Authored By:
Tae-Kyu Lee, Mohan Nagar, Gnyaneshwar Ramakrishna,
Adnan Mahmud, Cesar Escobar, David Chan
Cisco Systems
CA, USA
Summary
Recent developments in high performance electronic devices require miniaturized but more complex configuration with higher power and higher functionality, consequently, an increasing number of interconnects are needed in a given size substrate and with the complexity, a package needs an increase in body size, which poses a constant challenge to the board assembly process due to the increase of the package warpage. The equally challenging process is the heatsink attachment, which need higher level of compression load to achieve a full contact at the already high coplanarity package, inducing a higher level of localized compression load per component and ultimately per solder joint.
In this study, an attempt to identify the maximum quantitative allowable compression load per solder ball in a large component configuration with 600μm in solder ball diameter is investigated. Knowing the maximum compression load, which does not induce any potential degradation to the performance and stability of the solder joint is an important data point to assure a reliable heatsink attachment process. A series of solder ball compression tests are performed and the damage accumulation per solder ball loading conditions are evaluated.
The correlation between compression load level, distribution of the compression load, and the damage accumulation are compared in a series of cross section analyses using optical polarized imaging and Electron–backscattered diffraction (EBSD) imaging. The analysis revealed the potential range of allowable compression load per solder ball and ultimately the maximum allowable compression load per component.
Conclusions
An approach to identify the maximum allowable compression load per large component were proposed and performed. Knowing the maximum compression load, which does not induce any potential degradation to the performance and stability of the solder joint, is an important parameter to assure a reliable heatsink attachment process. A series of solder ball compression tests are performed and the damage accumulation per solder ball loading conditions were evaluated. The correlation between compression load level, distribution of the compression load, and the damage accumulation are compared in a series of cross section analyses using optical polarized imaging and Electron–backscattered diffraction (EBSD) imaging.
The maximum compression load per single SAC305 solder ball was identified as 150gf with 30 second duration and 100gf considering the sub-grain microstructure development after applying thermal cycling. But the derived allowable maximum compression load per component cannot be simply derived with multiplying the allowable maximum load per single solder ball by the solder ball numbers. To get to the realistic condition embedded compression load condition, the distribution of the actual experienced load per solder balls need to be considered.
The study presented here has additional and various consideration factors, which need to implement for an accurate and final quantitative maximum load per component, but the first step and identification of the allowable maximum compression load per solder ball provides a direction towards a valid assessment methodology and baseline.
Initially Published in the SMTA Proceedings
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