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

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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

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Coefficient of Thermal Expansion -Materials Mismatch -

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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

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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

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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

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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

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Temp Cycle Induced Failures

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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.

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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.

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Moisture Sensitivity

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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

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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

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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

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Cracked Packages

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Wire Necking Damage

Wire Bond Damage

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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.

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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”

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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

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MicroElectrical Mechanical System devices can stick because of

moisture, called “stiction”

MEMS AND MOISTURE

MicroOptical EMS

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Moisture Accelerates

Dendrite Growth

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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

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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.

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See IPC-TM-650 for further details

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Dendrite growth studies

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Dendrites grow from the negative (cathode) towards the positive (anode) terminal

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Delicate Fern Dendrite grown between leads of PQFP package

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Dendrites can be classified by time to grow

What can this study of dendrite growths be used for?

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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

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Overview of Analysis Equipment

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METROLOGY LAB EQUIPMENT

Cross sectioning and polishing equipment.

UKAM Saws and blades

Gryphon C40 diamond band saw

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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

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3D STITCHING MICROSCOPE

Rows of stud bumps photographed

Wire bonds being photographed

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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

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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.

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X-RAY INSPECTION – CT (3D) - VIDEO

Virtual Cross Sections of components – non-destructively

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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.

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Can also be used for: • Materials characterization and control • Screening of parts • Counterfeit Detection • Forensics – metal grain structures.

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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

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CSAM Through-mode Scans:

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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

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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.

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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).

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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

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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

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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.

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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.

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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.

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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

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Any questions?

Follow-up info: Steve Greathouse Plexus Corporation Nampa, Idaho Email: steve.greathouse@plexus.com