Patent Application
20080191367
The technical field relates generally to semiconductor packages and, more specifically, to wire bonding techniques.
Semiconductor packages can be found in practically every electronic product manufactured today. As manufacturers strive to decrease the size while expanding the functionality of such products, the need for greater semiconductor package density and reliability increases. As such, wire bonding techniques play an ever-increasing role in the area of electronics manufacturing. Wire bonding is generally considered the most cost-effective and flexible interconnect technology, and is used to assemble the vast majority of semiconductor packages.
A wire bond is a welded electrical interconnection, usually from a semiconductor die to a non-common lead frame or substrate pad. Gold wire is usually used for interconnection techniques, though other wires such as aluminum and copper also have been used.
There are two main wire bonding techniques commonly used today: ball bonding and wedge bonding. Ball bonding is currently the most common method of wire bonding. Almost all modern ball bonding processes use a combination of heat, pressure, and ultrasonic energy to make a weld at each end of the wire. During this process, the end of the bond wire is converted to a ball shape by application of an electronic flame-off. The ball is then positioned just above the bond pad on a substrate or package and connected to the bond pad. An intermetallic bond is created by interdiffusion between the wire materials and the pad metallization.
Wedge bonding involves using ultrasonic energy and pressure to create a bond between the wire and the bond pad. Wedge bonding is generally a low-temperature process that uses frequencies between 20 and 60 kHz for standard applications and 120 kHz for fine pitch applications. This cold-welding process deforms the wire into a flat, elongated wedge shape. The most common method of wedge bonding is wedge-wedge bonding, where both the source bond and the destination bond are formed with wedge geometry.
Other wire bonding methods also can be used. For example, in ball-wedge bonding, the first bond (the source bond) takes a ball shape and the second bond (the destination bond) takes a wedge shape.
Demand for high-performance integrated circuit (IC) design may prompt an increase in the number of input/output (PO) connections, such as bond pads, for a given die. An increased number of I/O connections currently may be achieved by reducing bond pad size, thereby allowing a greater number of bond pads to be formed on a die. Decreased bond pad size, however, necessitates a reduced bonding wire diameter. Also, as packages become finer in structure, package thickness becomes thinner, resulting in increased wire length. Decreasing wire diameter, especially when coupled with increased wire length, presents multiple disadvantages, such as an increase in resistance and inductance in the wire and thus a decrease in IC performance quality.
Another disadvantage of decreasing wire diameter and/or increasing wire length is to exacerbate the effect of wire sweeping during molding. Wire sweeping generally refers to a situation involving a wire moving out of place. To counteract wire sweeping, wire length may be reduced, but reducing wire length increases manufacturing completely because, for example, bonding close to package walls is usually required, which can lead to mechanical interference.
Therefore, despite the advantages of the various developments in semiconductor packaging technology, there remains a need for increased semiconductor package density and reliability.
A semiconductor package can comprise a die coupled to a substrate, the die having multiple bonding areas such as bonding pads. A bonding wire supporting layer, such as a film or epoxy, for example, can be affixed to the top of the die. The bonding wire supporting layer can have a cut-out area to provide clearance for and access to the bonding areas on the die. Multiple bonding wires can be desirably attached to at least some of the bonding areas on the die and also to substrate bonding areas on the substrate. The bonding wires typically can be held in place proximate a first end by the bonding wire supporting layer. In some embodiments, the bonding wires can be held in place proximate a second end by a bond, such as a ball bond. In some embodiments, a bump can be located effectively to strengthen the physical connection of the bonding wire to the bonding area on the substrate. In some exemplary embodiments, multiple dies, each having its own bonding wire supporting layer having at least one appropriate cut-out area, can be stacked on top of each other.
In one exemplary embodiment, a method of making a semiconductor package can comprise providing an integrated circuit chip having a chip bonding area and coupling the integrated circuit chip to a substrate having a substrate bonding area. A bonding wire supporting layer can be provided and attached to the integrated circuit chip. A bonding wire can be attached to the chip bonding area at a first end or portion and to the substrate bonding area at the other end or portion, for example, by ball bonding. The bonding wire can be affixed to the bonding wire supporting layer. In some embodiments, multiple integrated circuit chips, each having its own bonding wire supporting layer, can be stacked on top of each other.
The foregoing and other objects, features, and advantages of the disclosed technologies will become more apparent from the following detailed description, which proceeds with reference to the accompanying figures.
As used in this application and in the claims, the singular forms “a,” “an,” and “the” include the plural forms unless the context clearly dictates otherwise. Additionally, the term “includes” means “comprises.” Further, the term “coupled” generally means electrically, electromagnetically, and/or physically (e.g., mechanically or chemically) coupled or linked and does not exclude the presence of intermediate elements between the coupled items.
Although the operations of exemplary embodiments of the disclosed method may be described in a particular, sequential order for convenient presentation, it should be understood that disclosed embodiments can encompass an order of operations other than the particular, sequential order disclosed. For example, operations described sequentially may in some cases be rearranged or performed concurrently.
Moreover, for the sake of simplicity, the attached figures may not show the various ways (readily discernable, based on this disclosure, by one of ordinary skill in the art) in which the disclosed system, method, and apparatus can be used in combination with other systems, methods, and apparatuses. Additionally, the description sometimes uses terms such as “produce” and “provide” to describe the disclosed method. These terms are high-level abstractions of the actual operations that can be performed. The actual operations that correspond to these terms can vary depending on the particular implementation and are, based on this disclosure, readily discernible by one of ordinary skill in the art.
In other embodiments, a bonding bump may be omitted. A bonding bump may, however, advantageously increase the strength of holding bonding wire 108 in place at the end closest to the substrate 104, thereby further decreasing the chances of wire sweeping and wire breakage.
Various other advantages flow from the disclosed technologies such as the exemplary arrangement of
In some embodiments, one or both of the bonding wire supporting layers 106, 112 are epoxies. In this example, the exemplary bonding wires 108 remain fixably attached to the bonding wire supporting layer 106. In some embodiments, the bonding wires 108 are fixably attached to both bonding wire supporting layers 106, 112. In some embodiments, the die 102 with bonding wire supporting layer 106 is placed on a heat block. Because of the generally high temperature of the heat block (e.g., 150 degrees Celsius) the bonding wire supporting layer 106 can turn into postage (e.g. between liquid and solid) such that the bonding wires 108 can sink to the edge surface of the bonding wire supporting layer 106. The second die 114 with bonding wire supporting layer 112 attached can be attached to the first die 102 with bonding wire supporting layer 106 using, for example, WBL, after which the bonding wires 108 are thus fixably attached to both of the bonding wire supporting layers 106, 112.
The exemplary embodiments of the disclosed system, method, and apparatus should not be construed as limiting in any way. Instead, the present disclosure is directed toward all novel and nonobvious features, aspects, and equivalents of the various disclosed embodiments, alone and in various combinations and sub-combinations with one another. The disclosed technology is not limited to any specific aspect, feature, or combination thereof, nor do the disclosed system, method, and apparatus require that any one or more specific advantages be present or problems be solved. The scope of the invention is defined by the following claims. We therefore claim as our invention all that comes within the scope and spirit of these claims.
