Parametric Analysis of TEBGA Reliability Using a Finite-Volume-Weighted Averaging Technique

Transcription

1 May 23, 2003

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3 ( ) BGA: PBGA, CBGA, TBGA, CCGA PBGA over CBGA: Lower cost of substrate Smaller global CTE mismatch from PCB Lower profile Conventional Over Molded PBGA Packages Experience: Excessive moisture sensitivity of substrate Poor thermal performance of over molded compound TEBGA Provides: The enhanced thermal performance over PBGA Relatively cost-effective over CBGA With Solder Joint Reliability(SJR) in Concern: Similar to PBGA, potential SJR problems still occur in TEBGA.

4 ( ) Characterization of Strain/Stress Concentration Field is Critical. Fatigue life Stress/Strain Information Stress/Strain Information Geometry/Material Geometry/Material Mesh Desnsity Due to material and geometry singuarities Techniques: Explicit geometry representation (Fillet) High mesh density Material-nonlinear modeling Work only for Stress Concentration Problem NSMD Averaging Technique (Clark and Mcgregor, 1993; Akay et.al., 1997) Considerably conservative result is obtained due to the whole domain area is averaged SMD

5 TEBGA The structural response is averaged in a finite zone instead of averaging the response within the whole domain, An engineering empirical approach is used to determine the dimension of the finite zone

6 BGA Vacuum Device BGA Ball Placement and Reflow IR Reflow BGA on Board Surface Mount Process

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8 ( ) F r θ l θ u F w R h R 0

9 ( ) o = 0 θ Nonwettable o 0 < θ < 180 o Partially wettable θ o = 180 θ Fully wettable Bridging

10 ( ) Surface Evolver Numerically estimate the restoring force and shape of round/elliptical/rectangular pads Assumed : Eutectic solder ((63%Sn/37%Pb) is perfectly wettable to the copper pad. Static Equilibrium Condition The total energy of a liquid body: Surface tension energy Gravitational energy External energy

11 ( ) Variational free energy and restoring force along the gravitational direction of the solder ball: δe = T F r E E = ( divh n Dg n) da + ρg (( div k ) h curl( h k ) da P h S E H v surface _ tension gravity H E H v v v S 2 z 2 = ( Esurface _ tension + Egravity + Eexternal _ = ρg external _ force H = T s v v v v ( h n Dh n) da [ ( k ) h ( h s z 2 2 v v v 2 v V = P H = P z 2 s k )] da v v h da v v v force 2 z 2 r ) / H r S v r da

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13 256-Pin TEBGA PCB Table: TEBGA Material Property Materials Heat Spreader BT Substrate Silicon Chip Eutectic Solder Ball Epoxy Die Attach Epoxy Encapsulant FR-4 PCB Young s Modulus (GPa) Poisson Ratio CTE (ppm/ o C ) ~16.7(X,Y) 57.0 (Z) o C < o >0 C (X,Y) 72.0 (Z) Table: TEBGA Geometry Data Components Die PCB BT Heat Spreader Die Attach Size 6x6x x32.4x x5.836x x5.836x x27x0.28 6x6x0.047

14 Temperature-dependent (Plasticity) Time-dependent (Creep) ε A B n σ H R T & cp Garfolo Hyperbolic Sine Law cp n H ε& = A(sinh B σ ) exp RT = The uniaxial = 147.9(1/se c) equivalent creep strain = (1/M Pa) = Stress exponent : 3 = Equivalent stress = Activatio n energy : (J/mol) = The = The gas constant : 8.31 (J/mol/k) absolute temperatur e rate Stress (MPa) o C o C Strain

15 An Empirical Coffin-Manson Relationship N f = 1 2 ε 2ε IE f (1 / c) Equivalent Plastic Strain De eq (%) N f = ( ε eq ) 1/ Gull-Wing Lead Butt Lead J-Lead ,000 10,000 Number of Cycles to Failure

16 Finite-Volume-Weighted Averaging Technique = n n edω e= 1Ω e= 1Ω ~ ε ε e dω e n ε e Ω ~ ε e = = = = The total number of elements in the zone The strain of the e - th element The volume (area) of the e - th element The volume - weighted averaging strain in the zone Rules to Determine the Dimension of the Finite Zone In an empirical engineering approximation manner: Small enough to capture the maximal strain field Large enough to obtain a converging solution as the mesh density increases

17 # of Elements within the fan shape: 18, 66, 192, 504 Four different radii are defined: 0.01, 0.02, 0.04, 0.06 mm. o 100 C A net termperature swing = ; plastic behaviors considered. 20 µm zone provide considerable agreement to the proposed criterion. A C B D Fan-shape circular sector 0.12 mm Averaged Equivalent Plastic Strain radius=10 (Micro meter) radius= radius=40 radius= A B C Mesh Density D

18 1/2 package is modeled due to the symmmetric condition 2-D plane strain finite element model Elements: Nodes: The inelastic strain within the characterized finite zone will be averaged using a Volume-Weighted Averaging Technique. MARC+MENTAT

19 Portable Engineering Moire Interferometer (PEMI) with phaseshifting technique m /fringe; High frequency of 2400 lines/mm o 25 ~ 125 o C C µ U Displacement Field V Displacement Field

20 Moire Interferometry Plane Strain F.E. Modeling 3-D Solid F.E. Modeling U-Displacement V-Displacement Field (um) Field (um) CPU time ( Second) Plane Strain F.E. M odeling 3-D Solid F.E. M odeling

21 Design Parameters: Geomertry/Thickness Die/PCB/Die Attach/Heat Spreader Geometry/Size Die Material/Young s Modulus/CTE FR-4 Thermal Cycling-ATC Test 5 min linear temperature loading/unloading 20 min low/high termperature dwell periods 50 min/cycle o Test temperature range: -40 C~ 125 Stress free temperature: 25 o C o C

22 When a System is Subjected to a Reversal Cyclic Stress, a Creep Strain can be Accumulated σ 12 Ratcheting Maximum Averaged Equivalent Strain ε 12 Ratcheting: A Relative Motion Between the Pad and Paste Is Generated, Leading to Crack Initiation The ε IE is stablized within 10 cycles Temperature Cycles

23 ( ) Nonlinear Relationship is Detected between: Solder Joint Fatigue Life -vs.- Die Size The maximum fatigue life appears at die size = 7 mm Cavity-down TEBGA / / Cavity-up PBGA Cavity-up PBGA: The larger the die size; the shorter the fatigue life The location experiencing with the largest CTE mismatch is right beneath the chip Cavity-down TEBGA: A nonlinear relationship is obtained A more complicated failure mechanism) Cycles to Failure Die Size (mm)

24 ( ) Two Major Failure Mechanisms: Global Mismatch: CTE of PCB >> CTE of the Package The farther distance from the center of the package, the larger the deformation Local Mismatch: CTE mismatch between the heat sprader and the die Maximum Average Inelastic Strain Die Size=2. Die Size=6. Die Size= Ball Numbering Ball Numbering

25 (a) Die Size = 2.0 mm (b) Die Size = 6.0 mm (c) Die Size = 10.0 mm

26 (a) Die Size = 2.0 mm 1.912e+02 (b) Die Size = 6.0 mm (c) Die Size = 10.0 mm

27 Cycles to Failue Cycles to Failure Die Thickness (mm) PCB Thickness (mm) Die Thickness PCB Thickness Cyclles to Failure Cycles to Failure Die Attach Thickness (mm) Heat Spreader Thickness (mm) Die Attach Thickness Heat Spreader Thickness

28 Cycles to Failure Cycles to Failure PCB Young's Modulus (GPa) 0 1.0E E E E E E-05 PCB CTE (ppm/degree of Celcius) PCB Y s Modulus PCB CTE

29 FCOG

30 NCA Type FCOG using the MBB Technology Hatada et. al.,1988 Masuda et. Al.,1989 Hu et. Al.,1996 LSI Chip UV Resin Glass Substrate Electrode Bump

31 Bonding Structure Conduction Underfill Reworkability Solder Bump IC Metal Fusing Need Expensive MBB IC Mechanical contact Not Need Yes

32 Contraction of the adhesive during hardening Loss of electrical contact Adhesive expands in the Z-dir due to thermal expansion Delamination and cracking occurring in adhesive The bonding stresses are excessive

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34 Solid Metal / Compliant Bumps Parametric analysis over numbers of parameters Au Solid Metal Bump Compliant Bump PI AL/Au alloy

35 Al Pad Si 3 N 4 Passivation Silicon TiW/Au UBM Photoresist Au Bump Sputtering of TiW and Au Electroplating Au Photoresist Resist Removal

36 FCOG LSI chip Bump Size = Pitch = 100µm 60 µ m 60µ m A Bump Chip A Section A-A

37 FCOG Light-Setting NCA Drop light-setting resin on the substrate Electrode Align LSI chip and substrate Glass Substrate Chip Apply pressing force and perform UV lightsetting Alignment Bonding Pressure Release the Bonding Pressure Chip Glass Substrate UV

38 (External Pressure) uniformity/hardness and flatness of the bumps/the configuration of the assembly A daisy chain resistance test

39 P & Current The contact resistance may be expressed as: R = c [ ] 2 ρ ηπh/4p 1/2 (Timisit, 1999) η :empirical coefficient ρ :electrical resistivity H :hardness

40 LSI chip Bump 260 I/O 3-D Sliced nonlinear model nodes 3945 elements

41 Gold Al Stress (MPa) Stress (MPa) Strain Strain Gold AL alloy Young's Modulus(Mpa) Poisson Ratio CTE(/C) DENS(Kg/m**3) Silicon 1.90E E UV Fig Fig OCG 1.16E Fig.3 DUPON 2.40E Fig.4

42 ( ) Young's Modulus (MPa) CTE Temperautre Temperature Young s Modulus of UV resin CTE of UV resin OCG CTE CTE Temperature Temperature CTE of OCG PI CTE of DUPON PI

43 FCOG FE simulation applies a death and birth technique Apply External Pressure at T=100 ºC on the Top of Dies FE model include Dies,Bumps,Electrodes,Glass Substrate Perform UV Light Exposure and Cure at T=100 ºC FE model includes Dies,Bumps,Electrodes,Glass Substrates,and Resin Release the External Pressure at T=100 ºC FE model includes all the components Cool Down to Room Temperature at T=25 ºC FE model includes all the components

44 The compliant-bump exhibits a higher contact stress than the Au-bump Average Contact Stress (MPa) GOLD BUMP OCG PI DUPON PI Process Steps External force 5 Kg g/pad Au Bump 25 um Compliant Bump 8 um Bump Size 60 X 60 um

45 The Au-bump assembly achieves a more stable contact stress Average Contact Stress (MPa) Temperature ( ) GOLD BUMP OCG PI DUPON PI

46 Adhesion stress at each step (UV Resin) = 15 Mpa The Au-bump drives an excessive adhesion stress The OCG-PI-bump presents the min. adhesive stress Adhesion Stresses(MPa) GOLD BUMP OCG PI DUPON PI STEPs

47 Possible Location for Crack Initiations The Au bump case => between the substrates and resin The Compliant bump case =>between the dies and resin GOLD BUMP OCG PI DUPON PI σ max =19.83MPa σ max = 9.85MPa σ =11.42 max MPa

48 ( ) 280 OCG PI DUPON PI 220 GOLD BUMP OCG PI DUPON PI Contace Stress(MPa) Al Thickness (um) Average Contact Stress (MPa) Bump Size (µm 2 ) Aluminum thickness Alum. thickness Contact stress Bump Size Bump Size Contact stress

49 ( ) Average Contact Stress (MPa) Bump Height (µm) OCG PI DUPON PI Average Contact Stress(MPa) Bump Height ( µ m) GOLD BUMP Average Contact Stress (MPa) GOLD BUMP OCG PI DUPON PI Bonding Force (Kg) Bump Height Bonding Force Bump Height Contact stress Bonding Force Contact stress

50 ( ) Average Contact Stress (MPa) Young's Modulus of UV Resin (%) B C D Average Contact Stress (MPa) Young's Modulus of PI (%) OCG PI DUPON PI UV Y s Modulus UV Y s Modulus Contact stress PI Y s Modulus PI Y s Modulus Contact stress

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52 LIGA

53 (a) (b) (c) (d) Courtesy by Dr. Yao, NCHC

54 CMOS batch process)

55 Membrane Structure Fabricated By: Surface Micromachined by Isotropic Etching of Sacrificial Layer Bulk Micromachined by Anisotropic Etching of Substrate Material Primary Application of Suspended Membrane Structure Optical Deflection Capacitance Detection Isolated Thermal Massa An Isolated Thermal Mass for thermal radiation detection Electrical connection was furnished through suspension arms

56 Test Keys Process Flow Single-Poly-Double-Metal (SPDM) CMOS Process LOCOS(local oxidation of silicon) NSG(nondoped silicate glass) Ti PECVD Oxide PSG PECVD Nitride Dry etching opening RIE etching Suspended structure Front side bulk micromachining CMOS Process RIE Etching Bulk Micromachining

57 LOCOS and NSG Material Parameters concerned: Residual Stress (in-plane stresses) Intrinsic stress: Grown lattice mismatch Extrinsic stress: Thermal property mismatch Poisson ratio CTE Young s modulus

58 6 layer (45 um X27 um Suspended Membrane) Membrane Suspended by a pair of 2.5 um wide serpentine arms at each side 0.7 um wide titanium line in serpentine shape A temperature sensing resister Electrical Connection Silicon beneath the membrane was etched by heated TMAH solution Courtesy by NCHC/METRODYNE MICROSYSTEM CO.

59 Courtesy by NCHC/METRODYNE MICROSYSTEM CO.

60 y = x x y = x x Data 0.4 Parabolic Membrane Measured Simulated Courtesy by NCHC/METRODYNE MICROSYSTEM CO.

61 Acknowledgement