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Residual stress mapping of epoxy molding compound in a ball grid array microelectronic package using a fluorescent
Naoki Muraki1, Nobuhiro Matoba, Takayuki Hirano
1Material Science Laboratory, Toray Research Center, Inc., Sonoyama 3-3-7, Otsu-shi, Shiga 520-8567, Japan. naoki_muraki@trc.toray.co.jp
Applied Spectroscopy
|December 5, 2006
Summary
Residual stress in semiconductor molding can be accurately measured using fluorescence piezo-spectroscopy with embedded alumina sensors. This technique reveals higher stress concentrations than finite element method calculations, indicating potential delamination issues.
Area of Science:
- Materials Science
- Solid Mechanics
- Semiconductor Manufacturing
Background:
- Thermal residual stresses during semiconductor molding can impair device performance and reliability.
- Accurate assessment of these stresses is crucial for microelectronic device evaluation.
- Existing methods may lack microscopic resolution or accuracy.
Purpose of the Study:
- To apply fluorescence piezo-spectroscopy for microscopic residual stress assessment in semiconductor encapsulants.
- To investigate the stress transfer from molding compound to embedded fluorescent sensors.
- To compare experimental stress measurements with finite element method (FEM) calculations.
Main Methods:
- Embedding a low fraction of alumina powder as a fluorescent sensor into a silica/epoxy molding compound.
- Utilizing the shift in the Cr3+ fluorescence spectrum of alumina to monitor residual stress.
- Generating two-dimensional residual stress maps near the silicon chip edge.
- Comparing experimental data with linear FEM calculations.
Main Results:
- Fluorescence piezo-spectroscopy successfully mapped residual stresses at a microscopic level.
- Strong stress concentrations were observed in the molding compound near the chip edge.
- Experimental stress values were consistently higher than FEM predictions.
- Discrepancies were attributed to local delamination at the chip edge.
Conclusions:
- Fluorescence piezo-spectroscopy is a viable technique for micro-scale residual stress analysis in electronic packaging.
- The study highlights the importance of considering delamination in stress modeling.
- Alumina-based sensors provide reliable stress monitoring in molding compounds.
