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 1 EUFANET workshop 2006 – Wuppertal
Challenges 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 2 EUFANET workshop 2006 – Wuppertal
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 � … I nterconnection Bum p Die Molding Die pad com pound Substrate upon Via protection layer Substrate Solder m ask Electric via Therm al Via PCB Pad Technological design example Technological design I nterconnection Bum p 3 EUFANET workshop 2006 – Wuppertal
Thermo-mechanic stress: A key problem Therm al stress � Constant temperature : T [ °C] dT � [ °C s -1 ] (x , y , z) Dynamic situation : dt dT � [ °C z -1 ] (x , y ) Thermal flux : dz Mechanical stress � Screwing of PCB � Clamping of components in sockets � Mechanically fixed and tightened heat sinks � … 4 EUFANET workshop 2006 – Wuppertal
Experimental problem 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) � … 5 EUFANET workshop 2006 – Wuppertal
Classical development and analysis techniques 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 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 6 EUFANET workshop 2006 – Wuppertal
Reliability evaluation by TDM 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 : Δ z • I n-plane deformation : Δ x, Δ y • THUS : Deform ation is a failure risk indicator 7 EUFANET workshop 2006 – Wuppertal
Deformation under temperature variation S 2 S 1 S 3 z z 1 T = - 40°C z 2 z 3 0 Strain Compression Δ l/l T = 25°C Δ z Δ x 1 - CTE 1 CTE Δ z 1 z 1 + Δ z 1 Δ x 2 - CTE 2 z 2 + Δ z 2 Δ z 2 0 T = 260°C z 3 + Δ z 3 Δ z 3 Δ x 3 - CTE 3 Temperature Warpage ( Δ z) measurement variation Δ l/l measurement delamination risk CTE mismatch evaluation 8 EUFANET workshop 2006 – Wuppertal
New experimental approach TDM: Topography and Deformation Measurement under representative thermo-mechanical stress Camera Top heating Light Top source Cooling Top thermocouple Sample holder Bottom Bottom thermocouple Cooling Bottom heating • 3D absolute topography and deform ation analysis Spatial resolution : ~ 2 µm • • JEDEC type tem perature profiles capability 9 EUFANET workshop 2006 – Wuppertal
Application 1 : Brazing Al 2 O 3 on Cu Cu B Geometry variation during brazing process Al 2 O 3 : convex Al 2 O 3 Cu : concave B’ A A A’ A’ B B’ 1 0 EUFANET workshop 2006 – Wuppertal
Application 1 : Brazing Al 2 O 3 on Cu 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 1 1 EUFANET workshop 2006 – Wuppertal
Application 2 : Delamination during reflow Problem � 2 families of identical BGAs, produced at 2 different production sites profils de température sur les differents composants � One family ok, the other one fails during reflow 300 250 Tmax = 245°C 200 temperature (°C) 150 comp8 comp1et8 100 comp2et3 comp4et5 comp2et3 comp4et5 50 comp1 comp6et7 0 0 60 120 180 240 300 360 420 480 540 600 660 720 780 840 900 960 time (s) 1 2 EUFANET workshop 2006 – Wuppertal
Application 2 : Delamination during reflow BGA during reflow: Deformation analysis 183 °C 150°C 165 °C 173 °C 200 °C t0 = initial 157 °C * 200 °C * 225 °C * 143 °C * 170 °C * 245 °C Z [µm] t0 T max t1 = final T ambiant t1 1 3 EUFANET workshop 2006 – Wuppertal
Application 2 : Delamination during reflow Analysis for 2 components of each family comp1 comp2 comp3 comp4 T 23°C initial (t0) Warning rate z different = 260µm T max (245°C) T 23°C final (t1) 1 4 EUFANET workshop 2006 – Wuppertal
Application 2 : Delamination during reflow Delamination checked by SAM Series 1 and 2: no delam ination Series 3 and 4: delam ination Series 1 Series 2 Series 3 Series 4 2 3 Comp. 1 1 Comp. 3 Comp. 4 4 Comp. 2 5 6 7 8 1 5 EUFANET workshop 2006 – Wuppertal
Application 3 : CTE mismatch analysis I so-displacement fields Displacement field (vector x100) X direction Y direction Δ X~ 1pix.~ 16µm Δ Y~ 1pix.~ 16µm � Axi-symmetric displacement field Strain fields Y direction ( Δ L/ L) X direction � Mean strain ~ 1 7 0 0 ppm CTE ~ 1 4 × 1 0 -6 / ° C � 1 6 EUFANET workshop 2006 – Wuppertal
Application 3 : CTE mismatch analysis I so-displacement fields Displacement field (vector x100) X direction Y direction Δ X~ 0.7pix.~ 12µm Δ Y~ 0.8pix.~ 13µm Strain fields ( Δ L/ L) Y direction X direction � Mean strain ~ 1 2 0 0 ppm CTE ~ 1 0 × 1 0 -6 / ° C � 1 7 EUFANET workshop 2006 – Wuppertal
Application 3 : CTE mismatch analysis I so-displacement fields pixel pixel Displacement field (vector x100) X direction Y direction Δ X~ 0.8pix.~ 13µm Δ Y~ 0.9pix.~ 14µm � Axi-symmetric displacement field Strain fields X direction ( Δ L/ L) Y direction � Mean strain ~ 1 3 5 0 ppm CTE ~ 1 1 × 1 0 -6 / ° C � 1 8 EUFANET workshop 2006 – Wuppertal
Conclusions Challenges Thermal management TDM Contribution PCB deformation during reflow 3D deformation measurement BGA balls breaking Realistic thermal stress Delamination µm range resolution Fully PC controlled TDM Benefits Prevention and anticipation Failure understanding Reflow analysis Fatigue analysis 1 9 EUFANET workshop 2006 – Wuppertal
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 2 0 EUFANET workshop 2006 – Wuppertal
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