Browse Prior Art Database

Coating Application System

IP.com Disclosure Number: IPCOM000120097D
Original Publication Date: 1991-Mar-01
Included in the Prior Art Database: 2005-Apr-02
Document File: 2 page(s) / 56K

Publishing Venue

IBM

Related People

Yu, C: AUTHOR [+2]

Abstract

The most common failures of electronic assemblies caused by moisture are: 1. Moisture mobilizes ionic contaminants on the surface of the devices causing breakdown of electrical insulation (current leakage) 2. Moisture, in presence of impurity ions, causes electrolytic corrosion.

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This is the abbreviated version, containing approximately 70% of the total text.

Coating Application System

      The most common failures of electronic assemblies caused
by moisture are:
      1.   Moisture mobilizes ionic contaminants on the
           surface of the devices causing breakdown of
           electrical insulation (current leakage)
      2.   Moisture, in presence of impurity ions, causes
           electrolytic corrosion.

      A conformal coating is applied to TAB components to coat the
outer lead bonding area as a moisture barrier that hinders ionic
migration and electrolytic corrosion.  It also prevents
contamination.

      The coating spray has to be critically controlled so that
adjacent component will not be affected.  The current method, which
is spraying directly from a nozzle, is difficult to control due to
material properties and fluid dynamics.  As lead lengths becomes even
shorter, and the component spacing becomes tighter, it will not be
possible to spray coat the desired area (outer lead bonding area
ONLY).

      Disclosed here is a method to better control the coating spray
using a screen which has an opening preset for specific band width
(Fig. 1).  The dimension of the shield screen can be optimized for a
specific application.  The dimensions mentioned here are: opening
size "A" (Fig. 2) and standoff "B" which is the distance between the
shield and the surface of panel (Fig. 1).  Before the conformal
coating application, the shield screen is aligned wi...