Automated Inspection Protocols for Detecting Silent Silicon Stepping Changes in SMT Packages
Automated boundary scan extraction combined with transmissive X-ray die metrology catches silent silicon stepping changes before SMT placement lines fault.
Wire Sweep
Wire Displacement
Lateral movement of the internal interconnections during the plastic encapsulation process results from the high-velocity flow of the epoxy. This wire sweep pulls the gold or copper wires away from their intended positions, potentially causing electrical shorts between adjacent bonds. The risk is highest for long or high-looping wires used in dense multi die packages.
Flow Dynamic
The viscosity and the velocity of the mold compound determine the force exerted on the interconnections. As the fluid fills the cavity, it creates a drag force that bows the wire. If the wire sweep is excessive, the metal touches the edge of the silicon die or a neighboring lead.
Inspection Method
Real-time X-ray imaging provides a non-destructive way to measure the deformation of the wires inside the finished component. Automated software calculates the percentage of displacement relative to the original wire length. A wire sweep exceeding ten percent of the total span usually indicates a process failure that requires a change in the molding parameters.
Design Constraint
Reducing the wire length or increasing the wire diameter improves the resistance to the flow of the epoxy. Shorter spans are less likely to deform and produce a wire sweep under the pressure of the injection.