Thin Cu Stress Testing Project leader:Fujitsu Advanced Technologies Limited Facilitator: Hiko...
-
Upload
braden-shakespeare -
Category
Documents
-
view
216 -
download
4
Transcript of Thin Cu Stress Testing Project leader:Fujitsu Advanced Technologies Limited Facilitator: Hiko...
Thin Cu Stress Testing
Project leader:Fujitsu Advanced Technologies LimitedFacilitator: Hiko Nakamura
Feb. 27-28, 2013
© HDP User Group International, Inc.1
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.
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.
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.
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.
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]
Temperature dependency Thickness dependency
Mechanical Property
7
© HDP User Group International, Inc.
Temperature dependency Thickness dependency
Mechanical Property(in detail)
8
© HDP User Group International, Inc.
9
© HDP User Group International, Inc.
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?
Mechanical Property
Thickness[mm] Temp[K] Young’s Modulus [GPa]
Yield stress [MPa]
Work-hardening exponent
50
298 115 249 0.116
323 122 248 0.113
348 91 241 0.121
373 90 215 0.109
398 49 166 0.190
30 298 61 213 0.134
20298 45 208 0.120
348 42 192 0.102
10 298 29 1) - -Bulk copper 298 136 2) 60 3) 0.350 4)
References1) Kinji Tamakawa, Kazuhiko Sakutani, Hideo Miura: Journal of the Society of Materials Science Japan Vol.56 No.10,
(2007), pp.907-9122) 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.944) A. Misra, X. Zhang, D. Hammon, R.G. Hoagland: Acta Materialia 53, (2005), p.224
10
© HDP User Group International, Inc.
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 pushedagainst 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 testObserve X-section of thin Cu
Specimen: Hourglass shaped plastic sample with thin plated CuFatigue test: Amplitude 120mm, Ramp rate 240mm/sec
Fatigue test specimen20μm in thickness
Shape and dimensions
Preliminary low cycle fatigue test(tension & compression force)
12
© HDP User Group International, Inc.
1mm 0.5mm
Surface of specimen(after Fatigue test)
13
© HDP User Group International, Inc.
Fatigue test result (number of cycles vs. load reduction ratio)
Fatigue test result
14
© HDP User Group International, Inc.
Hysteresis loop of load and displacement in Fatigue test
15
© HDP User Group International, Inc.
Fatigue test result
• 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.
Meshed model
Solver : ANSYS ver. 14.0 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
)24067
- ( exp] )03.0([sinh 105 2.219ss T
Comparison of electroplated copper and bulk copper
Preliminary thermal fatiguesimulation of through hole via
Whole model Copper portion
17
© HDP User Group International, Inc.
Electroplated copper(Elast-creep analysis)
Bulk copper(Elastic analysis)
Contour map of total strain in y-direction after the 15 minuteduration at 125C heated from 25C in the first cycle of ATC
Simulated results
18
© HDP User Group International, Inc.
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
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
A plan for further experiments
© HDP User Group International, Inc.• We would like to propose our plan by the end of May.
Tension & compression forces Ratchet forces
Stress-strain characteristics Fatigue 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 Board FEM modeling
ATC testing FEM simulation
Analysis, consideration and final report
Number of samples andtest conditions should bediscussed among projectmembers and contributors
draft
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
Project Execution Plan
Project Task Plan Actual
Project plan draft(Fujitsu) 4/2012 5/2012
Preliminary testing 5/2012 7/2012
Detailed description and schedule 6/2012 9/2012
Thin Cu stress test and X-sectional observation,and trials of Low cycle fatigue test
10/2012-3/2013
10/2012-
Low cycle fatigue test of thin Cu, FEM simulations,and actual ATC test of a PWB
4/2013-2/2014
Final report 3/2014
23
© HDP User Group International, Inc.
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.