Microelectronic unit forming methods and materials

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Reexamination Certificate

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C435S004000, C435S283100

Reexamination Certificate

active

06361959

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to microelectronic packaging and more particularly relates to methods of making connectors and packaged microelectronic components. In various microelectronic devices, it is 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 certain preferred embodiments of U.S. Pat. No. 5,518,964 (“the '964 patent”) 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 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. During or after movement, a curable material such as a liquid composition is introduced between the elements. This is 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 so as to compensate for thermal effects. For example, 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.
Numerous variations of these processes and structures are disclosed in the '964 patent. For example, the package-forming process can be conducted on a wafer scale, so that the numerous semiconductor chips in a unitary wafer are connected to connection components in one sequence of operations. The resulting packaged wafer is then severed so as to provide individual units, each including one or more of the chips and portions of the dielectric body associated therewith. Also, the leads may be formed on the chip or wafer rather than on the dielectric body. In further embodiments, also disclosed in the '964 patent, a connector for use in making connections between two other microelectronic elements is fabricated by a generally similar 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 so as 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. Thus, the broad invention taught in the '964 patent offers numerous desirable ways of making electrical interconnections and connectors.
Additional variations and improvements of the processes taught in the '964 patent are disclosed in commonly assigned U.S. Pat. Nos. 5,578,286; 5,830,782; and 5,688,716 and in copending, commonly assigned U.S. patent application Ser. No. 08/690,532, filed Jul. 31, 1996 and Ser. No. 09/271,688, filed Mar. 18, 1999, the disclosures of which are hereby incorporated by reference herein.
SUMMARY OF THE INVENTION
The present application is directed to specific embodiments of the '964 patent process and certain embodiments thereof.
One aspect of the invention provides methods of making a microelectronic assemblies. The methods in accordance with this aspect of the invention desirably include a the steps of providing leads physically connected to a bottom surface of a support, each said lead having a tip end and a terminal end and engaging the support with a microelectronic element as, for example, a chip, a wafer or an assemblage of plural discrete chips, having contacts thereon so that the tip ends of the leads are aligned with the contacts of the microelectronic element. The methods further include bonding the tip ends of the leads to the contacts; and then after such bonding, selectively degrading the connection between the support and the leads at and adjacent the tip ends thereof so as to free the tip ends from the support and leave the terminal ends secured to the support. Preferably, the methods include the further step of moving the support and microelectronic element through a predetermined displacement away from one another after degrading the connection between the tip ends and the support so as to deform said leads towards a vertically-extensive disposition. Optionally, the connection between the terminal ends of the leads and the support may be degraded after the moving step, so as to free the support and allow removal of the support. A flowable material may be introduced around the leads during or after the movement step to form a dielectric layer surrounding said leads.
Where the material connecting the tip ends to the support is radiation-sensitive, the step of selectively degrading the connection may include selectively applying radiation through said support at and adjacent to the tip ends of the leads. Thus, in methods according to this aspect of the invention, there is no need to fabricate precise mechanical features such as frangible connections to hold the leads in place until they can be bonded to the microelectronic element. Instead, the tip ends of the leads are constrained reliably until such constraint is released by selective degradation of the connecting layer.
A related aspect of the invention provides methods of connecting a plurality of leads to one or more microelectronic elements. Methods according to this aspect of the invention desirably include the steps of providing the leads physically connected to a support by a connecting material so that said leads are maintained in position on the support at least partially by the connecting material; juxtaposing the support with the microelectronic element so that the leads are aligned with contacts on the microelectronic element and bonding the leads to the contacts of the microelectronic element. After the bonding step, the connection between the leads and the support is released by degrading the connecting material. The step of degrading the connecting material may include directing radiant energy through the support onto said connecting material. Preferably, the leads are flexible after they are released from the support. As further explained below, certain methods according to this aspect of the invention provide for conversion of constrained, inflexible leads to a flexible state simply by releasing the leads from the support, with or without a further step such as bending the leads.
A further aspect of the invention provid

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