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Browse Prior Art Database

Encapsulant Flow Containment

IP.com Disclosure Number: IPCOM000036047D
Original Publication Date: 1989-Aug-01
Included in the Prior Art Database: 2005-Jan-28
Document File: 3 page(s) / 54K

Publishing Venue

IBM

Related People

Jones, AS: AUTHOR [+3]

Abstract

This article describes methods of preventing the uncontrolled spread of uncured fluid encapsulant when applied to circuit-chips that are wire bonded onto flexible circuits. Use is made of formers to constrain, by surface tension, the wet encapsulant from encroaching onto undesired areas of the circuit layer.

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Encapsulant Flow Containment

This article describes methods of preventing the uncontrolled spread of uncured fluid encapsulant when applied to circuit-chips that are wire bonded onto flexible circuits. Use is made of formers to constrain, by surface tension, the wet encapsulant from encroaching onto undesired areas of the circuit layer.

The formers may or may not remain part of the cured encapsulated circuit.

The formers are typically plastic discs which may or may not be formed into caps and may or may not be provided with central apertures. They may be formed from sheet or produced as mouldings. Central apertures improve self- location, improve tolerance to variation in encapsulant volume, and provide a down-force which aids position retention through handling and curing processes.

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Control by Plates

In Fig. 1 (sectional view), a small controlled amount of encapulant 1 is placed on the chip 2 with bond wires 5, followed or preceded by a plate 3 with a central aperture 4. The plate is so dimensioned that its outer edge approximates to the desired extent of the encapsulation and its aperture approximates to the bond-full area of the chip. The effects of surface tension self-align the plate and constrain encapulant flow to the desired geometry on the substrate 6. The presence of the central aperture provides better self-alignment and tolerance to variations in encapsulant volume than having no aperture. In a typical application, the plate is an 8 mm diameter circular washer with a 5 mm diameter hole, and is made of plastic film, for example, KAPTON* polyimide. Control by Caps

A typical electronic equipment has bare silicon devices bonded through an aperture directly onto an aluminium heatsink laminated to a flexible circuit. The ...