Assessment of Accelerometer Versus LASER for Board Level Vibration Measurements

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 contact-based 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 also confirmed using a Finite Element Model (FEM).