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Discussion on Cracking/Separation in Filled Vias

Posted by Nathan Blattau on Jul 20, 2016 10:40:16 PM

The Knadle “PTH life curve" has been used for over 15 years to characterize new materials or PTH structures, and to calculate via life for any combination of temperatures. Error! Reference source not found. depicts these life curves to review the problem that drives all others—the CTE mismatch between the copper barrel and the laminate at reflow temperatures. This mismatch can produce deformations such that that even well plated vias can survive only a handful of assembly passes without cracking. Typically, 12 reflow cycles are required for SMT attach, and an additional 2 reflows for each rework (remove & replace). Therefore, 8 reflow cycles of greater than 220C could be possible during assembly. A methodology for increasing the reliability of these circuit boards was to epoxy fill the vias to add strength and extend the product life.

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Topics: PTH life curve, PTH structures, Filled Vias

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