Assessment of Accelerometer versus LASER for Board Level Vibration Measurements

Abstract

The ongoing trend to deploy ICs in more
complex and harsher applications, entails precise
evaluation of solder joint reliability of components
subjected to vibration loads. For this, a good
understanding of the PCB vibrational motion during a
board level vibration test is essential. This can only be
achieved by a well characterized vibration test setup. The
vibration motion can be recorded by using a contactbased
measurement approach, i.e. using an
accelerometer, or a contactless measurement
configuration, i.e. using a Laser Doppler Vibrometer
(LDV).
This paper evaluates both measurement techniques by
recording the PCB dynamic response, i.e. the resonance
frequency and peak-to-peak displacement, in a board
level vibration test set up. Bare and assembled printed
circuit boards (PCBs) are investigated using different
PCB form factors and package outlines (Wafer Level
Chip Scale Package (WLCSP) and Ball Grid Array
(BGA)), showing that LDV enables better lateral
resolution and a more accurate measurement solution.
Especially when the weight of the accelerometer cannot
be neglected compared to the weight of the component on
the PCB. An accelerometer is shown to perturb the PCB
vibration motion.
It is found that depending upon the test objectives and
PCB electronic system involved, both techniques can be
used as complementary to one another. The
accelerometer weight may give rise to substantial
modification of vibration response which can be used to
simulate the presence of a component on a bare PCB. In
addition, both methods are expected to recognize the
same trends when e.g. studying the environmental
impact during vibration tests. Finally, the experimental
observations are