Microvia Target Pad Interfacial Separation under Reflow Thermal Stress
Microvia target pad separation stems from z-axis thermal expansion strain exceeding electroless copper interfacial bond strength during assembly reflow.
D-RICE Thermal Test
Detection Purpose
Derivative Resistance Interconnect Circuit Evaluation reliability assessment using derivative resistance measurements identifies latent defects within vertical interconnect structures. This d-rice thermal test applies thermal cycles to a test coupon while continuously monitoring for minute resistance fluctuations that indicate barrel cracks or foil separation. The evaluation focuses on the integrity of copper plating within through holes and microvias under high temperature stress.
Resistance changes exceeding a specific threshold signal the onset of fatigue before a total electrical open occurs. The method provides a non destructive way to verify copper quality before final assembly.
Operational Sequence
Thermal loading cycles the board between ambient temperatures and lead free reflow peaks. Integration of the d-rice thermal test into a fabrication workflow allows for the early capture of plating instabilities that standard continuity tests often miss. The apparatus connects to four wire Kelvin probes to ensure measurement sensitivity.
Precision increases when the ramp rate mimics actual assembly conditions.
Performance Metric
Sensitivity of the hardware allows for the observation of sub milliohm shifts during the dwell period. Because the d-rice thermal test targets the plastic deformation of copper, it provides a clearer picture of long term survival than static testing. Results isolate weak interfaces between internal layers and the plated wall.