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A New LGA/BGA Socket Design of Different Sizes of Solder balls

IP.com Disclosure Number: IPCOM000210451D
Publication Date: 2011-Sep-06
Document File: 4 page(s) / 329K

Publishing Venue

The IP.com Prior Art Database

Abstract

Our disclosure proposes a plurality of variably-sized solder balls to achieve solder ball coplanarity. The characterization of our disclosure is in the provision of a plurality of variably-sized solder balls over the bottom surface of the substrate or LGA/BGA Socket, each solder ball having a specific size predetermined in accordance with premeasured package warpage or socket body warpage. Solder-ball pads and solder mask openings (for BGA package) are fixed-size.

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A New LGA/BGA Socket Design of Different Sizes of Solder balls

Introduction

HNP (Head and Pillow) is an open issue after SMT reflow. A head and pillow joint is composed of two metallurgically distinct masses formed from BGA ball and reflowed solder paste with incomplete or no coalescence (wetting).

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HNP could become more and more easily to occur after the conduction of Pb-free process and large size BGA (like SIP, PoP package). Also HNP failure is usually very difficult to be detected after assembly and relevant electronic tests, because sometimes it doesn't cause electronic open immediately but has a great potential to open in the future.

Problem Identification
The diagram below is a simplified modal of SKT's change at SMT reflow zone. During reflow, outer balls become molten and shrink, while inner balls still remains solid state, so inner balls support the whole socket. Meanwhile, outer balls are pulled up from solder paste because of SKT's dynamic warpage. The bigger the temperature delta between inner balls and outer balls, the longer the outer balls is suspended above solder paste before inner balls are collapsed. During the suspension time of outer balls, not only outer balls can easily get oxidized, but also flux in solder paste will be consumed.

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HNP Formatio...