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PCBA Flexural Fatigue Life Evaluation
www.cascade-eng.com
Reliability Engineering GroupCascade Engineering Services,
Inc.
6640 185th Ave NE Redmond WA 98052(425) 895-8617 x 564
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PCBA Flexural Fatigue Life Analysis
Test Objective• To evaluate PCB fatigue life under bending loads
• To quantify the effect of board modulus and thickness on fatigue
life
Methodology• Step 1: Geometry and Material Properties• Step 2:
Loads and Boundary Conditions• Step 3: FEA Result• Step 4:
Verification of FEA simulation with Test Data• Step 5: Fatigue Life
Estimation Result• Step 6: Design Parametric Study • Case Study
Benefits
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Step 1: Geometric Model & Material Properties
• Structure Dimensions L : W : T = 142.7 : 87.9 : 1.64 (mm)
• Material Properties for elastic model Young’s Modulus: 3.5 GPa
Poisson’s Ratio = 0.34
PCB Board Sample
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Step 2: Loads & Boundary Conditions
Displacement
Boundary constraints: X=Y=Z=0
Displacement
Boundary constraints: X=Y=Z=0
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Step 3: FEA Results
Displacement Plot at Z axis Strain Contour Plot
Von Mises Stress
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Step 4: Veri�cation of FEA simulation with Test Data
Displacement (mm)
Test Setup Load Displacement Curve
Variation of PCBA Strain with Applied Force
0
1000
2000
3000
4000
5000
6000
7000
8000
0 50 100 150 200 250 300
Force(N)
Str
ain
(uS
trai
n)
Experimental Data Simulation FR4-E1 Simulation FR4-E2
Calibrating Experimental and FEA Strain Data
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Step 5: Fatigue Life Estimation
bf
f NE
)(σ
ε =ε = elastic strain amplitude σf = fatigue strength
coefficient Nf = Cycles to failure
E = Young’s modulusb = fatigue strength exponentε = elastic
strain amplitude σf = fatigue strength coefficient Nf = Cycles to
failure
E = Young’s modulusb = fatigue strength exponentFatigue Model
:
Fatigue exponent and coefficient are material properties and
related to flexural strength and endurance limit
Effect of PCBA Strain on Flexural Fatigue Life
0
2000
4000
6000
8000
10000
12000
14000
16000
0 500 1000 1500 2000 2500 3000 3500 4000 4500Cycles to
failure
PC
BA
mic
roS
tra
ins
0
2
4
6
8
10
12
14
PC
BA
Dis
pla
cem
en
t (m
m)
Microstrains Displacement
0
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400
600
800
1000
1200
1400
1600
Cyc
les
to F
ailu
re
Life Test:8mm Life Test:12 mm Use Condition:4 mmPCBA
Displacement
PCBA Flexural Fatigue Life: Experiment vs Prediction
Prediction Experiment
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Step 6: Design Parametric Study
0
200
400
600
800
1000
1200
Cycle
s t
o F
ail
ure
Use Condition:4 mm Life Test:12mm
PCBA Displacement
Effect of PCBA Thickness on Flexural Fatigue
t=1.64mmt=0.82mm
0
1000
2000
3000
4000
5000
6000
Cyc
les
to F
ailu
re
Use Condition:4mm Life Test:12mmPCBA Displacement
Effect of PCBA Young's Modulus on Flexural Fatigue
E=3.5GPaE=7GPa
Fatigue life change with thickness change Fatigue life change
with Young’s Modulus change
• PCBA fatigue life deceased significantly when the thickness
decreased to half. Reducing thickness was not acceptable for the
current design.
• PCBA fatigue life increased with the increasing board modulus.
Choosing stiffer PCBA board was a viable alternative for the next
design revision.
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Case Study Bene�ts
A similar quick turnaround test-analysis-prediction methodology
can be useful for:
• Supplier qualification: Comparison of PCBA quality for
multiple vendors• Specification testing: Industry PCBA standard
test (JEDEC 3 Pt. bend, IPC etc.)• Design Limit Evaluation: Time
independent step stress test to failure• Design Sensitivity
Analysis: Virtually quantify effects of material and geometry
changes on product durability• Develop Accelerated life tests:
determine fatigue test limits for computing acceleration factors
for relevant failure mechanisms
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