BACKGROUND:  It is possible to use laser generated stress waves to measure the tensile strength of interfaces such as those between a coating and a substrate. However, these known laser spallation techniques are limited to planar interfaces, and are not suited to testing the tensile strength of geometrically heterogeneous interfaces such as solder joints.

INNOVATION:  The novel method extends the testing capabilities of laser spallation technology platforms. It enables the measurement of geometrically heterogeneous interfaces, such as those found in solder joints relating to flip-chip packages, chip-scale packages (CSPs), and ball grid array (BGA) packaging of integrated circuits commonly found in the electronics industry. The method can measure several joints simultaneously, and measure in-situ joints after a chip package has been joined.

POTENTIAL APPLICATIONS 

• Solder joints of integrated circuits utilizing flip-chip packages, chip-scale packages (CSPs), and ball grid array (BGA) packaging
• Solder joints on the interface between an exposed solder ball and underlying structure, or between an embedded, sandwiched solder ball and its surrounding structures in-situ
• Solder joints prior to joining and after reflow
• Comparing different thermal aging conditions or different metal pads

ADVANTAGES

• Aids in solder material selection to ensure stable solder joints when stressed thermally during manufacture and service
• Allows direct measurement of the tensile strength of each solder joint individually
• Enables measuring prior to joining or after joining the solder joints
• Enables measuring in-situ tensile strength of embedded solder joints without any need to polish the board or package to expose the joint
• Predicts solder joint adhesion degradation under high temperature processing and service conditions
• Improves solder joint reliability

Reference: UCLA Case No. 2005-451

PCT Application: PCT/US2006/005896