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.

Light emitting diodes (LEDs) are widely used throughout the electronics industry due to their high efficiency, lumen output, and expected lifetime. LEDs are semiconductor devices that are commonly used as indicator lights on printed circuit board assemblies (PCBAs). Some surface mount technology (SMT) LEDs consist of silver-plated copper lead frames within a molded housing. The die is commonly attached to the lead frames with a silver-filled adhesive, and the die is electrically connected with either 1 or 2 wire bonds. SMT LEDs are commonly encapsulated with either a silicone or epoxy material.

The LED materials set and assembly construction described above are susceptible to corrosion, especially when sulfur-bearing gases are present in the environment. Sulfur-bearing gases are common atmospheric pollutants in industrial locations, agricultural regions, and in regions of the world that rely heavily on coal-burning power plants. The silver-plated copper lead frames will corrode in the presence of sulfur-bearing gases, forming silver sulfide. This phenomenon is exacerbated by a silicone encapsulant, which is permeable to, and concentrates sulfur-bearing gases, leading to higher corrosion rates.

This study focuses on sulfur corrosion of LEDs. The sulfur-induced failure mechanism of LEDs, and the evaluation of field returned product is discussed. In addition, the susceptibility to sulfur corrosion of various LED package design configurations from different suppliers was determined via Flowers of Sulfur (FoS) testing. The FoS test followed a modified EIA-977 procedure. Finally, a recommendation will be made to reduce sulfur related LED failures in the field.

The proliferation of Artificial Intelligence (AI), big data, 5G, electric vehicles, Internet of Things (IoT), Edge Computing,High Performance Computing (HPC) and Electric Vehicle (EV) in recent years has necessitated the increased use of electronics. Therefore, the hardware reliability of electronics has received more attention in the industry. With prevalent environmental pollution, air quality will also directly or indirectly influence the life of electronics in indoor and outdoor applications. In general, the hardware reliability of electronics can be easily affected by corrosive gases, moisture, salts, contaminants and particulate matter, especially in environments with high sulfur-bearing gaseous contamination. Therefore, the next generation electronics require not only high performance but also robustness against harsher environments. It is very important to develop an effective accelerated corrosion test to verify the robustness of electronics in field environments. In this research, MFG testing method was adopted to validate the anti-corrosion capability of Printed Circuit Board (PCB) withvarious surface finish materials, including Hot-Air Solder Leveling (HASL), Immersion Tin (ImSn), Electroless Nickel Immersion Gold (ENIG) and Organic Solderability Preservative (OSP) from different PCB vendors. Besides, we introduced ammonia-gas as another acceleration factor, and benchmarked it against the acid-gases based MFG test. Several analytical methods were used in this work, including, Optical Microscope (OM) Inspection, Coulometric Reduction (CR), Cross section polisher, (CP), Scanning Electron Microscopy (SEM) and Energy-Dispersive X-ray spectroscopy (EDX). Finally, we found that ammonia-gas has specific synergistic effects of these contaminants on metal corrosion occurrence. Obvious silver and copper corrosion reactivity and corrosion feature were obtained in the acid-gases based MFG test containing ammonia-gas. Besides, a creep corrosion propensity was observed on OSP PCBs that was higher than the others surface finish materials after acid-gases based MFG test containing ammonia-gas. Therefore, the acid-gases based MFG test containing ammonia gas may be an effective accelerated corrosion test to verify the robustness of electronics, including copper and silver corrosion in the industry.

Key Words: Metal Corrosion, Creep Corrosion, PCB Surface Finish, Ammonia, Mixed Flowing-Gas (MFG).

In this study, a patent-pending new solder paste material has been developed for assembly of System in Package (SiP) with outstanding slump resistance without compromising the paste volume printed, and the solder joint service temperature. In the fine pitch solder paste using medium temperature solder powder (MTSP), low melting solder powder (LMSP) was introduced. At printing, the powder mixture behaved as regular fine-pitch solder paste. Upon heating, the LMSP melted and formed “Powder Cluster” with surrounding MTSP. The Powder Cluster resisted slump, thus avoided solder bridging, consequently enabled high yield of assembly. When 58Bi42Sn was used as LMSP in SAC305 solder paste, the desired LMSP content was found to be no less than 4% w/w of solder paste for great slump resistance at 100°C, 150°C, and 200°C, and no more than 8% w/w of solder paste for the 1st sign of melting of reflowed solder to be no lower than 179°C. The slump resistance achieved at 100°C which was lower than the melting temperature of 58Bi42Sn was attributed to Powder Cluster formation due to solid-state diffusion. The overall metal load tested was found to be acceptable at 82% w/w and can be further optimized for better print and slump-resistance performance. Higher print thickness and higher heating temperature resulted in a higher slump rate, suggesting the choice of LMSP and MTSP would affect the slump resistance potential. Print pattern was found to affect slump resistance through “Paste Crowdedness” factor, which can be used as a tool for assessing the potential of slump rate during stencil design phase.

Key Words SiP, solder paste, powder cluster, paste crowdedness, slump resistance, anti-slump, low melting solder powder, LMSP, medium temperature solder powder, MTSP

Use of low-cost Aluminum based flexible printed circuit boards or Al-PCBs has been growing in popularity. Integrating them with conventional Copper based PCBs or Cu-PCBs is essential for their large-scale adoption. This is because most complex electronic systems that use Al-PCBs require them to be connected to other PCBs for an electrical or data connection. Soldering is the preferred method for mounting Surface Mount Devices (SMDs) and connecting circuit boards. But that brings in processing challenges.

Soldering to aluminum requires an additional surface treatment or the use of conductive epoxy. These are cost-prohibitive and have reliability challenges. And existing products like solders, fluxes, tack agents, cleaners etc. are formulated for Cu-PCBs and do not work on aluminum.

A Surface Treatment technology will be presented that addresses all these constraints. Once printed on aluminum using conventional printing techniques such as screen, stencil etc., it is cured thermally in a convection oven at low temperatures, leaving a non-conductive deposit on the pads. This is followed by conventional process i.e. print solder over the treated pads, place components and then reflow resulting in finished Al-PCBs. Surface Treatment can also be used to solder Al-PCBs to flexible and rigid Cu-PCBs.

This is a paradigm shift in the industry which opens up many new applications, including those in the RFID, LED, and automotive industries. An increasingly popular method to make flexible circuits use Aluminum on PET (Polyethylene terephthalate) or Al-PET substrates. This paper provides cross-sections and shear data on soldered joints, including joints for Al-PET to Cu-PCB, and also for Al-PET to Cu-pigtails using aluminum metallization with low-temperature Bi-Sn-Ag solders. It will also show other processes such as hot-bar soldering to achieve good solder joints between Al/PET and Cu-PCBs.

The assembly of complex optical systems such as objective lenses for smartphone cameras, autonomous driving sensors / cameras, and light detection and ranging (LiDAR) require precise alignment during their production. This is accomplished via an Active Alignment process utilizing real-time measurements alongside light curable adhesives to fix the components in-place once aligned. The adhesive is critical towards maintaining alignment, bonding structural components, and fixing sensors and modules to the PCB substrates. Active alignment adhesives must conform to strict technical requirements: minimal volumetric shrinkage, low CTE, rapid cure, and high Tg. UV-curable cationic epoxy-based adhesives deliver on these requirements and allow for the assemblies to perform at a more demanding level as well as driving the assembly process efficiencies to significantly increase capacity and productivity. Their physical and mechanical properties will be discussed alongside applications and future developments.