Published on 22 January 2013
Electronic components need to be packaged to protect them from atmospheric contamination, mechanical damage, electrical interference and electrostatic damage. Traditionally, silicon chips have been packaged separately to the circuit boards. In order to reduce costs and component size the chip on board technique was developed. Using this technique, the chip is bonded directly to the board before interconnection and then glob topped. Glob topping is used to coat the chip and part of the board with a protective coating, however this can damage the component.
TWI investigated an alternative chip-on-board technique that involved ultrasonically welding a plastic cap over the chip. During welding trials, many chip failures were observed. It was suspected that the ultrasonic vibrations were causing resonance in the board/chip resulting in mechanical damage. Therefore the vibrational characteristics of the circuit board were investigated using finite element analysis.
Finite Element Analysis
The circuit board, a flat rectangle of FR4, was modelled and translated into a finite element mesh. The finite element analysis (FEA) was carried out in two stages.
- Determination of the natural frequencies and mode shapes of the circuit board.
- Calculation of the steady state dynamic response for a number of applied frequencies and amplitudes.