The Woodruff School

SUMMARY

The transition from traditional through-hole assembly to surface mount assembly is a significant step in the evolution of electronic packaging. Surface mount devices (SMDs), such as flip chip packages and ball grid array (BGA) packages are gaining more and more popularity in microelectronics industry. However, in flip chip packages and BGA packages, the solder bumps are sandwiched between the component and the substrate, making them no longer visible for usual visual inspection. Current non-destructive techniques for inspecting solder bumps like electrical testing, X-ray inspection, and acoustic inspection are suitable for specific inspection tasks, however, they do not necessarily encompass all the capabilities required for evaluating the quality of solder bump interconnections in industry. The non-destructive inspection system under development aims to provide a solution that can overcome some of the limitations of current non-destructive inspection techniques. This proposed inspection system is based on laser ultrasonic and interferometric techniques. This system uses a pulsed Nd:YAG laser to induce ultrasound in the chip packages in the thermoelastic regime; it then measures the transient out-of-plane displacement response on the package surfaces using a laser interferometer. The quality of the solder bumps can be evaluated by analyzing the out-of-plane displacement. Previous work in this area has shown the potential of using this laser ultrasonic-interferometric inspection system. However, there are still some research issues that need to be addressed before the system will be ready for industrial use. The main objectives in this proposed research include: 1) Develop a new signal-processing method for analyzing the transient out-of-plane displacement signals without the requirement of a known-good reference chip. 2) Expand the application scope of this inspection system on the 2nd level solder bump interconnects in BGA packages and construct a specific pass/fail threshold with statistic significance to separate the defective and defect-free chips. 3) Study thermo-mechanical reliability of solder bumps in BGA package under thermal cycling using the laser ultrasound inspection system and finite element method (FEM). The achievements of the proposed research objectives will enable the developed system to inspect a variety of packaged electronic devices with improved performance and flexibility.

SUBJECT:	Ph.D. Proposal Presentation

BY:	Jie Gong

TIME:	Friday, March 1, 2013, 2:00 p.m.

PLACE:	MARC Building, 431

TITLE:	Quality Assessments of Solder Bump Interconnections in Ball Grid Array Packages Using Laser Ultrasonics and Laser Interferometer

COMMITTEE:	Dr.Charles Ume, Chair (ME) Dr. Suresh K. Sitaraman (ME) Dr. Aldo A Ferri (ME) Dr. Jennifer Michaels (ECE) Dr. Jianjun Shi (IsyE) Dr. Kola Akinade (Cisco) Dr. Jaydeep Sinha (KLA-Tencor)

SUMMARY The transition from traditional through-hole assembly to surface mount assembly is a significant step in the evolution of electronic packaging. Surface mount devices (SMDs), such as flip chip packages and ball grid array (BGA) packages are gaining more and more popularity in microelectronics industry. However, in flip chip packages and BGA packages, the solder bumps are sandwiched between the component and the substrate, making them no longer visible for usual visual inspection. Current non-destructive techniques for inspecting solder bumps like electrical testing, X-ray inspection, and acoustic inspection are suitable for specific inspection tasks, however, they do not necessarily encompass all the capabilities required for evaluating the quality of solder bump interconnections in industry. The non-destructive inspection system under development aims to provide a solution that can overcome some of the limitations of current non-destructive inspection techniques. This proposed inspection system is based on laser ultrasonic and interferometric techniques. This system uses a pulsed Nd:YAG laser to induce ultrasound in the chip packages in the thermoelastic regime; it then measures the transient out-of-plane displacement response on the package surfaces using a laser interferometer. The quality of the solder bumps can be evaluated by analyzing the out-of-plane displacement. Previous work in this area has shown the potential of using this laser ultrasonic-interferometric inspection system. However, there are still some research issues that need to be addressed before the system will be ready for industrial use. The main objectives in this proposed research include: 1) Develop a new signal-processing method for analyzing the transient out-of-plane displacement signals without the requirement of a known-good reference chip. 2) Expand the application scope of this inspection system on the 2nd level solder bump interconnects in BGA packages and construct a specific pass/fail threshold with statistic significance to separate the defective and defect-free chips. 3) Study thermo-mechanical reliability of solder bumps in BGA package under thermal cycling using the laser ultrasound inspection system and finite element method (FEM). The achievements of the proposed research objectives will enable the developed system to inspect a variety of packaged electronic devices with improved performance and flexibility.