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Post placement defects are typically identified on a surface mount printed circuit board assembly line (i) just after components have been placed on wet solder paste and (ii) after solder reflow. These inspection steps should, in theory, help to identify the causes of the post placement defects and consequently assist in their correction. A 'typical' process sequence for the assembly of surface mount printed circuit boards includes the deposition of solder paste through stencil printing, the placement of components on wet solder paste, solder reflow using ovens with heat sources that utilize forced convection and/or infrared radiation, cleaning (if appropriate), testing, and inspection. This research focused on the identification and correction of post placement defects in an ultrafine pitch surface mount printed circuit board assembly environment.

The objective of this research was to (i) identify post placement defects and their causes and (ii) to suggest approaches that could be used to minimize their occurrence. A multi-pronged approach that combined experimentation with theory was used to reduce the incidence of post placement defects. The first step was to understand the types of defects that occurred and their frequency. This was done by examining available historical data and by subsequent experimentation. Efforts were made to compare the data that was collected just after the placement operation with the data collected after solder reflow. This process allowed the research team to study the impact and the necessity of collecting data after placement but prior to solder reflow. Next, the impact of vibratory trays used on the placement machine on post placement defects was studied. The observations that were made helped to draw inferences on the use of vibratory trays and to provide recommendations. Inferences were drawn based on statistical analysis of the results.


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