M h i l b h i f l i Mechanical behaviour of electronic components and assemblies studied components and assemblies studied

by full-field optical techniquesDan Borza

Ioana Nistea

Outline

Context

Full-field non-contact measurement techniques

• Interest, measured quantities

• Generally established techniques

Full-field optical measurement techniques at INSA de Rouen

• Speckle Interferometry

• Digital Holography

• Digital Image Correlation

• Application examples

Conclusion

Context

Loading in electronic assemblies :• Excess temperature (internal, environmental)• Excess current or voltage• Mechanical shock stress or impact• Mechanical shock, stress or impact• Dynamic loading• ...

Aggravating factors :• Highly inhomogeneous structures =>

materials with different thermo-mechanical properties• Increasing density of components small footprint• Increasing density of components, small footprint

Context

Mechanical failure:• Excess deformation (yielding or elastic), buckling• Ductile fracture, brittle fracture, cracking• Various types of fatigue• Various types of fatigue

Experimental analysis :Experimental analysis :• Detection and understanding of failure origins and

mechanisms, previously unknown• Development of new FEM models and testing of the existing

ones

DifferentDifferent existingexisting techniquestechniques areare oftenoften complementarycomplementary inin termsterms ofofresults,results, measuredmeasured quantities,quantities, measurementmeasurement range,range, etcetc..

Full-field non-contact techniques

Interests• Non-contact measurements, no damage to the test object

and no perturbation of the measured phenomena• High precision and high measurement sensitivityHigh precision and high measurement sensitivity• No transducer, no need for calibration• Simultaneous measurement of local values of the quantity

of interest in a large number of points => able to detectsingularities, and dynamic phenomena

Full-field non-contact techniques

Measured quantities• Kinematic quantities:

–displacementsd l i–speeds, accelerations

• Position of points (profilometry)• Material properties (indirectly):• Material properties (indirectly):

–CTEYoung's modulus–Young s modulus

–...

Full-field non-contact techniques

Techniques generally used:digital

light source

• Digital Image Correlation• Projection Moiré• IR Thermography light source

digital camera

test object

• IR Thermography• Near-Field Acoustic Holography• Shadow Moiré

CCDcamera

PZT

light source

test surface

laser

b

SignalProcessing

IR detector

∆T

SpecimenTest objecttest surface

illuminate

Processing∆T

Microphone array

view

gratingg g

Full-field optical techniques at INSA de Rouen

Interferometric techniques• Speckle Interferometry (SI)• Digital Holography• Holographic Interferometry• Holographic Interferometry

White-light techniquesWhite light techniques• Digital Image Correlation (DIC)• Fringe Projection• Structured Light Projection

Speckle Interferometry

• Continuous beam laser source (λ = 523nm)Th ibilit t d di th t t• The sensibility vector, depending on the system geometry,is either normal or tangent to the tested surface

BS1 2 beamsplitter BS1 M1BS1, 2 - beamsplitterL1, 2 - lensesM1, 2 - mirrorsIL - imaging lensPZT - piezoelectric transducer

BS1L1 M1

BS2

testPC IL

L2

Speckle Interferometry measurement Speckle Interferometry measurement setupsetup

surfacePZT M2

p yp y pp

Speckle Interferometry

• Continuous beam laser source (λ = 523nm)Th ibilit t d di th t t

BS1 M1

• The sensibility vector, depending on the system geometry,is either normal or tangent to the tested surface

BS1 2 beamsplitter BS1 M1BS1L1 M1BS1, 2 - beamsplitter

L1, 2 - lensesM1, 2 - mirrorsIL - imaging lensPZT - piezoelectric transducer

BS1L1 M1

BS2

IL

L2

testPC

ILL2

PZT M2

Speckle Interferometry measurement Speckle Interferometry measurement setupsetup

surfacePZT

p yp y pp

Speckle Interferometry

Characteristics• Spatial resolution determined by CCD detector and lens• Displacement measurement sensitivity up to several

nanometersnanometers• Sensitive to air flows and thermal gradients

Applications• Steady-state vibrations• Static, quasi-static and dynamic displacements

Speckle Interferometry

Principle:• Temporal phase stepping algorithm (four bucket)

Series of 4 specklegramsSeries of 4 specklegramsStatic displacements Steady-state vibrationsSeries of 4 specklegramsSeries of 4 specklegramsStatic displacements Steady state vibrations

Optical phase mapOptical phase map(modulo 2(modulo 2ππ) )

TAV hologramTAV hologram(Bessel fringes)(Bessel fringes)

phase unwrappingphase unwrapping specific algorithmsspecific algorithms

DisplacementDisplacementmapmap

Vibration Vibration amplitude mapamplitude map

Digital Holography

• The setup is almost identical to the one used for SI – themain difference is the absence of a camera lensmain difference is the absence of a camera lens

• We record the phase information of the interference field

BS1, BS2 - beamsplittersM1, M2 - mirrorsSF - spatial filterPZT - piezoelectric transducer

LASER BS1 lensCCD

M1

test BS2

CCD

surface BS2

PCSF

IL

Digital Holography measurement setupDigital Holography measurement setup

PC

M2PZT

g g p y pg g p y p

Digital Holography

Virtual wavefront reconstruction• We apply the same principle as in classical holography• Numerical simulation of diffraction by "illuminating" the

digital hologram with a numerical reconstruction wave (RN)digital hologram with a numerical reconstruction wave (RN)

HologramVirtual image

HologramObject

OO

((a)a) Recording (Recording (b)b) ReconstructionReconstruction

RNObserver

R

((a) a) Recording (Recording (b) b) ReconstructionReconstruction

Digital Image Correlation

• Successive images are recorded during surface deformationCh i th i l i t it t k d i d t bt i• Changes in the pixel intensity are tracked in order to obtainthe in-plane displacement map (single camera)

li ht thermal chamber

light source

digital camera

light sourcetemperaturemonitorlight source monitor

DIC measurement setup for thermal testing application DIC measurement setup for thermal testing application p g ppp g pp

Digital Image Correlation

Principle:• We determine the displacement

field between images (a) and (b)by applying a correlation algorithmy pp y g g

• Subpixel resolution can be attainedby interpolating the correlationmatrix (a)matrix

• The measurement resolutiondepends on the choice of size for

(a)

the correlation window• More complex algorithms take into

account the deformation of theaccount the deformation of thecorrelation window

(b)

Application examples (Audace)

Thermal deformations• External thermal stressing by local convection heating in

surface mount PCBs• Transient deformations induced by internal time-Transient deformations induced by internal time

dependant stress in active components

Steady state vibrations• At assembly level, board level, component level, die level

Mechanical deformations • Side effects of fastening screws

Measurement of material propertiesCTE t i lti l PCB d i PQFP• CTE measurements in multi-layer PCBs and in PQFPcomponents

Conclusion

Full-field optical techniques• Capability of experimental analysis of electronic assemblies

• Synchronous measurement of all sampled points• Synchronous measurement of all sampled points

• Ever-increasing measurement capabilities and processingg p p gpower

Each technique has specific measurement characteristics• Each technique has specific measurement characteristics,advantages/inconvenients that make it more or lessconvenient for certain applications

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