PCBA Flexural Fatigue Life Evaluation - Cascade...
Transcript of PCBA Flexural Fatigue Life Evaluation - Cascade...
-
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
-
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
-
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
-
Step 2: Loads & Boundary Conditions
Displacement
Boundary constraints: X=Y=Z=0
Displacement
Boundary constraints: X=Y=Z=0
-
Step 3: FEA Results
Displacement Plot at Z axis Strain Contour Plot
Von Mises Stress
-
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
-
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
200
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
-
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.
-
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
CS02_pg01CS02_pg02CS02_pg03CS02_pg04CS02_pg05CS02_pg06CS02_pg07CS02_pg08CS02_pg09