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By Jim
Adriance, Process Research Engineer, Surface Mount Technology Laboratory,
Universal Instruments,
and Jeff Schake, Process Research Engineer, DEK
Abstract
The research summarized in this paper will help to address some of the
issues associated with solder paste mass reflow assembly of 0201 components.
Attachment pad design, stencil design, component to component spacing,
component orientation, flux type, and solder paste reflow atmosphere
were the major variables researched during the project. The two major
responses from the experimentation were assembly yield and assembly
quality. Assembly yield defects, such as tombstones (open solder joints),
solder bridges, and solder balls (beads) were used to determine the
assembly yield. Solder joint shape, solder appearance, and solder volume
(unacceptable low, acceptable or unacceptable high) responses were used
to determine the quality of the assem-bly process. The combination of
flux type and reflow environment were found to have the largest impact
in the number of assembly defects produced. Boards assembled with no-clean
solder paste and reflowed in an air atmosphere exhibited the best yields
with the highest tolerance for attachment pad dimension variation. Conversely,
assembly processes using no-clean solder paste with a Nitrogen reflow
atmosphere generated the largest number of assembly defects and was
found to be the most sensitive to changes in the attachment pad design.
This paper is available
in PDF format. Please down load.(uic0201.pdf.
file size: 549Kb)
(A 12/07/2000)
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