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BGA Reballing and Influence on Ball Shear Strength
BGA Reballing and Influence on Ball Shear Strength
This paper focuses on the effect of various parameters that are used to reball a BGA component and their effect on the overall shear strength.
Analysis Lab

Authored By:
S. Manian Ramkumar Ph.D.
Andrew J. Daya, Daniel B. Lewanda
Center for Electronics Manufacturing and Assembly
Rochester Institute of Technology, Rochester, New York

Scott Rushia
Martin Rework Systems
Manchester, New Hampshire
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Transcript
As more components are becoming lead free and not available in the tin lead alloy, there is an industry wide interest when it comes to the reballing and the subsequent effects it has on the strength of those components.

This is particularly true for legacy parts needed for military applications some of which use tin lead solder. There is cause for concern due to the potential mixing of alloys and the differences in reflow temperatures of the two different alloys.

Additionally, there are unknown characteristics regarding the intermetallics that are formed due to the potential of mixed alloys. This paper focuses on the effect of various parameters that are used to reball a BGA and their effect on the overall shear strength.

Factors looked at include the type of BGA, the alloy used to reball, the type of flux used (Water Soluble or No Clean), and the environment in which reballing takes place (Nitrogen or Ambient).

Being most relevant to industry demands, the focus was on the effects of reworking a BGA with a base alloy of SAC305 and reballing it with 63Sn/37Pb.   After the reballing of the component, samples will be both shear tested and cross sectioned as a method of evaluation.

The shear tests determine the strength of the newly formed solder balls while the cross sections allow for the observation of the solder ball and the bonding characteristics of the new solder alloy to the pad on the BGA.

The cross sections allow for observation of any defects or abnormalities through the reballing process. The goal was to determine the optimal factors that should be used in the creation of a robust process for BGA reballing.

So what were the conclusions?

The overall experiment was successful in reballing SAC components with 63Sn/37Pb and vice versa which show similar shear strengths from the baseline values. Reballing a BGA may take more time for operators, but can save in scrap and shelved inventory.

The ability to rework components which maintain their original characteristics is a huge advantage for this industry. There was an overall increase in shear strength from the baseline for both BGA components reballed with SAC405 and 63Sn/37Pb alloys.

63Sn/37Pb showed higher shear strength than SAC405 on average. From the experiment setup and observations in cross sectional analysis, it was observed that the shear failure occurred on the ball, and not at the intermetallic.

The interaction between the BGA type and the solder alloy to be reballed had a significant effect on the overall shear strength. And overall water soluble flux showed higher shear strength over no clean flux.
Summary
As more components are becoming lead free and not available in the tin lead alloy, there is an industry wide interest when it comes to the reballing and the subsequent effects it has on the strength of those components.

This is particularly true for legacy parts needed for military applications some of which use tin lead solder.

There is cause for concern due to the potential mixing of alloys and the differences in reflow temperatures of the two different alloys.

Additionally, there are unknown characteristics regarding the intermetallics that are formed due to the potential of mixed alloys.

This paper focuses on the effect of various parameters that are used to reball a BGA and their effect on the overall shear strength.

Factors looked at include the type of BGA, the alloy used to reball, the type of flux used (Water Soluble or No Clean), and the environment in which reballing takes place (Nitrogen or Ambient).

Being most relevant to industry demands, the focus was on the effects of reworking a BGA with a base alloy of SAC305 and reballing it with 63Sn/37Pb.

After the reballing of the component, samples will be both shear tested and cross sectioned as a method of evaluation.

The shear tests determine the strength of the newly formed solder balls while the cross sections allow for the observation of the solder ball and the bonding characteristics of the new solder alloy to the pad on the BGA.

The cross sections allow for observation of any defects or abnormalities through the reballing process.

The goal was to determine the optimal factors that should be used in the creation of a robust process for BGA reballing.
Conclusions
The overall experiment was successful in reballing SAC components with 63Sn/37Pb and vice versa which show similar shear strengths from the baseline values.

Reballing a BGA may take more time for operators, but can save in scrap and shelved inventory.

The ability to rework components which maintain their original characteristics is a huge advantage for this industry.

There was an overall increase in shear strength from the baseline for both BGA components reballed with SAC405 and 63Sn/37Pb alloys.

63Sn/37Pb showed higher shear strength than SAC405 on average.

From the experiment setup and observations in cross sectional analysis, it was observed that the shear failure occurred on the ball, and not at the intermetallic.

The interaction between the BGA type and the solder alloy to be reballed had a significant effect on the overall shear strength.

And overall water soluble flux showed higher shear strength over no clean flux.

Initially Published in the IPC Proceedings
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