Voids in solderjoints have been considered as a defect in electronics assembly. The factors that affect void formation are complex and involve the interaction of many other factors. There are no established standards for void size and void area in a solder joint for it to be deemed defective. Inspection criteria have been very subjective. The effect of voids on the reliability of a BGNCSP solder joint may depend not only on the size, but also on other factors such as frequency and location. This study focussed on investigating the effect of voids on the reliability of solder joints. The effect of size, location and frequency of voids on reliability were studied. Testing was done by a mechanical deflection testing (torsion) system and Air to Air Thermal Cycling (-40 Cl125 C). Failures were analyzed and failure modes were identified by cross sectional analysis. Additionally, a finife element model was developed for a package with voids of varying sizes in the comer solderjoint of the package. The results from the model were compared with the results from reliability testing and are presented in this paper, Analysis indicates that voids reduce the life of the solder joint. Voids which are greater than 50 % of the solder joint area decrease the mechanical robustness of the solder joints. Small voids also have an effect on reliability. However, its effect is dependent on the frequency of voids and their location.

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Efficient and accurate finite element (FE) modelling of bolted joints is essential for increasing confidence in the investigation of structural vibrations. However, modelling of bolted joints for the investigation is often found to be very challenging. This paper proposes an appropriate FE representation of bolted joints for the prediction of the dynamic behaviour of a bolted joint structure. Two different FE models of the bolted joint structure with two different FE element connectors, which are CBEAM and CBUSH, representing the bolted joints are developed. Modal updating is used to correlate the two FE models with the experimental model. The dynamic behaviour of the two FE models is compared with experimental modal analysis to evaluate and determine the most appropriate FE model of the bolted joint structure. The comparison reveals that the CBUSH element connectors based FE model has a greater capability in representing the bolted joints with 86 percent accuracy and greater efficiency in updating the model parameters. The proposed modelling technique will be useful in the modelling of a complex structure with a large number of bolted joints.

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Abstract. Mechanical joints, particularly fasteners such as bolted joints have a complex non-linear behaviour. The non-linearity might emerge from the material, geometry or by the contacts in the joints. However, damage to a structure can be happened either their connections or the material of components. The effect of damage can change the dynamic properties of the structure such as natural frequencies and mode shapes and structural performance and can cause premature failure to structure. This paper presents a damage detection method using a vibration based damage detection method based on the frequency response function (FRF) data. A combination of numerical model and physical bolted jointed structure of damaged and undamaged structure will be investigated. The validation is employed to detect the presence of damage in the structure based on the frequency response function (FRF) data from the parameter values used in the benchmark model and damaged model. The comparisons of the undamaged and damaged structure of the FRF have revealed the damaged structure was shifted from the undamaged structure. The effect of the FRF between undamaged and damaged structure is clearly affected by the reduction of stiffness for the damaged structure.