18 TH INTERNATIONAL CONFERENCE ON COMPOSITE MATERIALS NUMERICAL EVALUATION OF THERMAL WARPAGE ON FLIP CHIP PACKAGE WITH RESPECT TO LAYER RESIDUAL RATE W. Song 1 , Y. Byun 2 , T. Ku 1 , J. Kim 2 , M. Kim 3 , H. Kang 3 , B. Kang 2 * 1 Industrial Liaison Innovation Center, Pusan National University, Busan, S. Korea, 2 Dept. of Aerospace Eng., Pusan National University, Busan, S. Korea, 3 BGA R&D Group, Samsung Electro-Mechanics Co., Ltd., Chungcheongnamdo, S. Korea * Corresponding author (H bskang@pusan.ac.krH ) Keywords : flip chip package, thermal warpage, finite element method, thermal expansion coefficient, glass fiber reinforced epoxy composite, layer residual rate 1 Introduction PCB, in case that the material selection and The reliability problems of flip chip (FC) packages thickness of each layer are under the restriction subjected to temperature change during the without change. It is noted that the coplanarity of FC packaging process mainly occur due to mismatches package can be enhanced with about 30% as only in the coefficients of thermal expansion [1]. FC adjusting the residual rates of Cu and SR film in package is generally consisted with main chip bare PCB. (Silicon), underfill and bare printed circuit board (PCB), as shown in Fig. 1. Resin molding 2 Finite Element Analysis compounds like underfill and glass fiber reinforced epoxy composites (GFRC) used in FC package 2.1 Finite Element Model strongly exhibit temperature-dependent material Numerical simulation is performed for the whole properties [2, 3]. In this study, the thermal warpage body of FC package with main chip, underfill and of FC package is evaluated using finite element bare PCB. Finite element model of FC package is analysis (FEA). The thermal warpage of FC package shown in Fig. 2. Bare PCB is constructed by SR film, was simulated and compared with respect to the GFRC prepreg and Cu layers. Main chip and variation of Cu and SR film residual rates in bare underfill area are modeled by solid element and bare PCB is modeled by layered shell element. The nodes Numerical Evaluation Part Die in the sharing region between underfill and bare Epoxy Bump SR Via ABF PCB are merged in the finite element model. Solder Cu Land Plugging bumps in the underfill region are ignored in this Prepreg analysis due to the relatively weak mechanical characteristics of the bump. The residual rates on Cu Solder Chip (Silicon) Fig.1. Schematic diagram of flip chip package. Underfill Table 1. The given condition on Cu & SR residual Bare rate in bare printed circuit board. Printed Circuit Layer Residual Rate [%] Board Upper SR 89.2 Cu 56.6 Fixed condition Prepreg - Cu 60.2 Prepreg - Cu 47.0 Prepreg - Cu 52.1 Fig.2. Finite element model and layer construction Lower SR 76.6 of bare printed circuit board.
Coefficient of Thermal Expansion, α [ppm] Prepreg (horizontal direction on the in-plane) Underfill 4 2.5x10 200 Prepreg (vertical direction on the in-plane) SR film Prepreg (thickness direction on the out-of-plane) Elastic Modulus [MPa] Underfill 4 160 2.0x10 4 120 1.5x10 4 80 1.0x10 40 3 5.0x10 0 0.0 80 120 160 200 240 80 120 160 200 240 o C] Temperature [ o C] Temperature [ (a) CTEs of underfill and SR film (a) Young’s moduli of GFRC and underfill Coefficient of Thermal Expansion, α [ppm] 50 Prepreg (horizontal direction on the in-plane) Cu Prepreg (vertical direction on the in-plane) 150 Prepreg (thickness direction on the out-of-plane) 40 Cu Effective Stress [MPa] 120 30 90 20 60 10 30 0 80 120 160 200 240 0 0.00 0.01 0.02 0.03 0.04 0.05 0.06 o C] Temperature [ Effective Strain (b)CTEs of GFRC and Cu (b) Stress-strain relationship of Cu Fig.4. Thermal properties of layer materials in flip Fig.3. Mechanical properties of layer materials in chip package. flip chip package. Flip Chip Package Bare PCB Level and SR layer were given in Table. 1. In this study, Level 300 the residual rates are main parameters to evaluate the Heating & Cooling rate : 10 O C/ min Peak thermal coplanarity of FC package. 250 240 O C Peak 220 O C 2.2 Material Properties O C] 200 175 O C 165 O C 1 hr Temperature [ 150 O C 1 hr Mechanical properties of underfill and GFRC 1 hr 150 125 O C Prepreg are shown in Fig. 3, which are temperature 1 hr dependent and measured by DMA Q800 of TA 100 instruments. Thermal properties of underfill, GFRC 50 Prepreg, SR film and Cu are also shown in Fig. 4, 25 O C 25 O C 25 O C which are also temperature dependent and measured 0 0.0 5.0k 10.0k 15.0k 20.0k 25.0k 30.0k 35.0k 40.0k by TMA 4000SA of Material Analysis & Time [sec] Characterization. The mechanical and thermal Fig.5. Thermal environment in the package process properties of GFRC were tested in orthogonal of FC package. directions due to the orthogonal material characteristics of GFRC. Fig. 3 shows the stress- Thermal environment in the packaging process of strain relation of Cu. Silicon is considered as an FC package is shown in Fig. 5. In this simulation, isotropic, perfectly-elastic and temperature- the temperature change is assigned in the whole independent material with E: 169GPa, CTE: 3.0E-6. finite element models with room temperature (25 o C) after peak value (240 o C). To evaluate the thermal 2.3 Simulation Conditions
Table 2. Parametric study conditions on Cu & SR No.1 No.2 residual rates. Variation of Cu & SR Residual Rate [%] Layer No.1 No.2 No.3 No.4 No.5 No.6 No.7 No.8 No.9 � 1 � 5 � 10 � 1 � 5 � 10 U_SR - - - � 1 � 5 � 10 � 1 � 5 � 10 Cu - - - 58.2um 50.2um PPG - - - - - - - - - � 1 � 5 � 10 � 1 � 5 � 10 Cu - - - PPG - - - - - - - - - No.3 No.4 � 1 � 5 � 10 � 1 � 5 � 10 Cu - - - PPG - - - - - - - - - � 1 � 5 � 10 � 1 � 5 � 10 Cu - - - � 1 � 5 � 10 � 1 � 5 � 10 L_SR - - - 59.1um 43.2um B-B’ No.5 No.6 25 O C Thermal B-B’ 54.5um 50.9um Warpage � 60.8um Fig.6. Thermal warpage and deforming No.7 No.8 configuration of the given FC package model. 0.09 Thermal Warpage(Coplanarity) [mm] 0.08 56.8um 46.7um 0.07 (16% � ) 60.8um (23% � ) 50.9um (30% � ) 0.06 46.7um (34% � ) No.9 43.2um 39.8um 0.05 40um 0.04 0.03 0.02 39.8um 0.01 0.00 The given model No.1 No. 2 NO. 3 No. 4 No. 5 No.6 No. 7 No. 8 No. 9 Fig.8. Thermal warpage configurations with respect to variation of Cu & SR residual rate. Fig.7. Thermal warpage comparison with the variation conditions of the residual rates on warpage of FC package, the Cu and SR film residual Cu and SR film as shown in Table 2, which rates in bare PCB were changed. The variations of conditions were determined from the primitive FEA Cu and SR film residual rates in bare PCB for each result for the given model. The results of the FEA of model (No.1 ~ 9) are shown in Table 2. Through the the model No.1 to 9 are shown in Fig. 7 and 8. As result of the FEA for the given residual rate model in you can see Fig. 7, the adjustment of the residual Fig. 6., it is noted that bare PCB was deformed as rates of Cu and SR film in bare PCB can improve the convex configuration and main chip was the coplanarity of FC package with about 30% for deformed as the concave configuration due to the the temperature change. coefficient of thermal expansion mismatch. It is concluded that the proposed concept of the adjustment of residual rates on Cu and SR film can play a feasible role to reduce the thermal warpage in 3 Results and Discussions the design stage of FC package as the design The thermal warpage of FC package was evaluated guideline in the semiconductor industry. 3
Acknowledgements This work was supported by grants-in-aid for the National Core Research Center program through the National Research Foundation of Korea funded by the MEST (No. R15-2006-022-02002-0). Also the last author would like to thank the partial support by the Korea governments (MEST / KOTEF) through the Human Resource Training Project for Regional Innovation. References [1] K. Oh and J. J “Submicro-displacement measuring system with Moire interferometer and application to the thermal deformation of PBGA package”. Trans. of the KSME(A) , Vol. 28, No. 11, pp 1646-1655, 2004. [2] B. Oliveira and G. Creus “An analytical numerical framework for the study of ageing in fiber reinforced polymer composites”. Composite Structures , Vol. 65, pp 443-457, 2004. [3] Y. He “Thermomechanical and viscoelastic behavior of a no flow Underfill material for flip chip applications”. Thermochimica Acta , Vol. 439, pp 127-134, 2005.
Recommend
More recommend
