by S. Manian Ramkumar Ph.D., Rita Mohanty Ph.D., CEMA, Chris Anglin, Toshitake Oda
The demand for product miniaturization, especially in the handheld device
area, continues to challenge board assembly industry. The desire to incorporate
more functionality while making the product smaller continues to push board
design to its limit. It is not uncommon to find boards with castle like components
right next to miniature components. This type of board poses special
challenge to the board assemblers as it requires wide range of paste volume
to satisfy both small and large components. One way to address the printing
challenge is to use creative stencil design to meet the solder paste requirement
for both large and small components. Example of stencil design includes step
stencil, dual printing, over size aperture, etc. Stencil printing process at its
most basic level involves pushing solder paste through a stencil (with various
size apertures) by a squeegee blade. As the squeegee blade and the stencil
are in constant contact with the paste during the printing process, their surface
characteristics play an important role in the printing process. The most
important attribute of a stencil is its release characteristic. In other word, how
well the paste releases from the aperture. The paste release in turn depends on
the surface characteristics of the aperture wall and stencil foil surface. Recent
introduction of a new technology, Nano-coating for both stencil and squeegee
blades, has drawn the attention of many researchers. As the name implies,
Nano-coated stencils and blades are made by conventional method such as
laser cut or Electoform then coated with nano functional material to alter the
surface characteristics. This study will evaluate nano-coated stencils for passive
component printing including 01005. Various print experiments will be
conducted using different stencil technology, stencil thicknesses, aperture size,
aperture orientation, aperture shapes, and selected paste type with optimal
print parameters, to understand the effect of chosen factors on the print quality.
Print quality will be determined by visual inspection and 3D measurement of
the paste deposit to understand the volume transfer efficiency.
Apex 2011, solder paste, transfer efficiency, area ratio, stencil technology, broadband printing, nano-coated stencil
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Posted on 11 Apr 2011
by Chris Anglin, David Sbiroli, Ed Briggs
The continual miniaturization of electronics components for personal electronics devices, coupled with the conversion to RoHS- and REACH-compliant lead-free assemblies, has put a tremendous strain on the electronics assembly industry. Introduction of 01005 passives, and active components on the order of 0.3mm pitch, initiates newly defined questions about specification limits for solder paste stencil print performance.
This paper discusses variability of solder paste print performance and its relationship to specification limits. The objective is to describe analyses to determine stencil print process character, using actual paste print measurement data. Aside from setting specification limits, application of statistical methods for the analysis of variation in stencil print performance could help understand appropriate production statistical process control (SPC) limits sought by SMT manufacturing and quality engineers from stencil print inspection results that are gathered during SMT assembly.
Effects on values of Cp and Cpk by various specification limits are presented. This discussion is based on recent application development experiments, to elucidate how average solder paste measurement and standard deviation measurement effect new print process capability challenges. From this work, a strategy to optimize a new 01005 stencil printing process is reviewed. Importantly, the discussion includes key factors with planning quality aspects of SMT assembly. SPC techniques presented will show how to measure stencil print performance capability, and result in opportunity for reduced assembly costs and increased sales income.
transfer efficiency, process capability study, capability ratio, statistical process control (SPC), control charts, stencil aperture design, pad design, solder paste, area ratio
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Posted on 24 Jan 2011
