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Method for a hybrid second-level solder system to improve solder-joint reliability

IP.com Disclosure Number: IPCOM000012712D
Publication Date: 2003-May-21
Document File: 4 page(s) / 53K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for a hybrid second-level solder system to improve solder-joint reliability. Benefits include improved reliability.

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Method for a hybrid second-level solder system to improve solder-joint reliability

Disclosed is a method for a hybrid second-level solder system to improve solder-joint reliability. Benefits include improved reliability.

Background

        � � � � � Temperature cycling reliability testing indicates that solder joint reliability must be improved for eutectic solder balls that are attached using a flux-only system. Test results with a eutectic solder ball attached onto a DIG surface finish indicate a 68% failure rate at 1250X reliability.

        � � � � � No conventional solution for this problem exists. A work around has been developed for determining the reliability limit of the conventional method and certifying product(s) that meet the reliability limit.

        � � � � � Conventionally, the second-level solder system is component-to-board attachment using eutectic solder balls for leaded products or lead-free solder balls for lead-free products. A eutectic solder ball is typically attached to the component using a flux system. The second level solder-ball system can be an electroless nickel immersion gold (ENIG, see Figure 1A) or a direct immersion gold (DIG, see Figure 1B) surface finish. Location A is a eutectic solder ball. Location C is solder resist. Location E is the Cu pad. Location F is dielectric material.

        � � � � � For the ENIG system, location B does not exhibit any sharp or high stress concentration due to the presence of Ni plating. Location D is the nickel-plating layer. An Sn-Ni intermetallic is formed where the eutectic solder meets the Ni plating layer.

        � � � � � For the DIG system, location B does exhibit a high-stress concentration area. Location D is where Cu-Sn intermetallic is formed. The thin gold layer is dissolved into the solder system during reflow.

Description

        � � � � � The disclosed method a hybrid second-level solder system to improve solder-joint reliability. Lead-free solder paste is used to attach a eutectic solder ball to a substrate with a dire...