Although an electronic device may operate perfectly when tested at rest, when it is subjected to motion, such as shock and vibration the device operation can be affected by bending modes, loosely adhered components, or loose particles. Particle detection systems have been used to screen out those devices that will malfunction due to loose particles. This study goes beyond the detection of, to a means to, determine the relative size of a particle loose in an enclosed cavity.
The objective of the NASA project is to use Particle Impact Noise Detection (PIND) to determine the probability that the devices currently in inventory, will manifest failures due to loose particles. Since the minimum shorting distance in some devices are 0.125", particles which are too small to cause a short circuit pose no threat. An initial study of several sample sensors was performed to evaluate the viability of utilizing PIND to screen the devices for loose particles. The size, number, material, and location of the particles within the package would all be helpful in determining product reliability.
Since the device under test (DUT) has a cylindrical package (in the area where the loose particles were found), a special fixture to "cradle" the device is used. This "cradle" allows the movement of the DUT longitudinally and permitted rotation about its axis to better define the location of the loose particle(s).
The study utilizes the characteristic of the particle sensor, a piezoelectric element that produces a current when pressure is applied. As the applied pressure is increased by larger particles impacting the sensor, so is the resultant output of the particle sensor increased.
There is a definite correlation between the particle mass/size and the amplitude of the particle noise. Those devices that indicate a high probability of failure due to loose particles in vulnerable areas could then be removed from use.