Active solid-state devices (e.g. – transistors – solid-state diode – Housing or package – Housing or package filled with solid or liquid electrically...
Reexamination Certificate
2002-05-06
2004-11-30
Lam, Cathy (Department: 1775)
Active solid-state devices (e.g., transistors, solid-state diode
Housing or package
Housing or package filled with solid or liquid electrically...
C257S690000, C257S774000, C257S777000
Reexamination Certificate
active
06825552
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates in general to the field of microelectronic element mounting and connection, and more particularly, to connection components and semiconductor chip packages using anisotropic conductive adhesive material interconnection and to assembly methods therefor.
Microelectronic elements such as semiconductor chips are connected to external circuitry, such as the circuitry of a supporting substrate or circuit panel, through electrical contacts on the front face of the chip. Various processes for making these interconnections use prefabricated arrays of leads or discrete wires. For example, in tape automated bonding processes, a dielectric supporting tape such as a thin film of polyimide, includes an array of metallic leads on one surface of the dielectric film. The metallic leads are aligned with the contacts on the front face of the chip. The dielectric film is juxtaposed with the chip so that the leads extend over the front or contact bearing surface on the chip. The leads are then bonded to the contacts of the chip, as by ultrasonic or thermocompression bonding. The terminals on the dielectric film may then be connected to external circuitry for electrically interconnecting the chip and the external circuitry.
The evolution of the semiconductor art in recent years has created a continued demand for semiconductor chip packages having progressively greater numbers of contacts and leads in a given amount of space. An individual chip may require hundreds or even thousands of contacts, all within the area of the front face of the chip. Certain complex semiconductor chips currently being used have contacts spaced apart from one another at extremely small center-to-center distances. With such closely-spaced contacts the leads connected to the chip contacts must be extremely fine structures, typically having a smaller bonded surface than the contacts onto which they are bonded so that the adjacent leads do not electrically short.
In the bonding process of some assembly methods, the bonding region of each lead is engaged by a bonding tool which bears on the top surface of the lead in the bonding region and forces the lead downwardly into engagement with the contact. Energy supplied through the bonding tool causes the bonding metal to join with the contact. Typically, the leads are bonded to the chip contacts with the bonding tool using heat, force, ultrasonic energy, or a combination of two or more thereof, for a given time period. If incorrect force, heat and/or ultrasonic energy is used, the bond between the leads and the contacts may be too weak to withstand thermal cycling stresses during operation of the chip (heating and cooling cycles during operation). Also, the bonding tool may create areas of the lead which are prone to early fatigue during thermal cycling because of excessive non-uniform deformation in the bonding region, typically causing early breaks in the lead at the point the lead bends up from the chip surface.
In various microelectronic devices, it is also desirable to provide a connection between two components, which can accommodate relative movement between the components. For example, where a semiconductor chip is mounted to a circuit board, thermal expansion and contraction of the chip and circuit board can cause the contacts on the chip to move relative to the corresponding electrically conductive features of the circuit board. This can occur during service and can also occur during manufacturing operations as, for example, during soldering operations on the circuit board.
As illustrated in U.S. Pat. No. 5,518,964 (“the '964 Patent”), the disclosure of which is incorporated herein by reference, movable interconnections between elements such as a semiconductor chip and another element can be provided by first connecting leads between the elements and then moving the elements away from one another through a preselected displacement so as to bend the leads. For example, a connection component may incorporate a dielectric body and leads extending along a bottom surface of the dielectric body. The leads may have first or fixed ends permanently attached to the dielectric element and connected to electrically conductive features such as terminals, traces or the like on the dielectric body. The leads may also have second ends releasably attached to the dielectric body. The dielectric body, with the leads thereon, may be juxtaposed with the chip and the second ends of the leads may be bonded to contacts on the chip.
Following bonding, the dielectric body and chip are moved away from one another, thereby bending the leads towards a vertically extensive disposition. During or after movement, a curable material such as a liquid composition may be introduced between the elements. This may be cured to form a compliant dielectric layer such as an elastomer or gel surrounding the leads. The resulting packaged semiconductor chip has terminals on the dielectric body connection component which are electrically connected to the contacts on the chip but which can move relative to the chip to compensate for thermal effects. The packaged chip may be mounted to a circuit board by solder-bonding the terminals to conductive features on the circuit board. Relative movement between the circuit board and the chip due to thermal effects is taken up in the moveable interconnection provided by the leads and the compliant layer.
There is further disclosed in the '964 Patent a connector for use in making connections between two other microelectronic elements which is fabricated by a generally similar thus far described process. For example, in one embodiment a dielectric body having terminals and leads as discussed above is connected to terminal structures on a temporary sheet. The temporary sheet and dielectric body are moved away from one another so as to bend the leads, and a liquid material is introduced around the leads and cured to form a compliant layer between the temporary sheet and the dielectric body. The temporary sheet is then removed, leaving the tip ends of the terminal structures projecting from a surface of the compliant layer. Such a component may be used, for example, by engaging it between two other components. For example, the terminal structures may be engaged with a semiconductor chip, whereas the terminals on the dielectric body may be engaged with a circuit panel or other microelectronic component. Variation of the above described structures are disclosed in U.S. Pat. No. 6,117,694 (“the '694 Patent”) the disclosure of which is incorporated herein by reference.
In copending U.S. patent application Ser. No. 09/237,072, filed Jan. 25, 1999 and entitled “Compliant Semiconductor Package With Anisotropic Conductive Material Interconnects and Methods Therefor” (“the '072 Application”), the disclosure of which is incorporated herein by reference, there is described a microelectronic package including a first microelectronic element having a front face including a plurality of contacts and a second microelectronic element including terminals accessible at a surface thereof and a plurality of flexible leads. Each of the flexible leads have a terminal end connected to one of the terminals and a tip end opposite the terminal end. Each flexible lead extends away from the second microelectronic element and is electrically interconnected with the plurality of contacts of the first microelectronic element. An anisotropic conductive material is interposed between each of the tip ends of the flexible leads and the contact associated therewith.
There is further described in the '072 Application a method of making a microelectronic package which includes providing a first microelectronic element having a front face including a plurality of contacts. An anisotropic conductive material is provided over each one of the plurality of contacts. A second microelectronic element is provided having terminals accessible at a surface thereof and including a plurality of flexible leads. Each of the leads has a terminal end att
Light David
Tostado Paula Lagattuta
Warner Michael
Lam Cathy
Lerner David Littenberg Krumholz & Mentlik LLP
Tessera Inc.
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