The subject of the thesis work is to study the solder joint strength for BGA packages after different thermal histories, which simulated the actual processing conditions used in today’s electronic packaging assembly industry. Ball Shear and Pull tests were conducted on fpBGA (Fine Pitch Ball Grid Array) substrates with a range of Au plating thickness from ~0.25 μm to 1.5 μm. Data points from the mechanical testing were taken after secondary reflow and after accelerated ageing or High Temperature Storage Levelling (HTSL) at 150 deg. C, for various time intervals. A cross reference was also made with solder joints aged solely in ambient....[ Read more ]

The subject of the thesis work is to study the solder joint strength for BGA packages after different thermal histories, which simulated the actual processing conditions used in today’s electronic packaging assembly industry. Ball Shear and Pull tests were conducted on fpBGA (Fine Pitch Ball Grid Array) substrates with a range of Au plating thickness from ~0.25 μm to 1.5 μm. Data points from the mechanical testing were taken after secondary reflow and after accelerated ageing or High Temperature Storage Levelling (HTSL) at 150 deg. C, for various time intervals. A cross reference was also made with solder joints aged solely in ambient.

To understand the failure mechanism associated in the fracture of the solder ball joint, the microstructure was examined Scanning Electron Microscope (SEM) and Electron Dispersive X-Ray (EDX) techniques. Information was gathered on the mechanisms that have occurred during solder joint formation and ageing, which can directly contribute to the strength of the solder joint. The results show that the ball pull method is a good addition to the ball shear test as it provides a good indication of the solder joint strength under tension. The Au layer is shown to be one of the major factors in the degradation of solder joint integrity and that secondary reflow can increase solder joint strength in ball pull and shear tests through a combination of micro-defect healing and redispersion of the intermetallic phases.