Browse Prior Art Database

Low Stress Tapecoat Structure

IP.com Disclosure Number: IPCOM000109468D
Original Publication Date: 1992-Aug-01
Included in the Prior Art Database: 2005-Mar-24
Document File: 1 page(s) / 55K

Publishing Venue

IBM

Related People

Horton, RR: AUTHOR [+3]

Abstract

A major concern in TAB and similar flex interconnections is dendrite formation between leads when an electrolyte and an electric field is present between any two adjacent leads. To avoid this situation, a preferred approach is to use flexcoating; that is, the deposition of a polymeric material over the flex. This coating prevents electrolytes from getting between the leads and prevents dendrite formation. The coating thickens the flex, making it less compliant and does have adverse effects in fatigue properties, causing fatigue fracture much earlier in life than uncoated parts.

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Low Stress Tapecoat Structure

      A major concern in TAB and similar flex interconnections is
dendrite formation between leads when an electrolyte and an electric
field is present between any two adjacent leads.  To avoid this
situation, a preferred approach is to use flexcoating; that is, the
deposition of a polymeric material over the flex.  This coating
prevents electrolytes from getting between the leads and prevents
dendrite formation.  The coating thickens the flex, making it less
compliant and does have adverse effects in fatigue properties,
causing fatigue fracture much earlier in life than uncoated parts.

      This invention envisions a structure where flexcoat is applied
only between leads that have a constant DC potential difference (such
as power and ground).  Since most of the signal lines switch polarity
regularly, dendrite formation between these lines will take much
longer compared to that in a constant potential field.  Thus, they
need not be protected.  On the other hand, the stiffness of the flex
and the total force applied to the end leads is a linear function of
the flexcoat volume.  Therefore, the total stress will decrease in
proportion to the uncoated areas on the flex.  The stress reduction
will be substantial if only one coats between power and ground leads.
Alternately, one can coat every other line and protect the entire
wiring from dendrite formation:  total stiffening and stress will be
significantly minimized.  These stru...