Water, Water, Everywhere” Moisture induced failures in electronics & the related FA equipment to analyze
them.
Steve Greathouse Sr. Staff Engineer/FA Lab Manager
Plexus Corp Nampa, Idaho
PLEXUS CONFIDENTIAL Water Water Everywhere
‘Water, water, everywhere, And all the boards did shrink; Water, water, everywhere, Nor any drop to drink” Samuel Taylor Coleridge The Rime of the Ancient Mariner
PLEXUS CONFIDENTIAL
Common Package and Board Failure Mechanisms
• 1. Moisture absorption of components or boards causing • moisture vaporization during reflow
2. Mismatch of coefficients of thermal expansion (CTE) of adjacent materials 3. Chemical and/or mechanical adhesion
• Poor adhesion between materials and surfaces • Low fracture toughness • Low strength modulus of materials • Non-uniformity due to warpage • Manufacturing defect
4. Contamination, voids, non-uniform bond line thicknesses (BLT), etc. • Mismatch in diffusivity of adjacent materials • Stress concentrations • Corrosion • Mechanical loads
5. Mechanical damage
PLEXUS CONFIDENTIAL
Coefficient of Thermal Expansion -Materials Mismatch -
PLEXUS CONFIDENTIAL
Packages Interconnect Definitions
Package connection definitions:
FR4 Circuit Board
2nd Level
Interconnect
(SLI)
Die
Wire Bonds
1st Level
Interconnect
(FLI)
0 Level
Interconnect
Mold Compound
1st bond
2nd bond
3rd Level Interconnect –
Board to System
Cards inserted into
computer case
PLEXUS CONFIDENTIAL
6
CTE of Various Materials
Material CTE Lower
CTE Typical
CTE Upper
Alloy 42 (Fe-42Ni) 4.4
Aluminum (40% Silicon) 13.5
Aluminum, T6061 23.6
Boron Aluminum (20%) 12.7
Copper, CDA 101 17.6
Copper / Invar / Copper 20/60/20 thick
5.7 5.8
Copper / Molybdenum / Copper 20/60/20 thick
7
Gold 14
Graphite / Aluminum 4 6
Invar 36 1.6
Invar 42 4.5
Kovar 5
Lead 29
95-5 Lead-Tin Solder 28
63-37 Sn-Pb Solder 23 25
Molybdenum 4.9
Ni-clad Molybdenum 5.2 6.0
Silver 19
Tungsten / Copper (90/10) 6.0 6.5
Tungsten 4
Material Direction CTE Lower
CTE Typical
CTE Upper
Glass-Ceramic >3.0
Silicon 2.6
Diamond 0.9
Aluminum Nitride 4.5
Silicon Nitride 3.7
Quartz, fused silica 0.5 0.6
Kevlar 49 -5
Beryllia 6
Cubic Boron Nitride X-Y Z
3.7 7.2
E Glass / Epoxy X-Y Z
14 55
20 90
E Glass / Polyimide X-Y Z
12 60 16
E Glass / PTFE X-Y Z
24 260
Kevlar / Epoxy X-Y Z
5.1 7.1
Kevlar / Polyimide X-Y Z
3.4 83 6.7
Quartz / Polyimide X-Y Z
5.0 68.4 8.0
Quartz / Bismaleimide, 35% Resin
X-Y Z
6.2 41 6.3
Alumina (90%) TFSubstrate
7.0
Alumina (Ceramic Chip Carrier)
5.9 6.5 7.4
Epoxy (70% Silica) Plastic Packaging
20 23
CTE Values for Selected Metallic Materials
CTE Values for Selected Nonmetallic Materials
IPC-SM-785 Guidelines for Accelerated Reliability Testing of Surface Mount Solder Attachments
PLEXUS CONFIDENTIAL
Temp Cycle Induced Failures
7
30 min.
cycle
TCB Target Temp & Tolerances: -55°C (-10/+0°C) to 125°C (-0/+15°C)
T
Typical Temp Cycle ‘B’ Profile
PLEXUS CONFIDENTIAL Temp Cycle Conditions
Test Condition Low Range-C High Range-C Cycle/Soak time
A (Commercial) 0, (+0, -5) 100, (+5, -0) 15, 30 min cycle
A (Mil 883) -55, (+0, -10) 85, (+10, -0) 15, 30 min cycle
B (Mil 883) -55, (+0, -10) 125, (+10, -0) 15, 30 min cycle
Short B (sB) -55, (+0, -10) 125, (+10, -0) 8, 16 Min cycle
C (Mil 883) -65, (+0, -10) 150, (+10, -0) 15, 30 min cycle
G -40, (+0, -10) 125, (+10, -0) 15, 30 min cycle
J -0, (+0, -10) 100, (+10, -0) 15, 30 min cycle
K -0, (+0, -10) 125, (+10, -0) 15, 30 min cycle
L -55, (+0, -10) 125, (+10, -0) 25, 50 min cycle
Q -25, (+0, -10) 100, (+10, -0) 15, 30 min cycle
R -25, (+0, -10) 125, (+10, -0) 15, 30 min cycle
S -40, (+0, -10) 85, (+10, -0) 23, 46 min cycle
X -40, (+0, -10) 85, (+10, -0) 30, 60 min cycle
These are the standard Temp Cycle conditions used for stressing.
PLEXUS CONFIDENTIAL
Temp Cycle Damage
Lead Free reflow @ 260 C
Eutectic Solder Reflow @ 220 C
Room Temp @ 23 C
Temp Cycle B @ -55
Temp Cycle C @ -65
0 C
Molding/Encap temp @ 175 C +
/- 24
0 C
+
/- 85
C
Neutral Stress Temperature
Most compressive stress (Highest Fail Point)
Most Tensile stress
Die attach cure
Temperature differential from the neutral stress point determines product reliability.
Damage from Temp cycle is done at the cold extreme.
PLEXUS CONFIDENTIAL
Moisture Sensitivity
PLEXUS CONFIDENTIAL
Moisture classification and handling
Main Industry Spec’s on Moisture Classification and Handling
IPC/JEDEC J-STD-020E: Moisture/Reflow Sensitivity Classification for Non-Hermetic Surface Mount Devices December 2014 IPC/JEDEC J-STD-033C: Handling, Packing, Shipping and Use of Moisture/Reflow Sensitive Surface Mount Devices, February 2012 Downloadable for free from www.jedec.org – but must register.
PLEXUS CONFIDENTIAL Moisture saturation curves
PLEXUS CONFIDENTIAL
Moisture Absorption
Lead Frame Plastic
Encapsulant Minimum
Plastic Thickness
Moisture Vaporization
Pressure Dome Delamination
Void
Plastic Stress Fracture
Crack Collapsed Void
Package materials (mold compound & die attach material) absorb moisture from the air.
Upon heating during board mounting at the customer, the moisture vaporizes and
explosively expands. The adhesive strength of the weakest interface (e.g. mold to lead frame) is exceeded, causing a vapor-filled
void or pressure dome to expand.
The pressure is released when the package cracks. The pressure dome
collapses and cracks form, emanating from the boundary of delamination. The
remaining void area concentrates stresses in subsequent temperature cycling,
leading to further crack propagation.
“Popcorning” Failure
13
PLEXUS CONFIDENTIAL
Acoustic images after L3 Precon show delam completely under die and out to
edge of encap.
ABOVE: SEM image of x-section confirming delam at Si-D/A interface
at pkg center and at D/A-soldermask interface beyond the die.
Popcorn Delam - 15mm PBGA
14
PLEXUS CONFIDENTIAL
Cracked Packages
15
PLEXUS CONFIDENTIAL
Wire Necking Damage
Wire Bond Damage
16
PLEXUS CONFIDENTIAL
Moisture + Reflow Induced Cracking:“Popcorning”
The main factors influencing the susceptibility to crack have been found to be:
• Moisture content of molding compound or substrate (% weight gain)
• Peak temperature reached during soldering (220 vs 240 vs 260 reflow)
• Physical size dimensions of die paddle
• Same package with different die can have different MSL
• Thickness of molding compound under paddle.
• Thinner dry’s out quicker.
• Mold/Encapsulation material type:
• Epoxy’s are worse than Silicones. Silicone’s easily release moisture
• Adhesion of molding compound to the die and/or leadframe or substrate.
PLEXUS CONFIDENTIAL
Die surface delamination in plastic package after moisture saturation
followed by vapor-phase reflow soldering at 215 oC
Cracking/Delamination of Plastic SMDs - “Popcorn Effect”
18
PLEXUS CONFIDENTIAL
Moisture Induce Delamination
Delamination leads to Bump Fracture in BGA packages.
PLEXUS CONFIDENTIAL Board Delamination Caused by Moisture
Moisture built up in the internal layers , during reflow, it turned to steam which forced the layers apart.
Delamination found with CSAM, then confirmed with cross section.
PLEXUS CONFIDENTIAL Understanding Max Floor Life Exposure Time
Preconditioning reflow traditionally @ 220C degrees, now is 260C (for no-lead solders).
MOISTURE SATURATION LEVELS PER IPC/JEDEC J-STD-020A
LEVEL DESCRIPTION TEST SOAK CONDITION MAX FLOOR LIFE@CUST.
MSL1 Non-moist sens. 168hrs @85oC/85%RH Unlimited at 30oC/85%RH
MSL2 Limited sensitivity 168hrs @85oC/60%RH 1 year at 30oC/60%RH
MSL2a Limited sensitivity 672hrs+MET@30oC/60%RH 4 weeks at 30oC/60%RH
MSL3 Moist. sensitive 168hrs+MET@30oC/60%RH 1 week at 30oC/60%RH
MSL4 Highly moist sens. 72hrs+MET@30oC/60%RH 3 days at 30oC/60%RH
MSL5 Extremely sens. 48hrs+MET@30oC/60%RH 2 days at 30oC/60%RH
MSL5a Extremely sens. 24hrs+MET@30oC/60%RH 1 day at 30oC/60%RH
MSL6 Time on label (TOL) TOL@30oC/60%RH TOL at 30oC/60%RH
MET=“Manufacturer’s Exposure Time”; Accounts for the time between baking and sealing
in a moisture barrier bag. Default minimum is 24hrs; Intel standard is 48 hrs.
PLEXUS CONFIDENTIAL Bake Times & Conditions to Dry Boards and
Components – JEDEC J-STD-0033
PLEXUS CONFIDENTIAL
Page 23
MicroElectrical Mechanical System devices can stick because of
moisture, called “stiction”
MEMS AND MOISTURE
MicroOptical EMS
PLEXUS CONFIDENTIAL
Moisture Accelerates
Dendrite Growth
PLEXUS CONFIDENTIAL
Copper dendrites after 40 hours of biased 156/85 HAST
Metal Migration Failure Mechanism
Interlead Leakage/Shorts
• Requires bias (electrical charge)
• Accelerated by temperature & humidity
• Seen as early as 20 hrs HAST
• Highly dependent on materials & process
PLEXUS CONFIDENTIAL Dendrite Failures During Humidity Testing
26
Dendrites caused failures of qualification products during 85% RH/85˚C and biased THB testing at a couple of the sites.
Dendrites as found in X-Ray inspection with high-end Inspection system
Task: Find a way to predict if a package will have problems with dendrites during reliability testing.
PLEXUS CONFIDENTIAL Accelerated Dendrite growth studies
Using the Video capabilities of a 3D Digital stitching microscope
Why Study Dendrites: Need a method of understanding the details about dendrite growth:
• If this method could be used to evaluate incoming boards and components
• Detect the susceptibility to grow dendrites in moisture life testing.
• See if this method can determine cleanliness of incoming materials.
Dendrite Growth Study Method: • A 9 volt power supply with small clips to grasp parallel leads of packages or adjacent
contacts on a board.
• Place one or two drops DI water to bridge the gap.
• Watch under microscope for bubbling on the surface (hydrolysis).
• Watch for small dendrites to start growing from the negative terminal side.
• When the dendrites grow to touch the other side, growth stops on that dendrite.
• Other dendrites will grow until the voltage differential is normalized.
27
See IPC-TM-650 for further details
PLEXUS CONFIDENTIAL
Dendrite growth studies
28
Dendrites grow from the negative (cathode) towards the positive (anode) terminal
PLEXUS CONFIDENTIAL
29
Delicate Fern Dendrite grown between leads of PQFP package
PLEXUS CONFIDENTIAL
Dendrites can be classified by time to grow
What can this study of dendrite growths be used for?
30
Time for dendrites to grow can be grouped into 3 categories.
Time to Grow Dendrite Concern about Board or Component
Under 1 ½ minutes: Ionic contamination, plating is porous (ie:
high phosphorus content, plating baths out
of tolerance, etc), high chlorine, sodium, or
bromine exposure on leads, etc.
Around 3-6 minutes: Represents standard plating process – little
contamination, or is not affecting plating surfaces
significantly. Should be OK through normal life
testing
At 6-12+ minutes: Very solid plating – little to no contaminates,
expected to pass long life reliability testing.
Should pass high rel testing.
PLEXUS CONFIDENTIAL Tin Whiskers (with Bright Tin Plating)
Growth rates increases in a vacuum
6 months of exposure to 50C/90%RH 16 months exposure to 50°C
6 months exposure to 50°C/90% RH 4 months exposure to 50°C/90% RH
PLEXUS CONFIDENTIAL
Overview of Analysis Equipment
32
PLEXUS CONFIDENTIAL
Page 33
METROLOGY LAB EQUIPMENT
Cross sectioning and polishing equipment.
UKAM Saws and blades
Gryphon C40 diamond band saw
PLEXUS CONFIDENTIAL
OPTICAL MICROSCOPE INSPECTION Microscopes are the most used piece of equipment in any failure analysis or inspection process. Standard zoom microscopes with high clarity and magnification up to 400X are required for military product inspection, but 150X magnification is used for most production products.
3D Digital Stitching
Leeuwenhoek’s Microscope
34
PLEXUS CONFIDENTIAL
3D STITCHING MICROSCOPE
Rows of stud bumps photographed
Wire bonds being photographed
35
PLEXUS CONFIDENTIAL
OTHER OPTICAL INSPECTION SCOPES
Fluorescence Microscope A fluorescence microscope is an optical microscope that uses fluorescence and phosphorescence instead of, or in addition to, reflection and absorption to study properties of organic or inorganic substances.
Laser Scanning Microscope Laser microscopes can perform non-contact profile, roughness, and film thickness measurements with nanometer-level resolution on any material or shape. Up to 28,000 X magnification. That’s in the SEM Range
36
PLEXUS CONFIDENTIAL
X-RAY INSPECTION
X-ray: Considered non-destructive method of evaluating a product’s internal structure . Inspection is mainly for metal layers, solder balls, solder joints, suspect vias, and other items that will show up in X-rays. Note that silicon chips and organic materials are invisible in X-ray.
37
PLEXUS CONFIDENTIAL
38
X-RAY INSPECTION – CT (3D) - VIDEO
Virtual Cross Sections of components – non-destructively
PLEXUS CONFIDENTIAL
SCANNING ACOUSTIC MICROSCOPE (SAM) INSPECTION
A Scanning Acoustic Microscope (SAM) a process called scanning acoustic tomography. The semiconductor industry has found the SAM useful in detecting voids, cracks, and delaminations within microelectronic packages Scanning acoustic microscopy works by directing focused ultrasound from a transducer at a small point on a target object. Waves hitting the object are either scattered, absorbed, reflected (scattered at 180°) or transmitted (scattered at 0°).
“C” mode is the reflective mode.
39
Can also be used for: • Materials characterization and control • Screening of parts • Counterfeit Detection • Forensics – metal grain structures.
PLEXUS CONFIDENTIAL
40
C-SAM Inspection (Cont.)
•Different types of failure images found with CSAM
Void over die in mold material
Cracks in expired underfill
Delamination on die pad
Large gaps in the underfill of two flip chip s
PLEXUS CONFIDENTIAL
CSAM Through-mode Scans:
41
BELOW: CSAM (left) & TSAM (right) of delam
in 2 different 2 die FC-PBGAs.
Left reflowed at 2A/225 C Right reflowed at 2a/260C
Thru Mode scans of same type of PBGA product
PLEXUS CONFIDENTIAL
42
Differential Scanning Calorimeters (DSC)
Used to evaluate pastes, glues, adhesives, etc. to determine the amount of time and temperature to cure material, understand the material properties, compare material lots (old vs new), etc.
PLEXUS CONFIDENTIAL
43
Ion Chromatography (IC)
Ion Chrome extraction Ionic Cleanliness testing
Ion Chromatography::
• Analytical technique used to validate cleaning and rinsing effectiveness . Analytical results are expressed in micrograms per unit area. Acceptable levels can change dependent on the product type or application.
IC is a universal technique for the detection of both anionic and cationic species. Reference IPC-TM-650, Method 2.3.28 “Ionic Analysis
of Circuit Boards, Ion Chromatography Method”, on either bare boards (PCB) or electronic assemblies (PCBA).
PLEXUS CONFIDENTIAL
XRF INSPECTION
• X-ray fluorescence (XRF) the emission of "secondary" (or fluorescence) by bombarding with high-energy X-rays.
• Used for elemental analysis, chemical analysis, and to determine plating thickness of various metals on a surface.
n= 73 Au 1 = 69.11 µ" Ni 2 = 88.00 µ" mq = 0.689
n= 74 Au 1 = 68.42 µ" Ni 2 = 87.08 µ" mq = 0.695
n= 75 Au 1 = 68.26 µ" Ni 2 = 87.78 µ" mq = 0.671
Au 1 µ" Ni 2 µ" mq
Min 67.05 80.91 0.612
Max 69.34 92.21 0.739
Mean 68.158 87.541 0.670
Standard Deviation 0.5396 2.1993 0.022
CoV (%) 0.79 2.51 3.42
Range 2.294 11.30 0.127
44
PLEXUS CONFIDENTIAL Fourier Transform Infrared Spectroscopy
(FTIR)
Fourier transform infrared spectroscopy (FTIR) is a technique which is used to obtain an infrared spectrum of absorption or emission of a solid, liquid or gas. An FTIR spectrometer simultaneously collects high spectral resolution data over a wide spectral range.
Libraries (~ 1 million) are now available for virtually all materials:
Chemical, Polymers, Pharmaceuticals, Oils, Pesticides, Explosives, Coatings, Forensics Semiconductor Chemicals, and even kidney stones.
Purchase libraries from ~$1000 to $80,000
Or you can buy subscriptions for ~ $5-7K/y.
Results Spectrum are compared to Library data
PLEXUS CONFIDENTIAL
Analysis work usually contracted externally
Electron Spectroscopy for Chemical Analysis (ESCA).
X-ray Photoelectron Spectroscopy – (XPS)
Auger Electron Spectroscopy – (Auger)
Focused Ion Beam – (FIB)
Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS)
Measuring only 10 micrometers across, the world's smallest snowman was created by scientists at the National Physical Laboratory, UK. It was made from two small balls normally used for calibrating electron microscopes. An ion beam was then used to etch eyes, nose and even a smile on the little sculpture.
Human hair with engraved cartoon strip
Cost on these systems are usually over $1M.
PLEXUS CONFIDENTIAL
Auger Surface Analysis
Auger Electron Spectroscopy (AES or Auger) is a surface-sensitive analytical technique that utilizes a high-energy electron beam as an excitation source. Atoms that are excited by the electron beam can subsequently relax, leading to the emission of “Auger” electrons. The kinetic energies of the emitted Auger electrons are characteristic of elements present within the top 3-10nm of the sample.
Auger has direct analytical benefits, from determining contamination sources in wafer processing equipment, analyzing defects in electronic devices, to investigate the root cause of failures (i.e., contamination, weak chemistry, etc).
PLEXUS CONFIDENTIAL Transmission electron microscopy (TEM)
Transmission electron microscopy (TEM) is a microscopy technique in which a beam of electrons is transmitted through an ultra-thin specimen, interacting with the specimen as it passes through it. An image is formed from the interaction of the electrons transmitted through the specimen; the image is magnified and focused onto an imaging device.
buckminsterfullerene
Nano sized particles that clump together naturally when fullerenes clump together in water.
PLEXUS CONFIDENTIAL
Focused Ion beam (FIB)
Chip level rerouting
Focused ion beam (FIB) is a technique used in the
electronics and semiconductor industry, materials
science, biological, and healthcare sciences.
Extremely accurate deposition and ablation of
materials. Resembles a scanning electron
microscope (SEM). SEM uses a focused beam of
electrons, FIB uses a focused beam
of ions instead. FIB can also be incorporated in a
system with both electron and ion beam columns,
allowing the same feature to be investigated using
either of the beams.
PLEXUS CONFIDENTIAL
FA Flow to minimize data loss
Failure Analysis Equipment, Techniques, and Processes
Microscopes/photography
• Electrical testing
• Optical
• 3D Digital Stitching
• CSAM
X-Ray Florescence (XRF):
• Proportional counter vs Solid State Detector (SDD)
X-ray inspection:
• 2D Xray and 3D CT
Decapsulation
• Mechanical, Chemical, and Plasma
Cross Sectioning
• Sawing
• Grinding/Polishing
Mechanical testing
Pull Testing
Shear Testing
Non D
est
ructi
ve
Dest
ructi
ve
PLEXUS CONFIDENTIAL Additional Background – Standards
Additional Information and details are contained in: • JEDEC – www.jedec.org. – a main standards site.
• JEDEC is the technical voice of the semiconductor industry. Their site has a through array of documentation that, for over 50 years, has been the global leader in developing open standards and publications for the microelectronics industry. JEDEC committees provide industry leadership in developing standards for a broad range of technologies.
• SEMI – http://www.semi.org/en/ - SEMI Standards Semiconductor Equipment and Materials International (SEMI) is a global industry association of companies that provide equipment, materials and services for the manufacture of semiconductors, photovoltaic panels, LED and flat panel displays, micro-electromechanical systems (MEMS), and related micro and nano-technologies.
• http://www.semi.org/en/semiconductor
• American National Standards Institute - www.ansi.org A private non-profit organization that oversees the development of voluntary consensus standards for products, services, processes, systems, and personnel in the United States.[3] The organization also coordinates U.S. standards with international standards so that American products can be used worldwide.
• Mil Spec 883K - TEST METHOD STANDARD for MICROCIRCUITS
PLEXUS CONFIDENTIAL
Any questions?
Follow-up info: Steve Greathouse Plexus Corporation Nampa, Idaho Email: [email protected]