Electronics Assembly Knowledge, Vision & Wisdom
Surface Mount Warpage Case Study
Surface Mount Warpage Case Study
A quantity of surface mount packages were measured by shadow moire metrology to capture warpage levels, as they were heated through a reflow profile.
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Authored By:
Neil Hubble
Akrometrix

Jerry Young, Kim Hartnett
Micron Technology

Summary
Surface mount components are commonly evaluated for out-of-plane warpage levels across reflow temperatures. Decision making from these measurements is primarily based on signed warpage of a single component surface, per industry standards. However, signed warpage as a gauge can mislead users when surface shapes are complex, or direction of warpage is uncertain. The presented case study analyzes a range of common surface mount components for signed warpage. This wide ranging case study is used to create newly proposed methods for further defining and characterizing surface warpage in a quantitative manner.

Analysis of the case study data focuses on two related surface parameters: signed warpage Signal Strength and surface shape naming. Signal Strength is used to classify samples that are in "transition" between positive and negative warpage directions. New methods are shown to represent these transition areas in signed warpage graphs. Surface shape naming is used to further classify surface types, wherein correlation between shape name and surface mount defects are discussed. Algorithms for calculation of Signal Strength and classifying shape names are offered. Real world examples are used to determine appropriate thresholds for sign transitions and shape names in said algorithms. The study proposes a new, industry wide, approach to how companies present component warpage data.

Conclusions
A large quantity of surface mount packages were measured by shadow moire metrology to capture warpage levels, as the samples were heated through a reflow profile. Found warpage data was used to improve upon new methods of communicating surface shape, when dealing with large quantities of data.

JEDEC Full Field Signed Warpage (JFFSW) is already an often preferred gauge over the industry standard signed warpage, used by many industry leading companies, as the critical gauge for package warpage. This paper goes a step further in refining understanding of package shape, by introducing a new gauge, 3S Warpage. 3S Warpage not only classifies shapes as positive and negative, but also mathematically defines a third indeterminate category,labeled as a transition surface. This added category is designed to limit confusion in summarizing package 3D surface shape with a single gauge.

Packages from the case study were also assigned a shape name, established by newly established algorithms. Shape naming algorithms were improved through an iterative process, when compared with qualitative shape assignments. The shape name adds a new variable that can be tracked and correlated over time with surface mount attachment reliability and surface to surface mating. These shape names can be used in establishing package trends and for further, future understanding of assembly yield based upon package warpage.

Initially Published in the IPC Proceedings

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