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.
Transient Inrush Current
Initial Surge
Current spikes drawn by electrical components during the moment of power application can exceed their steady state levels by orders of magnitude. This transient inrush current occurs as uncharged capacitors begin to fill and internal magnetic fields are established. This surge decays rapidly.
It is a common phenomenon in power supplies and sensor modules.
Capacitive Load
Decoupling capacitors connected across the power rails draw high current to charge themselves up when the power switch closes. This transient inrush current behaves like a short circuit for a fraction of a millisecond. This behavior drops the rail voltage.
It can cause reset loops in adjacent microcontrollers on the same power bus.
Component Protection
Limiting devices like thermistors or series resistors are inserted into the power path to reduce the magnitude of this start up surge. When these protection circuits are omitted, the transient inrush current can weld switch contacts or melt fuse elements. This destruction happens instantly.
It requires physical component replacement. The use of soft start circuits in power management integrated circuits is another common method to control this spike by slowly ramping up the output voltage.
Safety Factor
Electrical system design must account for these startup spikes to prevent premature component failure or circuit breaker tripping. Engineers design system fuses to withstand the transient inrush current without opening. This sizing is verified through pulse testing.
This verification occurs under the most severe operating conditions.