Technical Articles From DfR Solutions

Creep Corrosion Of Electronic Assemblies In Harsh Environments

Mar 16, 2022 | Petri Savolainen and Randy Schueller

Creep corrosion occurs in electronics assemblies and it is reminiscent to electromigration but does not require electrical field to drive the reaction. Corrosive elements and moisture must be present for creep corrosion to occur. Sulfur is the most prominent element to cause creep corrosion in environments such as paper mills, rubber manufacturing, mining, cement manufacturing, waste water treatment etc., also including companies and locations nearby such industries. The main part of printed circuit board assembly (PCBA) to be affected is the PCB surface finish. Especially immersion silver is prone to creep corrosion, but it sometimes occurs in NiPd (lead frames), and to a lesser extent in ENIG and OSP surface finishes. As the use of immersion silver is increasing as PCB surface finish and electronics are more and more used in harsh environments, creep corrosion is a growing risk. In this paper we will present the driving forces and mechanisms as well as suitable tests and mitigation strategies against creep corrosion...

Solderability after Long-Term Storage

Mar 02, 2022 | Joelle Arnold, Cheryl Tulkoff and Greg Caswell

The effect of long-term storage on manufacturability and reliability is an area of major concern for companies that attempt to proactively manage component availability and obsolescence. A number of issues can arise depending on the technology and storage environment. Mechanisms of concern can include solderability, stress driven diffusive voiding, kirkendahl voiding, and tin whiskering. Of all of these, solderability / wettability remains the number one challenge in longterm storage....

Counterfeit Detection Strategies: When to Do It / How to Do It

Oct 12, 2021 | Greg Caswell

Counterfeit components have been defined as a growing concern in recent years as demand increases for reducing costs. In fact the Department of Commerce has identified a 141% increase in the last three years alone. A counterfeit is any item that is not as it is represented with the intention to deceive its buyer or user. The misrepresentation is often driven by the known presence of defects or other inadequacies in regards to performance. Whether it is used for a commercial, medical or military application, a counterfeit component could cause catastrophic failure at a critical moment....

Coatings and Pottings: A Critical Update

Aug 11, 2021 | Greg Caswell

Conformal coatings and potting materials continue to create issues for the electronics industry. This webinar will dig deeper into the failure modes of these materials, specifically issues with Coefficient of Thermal Expansion (CTE), delamination, cracking, de-wetting, pinholes/bubbles and orange peel issues with conformal coatings and what mitigation techniques are available. Similarly, this webinar will look at the failure modes of potting materials, (e.g Glass Transition Temperature (Tg), PCB warpage, the effects of improper curing and potential methods for correcting these situations....

Best Practices in Selecting Coatings and Pottings for Solar Panel Systems; Junction Boxes and Inverters

Aug 13, 2020 | Greg Caswell [DfR], Matt Perry [H.B. Fuller], Haichuan Zhao [H.B. Fuller], Ralph Velazquez [H.B. Fuller]

The solar industry has driven solutions that result in electronics systems that are required to perform in outside environments for over 25 years. This industry expectation has resulted in solutions to protect the electronics from failure that can result from interaction with moisture, and various chemicals leading to corrosion and shorting of the systems. Potting and encapsulation compounds can impart the very high level of protection from environmental, thermal, chemical, mechanical, and electrical conditions that the solar applications demand....

Accurately Capturing System-Level Failure of Solder Joints

Feb 05, 2020 | Maxim Serebreni

Consortium Projects - Thermal Cycling Reliability</p> <ul> <li>Consortium projects allow for joint research to investigate the reliability of multiple solder alloys under a variety of environmental stress conditions. </li> <li>Project jointly sponsored by iNEMI and HDP User Group and including CALCE and Universal consortium currently assessing 15 third-generation solder alloys..</li> </ul>...

Temperature Cycling and Fatigue in Electronics

Jan 01, 2020 | Gilad Sharon, Ph.D., Greg Caswell

The majority of electronic failures occur due to thermally induced stresses and strains caused by excessive differences in coefficients of thermal expansion (CTE) across materials.</p><p>CTE mismatches occur in both 1st and 2nd level interconnects in electronics assemblies. 1st level interconnects connect the die to a substrate. This substrate can be underfilled so there are both global and local CTE mismatches to consider. 2nd level interconnects connect the substrate, or package, to the printed circuit board (PCB). This would be considered a "board level" CTE mismatch. Several stress and strain mitigation techniques exist including the use of conformal coating....

Effect of Encapsulation Materials on Tensile Stress during Thermo-Mechanical Cycling of Pb-Free Solder Joints

Mar 06, 2019 | Maxim Serebreni, Dr. Nathan Blattau, Dr. Gilad Sharon, Dr. Craig Hillman

Electronic assemblies use a large variety of polymer materials with different mechanical and thermal properties to provide protection in harsh usage environments. However, variability in the mechanical properties such as the coefficient of thermal expansion and elastic modulus effects the material selection process by introducing uncertainty to the long term impacts on the reliability of the electronics. Typically, the main reliability issue is solder joint fatigue which accounts for a large amount of failures in electronic components. Therefore, it is necessary to understand the effect of polymer encapsulations (coatings, pottings and underfills) on the solder joints when predicting reliability.

This paper presents the construction and validation of a thermo-mechanical tensile fatigue specimen. The thermal cycling range was matched with potting expansion properties in order to vary the magnitude of tensile stress imposed on solder joints...

Multilayer Ceramic Capacitors: Mitigating Rising Failure Rates

Dec 05, 2018 | Dock Brown

The multilayer ceramic capacitor (MLCC) has become a widely used electronics component both for surface mount and embedded PCB applications. The MLCC technologies have gone through a number of material and process changes such as the shift from precious metal electrode (PME) configurations which were predominantly silver/palladium to base metal electrodes (BME) dominated by nickel. Each of these changes were accompanied by both quality and reliability problems. The MLCC industry is now in the midst of an unprecedented set of challenges similar to the Moore’s Law challenges being faced by the semiconductor industry. While capacitor failures have historically been responsible for a significant percentage of product field failures (most estimates are ~30%) we are seeing disturbing developments in the low voltage (<250V) commodity part infant mortality and wearout failure rates....

Best Practices for Improving the PCB Supply Chain: Performing the Process Audit

Aug 03, 2018 | Greg Caswell, Dr. Craig Hillman

In the electronics industry, the quality and reliability of any product is highly dependent upon the capabilities of the manufacturing suppliers. Manufacturing defects are one of the top reasons why companies fail to meet warranty expectations. These problems can result in severe financial pain and eventual loss of market share. What a surprising number of engineers and managers fail to realize is that focusing on processes addresses only part of the issue. Supplier selection also plays a critical role in the success or failure of the final product....

How Mitigation Techniques Affect Reliability Results for BGAs

Nov 17, 2016 | Greg Caswell, Melissa Keener

Since 2006 RoHS requirements have required lead free solders to take the place of tin-lead solders in electronics. The problem is that in some environments the lead free solders are less reliable than the older tin-lead solders. One of the ways to solve this problem is to corner stake, edge bond or underfill the components. When considering what mitigation technique and material to use, the operating conditions must be characterized. The temperature range is important when selecting a material to use since the glass transition temperature (Tg) and coefficient of thermal expansion (CTE) are important properties. If improperly chosen, the mitigation material can cause more failures than an unmitigated component....

Predicting Fatigue of Solder Joints Subjected to High Number of Power Cycles

Jul 09, 2015 | Craig Hillman, Nathan Blattau, Matt Lacy

Solder joint reliability of SMT components connected to printed circuit boards is well documented. However, much of the testing and data is related to high-strain energy thermal cycling experiments relevant to product qualification testing (i.e., -55C to 125C). Relatively little information is available on low-strain, high-cycle fatigue behavior of solder joints, even though this is increasingly common in a number of applications due to energy savings sleep mode, high variation in bandwidth usage and computational requirements, and normal operational profiles in a number of power supply applications.

In this paper, 2512 chip resistors were subjected to a high (>50,000) number of short duration (<10 min) power cycles. Environmental conditions and relevant material properties were documented and the information was inputted into a number of published solder joint fatigue models. The requirements of each model, its approach (crack growth or damage accumulation) and its relevance to high cycle fatigue are discussed....

The Effect of Coating and Potting on the Reliability of QFN Devices.

Aug 28, 2014 | Greg Caswell, Cheryl Tulkoff.

The fastest growing package types in the electronics industry today are Bottom Termination Components (BTCs). While the advantages of BTCs are well documented, they pose significant reliability challenges to users. One of the most common drivers for reliability failures is the inappropriate adoption of new technologies. This is especially true for new component packaging like BTCs. Obtaining relevant information can be difficult since information is often segmented and the focus is on design opportunities not on reliability risks (...)

Commonly used conformal coating and potting processes have resulted in shortened fatigue life under thermal cycling conditions. Why do conformal coating and potting reduce fatigue life? This paper details work undertaken to understand the mechanisms underlying this reduction. Verification and determination of mechanical properties of some common materials are performed and highlighted. Recommendations for material selection and housing design are also given....

Gold Embrittlement In Lead-Free Solder.

Aug 07, 2014 | Craig Hillman, Nathan Blattau, Joelle Arnold, Thomas Johnston, Stephanie Gulbrandsen; DfR Solutions, Julie Silk, Alex Chiu; Agilent Technologies.

Gold embrittlement in SnPb solder is a well-known failure mechanism in electronic assembly. To avoid this issue, prior studies have indicated a maximum gold content of three weight percent. This study attempts to provide similar guidance for Pb-free (SAC305) solder. Standard surface mount devices were assembled with SnPb and SAC305 solder onto printed boards with various thicknesses of gold plating. The gold plating included electroless nickel immersion gold (ENIG) and electrolytic gold of 15, 25, 35, and 50 microinches over nickel. These gold thicknesses resulted in weight percentages between 0.4 to 7.0 weight percent....

Copper Wire Bond Failure Mechanisms.

Jul 24, 2014 | Randy Schueller, Ph.D.

Wire bonding a die to a package has traditionally been performed using either aluminum or gold wire. Gold wire provides the ability to use a ball and stitch process. This technique provides more control over loop height and bond placement. The drawback has been the increasing cost of the gold wire. Lower cost Al wire has been used for wedge-wedge bonds but these are not as versatile for complex package assembly. The use of copper wire for ball-stitch bonding has been proposed and recently implemented in high volume to solve the cost issues with gold. As one would expect, bonding with copper is not as forgiving as with gold mainly due to oxide growth and hardness differences.

This paper will examine the common failure mechanisms that one might experience when implementing this new technology....

Using Physics of Failure to Predict System Level Reliability for Avionic Electronics

Dec 11, 2013 | Greg Caswell, Sr. Member of the Technical Staff, DfR Solutions

Today's analyses of electronics reliability at the system level typically use a "black box approach", with relatively poor understanding of the behaviors and performances of such "black boxes" and how they physically and electrically interact (...) The incorporation of more rigorous and more informative approaches and techniques needs to better understand (...) Understanding the Physics of Failure (PoF) is imperative. It is a formalized and structured approach to Failure Analysis/Forensics Engineering that focuses on total learning and not only fixing a particular current problem (...) In this paper we will present an explanation of various physical models that could be deployed through this method, namely, wire bond failures; thermo-mechanical fatigue; and vibration....

Conformal Coating Why, What, When, and How

Jan 05, 2012 | Greg Caswell

Conformal coating is applied to circuit cards to provide a dielectric layer on an electronic board. This layer functions as a membrane between the board and the environment. With this coating in place, the circuit card can withstand more moisture by incre...

Manufacturability & Reliability Challenges with Leadless Near Chip Scale (LNCSP) Packages in Pb-Free Processes

Oct 27, 2011 | Cheryl Tulkoff, Greg Caswell

Leadless, near chip scale packages (LNCSP) like the quad flat pack no lead (QFN) are the fastest growing package types in the electronics industry today. Early LNCSPs were fairly straightforward components with small overall dimensions, a single outer row...

Alternative Pb-Free Alloys

Aug 25, 2011 | Dr. Randy Schueller

While SnAgCu (SAC) alloys still dominate Pb-free selection in North America, especially Sn3.0Ag0.5Cu (SAC305), there are alternative material systems available. Any OEM that is concerned about the high reflow temperatures of SAC or relies on ODM, it is im...

Accurate Quantitative Physics-of-Failure Approach to Integrated Circuit Reliability

Jun 02, 2011 | Edward Wyrwas, Lloyd Condra, Avshalom Hava

Modern electronics typically consist of microprocessors and other complex integrated circuits (ICs) such as FPGAs, ADCs, and memory. They are susceptible to electrical, mechanical and thermal modes of failure like other components on a printed circuit boa...

A New (Better) Approach to Tin Whisker Mitigation

Mar 03, 2011 | Craig Hillman, Gregg Kittlesen, and Randy Schueller

Most of the electronics industry by now knows about tin whiskers. They know whiskers are slim metallic filaments that emanate from the surface of tin platings. They know these filaments are conductive and can cause shorts across adjacent conductors. And they know that these shorts can cause some really bad failures (see nepp.nasa.gov/whisker/ for a list longer than you need). But, with all of this knowledge, the industry is still struggling on how to predict and prevent these "Nefarious Needles of Pain"....

0201 and 01005 Adoption in Industry

Feb 03, 2011 | DfR Solutions

First introduced in the year 2000, the 0201 package was sold in significant numbers in the electronics industry by 2003. According to some estimates, it currently accounts for approximately 20% of surface mounted component (SMC) demand worldwide1. This pu...

The Reliability Challenges of QFN Packaging

May 27, 2010 | Randy Kong, Cheryl Tulkoff, Craig Hillman (presented at: SMTA China East Conference 2010)

The quad flat pack no lead or quad flat non-leaded (QFN) is one of the fastest growing package types in the electronics industry today. While the advantages of QFNs are well documented, concerns arise with its reliability and manufacturability. Acceptance of this package, especially in long-life, severe-environment, high-reliability applications, is currently limited. One of the most common drivers for reliability failures is inappropriate adoption of new technologies, such as the case with QFN. In this presentation, we will review and discuss QFN related reliability concerns and challenges, and propose Physics-of-Failure (PoF) based approaches to allow the confident introduction of QFN components into electronics products....

A Review of Models for Time-to-Failure Due to Metallic Migration Mechanisms

Oct 14, 2009 | Elissa Bumiller and Dr. Craig Hillman

Electrochemical migration (ECM) is defined as the growth of conductive metal filaments across a printed circuit board (PCB) in the presence of an electrolytic solution and a DC voltage bias. ECM, also known as dendritic growth, is a critical issue in the electronics industry because the intermittent failure behavior of ECM is a likely root-cause of the high occurrence of field failures identified as no trouble found (NTF)/could not duplicate (CND)...

Solder Phase Coarsening, Fundamentals, Preparation, Measurement and Prediction

May 07, 2009 | Crina Rauta, Dr. Abhijit Dasgupta and Dr. Craig Hillman, DfR Solutions.

Thermal fatigue has been one of the most serious problems for solder joint reliability. Thermo-mechanical fatigue failure is considered to be closely related to micro-structural coarsening (grain/phase growth). Factors that influence the phase growth are studied and measurement methods are discussed, including the preparation of the eutectic solder sample for phase size measurement. Three categories of models used to predict grain growth in polycrystalline materials are presented. Finally, phase growth in solder during high temperature aging and temperature cycling and its use as a damage correlation factor are discussed....

Five Myths of Reliability

Dec 23, 2008 | Dr. Nathan Blattau, Dr. Bob Esser, Dr. John McNulty, and James McLeish.

Myth 1: I don't worry about design, because most of my problems are with defects from suppliers......

Bromide-Free Options for Printed Circuit Boards

Dec 11, 2008 | Craig Hillman, PhD & Seth Binfield

Flame retardants have been around since the Egyptians and Romans used alum to reduce the flammability of wood. Brominated flame retardants (BFRs) first experienced use after World War II as the substitution of wood and metal for plastics and foams resulted in materials that were much more flammable. The widespread use of BFRs initiated in the 1970s with the explosion of electronics and electrical equipment and housings. For the US market, all of these products must conform to the UL 94 flammability testing specifications. In fact, the most common printed circuit board (PCB) in the electronics industry, FR-4, is defined by its structure (glass fiber in an epoxy matrix) and its compliance to UL 94 V0 standard....