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Method for bond pads over redistribution layers for wire bonding

IP.com Disclosure Number: IPCOM000010073D
Publication Date: 2002-Oct-16
Document File: 3 page(s) / 36K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for bond pads over redistribution layers (RDLs) for wire bonding (WB). Benefits include improved reliability.

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Method for bond pads over redistribution layers for wire bonding

Disclosed is a method for bond pads over redistribution layers (RDLs) for wire bonding (WB). Benefits include improved reliability.

Background

� � � � � Conventional bond pads have problems with pad peeling during wire bonding and/or pad peeling during wire pulling, resulting in not meeting packaging requirements. Conventional solutions to this problem include:

•        � � � � Soldering thick Au-plated Cu disks (4-18 µm) to a thin metal bond pad to produce a rigid platform for bonding

•        � � � � On top of the plated Cu disks, add a thick layer of Ni (~3-8 µm) and overplate it with ~1‑µm Au

•        � � � � 0.5 µm or thicker Ti, Ti/W under layer

        � � � � � RDLs can be used to reroute bond pads for WB-to-WB applications. One of the approaches is to put bond pads on the very top of the redistribution layers. RDLs are comprised of one or more layers of soft materials, such as benzocyclobutene (BCB) and polyimide (PI). Bond pads conventionally designed for a rigid subpad surface (such as oxynitride on top of silicon) do not lend themselves to successful wire bonding.

        � � � � � RDL technology is comprised of commercially available flip-chip applications. However, the technology for wire-bond application is still under development. One of the major technical challenges is the wire bonding over RDL, such as benzocyclobutene (BCB) or polyimide (PI), with redistributing metal traces between the passivation layers. A PI passivation layer is typically placed on the wafer before redistribution layers are added to the surface. The exact number of add-on passivation layers (such as BCB) depends on the number of redistribution trace layers and whether the first layer in contact with the wafer is a metal trace or add-on passivation. However, all the passivation layers form a relatively soft integral layer on top of which the bond pads are placed.

        � � � � � The soft layer does not provide a solid support for the bond pad against wire bonding action and potentially leads to poor wire bonding. For example, the pad could be peeled off during wire bonding...