Meaning
Dynamic stress assessment measures the ability of a solder joint to withstand high G-force events during sudden physical impact. Mechanical failure within a drop shock test usually occurs near the corners of large components where stress concentrates most heavily. High speed cameras and daisy-chain monitoring capture the precise millisecond of electrical discontinuity.
Mechanical Impact
Rapid deceleration forces produce intense bending moments in the printed circuit board that pull components away from their pads. Performing the drop shock test requires an automated drop tower capable of hitting 1500G with a half-sine pulse width of 0.5 milliseconds as specified in JEDEC standards. Components that survive multiple cycles demonstrate high fracture toughness in their intermetallic layers.
Failure Mode
Analysis identifies cracks propagating through the bulk solder or along the brittle interface between the pad and the ball. Frequent observation of these cracks in the drop shock test indicates poor board finish quality or excessive formation of intermetallic compounds. Weak spots typically emerge at the first point of copper exposure.
Standard Compliance
Industrial electronics require repeatable results across several dozens of drops to meet ruggedization requirements for mobile devices. Results from the drop shock test dictate if an underfill material is necessary to reinforce the component leads against high-impact shock. Testing also helps refine the support locations inside the product casing.
