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Method for a hybrid solder ball pattern on BGA packages for solder-joint reliability improvement and process window expansion

IP.com Disclosure Number: IPCOM000009498D
Publication Date: 2002-Aug-28
Document File: 6 page(s) / 387K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for a hybrid solder ball pattern on ball-grid array (BGA) packages for solder-joint reliability improvement and process window expansion. Benefits include improved reliability.

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Method for a hybrid solder ball pattern on BGA packages for solder-joint reliability improvement and process window expansion

Disclosed is a method for a hybrid solder ball pattern on ball-grid array (BGA) packages for solder-joint reliability improvement and process window expansion. Benefits include improved reliability.

Background

              The BGA solder-joint reliability issue due to fatigue failure (see Figure 1) at die shadow and brittle fracture (see Figure 2) at package corners is problematic, as in a 1-mm flip-chip ball-grid array (FCBGA1).

              Conventionally, the solution is to maintain a keep-out-zone (KOZ, see Figure 3) area at the high-reliability risk area (die shadow and package corners). No critical-to-function (CTF) solder ball is designed for these areas. No CTF ball maintains an optimum package solder resist opening (SRO) to board pad size ratio (see Figure 4) while tightening the PCB margin at the specification of +/-2.3 mil.

              Conventional reflow conditions include a peak temperature of less than 225°C.

General description

              The disclosed method is the combination of 10Sn90Pb and 63Sn37Pb eutectic balls in a hybrid ball pattern to utilize the unique characteristics of each respective type of eutectic ball. The ball pattern is designed so that the 4 package diagonals and 4 package corners are replaced with 10Sn90Pb from the current type of eutectic solder ball, 63Sn37Pb.

              The 10Sn90Pb solder balls increase the standoff of the solder joint. The solder’s ductile characteristic helps to improve the solder joint strength that contributing to a solution to fatigue and brittle fracture. Despite 10Sn90Pb solder balls, the majority of solder balls are maintained with 63Sb37Pb to provide good package self-alignment and less package coplanarity.

              The key elements of the method include:

•             BGA packages on multiple pitches and package sizes

•             Combination of 10Sn90Pb and 63Sn37Pb eutectic ball at different ball pitches

•             Location of 10Sn90Pb balls at diagonal and package corners

Advantages

              The disclosed method provides advantages, including:

·        Improved reliability due to designing hybrid ball pattern of 2 eutectic types solder ball on BGA packages so that the unique characteristic of each type of solder ball compliment each other

·        Improved performance due to the use of a high temperature material that does not collapse under conventional reflow conditions, absorbing stresses on the solder ball at the package corners.

·        Improved performance due to the use of 63Sb37Pb, which melts in the reflow soldering, helping to provide good package self-alignment and solder joint collapse, making the package less coplanarity sensitive

·        Improved performance due to higher I/O count and smaller ball pitch

·        Improved cost saving due to higher...