Journal of SMT Article

Stencil and Solder Paste Inspection Evaluation for Miniaturized SMT Components

Authors: Robert Farrell and Chrys Shea
Company: Benchmark Electronics and Shea Engineering Services
Date Published: 4/1/2014   Volume: 27-2

Abstract: New stencil materials and manufacturing technologies promise improved performance over traditional options. To determine the best technologies for a contract electronics manufacturer assembling miniaturized SMT components, a test was designed to assess the performance of 11 different stencils, submitted by 3 different suppliers, using a variety of materials and coatings. Performance metrics include print volume repeatability and transfer efficiency for 0.5mm and 0.4mm pitch BGAs and for 0201 components with area ratios in the challenging range from 0.5 to 0.66.

The test also evaluated two methods of automated solder paste inspection to determine the accuracy and repeatability of the different machines and technologies at feature sizes of 10 mil or less. The novel accuracy test printed solder paste on paper labels and weighed the labels, then used the mass of the paste to determine the average volumes of the deposits and compared them to the machine readings.

Additional testing of the aperture surface roughness was also studied too investigate potential correlations between wall roughness and transfer efficiency. Setup, execution and results of all tests are presented and discussed.

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