Journal of SMT Article

Plasma Stencil Treatments: A Statistical Evaluation

Authors: Matt Kelly, P.Eng., William Green, Marie Cole, Ruediger Kellmann
Company: IBM Corporation
Date Published: 10/31/2013   Volume: 26-4

StenTech

Abstract: As printed circuit board complexities continue to increase, packing more functionality into smaller physical dimensions has become increasingly important. As a result, a wider variety of electronic components are being incorporated into product bills of materials. Large body ASICs (logic) and sub-system docking connectors generally drive large SMT pad designs, while fine pitch devices such as flip chip QFNs, 0402, and 0201 chip passives are now commonplace within electronic circuitry.

Integration of these large and small body components onto a single printed circuit board assembly (PCBA) with ever increasing population densities and tighter placement spacings, drives the need for consistent solder paste print deposits to ensure maximum first pass assembly yields and highest product quality / reliability levels. Balancing solder paste printing of large and small print deposits has been reported to be enhanced using various surface treatments on laser cut stencils. This study focused on examining the effects of a plasma coating compared to conventional stainless steel (SS), laser cut technology. Printing performance on a variety of components was evaluated including five different BGAs, flip chip QFNs, SMT electrolytic capacitors, 0805, 0402, and 0201 chip passives. Leadfree no clean and water soluble paste chemistries were included, along with two different aperture ratio (A/R) design points for all components studied. For assessing the durability of the plasma coating, production volume cleaning simulations were conducted with twenty four different solvents.

Statistical analysis was conducted to evaluate any observed differences between conventional stencil technology and a plasma treated alternative. A design of experiments (DOE) was conducted to evaluate main effects and interactions, helping to make data generated decisions to answer the question: Do plasma treated stencils offer benefits over conventional technology stainless steel laser cut stencils?

Keywords: 

Plasma treatment, Stencil printing, Stencil cleaning, Design of experiments, Design for Six Sigma



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