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Mixed Board Pad Size Design Concept for Fine Pitch Flip-Chip Packages

IP.com Disclosure Number: IPCOM000016814D
Publication Date: 2003-Jul-16
Document File: 2 page(s) / 92K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method that uses an innovative fine pitch board design (i.e. equal to, or less than, 1mm ball-pitch) to decrease solder fatigue failure rate. Benefits include increased performance reliability.

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Mixed Board Pad Size Design Concept for Fine Pitch Flip-Chip Packages

Disclosed is a method that uses an innovative fine pitch board design (i.e. equal to, or less than, 1mm ball-pitch) to decrease solder fatigue failure rate. Benefits include increased performance reliability.

Background

Currently, the state of the art uses specific ball pattern designs with sacrificial balls or joints under high risk areas (see Figure 1). Interconnect pitch has been tightened to reduce the total package and board cost, which reduces the package and board form-factor significantly. With the current desktop motherboard capability and cost pressure, the maximum board pad opening size is limited to <18 mils in order to maintain a 4-layer motherboard for cost competitiveness. However, current small board pad opening designs have been evaluated to have high solder fatigue reliability failures.

General Description

The disclosed method is based on preliminary empirical data showing that board pad size is the dominant factor affecting board level solder fatigue. Fatigue stress during temperature cycling conditions is induced by a co-efficient of thermal expansion (CTE) mismatch between component and board. Current technology for 1mm ball-pitch is very marginal due to the constraint of board manufacturing capability and cost pressures. In order for a 4-layer motherboard design to be cost effective, the board pad size opening for a 1mm ball-pitch package is limited to a maximum of 18 mils diameter.

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