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UNDERCUT CONTROL OF BUMPS IN TAPE AUTOMATED BONDING (TAB)

IP.com Disclosure Number: IPCOM000005642D
Original Publication Date: 1987-Oct-01
Included in the Prior Art Database: 2001-Oct-23
Document File: 1 page(s) / 63K

Publishing Venue

Motorola

Related People

George F. Carney: AUTHOR [+3]

Abstract

A process of plating bumps to control undercut in TAB processing is described. The problems addressed here are two fold. Primarily, there is a physical problem caused by undercutting TAB bumps during processing in that the attachment of the bump to the surface is weakened A secondary problem is the re-sputtering of the titanium-tungsten/titanium-tungsten-nitride (TiWITiWN,) barrier layer on to the bump during reactive ion etching.

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MOTOROLA Technical Developments Volume 7 October 1987

UNDERCUT CONTROL OF BUMPS IN TAPE AUTOMATED BONDING (TAB)

by George F. Carney, Douglas G. Mitchell and Ronald M. Lahti

   A process of plating bumps to control undercut in TAB processing is described. The problems addressed here are two fold. Primarily, there is a physical problem caused by undercutting TAB bumps during processing in that the attachment of the bump to the surface is weakened A secondary problem is the re-sputtering of the titanium-tungsten/titanium-tungsten-nitride (TiWITiWN,) barrier layer on to the bump during reactive ion etching.

   The cause of the former problem comes from the use of wet etching. Wet etching is an oxidation reduction reaction which will inherently cause undercut due to galvanic cell potentials in gold bimetal systems. As shown in accompanying Figure 1, a gold TAB bump is shown secured to a substrate by a titanium-tungstenltitanium- tungsten-nitride (TiWITiWN,) barrier layer under a layer of sputtered gold. A portion of the TAB process in- cludes a metallization removal step. As shown in Figure 1, the gold bump is being undercut because of the lateral etching of the sputtered gold layer at the barrier layer. This results from the tendency of gold to etch faster laterally and to galvanic cell potentials between the sputtered gold and the barrier layer.

   In order to eliminate this problem, a method was developed to encapsulate the bumps prior to metalliza- tion removal. As sho...