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This presentation will cover test and management strategies that can be used to protect your company and products against obsolescence risk. Topics include relevant industry standards, use of Managed Supply Programs (MSP) and Contract Pooled Options, long term storage recommendations and practices, and descriptions of the appropriate tests to use in various situations. Component obsolescence management is a strategic practice that also mitigates the risk of counterfeit parts. Left unchecked, obsolescence issues increase support, development and production costs. So, planning ahead is critical. For companies that proactively manage component availability and obsolescence, the impact of long-term storage on manufacturability and reliability is an area of major concern. Effective test strategies are crucial in detecting and preventing problems.
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Reliability Strategies for Combating Obsolescence
Risks
Presented by:
Cheryl Tulkoff
DfR Solutions
Abstract Component obsolescence management is a strategic practice that also mitigates the risk of counterfeit parts. Left unchecked, obsolescence issues increase support, development and production costs. So, planning ahead is critical. For companies that proactively manage component availability and obsolescence, the impact of long-term storage on manufacturability and reliability is an area of major concern. Effective test strategies are crucial in detecting and preventing problems. When component obsolescence isn’t planned for, the secondary market is often the supply chain of last recourse. While it is possible to get high quality, genuine parts, it is also possible to get nonconforming, reworked, or counterfeit components. And, it is increasingly difficult to differentiate genuine parts from their counterfeit equivalents. This is an area where appropriate testing can help. Historically, the secondary market provided a mechanism for finding parts in short supply or at reduced cost. Today, high-reliability system manufacturers are less willing to risk contamination of their supply chain with potentially substandard parts in order to save a few dollars on the cost of a part. This presentation will cover test and management strategies that can be used to protect your company and products against obsolescence risk. Topics include relevant industry standards, use of Managed Supply Programs (MSP) and Contract Pooled Options, long term storage recommendations and practices, and descriptions of the appropriate tests to use in various situations. Testing and analysis always starts with non-destructive evaluation (NDE). This practice is designed to obtain maximum information with minimal risk of damaging or destroying physical evidence with an emphasize the use of simplest tools first. Testing strategies including visual inspection, mechanical robustness, solderability assessment, X-Ray, XRF, C-SAM, electrical characterization, decapsulation, and marking evaluations will be compared and contrasted. More intensive thermal cycling and degradation testing will also be covered.
Obsolescence Management
• Strategic practice that also mitigates the risk of counterfeit parts
• Anticipate & plan for:
– Supplier disruption
– End of life parts
– Aging technologies
– Long life programs
The Reliability Issues….
• Effect of long-term storage on manufacturability and reliability is an area of major concern
• Many issues can arise depending on the technology and storage environment
– Components fail in storage
• Planning is key!
The Reliability Issues….
• Mechanisms of concern include:
– Solderability
– Moisture
– Tin whiskering
• Of these, solderability / wettability remains the #1 challenge in long-term storage of electronic components
So, What do You Need to Know?
• Industry Standards for Storage Reliability
• Use of Managed Supply Programs (MSP) and Contract Pooled Options
• Long Term Storage Recommendations and Practices
• Awareness of Long Term Storage Reliability Issues
• Testing Recommendations
Industry Standards: JEDEC JEP160
• “Long-Term Storage for Electronic Solid-State Wafers, Dice, and Devices”
– Age does not adversely affect most solid-state electrical performance provided no degradation in materials occurs
– Provides the industry with the best practices and recommendations for packing and storing solid-state electronics for long-term storage
– Addresses continuous storage where J-STD-033 does not apply
Industry Standards: ANSI-GEIA-STD-0003
• “PROCEDURES FOR LONG TERM STORAGE OF ELECTRONICS”
• Provides an industry standard for Long Term Storage (LTS) of electronic devices by drawing from best long term storage practices
• LTS is > 12 months
– Typically much longer
• Addresses storage of unpackaged semiconductors and packaged electronic devices
MIL-HDBK-338B Viewpoint
• “ELECTRONIC RELIABILITY DESIGN HANDBOOK”
• Assumed failure rate is insignificantly small or even 0 during the times when the equipment is switched off
• Experiments indicate that failure rates of many components are very significant even when no electrical stresses are applied
– Other stressors are still present
MIL-HDBK-338B Viewpoint
• For some components, the storage failure rate is even greater than the operating failure rate at lower stress levels
– Some types of resistors (eg. carbon composition) where, under storage conditions, there is no internal heat generation to eliminate humidity effects
– Certain types of electrolytic capacitors need a reforming process after a long period of storage
Critical Elements of a Long Term Storage Program
• Asset Security
– Protect against loss, theft
• Component Inspection
– Authenticity & quality
• Product genealogy (origins) & condition
– Data records for manufacture, transportation, and short term storage
• Environmental data, Lot codes, Date codes
Critical Elements of a Long Term Storage Program
• Storage Environment
– GEIA Standards
• Active desiccant storage at less than 5% relative humidity
• Dry nitrogen storage per MIL-PRF-27401
• Data Management • Maintain and manage individual date and lot codes.
• Assured Supply
Product Genealogy – Example of Supply Chain Complexity
Courtesy of Lloyd Condra, Boeing
Managed Supply Programs (MSPs)
• Companies offer MSPs as an industry service. Some offerings include:
– Purchasing and holding of obsolete components
– Long term storage services
– Component contract financing
– Stock pooling and optional stock holdings
– Product quality inspection and management
– Contract terms up to 20 years
Contract / Stock Pooling Options
• Pay a percentage of part cost over some defined time interval from mfg or MSP provider
• Less Purchase Investment – Purchasing parts means an upfront cost for the value of the parts. – The percentage will ensure that the part or parts that you need
are stocked and available when needed
• Less Inventory Cost – Insurance – Risk of losing or damaging stocked parts – Storage space
• Warranty – The warranty starts when a part is purchased from the pool – With purchased parts, the 1st year warranty granted already starts
on the date of purchase
Proper IC Storage • Die / Wafer
• Hermetic Packages
• Plastic Packages
Proper IC Storage
• For long-term programs, some form of storage should be considered. But, it does present problems:
– Practical/physical space, mechanical, financial, and counterfeit products
• What do we mean by long-term storage?
– Commercial: 2 years is very long-term
– Military: 20 years and beyond is common
Die/Wafer Storage :“Die Banking”
• Successful storage methodologies include special bagging, environmental controls and periodic monitoring.
– Requires care, cleanliness (particulates and gases), and benign temperatures
– Controlled atmosphere “dry boxes” (dry nitrogen purged storage)
– Dry bagged/vacuum storage • Oxygen barrier bags designed specifically for long-
term storage
Die/Wafer Storage Advantages
• Compact container, holds 9 wafers with gross die count of 64,000
• Flexible form factor, can build parts in any desired package
Courtesy John O’Boyle – QP Semiconductor
Hermetic Packages
• Minimize moisture intrusion
• 20 year storage is routine
– Metal TO-3 “can”
– Ceramic and side-brazed packages
• DIP, LCC, flat pack, and PGA
• Keep them dry and in environments low in sulfur, chlorine, and hydrocarbons to preserve solder finish on lead frame
Hermetic Disadvantages/Advantages
• Cannot change package type
• Slightly more expensive to store than die bank
• Large storage space required
• Easy storage infrastructure
• Long life time storage
Common Misconceptions about Plastic
• Come from the manufacturer in sealed packaging and thus don’t need special handling/storage
• Not rated as moisture sensitive therefore okay
• Safe to store in a “normal room” environment
Plastic Packages
• Plastic is hygroscopic
– Attracts water molecules from the environment.
– Achieve equilibrium in 4 to 28 days depending on molding compound.
– Normal room considered “wet” for plastic ICs (LAX annual average RH: +70%*)
– Store in “dry bags” or in a <10% RH environment
Source: Plastic Package Moisture-Induced Cracking, April 2006,
National Semiconductor Application Note
* LAX weather station - indoor data over 31 years.
But, Water doesn’t hurt Plastic!
• It’s not the plastic we’re worried about!
– Water leaches and reacts
– Water corrodes and degrades the metal pads and wires and results in device failure
• Isn’t plastic “rated” as non-moisture sensitive?
– Yes. But this rating is for IC/board assembly for reflow solder heat induced delamination and popcorning
• Contrary to popular belief, it is not a rating for long-term storage!
Storage Options: Summary
Long Term Storage Case Study
• In this case study, solderability was assessed for:
– Components from three different reels
– Stored for up to five years to determine how much additional storage life was available
– Either an ASIC in a SOIC package or a MOSFET in a TO-252 package
– In both package styles, the lead frame plating was tin-based
Case Study (continued)
• Type of plating material drives the appropriate solderability test – In this case, tin can either oxidize and/or form intermetallics with the base
metal underneath
– Both reactions can detrimentally reduce the solderability of the component
• To assess these reactions, the components were subjected to steam aging to accelerate storage related effects on solderability – Elevated temperature accelerates tin-copper intermetallic growth
– Steam accelerates tin oxide formation
– Components were then tested for solder wettability using a wetting balance test
Solderability Measurements
• Measurements of wettability of the leads performed using a solder meniscus measuring device (Wetting Balance) for each component
• Parts were tested with a standard RMA flux – Procedure detailed in IPC/EIA J-STD-
002C
• 3 components from each reel were tested
Case Study Results
• TO252 (production year 2003). Solderability is already impaired. – Dashed line indicates a part which was tested with a more active
water soluble flux. Notice the significant improvement in wettability
– Suggests the mechanism for poor wetting is thick oxide (as opposed to intermetallic formation)
Wetting Force
DCC03994DC
-100
-50
0
50
100
150
200
250
300
350
400
-0.5 0.5 1.5 2.5 3.5 4.5 5.5
time (seconds)
Forc
e (u
N/m
m)
000121212242424484848727272
Hours
Aged
Case Study Results
• TO252 (production year 2000). Even though this part is older, initial solderability is superior to the 2003 part
• After 12 hours of steam aging (equivalent to six months), solderability has deteriorated
Wetting Force
DK0060112G
-100
-50
0
50
100
150
200
250
300
350
400
-0.5 0.5 1.5 2.5 3.5 4.5 5.5
time (seconds)
Fo
rce (
uN
/mm
) 000121212242424484848727272
Hours
Aged
Case Study Results
• SOIC (production year N/A). Solderability degrades slowly
• The part does not become completely unwettable, like the TO252 parts, but fails IPC criteria after 24 hours of steam aging (equivalent to 1 year of storage)
Wetting Force
SOIC
-100
-50
0
50
100
150
200
250
300
350
400
-0.5 0.5 1.5 2.5 3.5 4.5 5.5
time (seconds)
Forc
e (u
N/m
m) 0
00121212242424484848727272
Hours
Aged
Discussion and Conclusions
• The same components produced by the same manufacturer can display very different behaviors in regards to long-term solderability
– This was seen with the TO252 parts, where the parts fabricated in 2000 had better wettability than the parts fabricated in 2003
– Therefore, any component or obsolescence storage strategy should involve an initial solderability assessment of each part and date code combination
Some Long Term Storage Reliability Issues
• Intermetallics
• Tin whiskering
• Moisture
Intermetallics & Oxidation
• Intermetallic compounds form when two unlike metals diffuse into one another creating species materials which are combinations of the two materials
• There are a number of locations where these dissimilar metals are joined including:
– Die level interconnects, wire bonds
– Plating finishes on lead frames
– Solder joints, flip chip interconnects, etc...
Tin Whiskers
• Single crystal growth that can occur on tin plated lead frames
• Mechanism for the growth is not clearly understood – Appears to be related to
compressive stresses in the plating, moisture, and contamination
• Can lead to shorting, intermittent errors, and high frequency issues
Moisture
• Depending on storage time & conditions, parts may be subjected to moisture.
• May be from
– Overloading of the desiccant with moisture
– Failure of the storage bags
– Improper storage
• Presence of moisture can lead to corrosion issues and other failures such as popcorning
Summary
• Managing obsolescence issues is critical! • Anticipate and plan • Implement a robust obsolescence & anti-counterfeiting
program which considers: – Asset Security – Component Inspection – Product genealogy (origins) & condition – Storage Environment – Data Management – Assured Supply
• Be aware of the potential reliability issues! • Use available testing protocols
Presenter Biography
• Cheryl has over 22 years of experience in electronics manufacturing focusing on failure analysis and reliability. She is passionate about applying her unique background to enable her clients to maximize and accelerate product design and development while saving time, managing resources, and improving customer satisfaction.
• Throughout her career, Cheryl has had extensive training experience and is a published author and a senior member of both ASQ and IEEE. She views teaching as a two-way process that enables her to impart her knowledge on to others as well as reinforce her own understanding and ability to explain complex concepts through student interaction. A passionate advocate of continued learning, Cheryl has taught electronics workshops that introduced her to numerous fascinating companies, people, and cultures.
• Cheryl has served as chairman of the IEEE Central Texas Women in Engineering and IEEE Accelerated Stress Testing and Reliability sections and is an ASQ Certified Reliability Engineer, an SMTA Speaker of Distinction and serves on ASQ, IPC and iNEMI committees.
• Cheryl earned her Bachelor of Mechanical Engineering degree from Georgia Tech and is currently a student in the UT Austin Masters of Science in Technology Commercialization (MSTC) program. She was drawn to the MSTC program as an avenue that will allow her to acquire relevant and current business skills which, combined with her technical background, will serve as a springboard enabling her clients to succeed in introducing reliable, blockbuster products tailored to the best market segment.
• In her free time, Cheryl loves to run! She’s had the good fortune to run everything from 5k’s to 100 milers including the Boston Marathon, the Tahoe Triple (three marathons in 3 days) and the nonstop Rocky Raccoon 100 miler. She also enjoys travel and has visited 46 US states and over 20 countries around the world. Cheryl combines these two passions in what she calls “running tourism” which lets her quickly get her bearings and see the sights in new places.
