The effect of wall-slip formation on the rheological behaviour of lead-free solder pastes

Wall-slip plays an important role in the flow behaviour of solder paste materials. The wall-slip arises due to the various attractive and repulsive forces acting between the solder particles and the walls of the measuring geometry. These interactions could lead to the presence of a thin liquid layer adjacent to the wall, which causes slippage. The aim of this study is to investigate the influence of the solder paste formulation on wall-slip formation and its effect on the printability of these pastes material. A wall slip model is utilised to calculate the true viscosity and slip velocity for the lead-free solder pastes samples used in this study. The difference in the measured viscosity and the true viscosity could indicate wall-slip formation between the solder pastes and the parallel plate. Sample P1 showed a higher slip velocity compared to sample P2. The slip velocity calculated for the solder pastes could be used as a performance indicator to understand the paste release characteristics in the stencil printing process.

Assessment of existing soakaways for reuse

This paper describes a practical approach for the investigation, assessment and design of existing soakaways. This method can be utilised for measuring the performance and capacity of the systems and examining whether the systems are suitable for reuse when information about the design and installation of the systems is not available. The requirements for field observations and the procedure for a soil infiltration test for the installed system are suggested for successful assessment. The soil infiltration rate of the system is estimated from the field test data without requiring information on the design and construction details of the system. The system's working condition is measured by a performance indicator related to the time taken to empty the soakaway. This is then employed to evaluate the potential reuse of the system. The system's drain capacity is determined by the design principles of current practice and the effect of climate change on its drain capacity is considered. Contamination of soils around the systems after long-term use of discharge service and the water present in soakaway chambers are also investigated. A detailed case study for the reuse of four installed soakaways for a new housing development demonstrates how the proposed approach provides a straightforward process for the infiltration performance and drain capacity assessment of the existing systems. The effectiveness and applicability of the proposed approach are further demonstrated from the assessments for a number of installed systems over various sites