Authored By:
Mumtaz Y. Bora
Peregrine Semiconductor
Summary
The growth of portable and wireless products is driving the miniaturization of packages resulting in the development of many types of thin form factor packages and cost effective assembly processes. Wire bonded packages using conventional copper lead frame have been used in industry for quite some time. However, the demand for consumer electronics is driving the need for flip chip interconnects as these packages shorten the signals, reduce inductance and improve functionality as compared to the wire bonded packages. The flip chip packages have solder bumps as interconnects instead of wire bonds and typically use an interposer or organic substrate instead of a metal lead frame.
The integration of these packages in high volume SMT assembly demands good assembly process controls at the package level and clear understanding of the failure modes to minimize defect escape to subsequent assembly operations. This challenge is enhanced with the transition to lead free reflow as the higher peak reflow temperatures results in more thermal and CTE mismatch between package and PWB.
The paper provides a general overview of typical defects and failure modes seen in package assembly and reviews the efforts needed to understand new failure modes during package assembly. The root cause evaluations and lessons learned as the factory transitioned to thin form factor packages are shared.
Conclusions
Wire bonded and flip chip bumped interconnects are a reliable form of interconnect if bond parameters, reflow process, mold material sets, substrate pads and solder mask are optimized. Successful assembly and reliability of these packages can be achieved with careful understanding of failure modes, clear ,concise documentation, training and teamwork with subcontract facilities.
Initially Published in the IPC Proceedings
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