A dynamic flex test was performed on a spacecraft instrument harness composed of multiple individual flex cables, with each flex cable containing multiple copper traces. The purpose of the test was to demonstrate the capability of the harness to survive the number of expected flex cycles during the planned mission with appropriate margin. However, during testing, increased trace resistances and open circuits were observed beginning at approximately 10% of the total number of planned flex cycles. This paper discusses the various proximate causes that contributed to increased and open resistance in the flex cables and the subsequent redesign, manufacturing, reliability, and quality-related changes that were instituted. An analysis process, including failure analysis, non-destructive evaluation, digital imaging correlation, and parametric modeling, will also be discussed. The paper will cover the development of a robust dynamic flex harness design and include recommendations to extend flex harness life; make changes to the flex harness life test; and improve flex cable manufacturing, quality, and reliability.

Miniaturization and harsh environment market drivers within the electronics industry are presenting new challenges in terms of predictive reliabilities of control standards. As consumers demand longer product lifecycles, it is important for the industry to recognize the predictive reliability connections between their control standard, build design and quality control procedures in order to mitigate failures such as Ag migration, ECM and corrosion. A major criticism is the speed at which new industry standards or revisions are keeping pace with reliability requirements. One current example is IPC TM-650 2.6.3.7 (SIR) test that was developed for conventional applications BUT overlooked low and high voltage effects in fine pitch and electric vehicle type assemblies. As such the current accelerated testing can create defects that don’t align to field application failures.

This paper will review the latest “electro-chemical migration” methodologies and discuss the main factors of consideration – ranging from field strength, environmental conditions, test duration and process (interconnect and encapsulant chemistry, cleanability and component quality) that could be considered suitable for various markets such as Power Automation, Telecom, Automotive, and Industrial service equipment.

Buzz words to include Ag migration, SIR, ECM, potting material, conformal coating, through hole technology, Circuit board protection, flux resides, compatibility, voltage, test vehicle, Tg (Glass transition temperature)

In 2017, the Society of Automotive Engineers (SAE) G-24 committee approved revision activity for GEIA-STD-0005-1A, “Standard for Managing the Risks of Pb-free Solders and Finishes in ADHP Electronic Systems” (formerly known as “Performance Standard for Aerospace and High-Performance Electronic Systems Containing Lead-free Solder”). During the IPC COUNCIL PERM quarterly meeting, held in February 2020, a decision was made to re-organize the structure of the spec to align with Pb-free/Tin Whisker application risk areas, namely 1) Pb-free piece parts and mixed assembly technology, 2) Commercial-off-the-shelf (COTS) modules and assemblies, and 3) Pb-free design and assemblies for Aerospace & Defense (A&D). This paper will discuss the purpose behind the reorganization and will provide details on the risk areas and use of the document.

Electrical contacts, although critically important for a wide range of applications, are susceptible to degradation due to fretting corrosion, especially when sliding and vibrations occur. To overcome fretting corrosion and sliding wear, lubricants are often used. However, the use of lubricants can cause other detrimental issues. Lubricants usually consist of non-conductive fluids such as hydrocarbons and fluorocarbons. Due to fluid dynamics, when sliding, vibration or other excitation occurs, these fluids can cause prolonged gaps between the conducting metal surfaces. Practically, this has been observed in data centers where vibrations due to technician maintenance or even earthquakes can occur. Depending on the viscosity and roughness of the surfaces, the time it takes these connector surfaces to return to solid conductive contact can be many seconds or longer. This work uses a novel theoretical model of the coupled fluid and solid mechanics between the rough metallic surfaces to evaluate these intermittent breaks in contact due to sliding. The influence of variation in lubricant properties, roughness and solid material properties are considered by the model.

This work provides analytical solutions to the temperature rise of one-dimensional conductors such as whiskers and wires. Whisker growth from metal surfaces of electrical connectors and other components has shown itself to create reliability issues. If a whisker grows in a location that bridges between two conducting surfaces not previously electrically connected, a short can occur, resulting in faulting components. The current passing through the whisker or wire will cause its temperature to rise due to Joule heating. This can eventually cause the conductor to melt, which can than disconnect the short circuit. Therefore, whisker shorts are limited by this melting current. thermal fields of a solid cylindrical conductor including the heat convection, which dissipates some of the heat and reduces the temperature rise. This work examines the influence of convection on the melting of a shorted whisker via a finite difference model that considers the temperature dependent conductivities when solving the coupled one-dimensional heat and electrical conduction equations. Finally, the properties of tin, indium, bismuth and zinc are considered in modeling whisker melting since they are all known to form whiskers.

The FIDES guide 2009 (Edition A) proposes a methodology for the reliability assessment of electronic to evaluate and control product reliability progress throughout life cycle. The reliability control approach considers rounds of results evaluation to identify and implement activities to improve reliability.

Considering the product development phases according to DO-254, this work recommends four rounds of reliability assessment, during the PDR (Preliminary Design Review), CDR (Critical Design Review), SoF (Safety of Flight Review) and EIS (Entrance into Service). For these phase gates, a new approach for the process factor (ПProcess_Phase) is proposed based on a new equation, reduced number of recommendations (audit questions) and considering the effects and risks of the “lead-free transition” through incorporating and updating the 'lead-free process factor' (ПLF).

The FIDES methodology was updated in 2010, at this time the effects of lead-free could not be incorporated in the reliability models, and, in the initial phases of this transition, the industry had relatively little experience with lead-free soldering. Therefore, the basic failure rate (λ0) values, the component manufacturing process factor (ПPM), and the process factor (ПProcess) did not change, however, FIDES has introduced the 'lead-free process factor' (ПLF) to consider the variation of the risk of product failure related to modifications applied to the design and manufacturing processes. The current lead-free process (ПLF) considers 21 audit questions, and the current process factor (ПProcess) considers 155 recommendations; these questionnaires may be a very time-consuming activity during product development phases and very difficult if answering it without perform the audits.

The new approach for the process factor (ПProcess_Phase) can be applied with more agility because it considers a modified equation and ‘Process Grade’ that gather, in a simpler and update manner, a reduced number of recommendations for the ПProcessand ПLF. Furthermore, the new process factor (ПProcess_Phase) will respect the ranges of current ПProcess and ПLF (1 to 8 and 1 to 2, respectively). The agility of the new process factor approach makes it possible to perform the reliability assessment in four rounds during the product development.

Key Words: Failure rate, FIDES, lead-free, Pb-free, pi-factors, Process Factor, reliability evaluation

Compliant press-fit connections using a pure tin finish are prone to spontaneous long whisker growth after press-in, which may result in malfunction of the electronic circuits. The origin of those whiskers is case dependent and difficult to observe by optical microscopy methods. This paper provides insight into a method to analyze the press-fit zone and the press-in process by finite element analysis (FEA). A detailed view to the simulation results enables the identification of the whisker growth position by considering established theories for whisker growth mechanisms. The importance of using the exact zone geometry of the manufactured part which might deviate from the nominal values of the drawing is demonstrated. In general, the method enables design optimization on the press-fit zone to minimize stresses and stress gradients

The method to measure intermetallic compound layer thickness is discussed in a paper recently published by the author[1]. The method uses voltage/current sources, voltmeters, and electrolytes depending on the measurements and the type of material. The method consists of the combination of X-Ray Fluorescence (XRF) and Coulometric Stripping (CS) Methods. These methods are combined because XRF is not capable to distinguishing a pure or combined material directly from the analyzed layer; however, CSM can measure pure layers from a material. Using both methods, it is possible to determine intermetallic (IMC)layer thickness and follow its growth through several thermal processes. In this article, firstly, we compare the results with theXRF-CS method and the profiles obtained using Auger Depth Profiling of several immersion tin PCB that had different thermal treatments. Therefore, it is possible to correlate its results and IMC thickness. The Auger profile graphs show a diffusion similar to Fick Law. Additionally, several immersion tin PCBs that were treated with similar reflow profiles but with different peak temperatures were evaluated with the new method. It was found several transitions of IMC growth. These are: a slight acceleration at 165°C, a strong acceleration of IMC between 217°C and 230°C. a decreasing of IMC thickness at 230°C and a slow growth over 230°C. These would correspond to a phase change, plastic transformation transition, structure modification due to liquid transition and material depletion. These are explained with more details based the measurements, last experiences, and with SEM images. This information can be useful to understand intermetallic growth stages and its possible impact on its prediction and assembles quality.