Pulse Propagation
Kinetic energy travel through a rigid substrate results from an impact or the rapid engagement of testing machinery. A mechanical shock wave moves at the speed of sound within the epoxy material and creates instantaneous stress spikes at every mounting point. This energy surge tests the physical tenacity of every connection between heavy parts and the surface.
Impact Mechanism
Initial contact at one board location sends an expanding energy front outward across the surface of the laminate. In board assemblies, the mechanical shock wave encounters boundaries where components are soldered, forcing these joints to absorb the energy as shear or tensile load. Capacitors and high-count pin grid arrays are vulnerable due to their mass and the lack of flexibility in their connections.
Standard tests simulate these waves by dropping a pallet onto a hard surface or using an pneumatic hammer to deliver a quantified impulse. The shape of the pulse, measured in g-force over time, determines the level of damage to internal via barrels and buried trace transitions.
Failure Sequence
Joints fail when the wave velocity causes the local acceleration of the component body to lag behind the movement of the board. This lag induces a snap force that can separate the pad from the resin.
