Yoga Poses May be Good For You, but Not Your Ceramic Capacitor

1. Yoga Poses May be Good for You, but
Not Your Ceramic Capacitor

2. 2© KEMET Electronics. All Rights Reserved.
Outline
Introduction
Materials Background
Flex Cracks, Causes, and Design Tips
Flex Mitigation Solutions
Thermal Shock and How to Avoid

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MLCCs
C = Design Capacitance
K = Dielectric Constant
A = Overlap Area
d = Ceramic Thickness
n = Number of Electrodes
C = e0KA(n-1)
d
Detailed Cross Section
Inner Electrode
End Termination
Barrier Layer
Termination Finish
Dielectric Material

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Ceramic Materials are Inherently Brittle
Ceramic Properties
• High chemical bond strength
• High Elastic Modulus
• Low Ductility
• Very Hard

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Mechanical Forces
Compression
F
F
F
F
F
F
F
F
Tension Shear Torsion

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Material Toughness
Strain
∆l
𝑳
Stress
𝐹
𝐴
Ceramics
Metals
Soft Polymers
F F
L ∆l
A

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External Forces on Ceramic Material
Force
Compression
Strong under compression
Force Force
Tension
Weak under tension
Force

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Concreate Analogy

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Circuit Board
Flex Cracking

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Flex Cracking
Convex Bend
MLCC Under Tension
Δd

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High Stress Region
Flex Cracking
Excessive Bending
MLCC Under Tension
Finite Element Analysis

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Flex crack signature
MLCC Active Area
Flex Crack Signature
Starts here

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MLCC Active Area
Moisture entrapment
Short Circuit!!
Flex Crack Failures
+
-
+
-
+
-
Opposing
Electrodes
Note: Failure may be
delayed

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Flex Cracking
Concave Bend
MLCC Under Compression

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Main Causes of Flex Cracks
Too Close to Connectors
Design Tips
• Mount MLCCs further away from connector if possible
• Better support near connector to reduce flexing

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Main Causes of Flex Cracks
Board Singulation (Depanelization)
Side View
PCB Scribe Line
Design Tips
• Avoid excessive bending techniques
• Mount MLCCs parallel to boards edge if close
Scribe Line

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Capacitor Mitigation Solutions
Level 1 Protection – Basic Level of Crack Protection
Floating Electrode Open Mode
Pros
• Serial design
• Fails open
Cons
• Reduced capacitance in the same volume
Pros
• Crack doesn’t go through active area
• Fails open
Cons
• Reduced capacitance in the same volume

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Capacitor Mitigation Solutions
Level 2 Protection – Intermediate Level of Crack Protection
Pros
• Increased flex capability
• High volumetric efficiency
Cons
• Fail short
Flexible Termination (FT-CAP)
End Termination/
External Electrode
(Cu)
Flexible
Termination
Epoxy Layer
(Ag)
Barrier
Layer (Ni)
Termination Finish
(100% Matte
Sn/SnPb–5% Pb min)

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Capacitor Mitigation Solutions
Level 2 Protection – Intermediate Level of Crack Protection
These pieces
did not fail up
to 10mm

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Capacitor Mitigation Solutions
Level 3 Protection – High Level of Crack Protection (Hybrid Technology)
Pros
• Increased flex capability
• Floating Electrode design
• Fail Open
Cons
• Reduced capacitance in the same volume
Flexible Termination (FT-CAP) +
Floating Electrode
Flexible Termination (FT-CAP) +
Open Mode

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KEMET Solutions
Flexible Termination (FT-CAP)
C0G X7R
Ultra Stable
X8R
X8L
Protection
Level
2 2 2 2
Cap 0.5pF – 470nF 180pF - 22µF 430pF – 220nF 12nF - 10µF
Voltage
(VDC)
10 – 3kV 6.3 – 3kV 25 – 100 6.3 - 50
Case (EIA) 0603 - 2225 0603 – 2225 0603 - 1812 0603 - 1210
VW80808
Qualified
Currently Available
Specific range of parts meeting
the VW/AUDI specification.

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KEMET Solutions
Floating Electrode, Open Mode, and Hybrid Solutions
Open Mode Floating Electrode
Hybrid
Flexible Termination
+ Open Mode
Hybrid
Flexible Termination
+ Floating Electrode
Protection
Level
1 3
Dielectric X7R X7R X7R X7R
Cap ​1.0 nF – 6.8 µF 150 pF – 220 nF 1.0 nF – 6.8 µF 180 pF – 220 nF
Voltage
(VDC)
16 – 200V 6.3 – 250V 16 – 200V 6.3 – 250V
Case (EIA) 0805 – 1812 0402 – 1812 0805 – 1812 0603 – 1812
Grades
Available
Commercial and
Automotive Grade
Commercial and
Automotive Grade
Commercial and
Automotive Grade
Commercial and
Automotive Grade

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Circuit Board
Thermal Shock
Why is it an issue?
Inner Electrode
End Termination
Barrier Layer
Termination Finish
Dielectric Material
CTE – Coefficient of Thermal Expansion
Thermal Shock Cracks  CTE Mismatch

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Thermal Shock
Causes – Hand Soldering
Internal Temperature Gradients
Uneven Expansion and Contraction
COLD HOT
Hand Solder Tips
• Don’t touch capacitor termination
• Pre-heat assembly
• Larger case sizes are more sensitive

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Thermal Shock
Causes – Solder Wave
Solder Wave
Molten Solder
PCB Travel

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Thank You!!!
Mark R. Laps
Technical Product Manager
Ceramic Business Unit
KEMET Electronics
Cell Phone: +1-864-399-4879
Office Phone: +1-864-963-6383
www.kemet.com | marklaps@kemet.com