parametric analysis of tebga reliability using a finitevolume 采用有限體積tebga可靠性參數(shù)分析

1、Parametric Analysis of TEBGA Reliability Using a Finite-Volume-Weighted Averaging Technique,Hsien-Chie Cheng Computational Solid Mechanics Laboratory National Center for High-Performance Computing Kuo-Ning Chiang Power Mechanical Engineering National Tsing Hua University Chao-Kuang Chen Computationa

2、l Solid Mechanics Laboratory National Center for High-Performance Computing,Outline,Introduction Modeling The Finite-Volume-Weighted Averaging Technique Parametric Design of The TEBGA Reliability Conclusions,Introduction,BGA: PBGA, CBGA, TBGA, CCGA PBGA over CBGA: Lower cost of substrate Smaller glo

3、bal 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 Rel

4、iability(SJR) in Concern: Similar to PBGA, potential SJR problems still occur in TEBGA.,Introduction (Cont.),Many Studies on C-up PBGA Reliability: Paydar et. al., 1994; Pan, 1994; Hong, 1997; Jung et. al,1997; Winter and Wallach, 1997; Lau and Pao, 1997, etc. Few Investigations on C-down TEBGA: Pao

5、 et. al, 1998; Lee and Lau, 1998, etc. Most focus on the prediction of SJR. SJR is function of many parameters. Appropriate combinations of these parameters can signigicantly enhance SJR. Two Techniques for this Purpose: Design of Optimization (DO) or Design of Experiment (Box, 1978) Require tremend

6、ous, time-comsuming trials Parametric FEA (Yeh et. al, 1996) More cost-effective Reflect the effect of each parameter on the problem in concern,Introduction (Cont.),Characterization of Strain/Stress Concentration Field is Critical. Fatigue life Stress/Strain Information Stress/Strain Information Mes

7、h Desnsity (Due to material and geometry singuarities) Techniques: Explicit geometry representation (Fillet) High mesh density Material-nonlinear modeling Work only for Stress Concentration Problem Averaging Technique (Clark and Mcgregor, 1993; Akay et.al., 1997) Considerably conservative result is

8、obtained due to the whole domain area is averaged,Purposes,An Improved Averaging Technique: Finite-Volume-Weighted Averaging Technique Instead of averaging the response within the whole domain, the structural response is averaged in a finite zone Determine the dimension of the finite zone using an e

9、ngineering emprirical approach Design Parametric Finite Element Analysis Design parameters: Geomertry/Thickness : Die/PCB/Die Attach/Heat Spreader/BT Substrate Geometry/Size : Die Material/Youngs Modulus : FR-4/BT/Die Attach Material/CTE : BT/FR-4,PBGA and Thermal Enhanced BGA,256-Pin TEBGA and Mode

10、ling,Solder Joint Material Property,Temperature-dependent (Plasticity) Time-dependent (Creep) Garfolo Hyperbolic Sine Law,Fatigue Life Prediction,An Empirical Coffin-Manson Relationship,Improved Volume-Weighted Averaging Technique,Finite-Volume-Weighted Averaging Technique Rules to Determine the Dim

11、ension 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,Determination of the Finite Zone,# of Elements within the fan shape: 18, 66, 192, 504 Four different

12、 radii are defined: 0.01, 0.02, 0.04, 0.06 mm. A net termperature swing = ; plastic behaviors considered. 20 zone provide considerable agreement to the proposed criterion.,A,B,C,D,Finite Element Modeling,1/2 package is modeled due to the symmmetric condition 2-D plane strain finite element model Ele

13、ments: 20685 Nodes: 21129 The inelastic strain within the characterized finite zone will be averaged using a Volume-Weighted Technique.,Parametric Design of TEBGA Reliability,Design Parameters: Geomertry/Thickness : Die/PCB/Die Attach/Heat Spreader/BT Geometry/Size : Die Material/Youngs Modulus : FR

14、-4/BT/Die Attach Material/CTE : BT/FR-4 Thermal Cycling 5 min linear temperature loading/unloading 20 min low/high termperature dwell periods Test temperature range: -40 125 Stress free temperature: 25 Assume the is stablized within two cycles,Geometry: Die Size,Nonlinear relationship is detected Be

15、tween: 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 T

16、EBGA: A nonlinear relationship is obtained A more complicated failure mechanism),Die Size,Geometry: Die Size (Cont.),Two Major Failure Mechanisms: Global Mismatch: CTE of PCB CTE of the Package The farther distance from the center of the package, the larger deformation Local Mismatch: CTE mismatch b

17、etween the heat sprader and the die,Ball Numbering,Geometry:Thickness,Die Thickness,PCB Thickness,Die Attach Thickness,Heat Spreader Thickness,BT Thickness,Materials: Youngs Modulus/CTE,PCB Ys Modulus,BT Ys Modulus,Die Attach Ys Modulus,BT CTE,PCB CTE,Conclusions,Introduction of a Finite-Volume-Weig

18、hted Averaging Technique: Dimension of the zone determined using an empirical approximation mehtod. The strain/stress concentrtion responses can be characterized, and would no more be mesh-sensitive/dependent. Further experimental verification to really predict fatigue life of Solder Joints. A parametric study of the reliability