Digital Speckle Correlation (DSC)

The Digital Image Speckle Correlation Project (DISC) is an experimental physics-based study, which will assess whether a unique but mature Digital Image/Speckle Correlation test method for the measurement of the thermal stress in microvias and surrounding areas can be used to predict the relative reliability differences in PWB stackup structures. The unique quantitative measurement of the strain and other deformation kinematic parameters makes it possible for a relatively short term mechanistic-based failure analysis instead of having to perform long term traditional reliability studies.

Project stage: 
Lead company: 
Celestica

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Idea Information

Background: 

There are strong interests in understanding the reliability behavior of the stacked microvias, especially the effect of the structure designs such as the number of stacks, the pitch between the vias, and the stacking microvia on/off a buried via, etc.

The main reliability challenges have been the microvia separation, interfacial delamination and the copper fatigue failure.  Experimental evidence suggests that HDI structures experience different stresses and failure modes during thermal operation, and the challenges become tougher under the Pb-free assembly.

Problem: 

There are strong interests in understanding the reliability behavior of the stacked microvias, especially the effect of the structure designs such as the number of stacks, the pitch between the vias, and the stacking microvia on/off a buried via, etc. which was the purpose of the recently completed HDPug Multiple Laminations Project.The main reliability challenges have been the microvia separation, interfacial delamination and the copper fatigue failure.  Experimental evidence suggests that HDI structures experience different stresses and failure modes during thermal operation, and the challenges become tougher under the Pb-free assembly.

Definition Information

Goals / Benefits: 

Phase 1 is a proof-of-concept study. This study will make use of available micro-via PWBs from the recently completed Multi-lam project which performed at opposite ends of the reliability spectrum. The goal is to correlate with the IST data. Three specific samples will be included in the Phase 1 evaluation:

             Hi CTE, 18 layer, 3 stack “off buried”, 0.8 mm pitch-Delamination Early Failures

             Lo CTE, 12 layer, via stack “on buried”- Buried via/cap failures

             Hi CTE, 12 layer, via stack “on buried”- Good reliability performance

Non-stressed samples of as-fabricated PWBs will be prepared for digital speckle correlation testing; then the test method applied to see if it can quantify the stresses applied by material to the structures. If so this would advance the State of the Art both from a reliability prediction method but also from an evaluation of design trade-offs perspective.

Based on the empirical data from these tests, future phases of this project may lead to development of Finite Element models to allow for evaluation of different structures and material types and their impact on reliability.

High level objectives: 

Verify if results from digital speckle analysis could have predicted the reliability of known microvia failures.

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