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Browse Prior Art Database

High Fatigue Life Leads for Thin Film Circuitry

IP.com Disclosure Number: IPCOM000110380D
Original Publication Date: 1992-Nov-01
Included in the Prior Art Database: 2005-Mar-25
Document File: 2 page(s) / 76K

Publishing Venue

IBM

Related People

Coteus, PW: AUTHOR

Abstract

Lead breaks in TAB inner lead bonds due to material fatigue from thermally induced cyclic strains have been observed. Disclosed is a redesigned shape of the TAB inner lead, which significantly reduces material strain.

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This is the abbreviated version, containing approximately 52% of the total text.

High Fatigue Life Leads for Thin Film Circuitry

       Lead breaks in TAB inner lead bonds due to material
fatigue from thermally induced cyclic strains have been observed.
Disclosed is a redesigned shape of the TAB inner lead, which
significantly reduces material strain.

      It is well know that fatigue life is related to cyclic strain.
A typical relation is Nf = A(1/e)b  where Nf is the mean number of
cycles to failure, e is the cyclic strain, and A and b are positive
constants.  In Fig. 1a we show a typical rectangular lead of length
l, thickness t, and width w.  We also show a tapered lead (Fig. 1b),
where the width is a function of distance (x) from the lead end.  For
the first 3/4 of the length, the width changes parabolically as w(x)
= wo ! x/1, and then returns smoothly to a constant width w = wo/2.

      For the case of a simple cantilever fixed at one end and
subjected to a maximum displacement wy, the maximum fiber strain for
the beam of Fig. 1a is em = 1.5wyw/12.  The maximum strain occurs at
the outer surface of the lead, at the location of the fixed point.
This is the location where lead breaks originate.  For the lead Fig.
1b, the maximum strain is also at the fixed lead edge but is now
constant everywhere along the tapered surface, and is equal to sm =
wywo/12, or 2/3 of the maximum fiber strain of lead 1a.  Since the
strain is constant everywhere, it is the minimum strain that can be
obtained subject to the constraint that wo is a constant.

      The case of one end fixed and the o...