Results of Experimental Vibration Measurements as Input of Numerical Reliability Valuations

Vibrations are one the important parameter which influence the reliability of structures, also of microstructures. The paper describes an evaluation framework of circuit board reliability based on measured eigenfrequencies and amplitudes. The valuation includes the following main steps: 1. Experimental vibration investigations of the board by means of a laser scanning vibrometer By a special structure borne noise ecxitation in a definite frequency range the vibration behaviour of a mobile measuring system´s circuit board is investigated. Electronic components on this board with high amplitudes have to be detected. 2. Microscopic analysis of solder joints A metallographic analysis of solder joints of components with a high amplitude is performed to get exact geometry data for stress calculation. 3. Stress calculation of solder joints A local 3-dimensional FE-model based on the experimental results is created. Stress has to be calculated under test conditions and compared with critical stress values. 4. Estimation of solder joint damage A so called "Cumulativ Damage Index" which is a measure for a failure-probability has to be calculated. Is the index lower than 1 no solder joint damage has to be expected. The vibration investigation of a first example showed a high load at a board-mounted plug. Amplitudes of 140 µm (10 Hz) and 1,2 µm (64,4 Hz) are used as input values for the numerical simulation. The calculated "Cumulativ Damage Index" are 10-22 (10 Hz) and 10-2 (64,4 Hz). This means that no solder joint damage due to vibrational fatigue has to be expected. A same valuation was done with a second circuit board. Here a PQFP (Plastic Quad Flat Package) was identified as a critical component.