Microscale Reliability

A free application note describing how IMEC uses Optimus to perform thermo-mechanical optimization of electronic packages

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Finite element modeling is widely used for estimating the solder joint reliability of electronic packages. In this application note, the electronic package is a silicon Chip Scale Package (CSP) mounted on a Printed Circuit Board (PCB) using solder interconnections. Two analyses are performed. In the first one, three shape parameters of the solder joint are investigated and optimized to maximize reliability. In the second one, six parameters are considered in a Monte Carlo analysis and the most sensitive ones are identified. The presented results are based on work conducted at IMEC, Europe’s leading

The problem

Due to the large Coefficient of Thermal Expansion (CTE) mismatch between the chip and the PCB, stresses and strains are induced in the solder joint when the structure is subjected to internal and environmental temperature changes. After a number of temperature cycles, fatigue cracks propagate. Finally, a complete rupture of the solder joint occurs, resulting in an electrical disconnection. This phenomenon is called a ‘thermal fatigue failure’, and is analyzed with MSC Marc in order to characterize the stress/strains induced in electronic assemblies due to thermo-mechanical loads.

Solution approach

The simulation workflow is captured using the Optimus graphical user interface. This workflow includes the MSC Marc & MSC Marc Mentat software, as well as the related input and output files. The engineer selects the input parameters and responses which are required for optimization, from the automatically generated parameter list. Optimus parameterizes the input file and parses the output file for the desired combination of output parameters, allowing for an automated execution of the engineering workflow.

Optimus successfully optimizes the shape design of a solder joint in order to increase the reliability of the Chip Scale Package. Using Monte Carlo analysis techniques, Optimus identifies substrate pad diameter and solder volume as the most influential parameters on CSP reliability.


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