuitry in the form of conductive elements 128 and traces 131 were then formed over surface 144 of encapsulation layer 142 to connect wire bonds 132 with microelectronic element 122.
At such a point, package 110 can be further processed by grinding, polishing, lapping or other techniques as described above to remove material to result in the package 110 shown in FIG. 15. Alternatively, additional routing can be formed by patterning conductive material layer 128′ to form conductive elements 128 and traces 131 in the desired configuration, as described above with respect to FIGS. 8 and 9.
FIGS. 17-21 show various arrangements of packages of a similar general structure to those described above but utilizing multiple microelectronic elements. In one example, FIGS. 17 and 18 show a microelectronic package 210 having one microelectronic element 222A embedded within encapsulation layer 242 in a face-down arrangement and another microelectronic element 222B in a face-up arrangement. Such a package 210 can utilize electrically conductive routing circuitry in the form of interconnected conductive elements 228 and traces 231 over both surface 244 and surface 245 of encapsulation layer 242. Additionally, designated wire bonds 232 can be used to electrically connect microelectronic element 222A with microelectronic element 222B by routing circuitry that connects with such a designated wire bond over each end surface 35 and 38 and respectively to at least one contact 224 of each other microelectronic elements 222A and 222B. Such a package 210 can be made by a method that is similar to those described above with respect to FIGS. 1-16.
FIGS. 19 and 20 show an arrangement of a microelectronic package 310 that is similar to that shown in FIGS. 17 and 18, but with an additional microelectronic element 322C in a face-up arrangement bonded over face 326 of microelectronic element 322B. To facilitate connection of microelectronic element 322B to electrically conductive routing circuitry over surface 344, microelectronic element 322C can be smaller than microelectronic element 322B or can be offset therefrom such that contacts 324 of microelectronic element 322B are uncovered by microelectronic element 322C. Such a connection can be achieved by metalized vias 325 that connect with the element contacts 324 or by additional wire bonds 364 that are joined to contacts 324 of microelectronic element 322B and are uncovered by encapsulation layer 342 on surface 344. As discussed above, routing between any of the microelectronic element 322A, 322B, and 322C can be achieved by designated wire bonds 332 with appropriately configured routing circuitry connected therewith.
In a further example shown in FIG. 21, a microelectronic package 410 can be similar to that shown in FIGS. 17 and 18, but with additional wire bonds 466 that connect between one or more contacts 424 of microelectronic element 422B (which are disposed toward surface 444 of encapsulation layer 442) and a portion of the routing circuitry over surface 445 of encapsulation layer 442. In the example shown, such a wire bond 466 can be used to achieve a connection between microelectronic element 422B and microelectronic element 422A, which has contacts 424 disposed toward surface 445 of encapsulation layer 442. As shown wire bond 466 can join with a trace 431 (or a conductive element, if desired) that is further connected to a metalized via 425 that electrically connects with element contacts 424 of microelectronic element 422A.
The structures discussed above can be utilized in construction of diverse electronic systems. For example, a system 611 in accordance with a further embodiment of the invention includes microelectronic package 610, as described above, in conjunction with other electronic components 613 and 615. In the example depicted, component 613 is a semiconductor chip whereas component 615 is a display screen, but any other components can be used. Of course, although only two additional components are depicted in FIG. 24 for clarity of illustration, the system may include any number of such components. The microelectronic package 610 as described above may be, for example, a microelectronic package as discussed above in connection with FIG. 9, or a structure incorporating plural microelectronic packages as discussed with reference to FIG. 23. Package 610 can further include any one of the embodiments described in FIGS. 13-22. In a further variant, multiple variations may be provided, and any number of such structures may be used.
Microelectronic package 610 and components 613 and 615 are mounted in a common housing 619, schematically depicted in broken lines, and are electrically interconnected with one another as necessary to form the desired circuit. In the exemplary system shown, the system includes a circuit panel 617 such as a flexible printed circuit board, and the circuit panel includes numerous conductors 621, of which only one is depicted in FIG. 24, interconnecting the components with one another. However, this is merely exemplary; any suitable structure for making electrical connections can be used.
The housing 619 is depicted as a portable housing of the type usable, for example, in a cellular telephone or personal digital assistant, and screen 615 is exposed at the surface of the housing. Where microelectronic package 610 includes a light-sensitive element such as an imaging chip, a lens 623 or other optical device also may be provided for routing light to the structure. Again, the simplified system shown in FIG. 24 is merely exemplary; other systems, including systems commonly regarded as fixed structures, such as desktop computers, routers and the like can be made using the structures discussed above.
Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.

## Claims

1. A method for making a microelectronic unit, comprising the steps of:
forming a plurality of wire bonds on a first surface that is a conductive bonding surface of a structure comprising a patternable metallic element, the wire bonds having bases joined to the first surface and end surfaces remote from the bases and remote from the first surface, the wire bonds further having edge surfaces extending between the bases and the end surfaces;
forming a dielectric encapsulation layer over at least a portion of the first surface of the conductive layer and over portions of the wire bonds, such that unencapsulated portions of the wire bonds are defined by at least one of the end surface or a portion of the edge surface thereof that is uncovered by the encapsulation layer; and
then patterning the metallic element selectively to form first conductive elements insulated from one another by at least portions of the encapsulation layer, wherein at least some of the wire bonds are disposed atop the first conductive elements.

2. The method of claim 1, wherein a microelectronic element is included in the structure and is electrically connected with the conductive layer when the step of removing portions of the conductive layer is performed.

3. The method of claim 2, wherein the step of forming the dielectric encapsulation layer is carried out with the microelectronic element electrically connected with the conductive layer and such that the encapsulation layer at least partially covers at least one surface thereof.

4. The method of claim 2, wherein at least some of the first conductive elements are electrically connected between respective ones of the wire bonds and the microelectronic element.

5. The method of claim 1, further including the step of forming a redistribution layer over the second surface of the encapsulation layer, the redistribution layer including conductive contacts displaced in at least one lateral direction from the unexposed portions of the wire bonds.

6. The method of claim 1, wherein at least some of the wire bonds are formed such that the end surfaces thereof are displaced in one or more lateral directions from the bases thereof.

7. The method of claim 1, wherein the bases are arranged in a first pattern having a first minimum pitch and wherein the unencapsulated portions of the wire bonds are arranged in a pattern having a second minimum pitch that is greater than the first minimum pitch.

8. The method of claim 1, wherein the bases are arranged in a first pattern having a first minimum pitch and wherein the unencapsulated portions of the wire bonds are arranged in a pattern having a second minimum pitch that is less than the first minimum pitch.

9. The method of claim 1, wherein the bases of the wire bonds are in the form of ball bonds.

10. The method of claim 1, wherein the edge surfaces of the wire bonds extending between the bases and the end surfaces are first edge surface portions, and wherein the bases of the wire bonds are second portions of the edge surfaces that extend along the first conductive elements.

11. The method of claim 1, further including forming second conductive elements overlying the second surface of the dielectric layer, at least some of the second conductive elements being connected with respective ones of at least some of the unencapuslated portions of the wire bonds.

12. The method of claim 1, wherein the step of selectively removing portions of the conductive layer includes forming at least some first conductive elements as contact pads to which bases of wire bonds that are not electrically connected with other elements of the unit are electrically connected.

13. The method of claim 1, further including the step of thinning the unit by one of grinding or polishing.

14. The method of claim 13, wherein the encapsulation layer is formed having an initial thickness such that the end surfaces of the wire bonds are substantially covered, and wherein the step of thinning the unit includes removing a portion of the encapsulation layer such that the end surfaces are unencapsualted by the encapsulation layer.

15. The method of claim 1, wherein the step of forming the encapsulation layer includes dispensing an encapsulant onto the first surface of the conductive layer and at least edge surfaces of the wire bonds.

16. The method of claim 2, wherein the step of forming the encapsulation layer includes molding an encapsulant in contact with the conductive layer, at least edge surfaces of the wire bonds, and at least surface of the microelectronic element.

17. The method of claim 1, further including removing a carrier from a surface of the conductive layer opposite the wire bonds prior to performing the step of selectively removing portions of the conductive layer.

18. The method of claim 17, wherein the conductive layer has a thickness of less than 20 microns.

19. A method for making a microelectronic package, comprising the steps of:
forming a plurality of wire bonds on a first surface of a conductive layer of an in process unit, the in-process unit having at least one microelectronic element joined thereto and electrically connected with portions thereof, the wire bonds being formed having bases joined to the first surface and end surfaces remote from the bases and remote from the first surface, the wire bonds further having edge surfaces extending between the bases and the end surfaces;
forming a dielectric encapsulation layer over at least a portion of the first surface of the conductive layer, over at least a portion of the at least one microelectronic element, and over portions of the wire bonds such that unencapsulated portions of the wire bonds are defined by at least one of the end surface or a portion of the edge surface thereof that is uncovered by the encapsulation layer; and
selectively removing portions of the conductive layer to form first conductive elements thereof, wherein at least some of the first conductive elements are electrically connected with at least some of the wire bonds and at least some of the first conductive elements include at least some of the portions of the conductive layer with which the microelectronic element is electrically connected.

20. A method for making a microelectronic unit, comprising the steps of:
forming a plurality of wire bonds on a first surface that is a conductive bonding surface of structure comprising a patternable metallic element, the wire bonds having bases joined to the first surface and end surfaces remote from the bases and remote from the first surface, the wire bonds further having edge surfaces extending between the bases and the end surfaces, wherein when forming the wire bonds, the conductive layer includes a plurality of regions attached to one another at at least some edges thereof;
forming a dielectric encapsulation layer over at least a portion of the first surface of the conductive layer and over portions of the wire bonds, such that unencapsulated portions of the wire bonds are defined by at least one of the end surface or a portion of the edge surface thereof that is uncovered by the encapsulation layer, wherein when performing the step of selectively removing portions of the encapsulation layer, a plurality of microelectronic elements are joined to the conductive layer, in the form of an in-process unit having at least one microelectronic element electrically connected with each of at least some of the regions of the conductive layer;
then patterning the metallic element selectively to form first conductive elements insulated from one another by at least portions of the encapsulation layer, wherein at least some of the wire bonds are disposed atop the first conductive elements; and
then severing the in-process unit into a plurality of microelectronic units, each including the first conductive elements of a region of the conductive layer and the at least one microelectronic element electrically connected therewith.

21. A method for making a microelectronic assembly, comprising:
making a first microelectronic package by steps including:
forming a plurality of wire bonds on a first surface of a conductive layer of an in process unit, the in-process unit having at least one microelectronic element joined thereto and electrically connected with portions thereof, the wire bonds being formed having bases joined to the first surface and end surfaces remote from the bases and remote from the first surface, the wire bonds further having edge surfaces extending between the bases and the end surfaces;
forming a dielectric encapsulation layer over at least a portion of the first surface of the conductive layer, over at least a portion of the at least one microelectronic element, and over portions of the wire bonds such that unencapsulated portions of the wire bonds are defined by at least one of the end surface or a portion of the edge surface thereof that is uncovered by the encapsulation layer; and
selectively removing portions of the conductive layer to form first conductive elements thereof, wherein at least some of the first conductive elements are electrically connected with at least some of the wire bonds and at least some of the first conductive elements include at least some of the portions of the conductive layer with which the microelectronic element is electrically connected; and

joining the first microelectronic package with a second microelectronic package overlying the second surface of the encapsulation layer of the first package, the second microelectronic package including a plurality of contacts exposed at a first surface thereof;
wherein joining the first microelectronic package with the second microelectronic package includes electrically connecting the unencapsulated portions of the wire bonds of the first microelectronic package with the contacts of the second microelectronic package.