Method of using pre-applied underfill encapsulant

Abstract

The present invention relates to the application of electronic components, most commonly chip-scale packages (CSP's), to substrates utilizing one or more underfill encapsulant compositions, which may be B-staged or preformed. method. One such composition includes a thermoplastic resin system comprising a phenoxy resin, expandable polymer spheres, or a thermosetting composition, optionally including an epoxy resin such as a high molecular weight epoxy resin, a solvent, An imidazole-anhydride catalyst or equivalent effective catalyst, and may optionally include a flux and / or wetting agent. The underfill encapsulant can be B-stageable to provide a smooth and non-tacky coating on the substrate or component. In an alternative embodiment, the underfill sealant is a preformed film. In both embodiments, the expandable filler material expands upon exposure to higher temperatures, forming a closed cell foam structure at the desired location in the assembly. The present invention provides a method of applying an underfill by applying the underfill to a component or substrate, bonding the component and substrate, and heating the assembly sufficiently to cause the expandable thermoplastic or thermosetting composition to become a foam temperature. A second pre-coat underfill composition comprising epoxy resin, anhydride curing agent, and catalyst, either alone or with an expandable underfill, may also be applied. The second composition acts as a pressure sensitive adhesive and can be selectively applied to a portion of the CSP, such as a solder bump. The pressure sensitive adhesive properties of the composition impart sufficient tack to hold the electronic assembly in place during the assembly process.

Description

technical field [0001] The present invention relates to methods of applying underfill encapsulants to electronic devices. Background technique [0002] The present invention relates to a method of applying an underfill sealant compound that contains one or more expandable fillers and / or acts as a pressure sensitive adhesive. Encapsulants are used to protect and strengthen the interconnections between electronic components and substrates in microelectronic devices. Microelectronic devices contain many types of circuit elements, primarily transistors but also resistors, capacitors and other components assembled together in integrated circuit (IC) chips. These electronic components are interconnected to form circuits and are ultimately connected to and supported by a carrier or substrate such as a printed wiring board. An integrated circuit component may include a single bare chip, a single encapsulated chip, or an encapsulated package composed of many chips. A single die ca...

AI Technical Summary

Problems solved by technology

Further, it is often very difficult to uniformly apply conventional underfill materials at the time of manufacture

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