AREA CONSORTIUM REPORTS
The reports below are the results of the research conducted by the Universal Instruments AREA Consortium and its funded University efforts. They have been placed in separate years to facilitate easier searches when looking for keywords. Using the “find” function on your browser may make it easier to find keywords on a given page. Typically the shortcut for that function is “Ctrl-F”.
2025 REPORTS
Accelerated Thermal Cycling of Mixed Microvia-under-Pad Structures
Author: Jeff Kurish
Abstract:
Via-In-Pad Plated over (VIPPO) geometry is a space saving innovation in circuit board design. Multiply reflowed mixed arrays of VIPPO and non-VIPPO pads are high risk of hot tearing mimicking defects. During reflow temperatures pads without copper vias expand far more than VIPPO pads. Expansion of the PCB in the non-VIPPO applies tensile force on the VIPPO pad solder, separating the intermetallic layer and bulk solder. Herein, the in-process defect has been mitigated through nitrogen atmosphere during reflow. The characteristic lifetime effects of VIPPO/non-VIPPO differential expansion are probed via accelerated thermal aging of VIPPO containing PCB boards.
Drop and Vibration Durability of High-Reliability Solder Joints
Author: Najmin Sultana, Ph.D. and Michael Meilunas
Abstract:
This study investigates the mechanical durability of high-reliability (HR) solder alloy pastes under dynamic loading conditions. Traditional alloys such as SnPb and SAC305, while widely used, present limitations: SnPb lacks vibration fatigue endurance, and SAC305 is brittle under mechanical shock. To address these shortcomings, three HR solder pastes, Cyclomax, Rel22, and Durafuse HR, were evaluated using a hybrid joint configuration (HR paste with SAC305 spheres) in BGA assemblies. Mechanical reliability was assessed through both drop shock testing at 340G, 900G, and 1500G levels, and sinusoidal vibration fatigue testing at resonant frequency (1.75G). Real-time strain and acceleration data were acquired using embedded sensors, and failures were detected via high-speed resistance monitoring. Weibull analysis was performed to determine the characteristic life and failure distribution for each alloy.
Shear Performance of High-Reliability Solder after Thermal Stress in LEDs on Aluminum-Clad PCBs
Author: Najmin Sultana, Ph.D.
Abstract:
This study evaluates several high-reliability (HRel) solder pastes for a high-temperature aluminum-clad PCB and ceramic Osram LED application. The assemblies, consisting of ENIG-finished boards and ENEPIG-finished LED packages, experienced long-term exposure near 100°C, raising concerns about solder joint degradation from thermal stress and microstructural evolution. PCBs were assembled using SAC305, Innolot, Durafuse HR, Rel22, and Innolot MXE solder pastes. Selected assemblies were annealed at 105°C for 1000 and 2000 hours before room-temperature device shear testing at 10 μm/s and 1000 μm/s. Aluminum-clad PCBs provide excellent heat spreading during device operation but introduce a greater coefficient of thermal expansion (CTE) mismatch with ceramic substrate LED devices. All HRel alloy joints demonstrated improved mechanical integrity and thermal stability compared to SAC305, maintaining shear strength through extended thermal aging. Device shear fractures occurred near the Ni layer on the PCB or LED side, with Durafuse HR showing slightly higher strength retention and reduced strain-rate sensitivity.
Impact of Temperature and Current Stressing on Solder Joint Shear Strength
Author: Najmin Sultana, Ph.D.
Abstract:
Electromigration and thermal stressing are known reliability concerns in electronic assemblies because they can drive atom movement, intermetallic growth, and gradual weakening of solder joints over time. This study evaluates how four solder alloys, SAC305, SnPb, Durafuse HR, and L29, respond to mild electromigration conditions and extended thermal aging when used with 0603 resistors. Samples were exposed to room temperature (RT) and 75°C, along with low current levels of 0 A, 0.33 A, and 0.66 A, for up to 120 days, and shear testing was performed to assess mechanical integrity. Overall, the results showed that none of the alloys experienced significant shear strength degradation under these mild stress conditions. Durafuse HR consistently demonstrated the highest shear strength, while SnPb showed the lowest. L29 performed well, and SAC305 maintained stable, moderate strength. Importantly, electromigration stressing did not produce measurable changes in the shear performance of any alloy.