Patent Application
20120318853
The present invention relates generally to wire bonding systems, and more particularly to a heater block for a wire bonding system.
Wire bonding systems typically are used to electrically connect an integrated circuit die to a chip carrier such as a lead frame using wires. Such systems include a heater block to heat the integrated circuit die and the lead frame to a temperature suitable for bonding.
Typically, the heater block is formed of a single piece of metal that supports the lead frame or chip carrier. During wire bonding, the entire lead frame surface is exposed to high temperatures, e.g., about 200° C., which leads to oxidation of copper elements of the lead frame. The oxidation typically initiates from a center runner of the lead frame adjacent to the heater element and propagates to the inner leads. Such excessive oxidation can be the cause of poor bonds between the wires and the leads of the lead frame.
Thus, there is a need for a wire bonding system that facilitates wire bonding but does not cause or reduces oxidation of the lead frame.
The present invention is illustrated by way of example and is not limited by the accompanying figures, in which like references indicate similar elements. Elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the thicknesses of layers and regions may be exaggerated for clarity.
Detailed illustrative embodiments of the present invention are disclosed herein. However, specific structural and functional details disclosed herein are merely representative for purposes of describing example embodiments of the present invention. The present invention may be embodied in many alternate forms and should not be construed as limited to only the embodiments set forth herein. Further, the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments of the invention.
As used herein, the singular forms “a,” “an,” and “the,” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It further will be understood that the terms “comprises,” “comprising,” “includes,” and/or “including,” specify the presence of stated features, steps, or components, but do not preclude the presence or addition of one or more other features, steps, or components.
It also should be noted that in some alternative implementations, the functions/acts noted may occur out of the order noted in the figures. For example, two figures shown in succession may in fact be executed substantially concurrently or may sometimes be executed in the reverse order, depending upon the functionality/acts involved.
In one embodiment, the present invention provides a heater block for a wire bonding system. The heater block includes a mounting base configured to receive a lead frame. A semiconductor die is mounted on the lead frame. A heating structure is removably coupled to a top surface of the mounting base. The heating structure includes a central heating surface and side heating panels surrounding the central heating surface. The heating structure selectively heats wire bonding areas of the lead frame.
In another embodiment, the present invention provides a method of wire bonding a semiconductor die to a lead frame. The method includes mounting the semiconductor die to the lead frame. The lead frame and the mounted semiconductor die are placed on a mounting base of a heater block of a wire bonding system. Wire bonding areas of the lead frame are selectively heated with a heating structure of the heater block and die pads of the semiconductor die are wire bonded to leads of the lead frame using bond wires.
Referring now to
The wire bonding station 16 includes a heater block 20 to facilitate wire bonding of a semiconductor die 22 to a lead frame 24. The heater block 20 includes a mounting base 26 configured to receive the lead frame 24, which has the semiconductor die 22 mounted on the lead frame 24. The heater block 20 also includes a heating structure 28 removably coupled to a top surface of the mounting base 26. The heating structure 28 is configured to selectively heat wire bonding areas of the lead frame 24.
The receiving unit 14 receives the lead frames on which wire bonding at the wire bonding station 16 has been completed. An automated transport mechanism may be used to move the lead frame assemblies (lead frames, dies wire bonded thereto) from the wire bonding station 16 to the receiving unit 14, such as guide rails 30. The wire bonding station 16 includes other components such as a capillary 32, integrated heating elements and so forth.
The heating structure 28 includes a central heating surface 50 and side heating panels 52 surrounding the central heating surface 50 to selectively heat wire bonding areas of a lead frame supported on the mounting base 26. The central heating surface 50 and the side heating panels 52 are formed of a thermally conductive material. In one exemplary embodiment, the central heating surface 50 and the side heating panels are formed of corrosion resistant steel, such as Corrax®, which is available from Uddenholms AKTiebolag of Sweden.
The semiconductor die 22 is mounted on the die flag 62 of the lead frame 24 using a die attach adhesive 68 such as epoxy. The lead frame 24 and attached semiconductor die 22 are mounted on the mounting base 26. Then, only the die flag 62 on the central heating area 50 and portions of the lead fingers 64 resting on the side heating panels 52 are heated. Heating is done with heater elements placed under the heater block 20. While it is also possible to place heating element inside the heater block 20, this method is not preferred because it complicates the heater block design and increases cost. The lead frame 24 then undergoes selective heating. Subsequently, the bonding pads of the semiconductor die 22 are electrically connected to the lead fingers 64 of the lead frame 24 using bond wires 74 via a wire bonding process. The wires 74 are formed from a conductive material such as aluminium or gold.
The present invention allows for selective heating of the wire bonding areas using the heating structure 28 while other parts of the lead frame 24 are isolated from the heating block, which reduces oxidation of the lead frame 24.
The present invention, as described above, allows for selective heating of wire bonding areas of the lead frame thereby reducing the energy requirements of the wire bonding system. Moreover, the non-functional areas of the lead frame are isolated from the heating areas thereby making the packages less susceptible to delamination issues and enhancing the reliability of such packages.
The technique employs attaching a heating structure attached to an insulative mounting base of the heater block. The heating structure includes a central heating surface and side heating panels configured to selectively heat the wire bonding areas of the lead frame while isolating the other areas of the lead frame from the heat source.
By now it should be appreciated that there has been provided an wire bonding system and a method of wire bonding a semiconductor die to a lead frame. Although the invention has been described using relative terms such as “front,” “back,” “top,” “bottom,” “over,” “under” and the like in the description and in the claims, such terms are used for descriptive purposes and not necessarily for describing permanent relative positions. It is understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the invention described herein are, for example, capable of operation in other orientations than those illustrated or otherwise described herein.
The use of introductory phrases such as “at least one” and “one or more” in the claims should not be construed to imply that the introduction of another claim element by the indefinite articles “a” or “an” limits any particular claim containing such introduced claim element to inventions containing only one such element, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an.” The same holds true for the use of definite articles.
Although the invention is described herein with reference to specific embodiments, various modifications and changes can be made without departing from the scope of the present invention as set forth in the claims below. Accordingly, the specification and figures are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of the present invention. Any benefits, advantages, or solutions to problems that are described herein with regard to specific embodiments are not intended to be construed as a critical, required, or essential feature or element of any or all the claims.
