BANNOCKBURN, IL – A new quantitative test methodology helps determine how much strain packages can take before reliability degradation.

“Spherical bend puts the most stress on a ball grid array’s corner interconnects,” said Aileen Allen, a reliability engineer at Hewlett-Packard and member of the IPC 6-10d SMT Attachment Reliability Test Methods Task Group that led the effort to develop the standard. “The aim of this test methodology is to impose the worst-case bend mode that the package may see in the field and to determine strain limits that envelope any bend modes that could be seen during manufacturing, assembly or test.”

The test methodology calls for eight points of contact arranged in a circular pattern. A PCA with a single BGA in the center of the printed board is placed component side down onto the support pins, and load is applied on the backside of the BGA.

Strain gages are placed adjacent to the component per the recommended gage placement. The PCA is deflected to strain levels of interest, and failure analysis is performed to determine the degree of damage induced by flexing to these strain levels. An iterative approach is used to determine the strain at which no damage is incurred, which is the strain limit.

“These strain limits can then be used in the field to reduce reliability risk by ensuring strain on products do not exceed these limits,” added Allen.

The new method is part of IPC/Jedec-9707, Spherical Bend Test Method for Characterization of Board Level Interconnects.

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