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|Package Reliability Challenges in Cavity-Down Thermally Enhanced Packages Containing Low-k Dies|
|Keywords: Low k, reliability, Packaging|
|The cavity-down thermally enhanced package such as Tape Ball Grid Array (TBGA) has the best thermal performance among the wire bonded packages because the silicon is attached directly onto a thick internal heat spreader. However, the TBGA package structure generates challenges in passing industrial-level package qualification requirement, especially for temperature cycling test under JEDEC condition C (-65/150C) for packages containing low-k silicon. Low-k interlayer dielectric (ILD) material usually has the dielectric constant k of less than 3. 3D finite element model simulations were performed to analyze the stress distribution in the low-k die area when the structural parameters in the cavity-down package structure were modulated. The simulation result explained as to why the TBGA package is more susceptible to failures in temperature cycling tests. Additionally, mechanical analyses were performed to identify the weakest adhesion interface within the stack of the back-end-of-line (BEOL) in the low-k die. The theoretical explanation was validated with experimental data. Corrective actions on how to handle low-k silicon in the TBGA package will be discussed.|
|Chu-Chung Lee, Principle Staff Engineer
Freescale Semicondcutor Inc.