Evaluation of risks due to therm al stress before physical failure - - PowerPoint PPT Presentation

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Evaluation of risks due to therm al stress before physical failure - - PowerPoint PPT Presentation

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Evaluation of risks due to therm al stress before physical failure appearance Michael Hertl Jean-Claude Lecomte I NSI DI X 24 rue du Drac 38180 SEYSSI NS France Tl. : + 33 (0)4 38 12 42 80 Fax : + 33 (0)4 38 12 03 22 E-mail

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Evaluation of risks due to therm al stress before physical failure appearance

Michael Hertl – Jean-Claude Lecomte I NSI DI X – 24 rue du Drac – 38180 SEYSSI NS France Tél. : + 33 (0)4 38 12 42 80 – Fax : + 33 (0)4 38 12 03 22 E-mail : michael.hertl@insidix.com

EUFANET workshop 2006 – Wuppertal

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Tendencies

Assemblies getting smaller and smaller, more and more integrated RoHS consequence : Solder temperature + 34°C Customers: I ncrease junction temperature: 150 -> 175-200°C

Dilem m a

I ncrease of thermal stress, but decrease of space and time for elimination of heat More and more thermal stress is seen by the components

Challenges

EUFANET workshop 2006 – Wuppertal

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Molding com pound Die Via Pad I nterconnection Bum p Electric via Therm al Via Solder m ask Die pad I nterconnection Bum p Substrate Substrate upon protection layer PCB Technological design Technological design example

Materials and interfaces

An electronics com ponent constitutes an assem bly of m ultiple very different m aterials

  • Variation of the coefficient of thermal expansion (CTE) of the

different materials

  • I nterface behavior under varying temperature
  • Fatigue
  • …

EUFANET workshop 2006 – Wuppertal

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Therm al stress

  • Constant temperature : T [ °C]
  • Dynamic situation :

[ °C s-1] (x , y , z)

  • Thermal flux :

[ °C z-1] (x , y ) dT dt Mechanical stress

  • Screwing of PCB
  • Clamping of components in sockets
  • Mechanically fixed and tightened heat sinks
  • …

dT dz

Thermo-mechanic stress: A key problem

EUFANET workshop 2006 – Wuppertal

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How to characterize the therm o-m echanical behavior :

  • Of an electronic component, before and after assembly ?
  • Of a PCB, before and after soldering of the components ?
  • For different temperatures, and different types of temperature variation

(e.g. during a reflow profile)

  • I n dynamic situations : ON / OFF
  • Under mechanical or thermo-mechanical stress (e.g. component

mounted on a heat sink)

  • …

Experimental problem

EUFANET workshop 2006 – Wuppertal

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Scanning acoustic m icroscopy ( SAM)

  • Powerful tool for delamination characterization
  • Consequences of stress only detectable post-mortem
  • No predictive power, no “warning” before failure
  • Only operational at ambient temperature

Therm o-m echanic sim ulation codes

  • Easy access to parameter studies
  • Time demanding
  • Material and interface characteristics often unknown
  • Failure appearance often related to “unknown” effects

Classical development and analysis techniques

EUFANET workshop 2006 – Wuppertal

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Delam ination m ay be considered as a relaxation of stress

  • through formation of cracks

Consequences of stress BEFORE delam ination :

  • Volume deformation in all three directions (x,y,z)
  • These volume deformations cause surface deformations
  • Out of plane deformation : Δz
  • I n-plane deformation : Δx, Δy

THUS : Deform ation is a failure risk indicator Reliability evaluation by TDM

EUFANET workshop 2006 – Wuppertal

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T = - 40°C T = 260°C T = 25°C Temperature variation Δl/l CTE

z

Warpage (Δz) measurement delamination risk Δl/l measurement CTE mismatch evaluation

z2 + Δz2 Δz1 Δz2 Δz3

Δx3 - CTE 3 Δx2 - CTE 2

Compression Strain z1 z2 z3 S1 S2 S3 z1 + Δz1

Δx1 - CTE 1

z3 + Δz3

Δz

Deformation under temperature variation

EUFANET workshop 2006 – Wuppertal

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Bottom thermocouple Bottom heating Top heating Camera Light source Sample holder Top thermocouple Bottom Cooling Top Cooling

TDM: Topography and Deformation Measurement under representative thermo-mechanical stress

New experimental approach

EUFANET workshop 2006 – Wuppertal

  • 3D absolute topography and

deform ation analysis

  • Spatial resolution : ~ 2 µm
  • JEDEC type tem perature

profiles capability

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A A’ B B’ A A’ B B’

Application 1 : Brazing Al2O3 on Cu

Geometry variation during brazing process Al2O3: convex Cu : concave Cu Al2O3

EUFANET workshop 2006 – Wuppertal

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During cooling : The hole generated by the opposite bending of the two components (due to different CTE) is filled up with brazing alloy in liquid state. After several therm al cylces : Initiation de delam ination detected by SAM, in the 4 corners of the assembly.

SAM im age

Application 1 : Brazing Al2O3 on Cu

EUFANET workshop 2006 – Wuppertal

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Problem

  • 2 families of identical BGAs, produced at 2 different production sites
  • One family ok, the other one fails during reflow

Application 2 : Delamination during reflow

profils de température sur les differents composants

50 100 150 200 250 300 60 120 180 240 300 360 420 480 540 600 660 720 780 840 900 960 time (s) temperature (°C)

comp8 comp4et5 comp2et3 comp1

comp2et3 comp4et5 comp6et7 comp1et8

Tmax = 245°C

EUFANET workshop 2006 – Wuppertal

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170 °C * 225 °C * t0 = initial 165 °C 173 °C 183 °C 200 °C 245 °C 200 °C * 143 °C * 150°C t1 = final 157 °C *

t0 t1 T max T ambiant

BGA during reflow: Deformation analysis

Z [µm]

Application 2 : Delamination during reflow

EUFANET workshop 2006 – Wuppertal

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Analysis for 2 components of each family

comp1 comp2 comp3 comp4 initial (t0) T max (245°C) final (t1) Warning rate z different = 260µm T 23°C T 23°C

Application 2 : Delamination during reflow

EUFANET workshop 2006 – Wuppertal

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Series 1 1 2 3 7 6 5

4

8 Series 2 Series 4 Series 3 Series 1 and 2: no delam ination Series 3 and 4: delam ination

Application 2 : Delamination during reflow

Delamination checked by SAM

  • Comp. 1
  • Comp. 2
  • Comp. 3
  • Comp. 4

EUFANET workshop 2006 – Wuppertal

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Displacement field (vector x100)

I so-displacement fields Strain fields (ΔL/ L)

  • Mean strain ~ 1 7 0 0 ppm
  • CTE ~ 1 4 × 1 0 -6 / °C

ΔX~ 1pix.~ 16µm

X direction

ΔY~ 1pix.~ 16µm

Y direction X direction Y direction

  • Axi-symmetric displacement field

Application 3 : CTE mismatch analysis

EUFANET workshop 2006 – Wuppertal

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Displacement field (vector x100)

I so-displacement fields Strain fields (ΔL/ L)

  • Mean strain

~ 1 2 0 0 ppm

  • CTE ~ 1 0 × 1 0 -6 / °C

ΔX~ 0.7pix.~ 12µm ΔY~ 0.8pix.~ 13µm

X direction Y direction X direction Y direction

Application 3 : CTE mismatch analysis

EUFANET workshop 2006 – Wuppertal

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Displacement field (vector x100)

I so-displacement fields Strain fields (ΔL/ L)

  • Mean strain

~ 1 3 5 0 ppm

  • CTE ~ 1 1 × 1 0 -6 / °C

pixel pixel

X direction Y direction X direction Y direction

ΔX~ 0.8pix.~ 13µm ΔY~ 0.9pix.~ 14µm

  • Axi-symmetric displacement field

Application 3 : CTE mismatch analysis

EUFANET workshop 2006 – Wuppertal

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Conclusions

TDM Benefits Prevention and anticipation Failure understanding Reflow analysis Fatigue analysis Challenges Thermal management PCB deformation during reflow BGA balls breaking Delamination TDM Contribution 3D deformation measurement Realistic thermal stress µm range resolution Fully PC controlled

EUFANET workshop 2006 – Wuppertal

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Thank you for your attention

I NSI DI X : System s and Service Topography and Deformation Measurem ent: Insidix TDM Acoustic Microscopy: Sonix SAM X-Ray Imaging and Tomography: Fein Focus X-Ray X-Ray Micro-Fluorescence: Edax/ Roentgenanalytik Eagle

  • EUFANET workshop 2006 – Wuppertal