electrical failures 11-6-10 · 2015-01-14 · e- electron / metal atom flow e- e- e- e- e- e- e- e-...
TRANSCRIPT
![Page 1: Electrical Failures 11-6-10 · 2015-01-14 · e- Electron / Metal Atom Flow e- e- e- e- e- e- e- e- e- e- e-M Anode Cathode Copper Silver M - + Galvanic Cell • Galvanic cell potential](https://reader033.vdocuments.site/reader033/viewer/2022042121/5e9bf0c0b58b9162e4760067/html5/thumbnails/1.jpg)
Electrical Failures Electrical Failures
IPC / SMTA Cleaning Workshop
November 16, 2010
IPC / SMTA Cleaning Workshop
November 16, 2010
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Content Content
• Technology Innovation
• Device Interactions
• Tin Whiskers
• Soil Effects
• Complexities
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Rapid Technology InnovationRapid Technology Innovation
• More performance in smaller platforms
– High Speed Processors
– Lead-Free Soldering
– Reliability critical driver
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ReliabilityReliability
• The capacity of a device to perform as
designed
– For specific interval under stated conditions
– Minimal failures
• The Goal: Performs as promised every time
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Device InteractionsDevice Interactions
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Device Interactions Device Interactions
Surface Mount
TechnologySemiconductor
Fabrication
Advanced
Packaging
-Photoresists
-Plating
chemicals
-Solder pastes
-Fluxes
-Coatings
-Wafer Bumping
-Flip Chip
-Package on Package
Mostly IPC
standardsMostly SEMI
standards
JEDEC
Standards
Mackie, A. (2009, Oct). Electromigration – Our Mutual Friend. SMTA IWLPC, Santa Clara, CA.
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Increase in Hardware FailuresIncrease in Hardware Failures
• Gaseous contamination– Chemical effects
• Creep Corrosion
– Mechanical effects• Compressive Stress
• Tin Whiskers
• Optical signal interference
• Friction
– Electrical effects• Circuit impedance
• Dendritic growth
• Arcing
ASHRAE (2008). Gaseous and Particulate Contamination Guidelines for Data Centers.
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ReliabilityReliability
• Manufacturers are in a constant struggle to
– Maintain the reliability of their hardware
– Every Shrinking feature sizes
– Decreased distance signals travel
White residue flux migration
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MiniaturizationMiniaturization
• Heat dissipation
– Air flow exposes circuits to gaseous contamination
• Non-hermetic sealed packages
– Moisture entrapment
• Decreased spacing
– Voltage differences increase the risk of ion migration
– Compressive stresses
• Corrosion
– Smaller component features reduces the distance corrosion needs to travel
ASHRAE (2008). Gaseous and Particulate Contamination Guidelines for Data Centers.
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Co-Planar Board FinishesCo-Planar Board Finishes
• Coplanar board finishes are especially susceptible
– Immersion silver plating (ImAg) over copper
– Organically Coated Copper (OSP)
• Silver and copper are highly reactive to sulfur
– Levels as low as 3 ppm is enough to induce corrosion
• Silver is more noble metal
than copper
– In the presence of atmospheric
water, forms an electrochemical
cell
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Sulfur Bearing Gases Sulfur Bearing Gases
• Even in absence of moisture can
– Attack copper and silver
–Migrate as silver and copper sulfide
– Breeches exposes
underlying board
finishes
– Corrosion grows
and leads to
electrical opens
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e-
Electron / Metal Atom Flow
e-
e-
e-
e-e-
e-
e-
e-
e-
e-
e- M
Anode
CopperCathode
SilverM
- +
Galvanic Cell Galvanic Cell
• Galvanic cell potential from copper and silver metal
reduction
– Copper, being more active metal, represents the anode when
electrochemical reactions with silver take place
– Copper corrodes faster than other based oxidizing
environment.
Mackie, A. (2009, Oct). Electromigration – Our Mutual Friend. SMTA IWLPC, Santa Clara, CA.
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Tin WhiskersTin Whiskers
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Tin Whiskers Tin Whiskers
• Lead-Free = High tin alloys
• Whiskers bridge the gap between conductors
• Cause shorts
• Carry enough current to stop the circuit from
functioning correctly
+_
Copper Trace
Lead-free Solder
Whisker
Howell et al. (2010) Effect of Soldering Method and Flux Type on Tin Whisker Growth in
SAC 305. SMTA IWLPC, Toronto, CA.
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Whiskers grow to relieve compressive stress in tin
Compressive Stress
Whiskers grow by atomic diffusion in a crystalline manner
Whisker GrowthWhisker Growth
Howell et al. (2010) Effect of Soldering Method and Flux Type on Tin Whisker Growth in
SAC 305. SMTA IWLPC, Toronto, CA.
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Greatest Incidence of whiskers on the edges of the traces
This is probably because
• Greatest concentration of flux residue
• Exposed copper / thin tin coating
Whisker Location Whisker Location
Howell et al. (2010) Effect of Soldering Method and Flux Type on Tin Whisker Growth in
SAC 305. SMTA IWLPC, Toronto, CA.
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Soil Effects
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Assembly Contamination Assembly Contamination
• Stencil cleaning– Wet solder paste – Chip bonder adhesives
• Bare Board– Oxides – Ionic contaminants
• Flux residues – Organic acids – Rosin– Resin structures – Polymers – Functional additives
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Flux Residues – A Common Enemy Flux Residues – A Common Enemy
Stencil
Printing
UnderfillSoldering FLUX
Conformal
Coating
Mackie, A. (2009, Oct). Electromigration – Our Mutual Friend. SMTA IWLPC, Santa Clara, CA.
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Soil EffectsSoil Effects
• Electromigration: “Electrochemical Migration” (ECM)
– Surface Mount Technology:
– Movement of ions under a potential gradient–
• Closely associated with SIR (Surface Insulation Resistance)
• BETWEEN adjacent metal conductors
• Electromigration (EM)
– Semiconductor / Packaging:
– Movement of atoms caused by electrons
flowing through a metal
– WITHIN a metal conductor
Mackie, A. (2009, Oct). Electromigration – Our Mutual Friend. SMTA IWLPC, Santa Clara, CA.
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Electrochemical Migration
No-clean, Halogen-free FluxesElectrochemical Migration
No-clean, Halogen-free Fluxes
Mackie, A. (2009, Oct). Electromigration – Our Mutual Friend. SMTA IWLPC, Santa Clara, CA.
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Tin Salt Migration Tin Salt Migration
• Partially removed flux residue under component
– Dendritic growth
– Creep corrosion
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Flux Residue Migration under
Conformal Coating
Flux Residue Migration under
Conformal Coating
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Flux Left under Components Flux Left under Components
• Feature size reduction
– Increase failure risks
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Ion Migration in an Electric Field Ion Migration in an Electric Field
• Propagated by
– The charge balance at the interface
– Current density entering and leaving the device
– Electrolyte from moisture causes ions to split and
form dendrites
AnodeCathode
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High VoltageHigh Voltage
Source: FET1_Drain_Joint_Failure_18018797_3_jpg.htm
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Shorting / Sparking / Failure Shorting / Sparking / Failure
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Electrochemical Migration
Key FactorsElectrochemical Migration
Key Factors
• Contamination– Soils
– Gaseous Moisture (%RH)
• Adjacent metallic conductors
• Electric field (potential gradient)
• Ionizable metals
• Hydrophilic / mildly-hydrophilic continuous phase
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Failure Region Failure Region
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ConclusionsConclusions
• Reliability of hardware is more prone to risk
due to ever shrinking feature sizes
• Move to Lead-Free increases risk factors
– Co-Planar Board Surfaces
– Creep Corrosion
– Tin Whiskers
• Flux residues bridge conductions
– Electromigration risks
• Removal and mitigation of contamination
sources is increasingly important to assure
reliable devices that perform as promised
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QuestionsQuestions