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Thin Cu Stress Testing Project leader:Fujitsu Advanced Technologies Limited Facilitator: Hiko Nakamura Feb. 27-28, 2013 © HDP User Group International,

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Presentation on theme: "Thin Cu Stress Testing Project leader:Fujitsu Advanced Technologies Limited Facilitator: Hiko Nakamura Feb. 27-28, 2013 © HDP User Group International,"— Presentation transcript:

1 Thin Cu Stress Testing Project leader:Fujitsu Advanced Technologies Limited Facilitator: Hiko Nakamura Feb , 2013 © HDP User Group International, Inc. 1

2 Problem statement Thickness of plated copper in a small through hole or in a through hole with a high aspect ratio of a PWB may be critical to securing adequate reliability for temperature cycling. The reliability of thin Cu has been carried out using ATC. However, it takes long time to get the result. Prediction of thin Cu reliability by FEM simulation also is required thin Cu mechanical properties. 2 © HDP User Group International, Inc.

3 Objectives To characterize material property of plated thin Cu To study the relationship between material properties and thickness for plated Cu by mechanical stress testing and FEM simulations 3 © HDP User Group International, Inc.

4 Project Goal Propose how to measure stress-strain property and creep property of thin Cu Find out the similarities and differences between temperature cycling test and FEM simulation with the above properties for thin Cu (in order to decide adequate thickness for designated life time of a PWB) 4 © HDP User Group International, Inc.

5 Scope: Do and Do not in this project Do ・ How to measure mechanical properties of thin Cu ・ Prediction of lifetime for stress test by using FEM ・ Prediction of lifetime for Accelerated Temperature Cycle test by using FEM Do not ・ Find key parameters for better reliability on Cu plating process 5 © HDP User Group International, Inc.

6 Approach: How to measure thin Cu Try a stress test for a thin Cu to confirm whether it can be used as alternative of plated through hole. 6 © HDP User Group International, Inc. Cu plated sheet (20,30,50um in thickness) Cut into a test sample (a dumbbell shape) Do stress test (tension test) Mechanical property(σ-ε) [Stress-strain test]

7 Temperature dependencyThickness dependency Mechanical Property 7 © HDP User Group International, Inc.

8 Temperature dependencyThickness dependency Mechanical Property(in detail) 8 © HDP User Group International, Inc.

9 9 Crystal orientation Bulk Copper Electroplated Copper(50μm) (In subsurface region) (The inside region) Images processed by changing the CI area less than 0.3 into black color Many defects in grain boundary per volume  Lower Young’s modulus? Will reflow stresses change crystal orientation and Young’s modulus?

10 Mechanical Property Thickness[  m] Temp[K]Young’s Modulus [GPa] Yield stress [MPa] Work- hardening exponent ) -- Bulk copper ) 60 3) ) References 1)Kinji Tamakawa, Kazuhiko Sakutani, Hideo Miura : Journal of the Society of Materials Science Japan Vol.56 No.10, (2007), pp )Yoshihara Mae : “A story about Copper and Aluminum”, JIS, (2000), p.11 (In Japanese) 3)M. F. Ashby, D. R. H. Jones : ENGINEERING MATERIALS, (2004), p.94 4)A. Misra, X. Zhang, D. Hammon, R.G. Hoagland : Acta Materialia 53, (2005), p © HDP User Group International, Inc.

11 11 © HDP User Group International, Inc. Approach: How to measure thin Cu [Low cycle fatigue test] Samples must have a stiffness which can be pulled and pushed against repeated shear stress cycles. We are trying to make samples as follows. (1)An hourglass shaped plastic sample (2)An hourglass shaped plastic sample with thin plated Cu (Cu thickness: 15-20μm, 40μm, 60μm) Do a low cycle fatigue test Desirable result? (1)(2) Do the low cycle fatigue test Observe X-section of thin Cu

12 Specimen: Hourglass shaped plastic sample with thin plated Cu Fatigue test: Amplitude 120  m, Ramp rate 240  m/sec Fatigue test specimen 20μm in thickness Shape and dimensions Preliminary low cycle fatigue test (tension & compression force) 12 © HDP User Group International, Inc.

13 1mm 0.5mm Surface of specimen (after Fatigue test) 13 © HDP User Group International, Inc.

14 Fatigue test result (number of cycles vs. load reduction ratio) Fatigue test result 14 © HDP User Group International, Inc.

15 Hysteresis loop of load and displacement in Fatigue test 15 © HDP User Group International, Inc. Fatigue test result

16 Design a test board Build an FEM model of the test board Estimate the relationship between the life time of PTH and the thickness of plated Cu by FEM simulations Prepare some boards and do ATC, and compare FEM results Approach: Life time estimation for ATC 16 © HDP User Group International, Inc.

17 Meshed model  Solver : ANSYS ver  Element type : hexahedron 20 nodes (SOLID186)  Modeling : one half of a model (51,468 nodes)  Thermal load : trapezoid wave (398K(15min) - 233K(15min))  Young’s modulus : electroplated = 29 GPa bulk = 136 GPa  Creep strain characteristics : Garofalo law Comparison of electroplated copper and bulk copper Preliminary thermal fatigue simulation of through hole via Whole model Copper portion 17 © HDP User Group International, Inc.

18 Electroplated copper (Elast-creep analysis) Bulk copper (Elastic analysis) Contour map of total strain in y-direction after the 15 minute duration at 125C heated from 25C in the first cycle of ATC Simulated results 18 © HDP User Group International, Inc.

19 Relation between y-direction total strain vs. accelerated temperature cycle 19 © HDP User Group International, Inc. Simulated results (maximum point) Electroplated copper get plastically strained in ramp-up period

20 20 Further study © HDP User Group International, Inc. From the observation in page 9, effects of reflow soldering stress on electroplated copper should be considered. From the observation in page 19, ratchet type loading can be also used for fatigue test of thin electroplated copper.

21 21 A plan for further experiments © HDP User Group International, Inc. We would like to propose our plan by the end of May. Tension & compression forcesRatchet forces Stress-strain characteristicsFatigue test Thickness dependency at RT Temperature dependency Decide forces No reflow stress Thickness dependency at RT Temperature dependency Reflow stress 2x (ex.) Fatigue test specification Design Test Board Fabricate BoardFEM modeling ATC testingFEM simulation Analysis, consideration and final report Number of samples and test conditions should be discussed among project members and contributors draft

22 Promising deliverables A stress test method of thin Cu Stress-strain characteristics of thin Cu Observations of the tested samples by SEM Creep characteristics of thin Cu Comparison between the mechanical fatigue of actual ATC and FEM simulation with the obtained material properties © HDP User Group International, Inc.22

23 Project Execution Plan Project TaskPlanActual Project plan draft(Fujitsu)4/20125/2012 Preliminary testing5/20127/2012 Detailed description and schedule6/20129/2012 Thin Cu stress test and X-sectional observation, and trials of Low cycle fatigue test 10/ / /2012- Low cycle fatigue test of thin Cu, FEM simulations, and actual ATC test of a PWB 4/ /2014 Final report3/ © HDP User Group International, Inc.

24 Team Members and Resources Fujitsu Advanced Technologies – Project leader (Samples preparation, ATC, Report) Hitachi Chemical (Samples preparation, material property (TCE)) Shibaura Institute of Technology [non-member] (Methodology, Stress test, observation, FEM simulation) HDP User Group (Hiko Nakamura) - Project facilitator 24 © HDP User Group International, Inc.


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