Modelling and computer simulation of the behaviour of solder paste in stencil printing for surface mount assembly

He, D

Abstract

One of the main challenges facing the electronics manufacturing industry in solder paste
printing for ultra-fine pitch surface mount and flip-chip assembly is the difficulty in
achieving consistent paste deposit volumes from pad-to-pad. At the very small aperture
geometries required for ultra-fine pitch and flip chip assembly, flow properties of the
paste becomes one of the dominant factors in the printing process. It is widely accepted
that over 60% of assembly defects originate from the solder paste printing stage, and
hence the urgent need for a better understanding of solder paste rheology, its behaviour
during printing, and its impact on defect generation. This understanding is essential for
achieving proper control of the printing process.
This thesis presents the result of work on the modelling and computer simulation of
solder paste behaviour during printing, and consists of three main parts. The first part
concerns the modelling of paste behaviour in stencil printing using a vibrating squeegee.
The performance of the vibrating squeegee is analysed and process models developed for
predicting the ideal printing conditions. In the second part, the random packing of solder
powder and the microstructure of solder paste are numerically simulated by applying
Monte Carlo method. The effect particle size distributions on the paste microstructure
is studied in this part. Based on the simulation results of the second part, the third part
concerns the study of the effect of particle size distribution on the paste viscosity and the
hydrodynamic interaction between adjacent particles during paste flow. A theoretical
enhanced model for predicting the viscosity of dense suspensions such as solder pastes
has been developed. This correlates relative viscosity with particle size distribution and
with solid volume fraction of dense suspensions.
The results of the work have wide applicability: firstly for solder paste manufacturers
in optimising paste printing performance at the development stage and for stencil printing
equipment manufacturers in specifying the ideal conditions for defect free printing. The
simulation algorithm and the viscosity model are also applicable for a wide range of
industrial processing applications; in particular metal or ceramic powder compaction,
material surface coating, chemical or food material transportation.

Citation

He, D. Modelling and computer simulation of the behaviour of solder paste in stencil printing for surface mount assembly. (Thesis). University of Salford

• Thesis Type: Thesis
• Deposit Date: Sep 26, 2011
• Publicly Available Date: Sep 26, 2011
• Award Date: Jan 1, 1998