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Method for a hybrid solder grid array structure

IP.com Disclosure Number: IPCOM000008823D
Publication Date: 2002-Jul-16
Document File: 3 page(s) / 92K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for a hybrid solder grid array structure. Benefits include improved reliability.

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Method for a hybrid solder grid array structure

Disclosed is a method for a hybrid solder grid array structure. Benefits include improved reliability.

Background

              Vf-BGA solder joint fatigue failure occurs at the component side or the PCB side of the interface due to high shear stress, especially at peripheral solder balls or underneath the die area.

              Conventionally, this issue is resolved by using larger diameter solder balls, which produce higher stand off and larger land pads to produce more contact area. These solutions reduce shear stress at the solder ball interface. However, these approaches limit the size reduction of vf-BGA components.

              Another approach is to use high melting-temperature solder balls with low melting-temperature solder paste at the component and PCB interface. This solution redistributes stress from the component or PCB interface to the high-temperature solder ball interface with low-temperature paste.

General description

      The disclosed method is a hybrid solder grid array structure for reliability enhancement for BGA or vf‑BGA components through selective PCB pad diameter enlargement. The PCB pad pattern should have a 1 or <1 diameter ratio (component pad to PCB pad), while others are >1 or in progressive incremental ratio mode.

              Solder grid array with 1 or > 1 diameter ratio forms a barrel shape structure which acts as stand-off support, while other vf-BGAs with <1 ratio tend to spread out on a larger PCB pad to produce a column-like structure. Full solder-paste coverage on PCB pads is needed to enhance spreading during the reflow process. 

      The key elements of the method include:

·        Same size pad opening on the component side maintains vf-BGA coplanarity.

·        A 1 or >1 pad diameter ratio (component pad diameter to PCB pad diameter) produces a barrel-shaped structure and maintains vf-BGA standoff. 

·        A <1 pad ratio produces a column-shaped structure and...