# Patent

## Title
Package-on-package assembly with wire bonds to encapsulation surface

## Abstract

A method of making a microelectronic package includes forming a dielectric encapsulation layer on an in-process unit having a substrate having a first surface and a second surface remote therefrom. A microelectronic element is mounted to the first surface of the substrate, and a plurality of conductive elements exposed at the first surface, at least some of which are electrically connected to the microelectronic element. Wire bonds have bases joined to the conductive elements and end surfaces remote from the bases and define an edge surface extending away between the base and the end surface. The encapsulation layer is formed to at least partially cover the first surface and portions of the wire bonds with unencapsulated portions of the wire bonds being defined by at least one of the end surface or a portion of the edge surface that is uncovered thereby.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application is a continuation of U.S. patent application Ser. No. 13/792,521, filed Mar. 11, 2013, which is a divisional of U.S. patent application Ser. No. 13/462,158, filed May 2, 2012, (which issued Dec. 31, 2013, U.S. Pat. No. 8,618,659) which claims the benefit of the filing date of Korean Patent Application No. 10-2011-0041843, filed May 3, 2011, the disclosures of which are incorporated herein by reference.


TECHNICAL FIELD
The subject matter of this application relates to microelectronic packages and fabrication methods thereof, particularly those which incorporate wire bonds for electrical connection with an element above a surface of an encapsulation layer.
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.
Microcontact elements in the form of elongated posts or pins may be used to connect microelectronic packages to circuit boards and for other connections in microelectronic packaging. In some instances, microcontacts have been formed by etching a metallic structure including one or more metallic layers to form the microcontacts. The etching process limits the size of the microcontacts. Conventional etching processes typically cannot form microcontacts with a large ratio of height to maximum width, referred to herein as “aspect ratio”. It has been difficult or impossible to form arrays of microcontacts with appreciable height and very small pitch or spacing between adjacent microcontacts. Moreover, the configurations of the microcontacts formed by conventional etching processes are limited.
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 embodiment of the present disclosure relates to a microelectronic package. The microelectronic package includes a substrate having a first region and a second region and a first surface and a second surface remote from the first surface. At least one microelectronic element overlies the first surface within the first region. Electrically conductive elements are exposed at at least one of the first surface and the second surface of the substrate within the second region, and at least some of the conductive elements are electrically connected to the at least one microelectronic element. The microelectronic package further includes wire bonds having bases joined to respective ones of the conductive elements and end surfaces remote from the substrate and remote from the bases, each wire bond defining an edge surface extending between the base and the end surface thereof. A dielectric encapsulation layer extends from at least one of the first or second surfaces and fills spaces between the wire bonds such that the wire bonds are separated from one another by the encapsulation layer. The encapsulation layer overlies at least the second region of the substrate, and 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. The substrate can be a lead frame and the conductive elements can be leads of the lead frame.
The unencapsulated portions of the wire bonds can be defined by the end surfaces of the wire bonds and portions of the edge surfaces adjacent the end surfaces that are uncovered by the encapsulation layer. An oxidation protection layer can be included contacting at least some of the unencapsulated portions of the wire bonds. At least a portion of at least one of the wire bonds adjacent the end surface thereof can be substantially perpendicular to a surface of the encapsulation layer. The conductive elements can be first conductive elements, and the microelectronic package can further include a plurality of second conductive elements electrically connected to the unencapsulated portions of the wire bonds. In such an embodiment, the second conductive elements can be such that they do not contact the first conductive elements. The second conductive elements can include a plurality of stud bumps joined to the end surfaces of at least some of the first wire bonds.
At least one of the wire bonds can extend along a substantially straight line between the base and the unencapsulated portion thereof, and the substantially straight line can form an angle of less than 90° with respect to the first surface of the substrate. Additionally or alternatively, the edge surface of at least one of the wire bonds can have a first portion adjacent the end surface and a second portion separated from the end surface by the first portion, and the first portion can extend in a direction away from a direction in which the second portion extends.
Another embodiment of the present disclosure relates to an alternative microelectronic package. Such a microelectronic package includes a substrate having a first region and a second region, and a first surface and a second surface remote from the first surface. At least one microelectronic element overlies the first surface within the first region. Electrically conductive elements are exposed at at least one of the first surface and the second surface of the substrate within the second region, and at least some of the conductive elements are electrically connected to the at least one microelectronic element. The microelectronic package further includes a plurality of wire bonds having bases joined to respective ones of the conductive elements and end surfaces remote from the substrate and remote from the bases. Each wire bond defines an edge surface extending between the base and the end surface thereof. A dielectric encapsulation layer extends from at least one of the first or second surfaces and fills spaces between wire bonds such that the wire bonds are separated from one another by the encapsulation layer. The encapsulation layer overlies at least the second region of the substrate, and unencapsulated portions of the wire bonds are defined by at least portions of the edge surfaces adjacent the end surfaces of the wire bonds that are uncovered by the encapsulation layer.
The encapsulation layer can be a monolithic layer formed on the substrate by depositing a dielectric material onto the first substrate after forming the wire bonds, and then curing the deposited dielectric material. The forming of the monolithic encapsulation layer can include molding the dielectric material.
At least one of the unencapsulated portions can be further defined by at least a portion of the end surface that is uncovered by the encapsulation layer. The portion of the edge surface that is uncovered by the encapsulation layer can have a longest dimension extending in a direction substantially parallel to the surface of the encapsulation layer. The length of the portion of the edge surface that is uncovered by the encapsulation layer and extends substantially parallel to the surface of the encapsulation layer can be greater than a cross-sectional width of the wire bond.
In either of the aforementioned embodiments, the first surface of the substrate can extend in first and second lateral directions, each lateral direction being transverse to a direction of a thickness of the substrate between the first and second surfaces. The unencapsulated portion of at least one of the wire bonds can further be displaced in at least one of the lateral directions from the conductive element to which the at least one wire bond is joined. At least one of the wire bonds can include a substantially curved portion between the base and the end surface thereof. The unencapsulated portion of the at least one wire bond can overlie a major surface of the microelectronic element.
In either of the aforementioned embodiments, a solder ball can be joined to the unencapsulated portion of least one of the wire bonds.
Additionally, in either of the aforementioned embodiments, the encapsulation layer can include at least one surface, and the unencapsulated portions of the wire bonds can be uncovered by the encapsulation layer at one of the at least one surface. The at least one surface can include a major surface that is substantially parallel to the first surface of the substrate, and the unencapsulated portion of at least one of the wire bonds can be uncovered by the encapsulation layer at the major surface. The unencapsulated portion of at least one wire bond can be substantially flush with the major surface. Alternatively, the unencapsulated portion of at least one wire bond can extend above the major surface. The at least one surface can include a major surface at a first distance from the first surface of the substrate and a recessed surface at a second distance from first surface of the substrate that is less than the first distance, and the unencapsulated portion of at least one of the wire bonds can be uncovered by the encapsulation layer at the recessed surface. The at least one surface can further include a side surface extending away from the first surface of the substrate at a substantial angle therefrom, and the unencapsulated portion of at least one wire bond can be uncovered by the encapsulation layer at the side surface. The encapsulation layer can have a cavity formed therein that extends from a surface of the encapsulation layer toward the substrate, and the unencapsulated portion of one of the wire bonds can be disposed within the cavity.
Further, in either of the aforementioned embodiments, the wire bonds can consist essentially of at least one material selected from the group consisting of copper, gold, aluminum, and solder. At least one of the wire bonds can define a longitudinal axis along a length thereof, and each wire bond can include an inner layer of a first material extending along the longitudinal axis and an outer layer of a second material remote from the longitudinal axis and having a length extending in a lengthwise direction of such wire bond. In such an embodiment, the first material can be one of copper, gold, nickel, and aluminum, and the second material can be one of copper, gold, nickel, aluminum, and solder.
In either of the aforementioned embodiments, the plurality of wire bonds can be first wire bonds, and the microelectronic package can further comprise at least one second wire bond having a base joined to a contact on the microelectronic element and an end surface thereof remote from the contact. The at least one second wire bond can define an edge surface extending between the base and the end surface, and an unencapsulated portion of the at least one second wire bond can be defined by a portion of at least one of the end surface of such second wire bond or of the edge surface of such second wire bond that is uncovered by the encapsulation layer. The at least one microelectronic element can be a first microelectronic element, and the microelectronic package can further comprise at least one second microelectronic element at least partially overlying the first microelectronic element. In such an embodiment, the wire bonds can be first wire bonds, and the microelectronic package can have at least one second wire bond having a base joined to a contact on the microelectronic element and an end surface remote from the contact. The at least one second wire bond can define an edge surface between the base and the end surface, and an unencapsulated portion of the second wire bond can be defined by at least one of a portion of the end surface of such second wire bond or of the edge surface of such second wire bond that is uncovered by the encapsulation layer.
In either of the above embodiments, a first one of the wire bonds can be adapted for carrying a first signal electric potential and a second one of the wire bonds can be adapted for simultaneously carrying a second electric potential different from the first signal electric potential.
Either of the above embodiments can further include a redistribution layer extending along the surface of the encapsulation layer. The redistribution layer can include a redistribution substrate having a first surface adjacent a major surface of the encapsulation layer, and the redistribution layer can further include a second surface remote from the first surface, first conductive pads exposed on the first surface of the redistribution substrate and aligned with and mechanically connected to respective unencapsulated portions of the wire bonds, and second conductive pads exposed on the second surface of the substrate electrically connected to the first conductive pads.
In a further embodiment, a microelectronic assembly can include a first microelectronic package according to either of the above embodiments. The assembly can further include a second microelectronic package having a substrate with a first surface and a second surface. A second microelectronic element can be mounted to the first surface, and contact pads can be exposed at the second surface and can be electrically connected to the second microelectronic element. The second microelectronic package can be mounted to the first microelectronic package such that the second surface of the second microelectronic package overlies at least a portion of the surface of the dielectric encapsulation layer and such that at least some of the contact pads are electrically and mechanically connected to at least some of the unencapsulated portions of the wire bonds.
Another embodiment of the present disclosure can relate to a microelectronic package including a substrate having a first region and a second region, and a first surface and a second surface remote from the first surface and extending in lateral directions. A microelectronic element overlies the first surface within the first region and has a major surface remote from the substrate. Electrically conductive elements are exposed at the first surface of the substrate within the second region with at least some of the conductive elements being electrically connected to the microelectronic element. The microelectronic package further includes wire bonds having bases joined to respective ones of the first electrically conductive elements and end surfaces remote from the substrate and remote from the bases. Each wire bond defines an edge surface extending between the base and the end surface thereof. A dielectric encapsulation layer extends from at least one of the first or second surfaces and fills spaces between the wire bonds such that the wire bonds are separated from one another by the dielectric layer. The encapsulation layer overlies at least the second region of the substrate, and 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. The unencapsulated portion of at least one wire bond is displaced in at least one lateral direction along the first surface from the conductive element to which the at least one wire bond is joined such that the unencapsulated portion thereof overlies the major surface of the microelectronic element.
The conductive elements can be arranged in a first array of a first predetermined configuration, and the unencapsulated portions of the wire bonds can be arranged in a second array of a second predetermined configuration that is different from the first predetermined configuration. The first predetermined configuration can be characterized by a first pitch and the second configuration can be characterized by a second pitch that is finer than the first pitch. An insulating layer can extend over at least a surface of the microelectronic element. The insulating layer can be disposed between the surface of the microelectronic element and the at least one wire bond that has an unencapsulated portion overlying the major surface of the microelectronic element. A plurality of the unencapsulated portions of respective ones of the wire bonds can overlie the major surface of the microelectronic element.
A microelectronic assembly according to an embodiment of the invention can include a first microelectronic package according the above description. The assembly can further include a second microelectronic package including a substrate having a first surface and a second surface, a microelectronic element affixed on the first surface, and contact pads exposed on the second surface and electrically connected to the microelectronic element. The second microelectronic package can be affixed on the first microelectronic package such that the second surface of the second package overlies at least a portion of the surface of the dielectric layer and such that at least some of the contact pads are electrically and mechanically connected to at least some of the unencapsulated portions of the wire bonds.
The electrically conductive elements of the first microelectronic package can be arranged in a first array of a first predetermined configuration, and the contact pads of the second microelectronic package can be arranged in a second array of a second predetermined configuration that is different from the first predetermined configuration. At least some of the unencapsulated portions of the wire bonds of the first microelectronic package can be arranged in a third array that corresponds to the second predetermined configuration. The first predetermined configuration can be characterized by a first pitch, and the second configuration can be characterized by a second pitch that is finer than the first pitch.
A further embodiment of the present invention can relate to a method of making a microelectronic package. The method includes forming a dielectric encapsulation layer on an in-process unit. The in-process unit includes a substrate having a first surface and a second surface remote therefrom, a microelectronic element mounted to the first surface of the substrate, and a plurality of conductive elements exposed at the first surface. At least some of the conductive elements are electrically connected to the microelectronic element. The in-process unit further includes wire bonds having bases joined to the conductive elements and end surfaces remote from the bases. Each wire bond defines an edge surface extending away between the base and the end surface. The encapsulation layer is formed so as to at least partially cover the first surface and portions of the wire bonds and such that unencapsulated portions of the wire bonds are defined by a portion of at least one of the end surface or of the edge surface thereof that is uncovered by the encapsulation layer. The substrate of the in-process unit can be a lead frame and the conductive elements can be leads of the lead frame. A stud bump can be formed on the unencapsulated portion of at least one of the wire bonds. A solder ball can be deposited on the unencapsulated portion of at least one of the wire bonds.
The step of forming the encapsulation layer can include depositing a dielectric material mass over the first surface and substantially all of the wire bonds and removing a portion of the dielectric material mass to uncover portions of the wire bonds to define the unencapsulated portions thereof. In a variation, at least one of the wire bonds can extend in a loop joined to each of at least two of the conductive elements. The dielectric material mass can then be deposited so as to at least partially cover the first surface and the at least one wire bond loop, and removing a portion of the dielectric material mass can further include removing a portion of the at least one wire bond loop so as sever it into first and second wire bonds having respective free ends that are uncovered by the encapsulation layer to form the unencapsulated portions thereof. The loop can be formed by joining a first end of a wire to the conductive element, drawing the wire in a direction away from the first surface, then drawing the wire in at least a lateral direction along the first surface, and then drawing the wire to the second conductive element and joining the wire to the second conductive element.
The encapsulation layer can be formed on the in-process unit by pressing a dielectric material mass over the wire bonds from a location remote from the substrate and into contact with the first surface of the substrate such that the at least one of the wire bonds penetrates the dielectric material mass. The wire bonds can be made of wire consisting substantially of gold, copper, aluminum, or solder. The first wire bonds can include aluminum, and the wire bonds can be joined to the conductive element by wedge bonding. The step of forming the encapsulation layer can additionally or alternatively include forming at least one cavity extending from a major surface of the encapsulation layer toward the substrate, the at least one cavity surrounding the unencapsulated portion of one of the wire bonds. The at least one cavity can be formed after depositing a dielectric encapsulation material onto the substrate by at least one of wet etching, dry etching, or laser etching the encapsulation material. The at least one cavity can further be formed by removing at least a portion of a mass of sacrificial material from a predetermined location of at least one of the wire bonds after depositing a dielectric encapsulation material onto the substrate and the at least one wire bond. The step of forming the encapsulation layer can be carried out such that a portion of the mass of sacrificial material is exposed on a major surface of the encapsulation layer, the exposed portion of the mass of sacrificial material surrounding a portion of the wire bond near the free end thereof and spacing apart a portion of the encapsulation layer therefrom. At least one of the wire bonds can define a longitudinal axis along a length thereof, and each wire bond can include an inner layer of a first material extending along the longitudinal axis and an outer layer formed by the mass of sacrificial material remote from the longitudinal axis and having a length extending in a lengthwise direction of such wire bond. A first portion of the mass of sacrificial material can be removed to form the cavity with a second portion of the mass of sacrificial material remaining adjacent to the base.
The first surface of the substrate can extend in lateral directions, and the unencapsulated portion of at least one of the wire bonds can be formed such that the end surface thereof is displaced in at least one of the lateral directions from the conductive element to which the at least one wire bond is joined. Accordingly, the in-process unit can be formed including a step of forming the wire bonds such that at least one of the wire bonds includes a substantially curved segment positioned between the conductive element and the end surface of the at least one wire bond.
In a further variation, the substrate can include a first region and a second region, and the microelectronic element can overlie the first region and can have a major surface remote from the substrate. The first conductive element can be disposed within the second region, and the in-process unit can be formed including a step of forming the wire bonds such that at least a portion of at least one of the wire bonds extends over the major surface of the microelectronic element.
The wire bonds can define a longitudinal axis along a length thereof, and the wire bonds can include an inner layer of a first material extending along the longitudinal axis and an outer layer of a second material remote from the longitudinal axis and extending along the length of the wire bond. In such a variation, the first material can be copper and the second material can be solder. A portion of the second material can be removed after the step of forming the encapsulation layer to form a cavity extending from a surface of the dielectric layer to uncover a portion of the edge surface of the inner layer of the wire bond.
A further embodiment of the present disclosure relates to a microelectronic package including a substrate having a first region and a second region, the substrate having a first surface and a second surface remote from the first surface. At least one microelectronic element overlies the first surface within the first region, and electrically conductive elements are exposed at the first surface of the substrate within the second region with at least some of the conductive elements electrically connected to the at least one microelectronic element. A plurality of bond elements, each having a first base, a second base, and an edge surface extending between the bases, the first base are joined to one of the conductive elements. The edge surface includes a first portion that extends away from the contact pad to an apex of the edge surface remote from the substrate. The edge surface further includes a second portion that extends from the apex to the second base, which is joined to a feature of the substrate. A dielectric encapsulation layer extends from at least one of the first or second surfaces and fills spaces between the first and second portions of the bond elements and between the plurality of bond elements such that the bond elements are separated from one another by the encapsulation layer. The encapsulation layer overlies at least the second region of the substrate. Unencapsulated portions of the bond elements are defined by at least portions of the edge surfaces of the bond elements surrounding the apexes thereof that are uncovered by the encapsulation layer.
In a variation of the above embodiment, the bond elements are wire bonds. In such a variation, the feature of the substrate to which the second base of the substrate is joined can be the conductive element to which the first base is joined. Alternatively, the feature of the substrate to which the second base is joined can be a respective conductive element different from the conductive element to which the first base is joined. Such a conductive element to which the second base is joined can be not electrically connected to the microelectronic element. In an alternative variation, the bond element can be a bond ribbon. In such a variation, a portion of the first base can extend along a portion of the respective contact pad, and the feature to which the second base is joined can be the length of the first base that extends along a portion of the respective contact pad.
In the embodiment, the first surface of the substrate can extend in first and second lateral directions, each lateral direction being transverse to a direction of a thickness of the substrate between the first and second surfaces. The unencapsulated portion of at least one of the wire bonds can then be displaced in at least one of the lateral directions from the conductive element to which the at least one wire bond is joined. Further, the unencapsulated portion of the at least one wire bond can overlie a major surface of the microelectronic element.
A further embodiment of the present disclosure can relate to a method of making a microelectronic assembly. The method of this embodiment can include joining a first microelectronic package made according to the above embodiment with a second microelectronic package, the second microelectronic package can include a substrate having a first surface and a plurality of contacts exposed at the first surface of the substrate, and joining the first microelectronic package with the second microelectronic package can include electrically and mechanically connecting the unencapsulated portions of the wire bonds of the first microelectronic package with the contacts of the second microelectronic package.
A further embodiment of the present invention can relate to an alternative method of making a microelectronic package. The method of this embodiment includes positioning a dielectric material mass over an in-process unit that includes a substrate having a first surface and a second surface remote therefrom, a plurality of thin conductive elements exposed at the first surface, and wire bonds having bases joined to at respective ones of the thin conductive elements and end surfaces remote from the substrate and remote from the bases. Each wire bond defines an edge surface extending between the base and the end surface thereof. The method also includes forming an encapsulation layer on the in-process unit by pressing the dielectric material mass over the wire bond into contact with the first surface of the substrate such that the wire bonds penetrate the dielectric material mass. The encapsulation layer, thus, fills spaces between the wire bonds such that the wire bonds are separated from one another both the encapsulation layer with the encapsulation layer overlying at least the second region of the substrate. Unencapsulated portions of the first wire bonds are formed by the wire bonds extending through a portion of the encapsulation layer such that portions of the first wire bonds are uncovered by the encapsulation layer.
A still further embodiment of the present disclosure relates to an alternative method for making a microelectronic package. The method of this embodiment includes forming a dielectric encapsulation layer on an in-process unit that includes a substrate having a first surface and a second surface remote therefrom, a plurality of thin conductive elements exposed at the first surface, and wire loops joined at a first base and a second base to respective ones of at least two of the thin conductive elements. The encapsulation is being formed so as to at least partially cover the first surface and the at least one wire loop. The method further includes removing a portion of the encapsulation layer and a portion of the wire loops so as sever each of the wire loops into separate wire bonds corresponding to a respective one of the first and second bases. The wire bonds, thus, have end surfaces remote from the substrate and remote from the bases, and each wire bond defines an edge surface extending between the base and the end surface thereof. The encapsulation layer fills spaces between the wire bonds such that the wire bonds are separated from one another by the encapsulation layer. The wire bonds have unencapsulated portions formed by free ends thereof that are at least partially uncovered by the encapsulation layer.
Another embodiment of the present disclosure relates to system that includes a microelectronic package or assembly according to one of the embodiments thereof discussed above and one or more other electronic components electrically connected to the microelectronic package. The system can further include a housing, in which the microelectronic package or assembly and the other electronic components can be mounted.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a microelectronic package according to an embodiment of the present invention;
FIG. 2 shows a top elevation view of the microelectronic package of FIG. 1;
FIG. 3 shows a microelectronic package according to an alternative embodiment of the present invention;
FIG. 4 shows a microelectronic package according to an alternative embodiment of the present invention;
FIG. 5 shows a microelectronic package according to an alternative embodiment of the present invention;
FIG. 6 shows a stacked microelectronic assembly including a microelectronic package according to an embodiment of the present invention;
FIG. 7 shows a microelectronic package according to an alternative embodiment of the present invention;
FIGS. 8A-8E show a detail view of a portion of a microelectronic package according to various embodiments of the present invention;
FIG. 9 shows a detail view of a portion of a microelectronic package according to an alternative embodiment of the present invention;
FIGS. 10A-10D show a detail view of a portion of a microelectronic package according to various embodiments of the present invention;
FIGS. 11-14 show a microelectronic package during various steps of fabrication thereof according to an embodiment of the present invention;
FIG. 15 shows a microelectronic package during a fabrication step according to an alternative embodiment of the present invention;
FIGS. 16A-16C show a detail view of a portion of a microelectronic package during various steps of fabrication thereof according to an embodiment of the present invention;
FIGS. 17A-17C show a detail view of a portion of a microelectronic package during various steps of fabrication thereof according to an alternative embodiment of the present invention;
FIG. 18 shows a top elevation view of a microelectronic package according to an alternative embodiment of the present invention;
FIG. 19 shows a top elevation view of a portion of a microelectronic package according to an alternative embodiment of the present invention;
FIG. 20 shows a top view of a microelectronic package according to a further alternative embodiment of the present invention;
FIG. 21 shows a front elevation view of the microelectronic package of claim 20;
FIG. 22 shows a front elevation view of a microelectronic package according to a further alternative embodiment of the present invention;
FIG. 23 shows a system according to a further embodiment of the present invention;
FIG. 24 shows a front elevation view of a microelectronic package according to a further alternative embodiment of the present invention;
FIG. 25 shows a front elevation view of a microelectronic package according to a further alternative embodiment of the present invention;
FIG. 26 shows a top view of a microelectronic package according to a variation of the embodiment of FIG. 25;
FIG. 27 shows a front elevation view of a microelectronic package according to a further alternative embodiment of the present invention; and
FIG. 28 shows a top view of a microelectronic package according to a variation of the embodiment of FIG. 27.



DETAILED DESCRIPTION
Turning now to the figures, where similar numeric references are used to indicate similar features, there is shown in FIG. 1 a microelectronic assembly 10 according to an embodiment of the present invention. The embodiment of FIG. 1 is a microelectronic assembly 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 assembly 10 of FIG. 1 includes a substrate 12 having a first surface 14 and a second surface 16. The substrate 12 typically is in the form of a dielectric element, which is substantially flat. The dielectric element may be sheet-like and may be thin. In particular embodiments, the dielectric element can include one or more layers of organic dielectric material or composite dielectric materials, such as, without limitation: polyimide, polytetrafluoroethylene (“PTFE”), epoxy, epoxy-glass, FR-4, BT resin, thermoplastic, or thermoset plastic materials. The first surface 14 and second surface 16 are preferably substantially parallel to each other and are spaced apart at a distance perpendicular to the surfaces 14,16 defining the thickness of the substrate 12. The thickness of substrate 12 is preferably within a range of generally acceptable thicknesses for the present application. In an embodiment, the distance between the first surface 14 and the second surface 16 is between about 25 and 500 μm. For purposes of this discussion, the first surface 14 may be described as being positioned opposite or remote from second surface 16. 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.
In a preferred embodiment, substrate 12 is considered as divided into a first region 18 and a second region 20. The first region 18 lies within the second region 20 and includes a central portion of the substrate 12 and extends outwardly therefrom. The second region 20 substantially surrounds the first region 18 and extends outwardly therefrom to the outer edges of the substrate 12. In this embodiment, no specific characteristic of the substrate itself physically divides the two regions; however, the regions are demarked for purposes of discussion herein with respect to treatments or features applied thereto or contained therein.
A microelectronic element 22 can be mounted to first surface 14 of substrate 12 within first region 18. Microelectronic element 22 can be a semiconductor chip or another comparable device. In the embodiment of FIG. 1, microelectronic element 22 is mounted to first surface 14 in what is known as a conventional or “face-up” fashion. In such an embodiment, wire leads 24 can be used to electrically connect microelectronic element 22 to some of a plurality of conductive elements 28 exposed at first surface 14. Wire leads 24 can also be joined to traces (not shown) or other conductive features within substrate 12 that are, in turn, connected to conductive elements 28.
Conductive elements 28 include respective “contacts” or pads 30 that are exposed at the first surface 14 of substrate 12. 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. The conductive elements 28 can be flat, thin elements in which pad 30 is exposed at first surface 14 of substrate 12. In one embodiment, conductive elements 28 can be substantially circular and can be interconnected between each other or to microelectronic element 22 by traces (not shown). Conductive elements 28 can be formed at least within second region 20 of substrate 12. Additionally, in certain embodiments, conductive elements 28 can also be formed within first region 18. Such an arrangement is particularly useful when mounting microelectronic element 122 (FIG. 3) to substrate 112 in what is known as a “flip-chip” configuration, where contacts on the microelectronic element 122 can be connected to conductive elements 128 within first region 118 by solder bumps 126 or the like that are positioned beneath microelectronic element 122. In another configuration as shown in FIG. 22, microelectronic element 622 is mounted face-down on substrate 612 and electrically connected to a conductive feature on the chip by wire leads 624 that extend over an outwardly-facing surface, such as surface 616, of substrate 612. In the embodiment shown, wire leads 625 pass through an opening 625 in substrate 612 and can be encapsulated by an overmold 699.
In an embodiment, conductive elements 28 are formed from a solid metal material such as copper, gold, nickel, or other materials that are acceptable for such an application, including various alloys including one or more of copper, gold, nickel or combinations thereof.
At least some of conductive elements 28 can be interconnected to corresponding second conductive elements 40, such as conductive pads, exposed at second surface 16 of substrate 12. Such an interconnection can be completed using vias 41 formed in substrate 12 that can be lined or filled with conductive metal that can be of the same material as conductive elements 28 and 40. Optionally, conductive elements 40 can be further interconnected by traces on substrate 12.
Microelectronic assembly 10 further includes a plurality of wire bonds 32 joined to at least some of the conductive elements 28, such as on the pads 30 thereof. Wire bonds 32 are joined at a base 34 thereof to the conductive elements 28 and can extend to a free end 36 remote from the respective bases 34 and from substrate 12. The ends 36 of wire bonds 32 are 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 assembly 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 solder ball or other features discussed herein, to a conductive feature external to assembly 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, base 34 is not free as it is either directly or indirectly electrically connected to microelectronic element 22, as described herein. As shown in FIG. 1, base 34 can be substantially rounded in shape, extending outward from an edge surface 37 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 and are described in U.S. Pat. No. 7,391,121 to Otremba and in U.S. Pat. App. Pub. No. 2005/0095835 (describing a wedge-bonding procedure that can be considered a form of wire bonding) the disclosures of which are both incorporated herein by reference in their entireties. Alternative embodiments are possible where wire bonds 32 are additionally or alternatively joined to conductive elements 40 exposed on second surface 16 of substrate 12, extending away therefrom.
Wire bond 32 can be made from a conductive material such as copper, gold, nickel, solder, aluminum or the like. 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 or the like. 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 other embodiments, including those in which wedge bonding is used, wire bonds 32 can have a thickness of up to about 500 μm. In general, a wire bond is formed on a conductive element, such as conductive element 28, a pad, trace or the like, using specialized equipment that is known in the art. 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 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 has an end surface 38. End surface 38 can form at least a part of a contact in an array formed by respective end surfaces 38 of a plurality of wire bonds 32. FIG. 2 shows 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. Such an array can be used to electrically and mechanically connect the microelectronic assembly 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. 6. In such a stacked arrangement, wire bonds 32 and conductive elements 28 and 40 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. Solder masses 52 can be used to interconnect the microelectronic assemblies in such a stack, such as by electronically and mechanically attaching end surfaces 38 to conductive elements 40.
Microelectronic assembly 10 further includes an encapsulation layer 42 formed from a dielectric material. In the embodiment of FIG. 1, encapsulation layer 42 is formed over the portions of first surface 14 of substrate 12 that are not otherwise covered by or occupied by microelectronic element 22, or conductive elements 28. Similarly, encapsulation layer 42 is formed over the portions of conductive elements 28, including pad 30 thereof, that are not otherwise covered by wire bonds 32. Encapsulation layer 42 can also substantially cover microelectronic element 22, wire bonds 32, including the bases 34 and at least a portion of edge surfaces 37 thereof. A portion of wire bonds 32 can remain uncovered by encapsulation layer 42, which can also be referred to as unencapsulated, thereby making the wire bond available for electrical connection to a feature or element located outside of encapsulation layer 42. In an embodiment, end surfaces 38 of wire bonds 32 remain uncovered by encapsulation layer 42 within major surface 44 of encapsulation layer 42. Other embodiments are possible in which a portion of edge surface 37 is uncovered by encapsulation layer 42 in addition to or as an alternative to having end surface 38 remain uncovered by encapsulation layer 42. In other words, encapsulation layer 42 can cover all of microelectronic assembly 10 from first surface 14 and above, with the exception of a portion of wire bonds 36, such as end surfaces 38, edge surfaces 37 or combinations of the two. In the embodiments shown in the Figures, a surface, such as major surface 44 of encapsulation layer 42 can be spaced apart from first surface 14 of substrate 12 at a distance great enough to cover microelectronic element 22. Accordingly, embodiments of microelectronic assembly 10 in which ends 38 of wire bonds 32 are flush with surface 44, will include wire bonds 32 that are taller than the microelectronic element 22, and any underlying solder bumps for flip chip connection. Other configurations for encapsulation layer 42, however, are possible. For example, the encapsulation layer can have multiple surfaces with varying heights. In such a configuration, the surface 44 within which ends 38 are positioned can be higher or lower than an upwardly facing surface under which microelectronic element 22 is located.
Encapsulation layer 42 serves to protect the other elements within microelectronic assembly 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.
FIG. 3 shows an embodiment of microelectronic assembly 110 having wire bonds 132 with ends 136 that are not positioned directly above the respective bases 34 thereof. That is, considering first surface 114 of substrate 112 as extending in two lateral directions, so as to substantially define a plane, end 136 or at least one of the wire bonds 132 is displaced in at least one of these lateral directions from a corresponding lateral position of base 134. As shown in FIG. 3, wire bonds 132 can be substantially straight along the longitudinal axis thereof, as in the embodiment of FIG. 1, with the longitudinal axis being angled at an angle 146 with respect to first surface 114 of substrate 112. Although the cross-sectional view of FIG. 3 only shows the angle 146 through a first plane perpendicular to first surface 114, wire bond 132 can also be angled with respect to first surface 114 in another plane perpendicular to both that first plane and to first surface 114. Such an angle can be substantially equal to or different than angle 146. That is the displacement of end 136 relative to base 134 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 132 can be displaced in different directions and by different amounts throughout the assembly 110. Such an arrangement allows for assembly 110 to have an array that is configured differently on the level of surface 144 compared to on the level of substrate 12. For example, an array can cover a smaller overall area or have a smaller pitch on surface 144 than at the first surface 114 level compared to that at first surface 114 of substrate 112. Further, some wire bonds 132 can have ends 138 that are positioned above microelectronic element 122 to accommodate a stacked arrangement of packaged microelectronic elements of different sizes. In another example, shown in FIG. 19, wire bonds 132 can be configured such that the end 136A of one wire bond 132A is positioned substantially above the base 134B of another wire bond 134B, the end 132B of that wire bond 134B being positioned elsewhere. Such an arrangement can be referred to as changing the relative position of a contact end surface 136 within an array of contacts, compared to the position of a corresponding contact array on second surface 116. Within such an array, the relative positions of the contact end surfaces can be changed or varied, as desired, depending on the microelectronic assembly's application or other requirements.
FIG. 4 shows a further embodiment of a microelectronic subassembly 210 having wire bonds 232 with ends 236 in displaced lateral positions with respect to bases 234. In the embodiment of FIG. 4, the wire bonds 132 achieve this lateral displacement by including a curved portion 248 therein. Curved portion 248 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.
Curved portion 248 can take on a variety of shapes, as needed, to achieve the desired positions of the ends 236 of the wire bonds 232. For example, curved portions 248 can be formed as S-curves of various shapes, such as that which is shown in FIG. 4 or of a smoother form (such as that which is shown in FIG. 5). Additionally, curved portion 248 can be positioned closer to base 234 than to end 236 or vice-versa. Curved portion 248 can also be in the form of a spiral or loop, or can be compound including curves in multiple directions or of different shapes or characters.
FIG. 5 shows a further exemplary embodiment of a microelectronic package 310 having a combination of wire bonds 332 having various shapes leading to various relative lateral displacements between bases 334 and ends 336. Some of wire bonds 332A are substantially straight with ends 336A positioned above their respective bases 334A, while other wire bonds 332B include a subtle curved portion 348B leading to a somewhat slight relative lateral displacement between end 336B and base 334B. Further, some wire bonds 332C include curved portions 348C having a sweeping shape that result in ends 336C that are laterally displaced from the relative bases 334C at a greater distance than that of ends 334B. FIG. 5 also shows an exemplary pair of such wire bonds 332Ci and 332Cii that have bases 334Ci and 334Cii positioned in the same row of a substrate-level array and ends 336Ci and 336Cii that are positioned in different rows of a corresponding surface-level array.
A further variation of a wire bond 332D is shown that is configured to be uncovered by encapsulation layer 342 on a side surface 47 thereof. In the embodiment shown free end 336D is uncovered, however, a portion of edge surface 337D can additionally or alternatively be uncovered by encapsulation layer 342. Such a configuration can be used for grounding of microelectronic assembly 10 by electrical connection to an appropriate feature or for mechanical or electrical connection to other featured disposed laterally to microelectronic assembly 310. Additionally, FIG. 5 shows an area of encapsulation layer 342 that has been etched away, molded, or otherwise formed to define a recessed surface 345 that is positioned closer to substrate 12 than major surface 342. One or more wire bonds, such as wire bond 332A can be uncovered within an area along recessed surface 345. In the exemplary embodiment shown in FIG. 5, end surface 338A and a portion of edge surface 337A are uncovered by encapsulation layer 342. Such a configuration can provide a connection, such as by a solder ball or the like, to another conductive element by allowing the solder to wick along edge surface 337A and join thereto in addition to joining to end surface 338. Other configurations by which a portion of a wire bond can be uncovered by encapsulation layer 342 along recessed surface 345 are possible, including ones in which the end surfaces are substantially flush with recessed surface 345 or other configurations shown herein with respect to any other surfaces of encapsulation layer 342. Similarly, other configurations by which a portion of wire bond 332D is uncovered by encapsulation layer 342 along side surface 347 can be similar to those discussed elsewhere herein with respect to the variations of the major surface of the encapsulation layer.
FIG. 5 further shows a microelectronic assembly 310 having two microelectronic elements 322 and 350 in an exemplary arrangement where microelectronic element 350 is stacked, face-up, on microelectronic element 322. In this arrangement, leads 324 are used to electrically connect microelectronic element 322 to conductive features on substrate 312. Various leads are used to electronically connect microelectronic element 350 to various other features of microelectronic assembly 310. For example, lead 380 electrically connects microelectronic element 350 to conductive features of substrate 312, and lead 382 electrically connects microelectronic element 350 to microelectronic element 322. Further, wire bond 384, which can be similar in structure to various ones of wire bonds 332, is used to form a contact surface 386 on the surface 344 of encapsulation layer 342 that electrically connected to microelectronic element 350. This can be used to directly electrically connect a feature of another microelectronic assembly to microelectronic element 350 from above encapsulation layer 342. Such a lead could also be included that is connected to microelectronic element 322, including when such a microelectronic element is present without a second microelectronic element 350 affixed thereon. An opening (not shown) can be formed in encapsulation layer 342 that extends from surface 344 thereof to a point along, for example, lead 380, thereby providing access to lead 380 for electrical connection thereto by an element located outside surface 344. A similar opening can be formed over any of the other leads or wire bonds 332, such as over wire bonds 332C at a point away from the ends 336C thereof. In such an embodiment, ends 336C can be positioned beneath surface 344, with the opening providing the only access for electrical connection thereto.
FIG. 6 shows a stacked package of microelectronic assemblies 410 and 488. In such an arrangement solder masses 52 electrically and mechanically connect end surfaces 438 of assembly 410 to conductive elements 440 of assembly 488. The stacked package can include additional assemblies and can be ultimately attached to contacts 492 on a PCB 490 or the like for use in an electronic device. In such a stacked arrangement, wire bonds 432 and conductive elements 430 can carry multiple electronic signals therethrough, each having a different signal potential to allow for different signals to be processed by different microelectronic elements, such as microelectronic element 422 or microelectronic element 489, in a single stack.
In the exemplary configuration in FIG. 6, wire bonds 432 are configured with a curved portion 448 such that at least some of the ends 436 of the wire bonds 432 extend into an area that overlies a major surface 424 of the microelectronic element 422. Such an area can be defined by the outer periphery of microelectronic element 422 and extending upwardly therefrom. An example of such a configuration is shown from a view facing toward first surface 414 of substrate 412 in FIG. 18, where wire bonds 432 overlie a rear major surface of the microelectronic element 422, which is flip-chip bonded at a front face 425 thereof to substrate 412. In another configuration (FIG. 5), the microelectronic element 422 can be mounted face-up to the substrate 312, with the front face 325 facing away from the substrate 312 and at least one wire bond 336 overlying the front face of microelectronic element 322. In one embodiment, such wire bond 336 is not electrically connected with microelectronic element 322. A wire bond 336 bonded to substrate 312 may also overlie the front or rear face of microelectronic element 350. The embodiment of microelectronic assembly 410 shown in FIG. 18 is such that conductive elements 428 are arranged in a pattern forming a first array in which the conductive elements 428 are arranged in rows and columns surrounding microelectronic element 422 and may have a predetermined pitch between individual conductive elements 428. Wire bonds 432 are joined to the conductive elements 428 such that the respective bases 434 thereof follow the pattern of the first array as set out by the conductive elements 428. Wire bonds 432 are configured, however, such that the respective ends 436 thereof can be arranged in a different pattern according to a second array configuration. In the embodiment shown the pitch of the second array can be different from, and in some cases finer than that of the first array. However, other embodiments are possible in which the pitch of the second array is greater than the first array, or in which the conductive elements 428 are not positioned in a predetermined array but the ends 436 of the wire bonds 432 are. Further still, conductive elements 428 can be configured in sets of arrays positioned throughout substrate 412 and wire bonds 432 can be configured such that ends 436 are in different sets of arrays or in a single array.
FIG. 6 further shows an insulating layer 421 extending along a surface of microelectronic element 422. Insulating layer 421 can be formed from a dielectric or other electrically insulating material prior to forming the wire bonds. The insulating layer 421 can protect microelectronic element from coming into contact with any of wire bonds 423 that extend thereover. In particular, insulating layer 421 can avoid electrical short-circuiting between wire bonds and short-circuiting between a wire bond and the microelectronic element 422. In this way, the insulating layer 421 can help avoid malfunction or possible damage due to unintended electrical contact between a wire bond 432 and the microelectronic element 422.
The wire bond configuration shown in FIGS. 6 and 18 can allow for microelectronic assembly 410 to connect to another microelectronic assembly, such as microelectronic assembly 488, in certain instances where the relative sizes of, for example, microelectronic assembly 488 and microelectronic element 422 would not otherwise permit. In the embodiment of FIG. 6 microelectronic assembly 488 is sized such that some of the contact pads 440 are in an array within an area smaller than the area of the front or rear surface 424 or 426 of the microelectronic element 422. In a microelectronic assembly having substantially vertical conductive features, such as pillars, in place of wire bonds 432, direct connection between conductive elements 428 and pads 440 would not be possible. However, as shown in FIG. 6, wire bonds 432 having appropriately-configured curved portions 448 can have ends 436 in the appropriate positions to make the necessary electronic connections between microelectronic assembly 410 and microelectronic assembly 488. Such an arrangement can be used to make a stacked package where microelectronic assembly 418 is, for example, a DRAM chip or the like having a predetermined pad array, and wherein microelectronic element 422 is a logic chip configured to control the DRAM chip. This can allow a single type of DRAM chip to be used with several different logic chips of varying sizes, including those which are larger than the DRAM chip because the wire bonds 432 can have ends 436 positioned wherever necessary to make the desired connections with the DRAM chip. In an alternative embodiment, microelectronic package 410 can be mounted on printed circuit board 490 in another configuration, where the unencapsulated surfaces 436 of wire bonds 432 are electrically connected to pads 492 of circuit board 490. Further, in such an embodiment, another microelectronic package, such as a modified version of package 488 can be mounted on package 410 by solder balls 452 joined to pads 440.
FIG. 7 shows a microelectronic assembly 10, of the type shown in FIG. 1 with a redistribution layer 54 extending along surface 44 of encapsulation layer 42. As shown in FIG. 7, traces 58 are electrically connected to inner contact pads 61 which are electrically connected to end surfaces 38 of wire bonds 32 and extend through the substrate 56 of redistribution layer 54 to contact pads 60 exposed on surface 62 of substrate 56. An additional microelectronic assembly can then be connected to contact pads 60 by solder masses or the like. A similar structure to redistribution layer 54 can extend along second surface 16 of substrate 12 in what is known as a fan-out layer. A fan out layer can allow microelectronic assembly 10 to connect to an array of a different configuration than the conductive element 40 array would otherwise permit.
FIGS. 8A-8E show various configurations that can be implemented in the structure of or near the ends 36 of wire bonds 32 in a structure similar to FIGS. 1-7. FIG. 8A shows a structure in which a cavity 64 is formed in a portion of encapsulation layer 42 such that an end 36 of wire bond 32 projects above a minor surface 43 of the encapsulation layer at cavity 64. In the embodiment shown, end surface 38 is positioned below major surface 44 of encapsulation layer 42, and cavity 64 is structured to expose end surface 38 at surface 44 to allow an electronic structure to connect thereto. Other embodiments are possible wherein end surface 38 is substantially even with surface 44 or is spaced above surface 44. Further, cavity 64 can be configured such that a portion of edge surface 37 of wire bond 32 near the end 36 thereof can be uncovered by encapsulation layer 42 within cavity 64. This can allow for a connection to wire bond 32 from outside of assembly 10, such as a solder connection, to be made from both end surface 38 and the uncovered portion of edge surface 37 near end 36. Such a connection is shown in FIG. 8B and can provide a more robust connection to a second substrate 94 using a solder mass 52. In an embodiment cavity 64 can have a depth beneath surface 44 of between about 10 μm and 50 μm and can have a width of between about 100 μm and 300 μm. FIG. 8B shows a cavity having a similar structure to that of FIG. 8A, but with tapered side walls 65. Further, FIG. 8 shows a second microelectronic assembly 94 electrically and mechanically connected to wire bond 32 by a solder mass 52 at a contact pad 96 exposed at a surface of a substrate 98 thereof.
Cavity 64 can be formed by removing a portion of encapsulation layer 42 in the desired area of cavity 64. This can be done by known processes including, laser etching, wet etching, lapping or the like. Alternatively, in an embodiment where encapsulation layer 42 is formed by injection molding, cavity 64 can be formed by including a corresponding feature in the mold. Such a process is discussed in U.S. Pat. App. Pub. No. 2010/0232129, which is hereby incorporated by reference in its entirety. The tapered shape of cavity 64 shown in FIG. 8B can be the result of a particular etching process used in its formation.
FIGS. 8C and 8E show end structures that include a substantially rounded end portion 70 on wire bond 32. Rounded end portion 70 is configured to have a cross-section that is wider than the cross-section of the portion of wire bond 32 between base 34 and end 36. Further rounded end portion 70 includes an edge surface 71 that extends outward from the edge surface 37 of wire bond 32 at the transition therebetween. The incorporation of a rounded edge portion 70 can act to secure wire bond 32 within encapsulation layer 42 by providing an anchoring feature wherein the change in direction of the surface 71 gives encapsulation layer 42 a location to surround end 70 on three sides. This can help prevent wire bond 32 from becoming detached from conductive elements 28 on substrate 12, resulting in a failed electrical connection. Additionally, the rounded end portion 70 can provide increased surface area that is uncovered by encapsulation layer 42 within surface 44 to which an electronic connection can be made. As shown in FIG. 8E, rounded end portion 70 can extend above surface 44. Alternatively, as shown in FIG. 8C, rounded end portion 70 can further, be ground or otherwise flattened to provide a surface that is substantially flush with surface 44 and can have an area greater than the cross-section of wire bond 32.
A rounded end portion 70 can be formed by applying localized heat in the form of a flame or a spark at the end of the wire used to make wire bond 32. Known wire bonding machines can be modified to carry out this step, which can be done immediately after cutting the wire. In this process, the heat melts the wire at the end thereof. This localized portion of liquid metal is made round by the surface tension thereof and is retained when the metal cools.
FIG. 8D shows a configuration for microelectronic assembly 10 where end 36 of wire bond 32 includes a surface 38 that is spaced above major surface 44 of encapsulation layer 42. Such a configuration can present benefits similar to that discussed with respect to cavity 64, above, specifically, by providing a more robust connection with a solder mass 68 that wicks along the portion of edge surface 37 that is uncovered by encapsulation layer 42 above surface 44. In an embodiment, end surface 38 can be spaced above surface 42 at a distance of between about 10 μm and 50 μm. Additionally, in the embodiment of FIG. 8D and any of the other embodiments in which a portion of edge surface 37 is uncovered by encapsulation layer 42 above a surface of encapsulation layer 42, the end can include a protective layer formed thereon. Such a layer can include an oxidation protection layer, including those made from gold, an oxide coating or an OSP.
FIG. 9 shows an embodiment of microelectronic assembly 10 with a stud bump 72 formed on end surface 38 of wire bond 32. Stud bump 72 can be formed after making microelectronic assembly 10 by applying another, modified wire bond on top of end surface 44 and optionally extending along a portion of surface 44. The modified wire bond is cut or otherwise severed near the base thereof without drawing out a length of wire. Stud bumps 72 containing certain metals may be applied directly to ends 38 without first applying a bonding layer such as a UBM, thus providing way of forming conductive interconnects to bond pads which are not directly wettable by solder. This can be useful when wire bond 32 is made from a non-wettable metal. In general, stud bumps consisting essentially of one or more of copper, nickel, silver, platinum and gold can be applied this way. FIG. 9 shows a solder mass 68 formed over stud bump 72 for electronic or mechanical connection to an additional microelectronic assembly.
FIGS. 10A-10D show configurations for ends 36 of wire bonds 32 that include a bent or curved shape. In each embodiment, end 36 of wire bond 32 is bent such that a portion 74 thereof extends substantially parallel to surface 44 of encapsulation layer 42 such that at least a portion of edge surface 76 is not covered by, for example, major surface 44. This portion of edge surface 37 can extend upwards outside of surface 44 or can be ground or otherwise flattened so as to extend substantially flush with surface 44. The embodiment of FIG. 10A includes an abrupt bend in wire bond 32 at the portion 74 of end 36 that is parallel to surface 44 and terminates in an end surface 38 that is substantially perpendicular to surface 44. FIG. 10B shows an end 36 having a more gradual curve near the portion 74 of end 36 that is parallel to surface 44 than that which is shown in FIG. 10A. Other configurations are possible, including those in which a portion of a wire bond according to those shown in FIG. 3, 4, or 5 includes an end with a portion thereof substantially parallel to surface 44 and having a portion of the edge surface thereof uncovered by encapsulation layer 42 at a location within surface 44. Additionally, the embodiment of FIG. 10B includes a hooked portion 75 on the end thereof, which positions end surface 38 below surface 44 within encapsulation layer 42. This can provide a more robust structure for end 36 that is less likely to become dislodged from within encapsulation layer 42. FIGS. 10C and 10D show structures that are, respectively, similar to those shown in FIGS. 10A and 10B, but are uncovered by encapsulation layer 42 at a location along surface 44 by cavities 64 formed in encapsulation layer 42. These cavities can be similar in structure to those discussed above with respect to FIGS. 8A and 8B. The inclusion of ends 36 including a portion 74 thereof that extends parallel to surface 44 can provide increased surface area for connection therewith by virtue of the elongated uncovered edge surface 75. The length of such a portion 74 can be greater than the width of cross-section of the wire used to form wire bond 32.
FIGS. 11-15 show a microelectronic assembly 10 in various steps of a fabrication method thereof. FIG. 11 shows microelectronic assembly 10′ at a step where microelectronic element 22 has been electrically and mechanically connected to substrate 12 on first surface 14 and within first region 18, thereof. Microelectronic element 22 is shown in FIG. 11 as being mounted on substrate 12 in a flip-chip arrangement by solder masses 26. Alternatively face-up bonding, could be used instead, as seen above in FIG. 1. In the embodiment of the method step shown in FIG. 11, a dielectric underfill layer 66 may be provided between microelectronic element 22 and substrate 12.
FIG. 12 shows microelectronic assembly 10′′ having wire bonds 32 applied on pads 30 of conductive elements 28 exposed on first surface 14 of substrate 12. 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 cut or otherwise 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.
In FIG. 13 encapsulation layer 42 has been added to microelectronic assembly 10′′′ by being applied over first surface 14 of substrate, extending upwardly therefrom and along edge surfaces 37 of wire bonds 32. Encapsulation layer 42 also covers underfill layer 66. Encapsulation layer 42 can be formed by depositing a resin over microelectronic assembly 10′ shown in FIG. 12. This can be done by placing assembly 10′ in an appropriately configured mold having a cavity in the desired shape of the encapsulation layer 42 that can receive assembly 10′. Such a mold and the method of forming a 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 or cavities 64 can be formed that uncover end surfaces 38 at a location within surface 63.
In the embodiment shown in FIG. 13, encapsulation layer is 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 38 can be removed, exposing a new surface 44′ that is substantially flush with end surfaces 42, as shown in FIG. 14. Alternatively, cavities 64, such as those shown in FIGS. 8A and 8B can be formed in which end surfaces 38 are uncovered by encapsulation layer 42. In a further alternative, encapsulation layer 42 can be formed such that surface 44 is already substantially flush with end surfaces 48 or such that surface 44 is positioned below end surfaces 48, as shown in FIG. 8D. 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. If desired, cavities 64 can also be formed after such a step, or stud bumps, as shown in FIG. 10 can also be applied. The resulting microelectronic assembly 10 can then be affixed on a PCB or otherwise incorporated in a further assembly, for example a stacked package, as shown in FIG. 6.
In an alternative embodiment shown in FIG. 15, wire bonds 32 are initially formed in pairs as portions 32′ of a wire loop 86. In this embodiment, loop 86 is made in the form of a wire bond as discussed above. The wire segment is drawn upward, then bent and drawn in a direction having at least a component thereof in the direction of the first surface 14 of substrate 13 and to a position substantially overlying an adjacent conductive element 28. The wire is then drawn substantially downward to a position near the adjacent conductive element 28 before being cut or otherwise severed. The wire is then heated and connected to the adjacent conductive element 28 by deposition bonding or the like to form loop 86. Encapsulation layer 42 is then formed so as to substantially cover loop 86. A portion of encapsulation layer is then removed by grinding, etching or the like by a process that also removes a portion of loop 86 such that the loop is severed and divided into its two portions 32′, thereby forming wire bonds 32 with end surfaces 38 uncovered by encapsulation layer 42 at a location along surface 44 which is formed on encapsulation layer 42. Subsequent finishing steps can then be applied to assembly 10, as discussed above.
FIGS. 16A-16C show steps in an alternative embodiment for making cavities 64, as discussed above, surrounding ends 36 of wire bonds 32. FIG. 16A shows a wire bond 32, of the general type discussed above with respect to FIGS. 1-6. Wire bond 32 has a mass of sacrificial material 78 applied on end 36 thereof. The sacrificial material mass 78 can be substantially spherical in shape, which can result from the material's surface tension during formation thereof, or other desired shapes that would be understood by a person of ordinary skill in the art. Sacrificial material mass 78 can be formed by dipping the ends 36 of wire bonds 32 in solder paste to coat the ends thereof. The viscosity of the solder paste can be adjusted prior to dipping to control the amount of solder mass that wicking and surface tension cause to adhere to ends 36. This can, accordingly, affect the size of masses 78 that are applied on ends 36. Alternatively, masses can be formed by depositing a soluble material onto the ends 36 of the wire bonds 32. Other possible masses 78 can be individual solder balls or other masses on ends or by other means using other materials, such as copper or gold flashing, used in microelectronic component fabrication, that can later be removed.
In FIG. 16B, a dielectric layer 42 is shown having been added to assembly 10, including upward along edge surfaces 37 of wire bonds 32. The dielectric layer also extends along a portion of the surface of the sacrificial material mass 78, such that it is spaced apart from the end 36 of the wire bond 32 thereby. Subsequently, sacrificial material mass 78 is removed, such as by washing or rinsing in a solvent, melting, chemical etching or other technique, leaving cavity 68 in dielectric layer 42 substantially in the negative shape of mass 78 before removal thereof, and exposing a portion of edge surface 37 near end 36 of wire bond 32.
Alternatively, sacrificial material mass 78 can be formed to coat substantially all of wire bond 32 by extending along the edge surface 37 thereof. This arrangement is shown in FIG. 17A. Such a coating can be applied over wire bonds 32 after formation on assembly 10, as discussed above, or can be applied as a coating to the wire used to make wire bonds 32. This would, essentially, be in the form or a coated wire or a two-part wire, for example, with an inner core of copper and a solder coating. FIG. 17B shows dielectric layer 42 applied over wire bonds 32 and the sacrificial mass 78 so as to extend along the edge surface 79 of the sacrificial mass 78, thereby spacing apart dielectric layer 42 from wire bond 32 substantially along the length thereof.
FIG. 17C shows the structure that results from removing a portion of the sacrificial material mass 78 to form cavity 64 around end 36 and exposing a portion of edge surface 37. In such an embodiment a majority of, or at least a portion of, the sacrificial material mass 78 can be left in place between dielectric layer 42 and wire bond 32. FIG. 17C further shows a solder mass 52 electrically and mechanically connecting wire bond 32 to a contact pad 40A of another microelectronic structure 10A.
FIGS. 20 and 21 show a further embodiment of a microelectronic assembly 510 in which wire bonds 532 are formed on a lead-frame structure. Examples of lead frame structures are shown and described in U.S. Pat. Nos. 7,176,506 and 6,765,287 the disclosures of which are hereby incorporated by reference herein. In general, a lead frame is a structure formed from a sheet of conductive metal, such as copper, that is patterned into segments including a plurality of leads and can further include a paddle, and a frame. The frame is used to secure the leads and the paddle, if used, during fabrication of the assembly. In an embodiment, a microelectronic element, such as a die or chip, can be joined face-up to the paddle and electrically connected to the leads using wire bonds. Alternatively, the microelectronic element can be mounted directly onto the leads, which can extend under the microelectronic element. In such an embodiment, contacts on the microelectronic element can be electrically connected to respective leads by solder balls or the like. The leads can then be used to form electrical connections to various other conductive structures for carrying an electronic signal potential to and from the microelectronic element. When the assembly of the structure is complete, which can include forming an encapsulation layer thereover, temporary elements of the frame can be removed from the leads and paddle of the lead frame, so as to form individual leads. For purposes of this disclosure, the individual leads 513 and the paddle 515 are considered to be segmented portions of what, collectively, forms a substrate 512 that includes conductive elements 528 in portions that are integrally formed therewith. Further, in this embodiment, paddle 515 is considered to be within first region 518 of substrate 512, and leads 513 are considered to be within second region 520. Wire bonds 524, which are also shown in the elevation view of FIG. 21, connect microelectronic element 22, which is carried on paddle 515, to conductive elements 528 of leads 515. Wire bonds 532 can be further joined at bases 534 thereof to additional conductive elements 528 on leads 515. Encapsulation layer 542 is formed onto assembly 510 leaving ends 538 of wire bonds 532 uncovered at locations within surface 544. Wire bonds 532 can have additional or alternative portions thereof uncovered by encapsulation layer 542 in structures that correspond to those described with respect to the other embodiments herein.
FIGS. 24-26 show a further alternative embodiment of a microelectronic package 810 having closed-loop wire bonds 832. The wire bonds 832 of this embodiment include two bases 834a and 834b that can be joined to adjacent conductive elements 828a and 828b, as shown in FIG. 24. Alternatively, the bases 834a,834b can both be joined on a common conductive element 828, as shown in FIGS. 25 and 26. In such an embodiment, wire bonds 832 define an edge surface 837 that extends between the two bases 834a,834b in a loop such that the edge surface 837 extends upward in respective portions 837a and 837b from the bases to an apex 839 at a surface 844 of the encapsulation layer 842 above the substrate 812. Encapsulation layer 842 extends along at least some of edge surface portions 837a,837b, separating the respective portions from one another, as well as from other wire bonds 832 in package 810. At apex 839, at least a portion of the edge surface 837 is uncovered by the encapsulation layer 842, such that the wire bond 832 is available for electrical interconnection with another component, which can be another microelectronic component or other component, e.g., a discrete element such as a capacitor or inductor. As shown in FIGS. 24-26, wire bonds 832 are formed such that apex 839 is offset from conductive element 828 in at least one lateral direction across the surface of the substrate 812. In one example, apex 839 can overlie a major surface of microelectronic element 820 or otherwise overlie a first region of the substrate 812 with which the microelectronic element 820 is aligned. Other configurations for wire bonds 832 are possible, including configurations in which apex 839 is positioned in any of the locations of the end surfaces of the wire bonds discussed in the other embodiments. Further, apex 839 can be uncovered within a hole, such as shown in FIG. 8A. Still further, apex 839 can be elongated and can be uncovered on surface 844 extending over a length thereof, as shown with respect to the edge surfaces in FIGS. 10A-10D. By providing a connection feature in the form of the uncovered edge surface 837 surrounding apex 839 that is supported a wire bond 832 extending between two bases 834a,834b, rather than one, more accurate placement of the connection feature in the directions defined by major surface 844 can be achieved.
FIGS. 27 and 28 show a variation of the embodiment of in FIGS. 24-26, in which bond ribbons 934 are used in place of wire bonds 834. Bond ribbons can be a generally flat piece of conductive material, such as any of the materials discussed previously for the formation of wire bonds. A bond ribbon structure can be wider than it is thick, in contrast to a wire bond, which can be generally circular in cross section. As shown in FIG. 27, bond ribbons 934 each include a first base 934a that can be bonded extending along a portion of conductive element 928. A second base 934b of ribbon bond 932 can be joined to a portion of first base 934a. Edge surface 937 extends between bases 934a and 934b in two corresponding portions 937a and 937b to apex 939. A portion of edge surface in the area of apex 939 is uncovered by encapsulant 942 along a portion of major surface 944, thereof. Further variations are possible, such as those described with respect to the wire bonds used in the other embodiments disclosed herein.
The structures discussed above can be utilized in construction of diverse electronic systems. For example, a system 711 in accordance with a further embodiment of the invention includes microelectronic assembly 710, as described above, in conjunction with other electronic components 713 and 715. In the example depicted, component 713 is a semiconductor chip whereas component 715 is a display screen, but any other components can be used. Of course, although only two additional components are depicted in FIG. 23 for clarity of illustration, the system may include any number of such components. The microelectronic assembly 710 as described above may be, for example, a microelectronic assembly as discussed above in connection with FIG. 1, or a structure incorporating plural microelectronic assemblies as discussed with reference to FIG. 6. Assembly 710 can further include any one of the embodiments described in FIGS. 2-22. In a further variant, multiple variations may be provided, and any number of such structures may be used.
Microelectronic assembly 710 and components 713 and 715 are mounted in a common housing 719, 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 717 such as a flexible printed circuit board, and the circuit panel includes numerous conductors 721, of which only one is depicted in FIG. 23, interconnecting the components with one another. However, this is merely exemplary; any suitable structure for making electrical connections can be used.
The housing 719 is depicted as a portable housing of the type usable, for example, in a cellular telephone or personal digital assistant, and screen 715 is exposed at the surface of the housing. Where microelectronic assembly 710 includes a light-sensitive element such as an imaging chip, a lens 723 or other optical device also may be provided for routing light to the structure. Again, the simplified system shown in FIG. 23 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 microelectronic package comprising:
a substrate having a first region and a second region, the substrate having a first surface and a second surface remote from the first surface;
at least one microelectronic element overlying the first surface within the first region;
first electrically conductive elements exposed at at least one of the first surface and the second surface of the substrate within the second region, at least some of the first conductive elements being electrically connected to the at least one microelectronic element;
wire bonds having bases joined to respective ones of the first conductive elements, and end surfaces remote from the substrate and remote from the bases, each wire bond defining an edge surface extending between the base and the end surface thereof;
a dielectric encapsulation layer extending from at least one of the first or second surfaces and filling spaces between the wire bonds such that the wire bonds are separated from one another by the encapsulation layer, the encapsulation layer overlying at least the second region of the substrate, wherein 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; and
a plurality of second conductive elements each electrically coupled with a respective first electrically conductive element through the wire bond joined to the respective first electrically conductive element.

2. The microelectronic package of claim 1, wherein the wire bonds serve as conductive elements.

3. The microelectronic package of claim 1, wherein at least a portion of the edge surfaces respectively of the wire bonds between the bases and the end surfaces thereof extend over the at least one microelectronic element, and
wherein the ones of the first conductive elements to which the bases of the wire bonds are joined are arranged in a first array of a first configuration having a first pitch and the end surfaces of the wire bonds are arranged in a second array of a second configuration having a second pitch, the first pitch being different than the second pitch.

4. The microelectronic package of claim 1, wherein at least a portion of at least one of the wire bonds is coated with a conductive material.

5. The microelectronic package of claim 1, wherein the encapsulation layer has a cavity formed therein extending from a surface of the encapsulation layer toward the substrate, and wherein the unencapsulated portion of one of the wire bonds is disposed within the cavity and a conductive material in the cavity coats at least a portion of the unencapsulated portion of the one of the wire bonds.

6. The microelectronic package of claim 1, wherein the second conductive elements comprise a plurality of stud bumps joined to the end surfaces of at least some of the first wire bonds.

7. The microelectronic package of claim 1, wherein the first surface of the substrate extends in first and second lateral directions, each lateral direction being transverse to a direction of a thickness of the substrate between the first and second surfaces, and the unencapsulated portion of at least one of the wire bonds is displaced in at least one of the lateral directions from the conductive element to which the at least one wire bond is joined.

8. The microelectronic package of claim 1, wherein the encapsulation layer includes a major surface at a first distance from the first surface of the substrate and a recessed surface at a second distance from first surface of the substrate that is less than the first distance, and wherein the unencapsulated portion of at least one of the wire bonds is uncovered by the encapsulation layer at the recessed surface.

9. The microelectronic package of claim 1, wherein at least one of the wire bonds defines a longitudinal axis along a length thereof, and wherein each wire bond includes an inner layer of a first material extending along the longitudinal axis and an outer layer of a second material remote from the longitudinal axis and having a length extending in a lengthwise direction of such wire bond.

10. The microelectronic package of claim 1, further comprising an oxidation protection layer contacting at least some of the unencapsulated portions of the wire bonds.

11. The microelectronic package of claim 3, wherein the second pitch is finer than the first pitch.

12. The microelectronic package of claim 4, wherein the conductive material is solder.

13. The microelectronic package of claim 4, wherein the solder extends above and around the end surface, and along at least a portion of the edge surface, of the at least one of the wire bonds.

14. The microelectronic package of claim 4, wherein the conductive material separates the at least a portion of the at least one wire bond from the dielectric encapsulation layer.

15. A microelectronic package comprising:
a substrate having a first region and a second region, the substrate having a first surface and a second surface remote from the first surface;
at least one microelectronic element overlying the first surface within the first region;
first electrically conductive elements exposed at at least one of the first surface and the second surface of the substrate within the second region, at least some of the first conductive elements being electrically connected to the at least one microelectronic element;
wire bonds having bases joined to respective ones of the first conductive elements, and end surfaces remote from the substrate and remote from the bases, each wire bond defining an edge surface extending between the base and the end surface thereof; and
a plurality of second conductive elements each electrically coupled with a respective first electrically conductive element through the wire bond joined to the respective first electrically conductive element.

16. The microelectronic package of claim 15, wherein at least the end surface of at least one of the wire bonds is coated with solder.

17. The microelectronic package of claim 15, wherein at least a portion of the edge surface of at least one of the wire bonds is coated with solder.

18. An imaging assembly comprising:
a substrate having a first region and a second region, the substrate having a first surface and a second surface remote from the first surface;
at least one microelectronic element overlying the first surface within the first region, the at least one microelectronic element having a third surface and a fourth surface remote from the third surface, the third surface confronting the first surface;
an optical device for routing light overlying the fourth surface of the at least one microelectronic electronic;
first electrically conductive elements exposed at at least one of the first surface and the second surface of the substrate within the second region, at least some of the first conductive elements being electrically connected with the at least one microelectronic element;
wire bonds having bases joined to respective ones of the first conductive elements, and end surfaces remote from the substrate and remote from the bases, each wire bond defining an edge surface extending between the base and the end surface thereof;
a dielectric encapsulation layer extending from at least one of the first or second surfaces and filling spaces between the wire bonds such that the wire bonds are separated from one another by the encapsulation layer, the encapsulation layer overlying at least the second region of the substrate, wherein 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; and
a plurality of second conductive elements electrically coupled with the first electrically conductive elements.

19. The imaging assembly of claim 18, wherein the at least one microelectronic element includes conductive contacts at the third surface, and
wherein at least second ones of the first conductive elements at the first surface of the substrate are electrically connected with at least some of the conductive contacts of the at least one microelectronic element through conductive masses, respectively.

20. The imaging assembly of claim 18 further comprising:
a light sensitive element.