Semiconductor device manufacturing: process – Packaging or treatment of packaged semiconductor – Encapsulating
Reexamination Certificate
2000-11-22
2003-08-05
Cuneo, Kamand (Department: 2829)
Semiconductor device manufacturing: process
Packaging or treatment of packaged semiconductor
Encapsulating
C438S106000
Reexamination Certificate
active
06602740
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to art of making electronic devices and more specifically relates to methods of encapsulating microelectronic assemblies.
2. Description of the Related Art
When making microelectronic assemblies, such as semiconductor chip packages, it has been found desirable to provide an encapsulant between and/or around the different components of the microelectronic assemblies. It is theorized that using an encapsulant minimizes strain and stress on the electrical connections between the microelectronic assemblies and supporting circuitized substrates during operation of the assemblies. An encapsulant may also seal the components of the microelectronic assemblies against corrosion, as well as insure intimate contact between the encapsulant and the other elements of the microelectronic assembly.
Microelectronic assemblies such as semiconductor chip packages are typically encapsulated using curable liquid compositions. Such liquid compositions frequently cure upon exposure to elevated temperatures or light.
When encapsulating microelectronic assemblies, the liquid composition is generally dispensed or injected around or into the assembly. In many instances, a fixture is placed around the microelectronic assembly prior to dispensing the liquid composition. The fixture generally serves as a dam that ensures that the dispensed liquid composition flows around and between the components of the microelectronic assembly. After the liquid composition has been dispensed, the fixture may be placed in an oven to cure the liquid composition. Once the composition is cured, the fixture is removed from the oven and the one or more microelectronic assemblies are removed from the fixture. In order to improve the rate at which the microelectronic assemblies are manufactured, it may be desirable to remove encapsulated assemblies from the fixture before the curing step in order to increase the number of fixtures available for use on other batches of microelectronic assemblies.
Methods of using curable liquid compositions to encapsulate microelectronic assemblies are described in certain preferred embodiments of commonly assigned U.S. Pat. No. 5,659,652; U.S. Pat. No. 5,766,987; U.S. Pat. No. 5,776,796; U.S. patent application Ser. No. 09/067,698, filed Apr. 28, 1998; and U.S. patent application Ser. No. 08/610,610, filed Mar. 7, 1997, the disclosures of which are hereby incorporated by reference herein. Certain preferred embodiments of the above-identified patents and patent applications describe methods of making microelectronic assemblies including a semiconductor chip and a flexible dielectric sheet having terminals and flexible leads connected to the terminals. During assembly, contacts on the chip are electrically interconnected to terminals on the dielectric sheet by attaching tip ends of the leads to the chip contacts. In certain preferred embodiments, the electrical interconnection is made using flexible, electrically conductive leads having first or tip ends attached to chip contacts and second ends connected with terminals of the dielectric sheet. The assembly may also include a compliant layer such as a cured elastomer or gel disposed between the dielectric sheet and the chip to mechanically decouple the terminals of the sheet from the chip. As disclosed in certain preferred embodiments of the aforementioned patents and patent applications, such compliant layers can be made by providing a porous layer, such as a plurality of compliant pads, between the chip and the dielectric sheet, electrically connecting the terminals to contacts on the chip using conductive leads and then encapsulating the resulting assembly with a curable liquid composition so that the liquid composition penetrates through the porous layer and around the leads. Upon curing, the composition provides a compliant layer between the chip and the dielectric sheet. When making microelectronic assemblies of this nature, it is desirable to ensure that the encapsulant completely fills the porous layer, to provide a substantially void-free compliant layer in the final assembly.
There are many preferred methods for introducing and curing a curable liquid composition in microelectronic assemblies. For example, in certain preferred embodiments of the above-identified '987 patent, one or more cover layers may be applied over the top and bottom surfaces of one or more microelectronic assemblies, each assembly including at least one semiconductor chip electrically interconnected to at least a portion of a dielectric sheet. Typically, several microelectronic assemblies are provided in a side-by-side arrangement so that a single top cover layer overlies the top surfaces of the chips and a bottom cover layer underlies the bottom surface of the dielectric sheet. The top and bottom cover layers and the microelectronic assemblies may then be placed in a fixture. The top and bottom cover layers define a space therebetween. A vacuum is desirably drawn in the space between the top and bottom cover layers to remove air from the enclosed space and to ensure that the outside pressure is greater than the pressure between the cover layers. The fixture is then tilted so that a curable liquid encapsulant stored in a pocket of the fixture is able to flow into the space between the cover layers. The curable liquid composition is then cured while the microelectronic assemblies and cover layers remain in place in the fixture.
As described in certain preferred embodiments of commonly assigned U.S. Pat. No. 5,659,952, the disclosure of which is hereby incorporated by reference herein, and the aforementioned U.S. Pat. No. 5,776,796, the encapsulant may be applied using a needle or syringe that is positioned around the periphery of each microelectronic assembly. The needle, desirably connected to an encapsulant dispenser, is moved around the peripheries of the individual microelectronic assemblies so that the encapsulant flows into the space between each chip and a dielectric sheet. A cover layer may be used to close any bond windows in the dielectric sheet during this process. In other preferred embodiments for encapsulating microelectronic assemblies, as described in U.S. patent application Ser. No. 08/975,590 filed on Nov. 20, 1997, the disclosure of which is hereby incorporated by reference herein, the encapsulant dispensing operation is conducted inside a chamber, while the microelectronic assembly is under vacuum. When the vacuum is released, and the chamber is brought to atmospheric or superatmospheric pressure, the pressure forces the encapsulant into the porous layer between the chip and the dielectric sheet. Further, as described in U.S. patent application Ser. No. 09/012,590, filed Jan. 23, 1998, the disclosure of which is also incorporated by reference herein, it is convenient to use a frame to hold the dielectric sheet during the assembly procedures. The frame enables an operator to handle the dielectric sheet without directly contacting the portions of the sheet that comprise part of the final assembly. For example, while the dielectric sheet is mounted on the frame, an array of compliant pads used to form the porous layer may be applied to the dielectric sheet, the chips may be attached to the pads, and the terminals of the dielectric sheet may be electrically interconnected with the chips using flexible leads.
In spite of the above-mentioned advances in the art, there remains a need for improved methods for encapsulating microelectronic assemblies.
SUMMARY OF THE INVENTION
The present invention provides methods of encapsulating one or more microelectronic assemblies and is specifically directed to encapsulating microelectronic assemblies mounted to a substrate, such as a printed circuit board. In one preferred embodiment, the method includes providing a substrate having a top surface and securing at least one microelectronic assembly over the top surface of a substrate. A dam is provided over the top surface of the substrate, the dam surrounding the at least one mi
Cuneo Kamand
Geyer Scott B.
Lerner David Littenberg Krumholz & Mentlik LLP
Tessera Inc.
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