Effect of PCB and Package Type on Board Level Vibration Using Vibrational Spectrum Analysis

Abstract

The resonance frequencies and mode shapes of aPCB are highly depended on form factor and stack-up. Moreover, the interaction with components mounted to the PCB cannot a priori be neglected. In the search for key parameters that might impact the outcome of a board level vibration test, it is important to asses the impact of these factors on the principal PCB vibrational characteristics. The resonance frequency and peak-to-peak displacement, which can be linked to the strain and strain rate during a board level vibration test, is obtained from the acceleration during a swept sine excitation on a shaker measured using a light weight accelerometer. Two PCB form factors are investigated: rectangular (132x77 mm2) and square (77x77 mm2). Both the first resonance frequency and the peak-to-peak displacement are found to be different. Finite element modeling is used to calculate the resonance mode and mode shapes. In addition, the in-plane and out-of-plane strain for both form factors is compared because of its relevance to application use conditions. After evaluating the bare board vibrational characteristics including small variations to the PCB stackup, component mounting will be discussed. Good agreement is obtained with numerical simulations which are then used to study the first resonance frequency as function of package type and size. The results indicate that detailed PCB specification is required. Moreover, a board level vibration test standard should include vibrational characterization of the overall PCB assembly.