Flip Chip and Underfills
While Flip Chip Ball Grid Array (FCBGA) has been used in consumer products, its use in automotive underhoods with unusually high temperatures and extensive thermal excursions is new. The degradation of material properties and their influence on the reliability of semiconductor packaging architectures is not well understood. Owing to the variations in the thermal expansion coefficient between the organic substrate and the die in thermal cycling, bumps can be subjected to shear strains. The underfill encapsulation between the substrate and die is used to provide greater mechanical support to the solder bumps and reduce plastic work during thermal excursions. FCBGAs are high I/O packages in which the robustness of the underfill is required over the operational life to prevent premature failure of the flip-chip solder interconnects.
Underfills are thermoset mechanical supportive materials used in the overall enhancement of Flip Chip (FC) and Chip-Scale Packages (CSP), which include applications in high end workstations, high performance CPUs, mobile phones (with 5G), AI technologies, SiP packages, microwave technological applications, and many other end user appliances. In addition to linking the chip to the substrate, underfill materials also provide mechanical protection to the solder bumps and a considerable improvement in solder fatigue resistance. During temperature instability, underfill provides uniformly spread and shortened solder ball strains life of a factor near or more than 10. Underfill material also serves as a barrier to the chip from outside influences such as moisture, radiation, shock, and vibration.
Area-Leader
Dr. Jeffrey Suhling (Research Leader)
Objectives
- Develop a Fundamental Understanding of the Influence of Package Design, Manufacturing, and Materials on the Reliability of Flip Chip Packaging in Harsh Environments
-- Flip Chip on Laminate
-- Flip Chip BGA packaging
-- CSP (e.g., Redistributed Die, UltraCSP, etc.) - Measure and Predict the Reliability of Flip Chip Packaging
-- Flip Chip on Laminate in Thermal Cycling and High Humidity Environments
-- High End Microprocessor Packaging - Study Next Generation Materials
-- Nano-Structured Underfills
-- High reliability substrates (e.g., STABLCOR)
-- Thermal Interface Materials
-- Chip-Level Interconnects - Develop a Detailed Understanding of Underfill Behavior and Properties
-- Material Behavior (Stress-Strain and Creep)
-- Interfacial Adhesion and Failure Criteria
-- Effects of Aging and Moisture Exposure
Posters
- Microstructural Characterization of Viscoelastic Properties of Underfills Exposed to High Temperature - Madhu Kasturi (ME)
- Effect of High Temperature Aging at the PCB-Underfill Interfaces under Three-Point Bend Load - Padmanava Choudhury (ME), Pradeep Lall (ME)
- Effect of Long-Term Isothermal Exposure on Underfill Material Properties - Madhu Kasturi (ME), Haotian Wu (MATL), Pradeep Lall (ME), Ed Davis (MATL)
- Characterization of Viscoelastic Response of Underfill Materials - Promod Chowdhury (ME), Jeffrey Suhling (ME)
- Modeling of Underfilled BGA Assemblies Using Viscoelastic and Elastic Properties - Promod Chowdhury (ME), Jeffrey Suhling (ME)
Representative Recent Publications
Lall, P., M. Kasturi, J. Suhling, and J. Williamson, Modeling of Effect of Underfill Properties on Flip Chip Bumps and Solder Balls of FCBGA Package in Automotive Underhood Applications, in Proceedings of the IEEE Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems, San Diego, CA, pp. 684-691, June 1-4, 2021.
Lall, P., Y. Zhang, M. Kasturi, P. Choudhury, H. Wu, J. Suhling, and E. Davis, Evolution of Viscoelastic Properties and Interface-Fracture Toughness Under Sustained High Temperature Operation Typical of Automotive Underhood for up to 1-year, in Proceedings of the IEEE Electronic Components and Technology Conference, pp. 971-982, June 1-4, 2021.
Lall, P., Y. Zhang, and J. Williamson, Degradation Mechanisms of Epoxy Molding Compound Subjected to High Temperature Long Term Aging, in Proceedings of the IEEE Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems, San Diego, CA, pp. 610-616, June 1-4, 2021.
Lall, P., Dornala, K., Deep, J., Lowe, R., Measurement and Prediction of Interface Crack Growth at the PCB-Epoxy Interface Under High-G Mechanical Shock, Proceedings of the IEEE 2018 Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems, San Diego, CA, pp. 1097-1105, May 29-June 1, 2018.
Nguyen, Q., Roberts, J.C., Suhling, J.C., Jaeger, R.C., Lall, P., A Study on Die Stresses in Flip Chip Package Subjected to Various Hygrothermal Exposures, Proceedings of the IEEE 2018 Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems, San Diego, CA, pp. 1339-1350, May 29-June 1, 2018.
Chen, C., Suhling, J.C., Lall, P., Improved Finite Element Modeling Strategies with Multipoint Constraints for BGA Packages Subjected to Thermal Cycling, Proceedings of the IEEE 2017 Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems, Orlando, FL, pp. 1456-1465, May 30-June 2, 2017.
Lall, P., Dornala, K., Deep, J., Lowe, R., Effectiveness of Potting Methods and Underfills on the Enhancement of Survivability of Fine Pitch Electronics at 25,000g Shock Loads, Proceedings of the IEEE 2017 Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems, Orlando, FL, pp. 1262-1274, May 30-June 2, 2017.
Chowdhury, P.R., Suhling, J.C., Lall, P., Experimental Characterization of Underfill Materials Exposed to Different Moisture Condition, Proceedings of the IEEE 2017 Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems, Orlando, FL, pp. 1-12, May 30-June 2, 2017.
Nguyen, Q., Roberts, J.C., Suhling, J.C., Jaeger, R.C., Lall, P., Characterization of Moisture Induced Die Stresses in Flip Chip Packaging, Proceedings of the IEEE 2016 Electronic Components and Technology Conference, Las Vegas, NV, pp. 789-798, May 31-June 3, 2016.
Roberts, J., Bhat, C., Suhling, J.C., Jaeger, R.C., Lall, P., Reliability of a CBGA Microprocessor Package Incorporating a Decoupling Capacitator Array, Proceedings of the IEEE 2016 Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems, Las Vegas, NV, pp. 278-284, May 31-June 3, 2016.
Lall, P., Dornala, K., Lowe, R., Foley, J., Survivability Assessment of Electronics Subjected to Mechanical Shocks up to 25,000g, Proceedings of the IEEE 2016 Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems, Las Vegas, NV, pp. 507-518, May 31-June 3, 2016.
Lall, P., Dornala, K., Suhling, J., Lowe, R., Foley, J., Life Prediction and RUL Assessment of Fine Pitch Solder Joint Fuze Electronics Under Mechanical Shock Loads Up to 50,000g, Proceedings of the IEEE 2016 Electronic Components and Technology Conference, Las Vegas, NV, pp. 232-243, May 31-June 3, 2016.