Quantifying Sputter Yield Scaling under Argon Gas Cluster Bombardment
Argon cluster sputter yields scale nonlinearly with energy per atom, where low energy partitioning suppresses matrix damage during depth profiling.
Crater Geometry
Defect Profile
Structural failures in high-density interconnect substrates produce a characteristic cavity when a copper pad detaches from the underlying resin matrix. This crater geometry is evaluated after mechanical stress tests, such as hot bump pull or ball shear tests, to determine whether the resin or the copper interface failed first. The resulting cavity provides a physical footprint of the failure mechanism.
Stress Distribution
Stress concentration under solder joints during thermal cycling dictates where the microcrack initiates. Cracking usually begins at the perimeter of the pad where the strain is highest and moves inward along the glass fiber reinforcement boundary. When the stress exceeds the cohesive strength of the epoxy resin, the entire joint separates and takes a circular portion of the laminate with it.
Analyzing this shape helps board fabricators adjust the resin cure cycle to increase the fracture toughness of the laminate. If the resin is under-cured, the cavity is shallow with a rough surface, while a fully cured resin yields a deep cavity with sharp, well-defined borders.
Inspection Protocol
Optical microscopy provides the initial means of evaluating the fractured region. Operators examine the board surface under high magnification to measure the depth and diameter of the missing material. In more complex cases, scanning electron microscopy determines whether resin remains on the pad or if the failure has exposed the raw glass fibers.
This inspection technique classifies the failure mode to prevent similar cracks during the board assembly stage.