The use of high performance electronic assemblies in harsh environments subject solder interconnects to complex loading conditions that are primarily driven by the behavior of circuit card assembly and mounting constraints. These assemblies contain a variety of surface-mount devices which are sensitive to thermo-mechanical (TM) fatigue. Stresses generated by placing certain components within the vicinity of mechanical structures,such as standoffs and connectors,can further influence solder fatigue by increasing PCB strains. The mounting constraints can subject packages to loads which are not expected to occur under non-constrained PCB configurations often used in accelerated testing. In order to determine the influence of complex board constraints on electronic components,thermal simulations are performed using finite element analysis (FEA). Detailed models of large electronic assemblies are often tedious and time consuming to construct. In this study,TM simulations of electronic assemblies are implemented to investigate the effect of mounting conditions on board strains. The software used in this analysis enables fast integration of package level and printed circuit board (PCB) features from design files into comprehensive models enabling efficient analysis of the entire board level assembly under thermal loads. These simulations capture the contribution of both local and global coefficients of thermal expansion (CTE) mismatch in the vicinity of mounting conditions and components. The software package implemented in this analysis enables the prediction of board behavior of complex electronic assemblies under TM loads and provides an efficient approach to enhancing circuit board layout.

When it comes to reliability assessment of an electronic system,consisting of several components,such as an assembled printed circuit board (PCBA),this often turns out to be a challenging task. The more different partners within the supply chain are involved the more a specimen and testing based approach becomes difficult,causing increased time demand and higher testing cost. One way to tackle this topic is to intensify the use of finite element based simulation for reliability assessment. While state of the art in many areas of industry,from aerospace industries to construction works the use of Finite Element Analysis (FEA) is still somewhat uncommon in printed circuit board (PCB) industry. The current paper presents a good use case for the application of FEA for the assessment of the thermal reliability of PCBAs. The samples have been stressed by thermal shock test (TST),with a distinct focus on the failure modes of the solder connections between surface mount devices (SMD) and the PCB. The defined PCBA systems were transferred into 3D finite element models,considering major material parameters such as the orthotropic behavior of the laminate layers or the highly non-linear behavior of copper and solder. The established models were then subjected virtually to TST in order to investigate the reliability performance of the systems. Based on the initial models the main phenomena influencing solder failure were identified and investigated more closely. Finally,the results obtained from the finite element based virtual assessment were compared to the results of the actual hardware based test series regarding the solder failure mode and system life time in order to show the current capabilities of FEA as a tool for reliability assessment.

Plasma is considered to be the 4th state of matter. Decomposed molecules interact with all exposed surfaces of the material,even the inner surfaces of open cell structures. In low pressure plasma technology,a stable and effective plasma is created by an electromagnetic discharge of a gas at low pressure and at low temperature. Splash-proof case study: Complex 3D-substrates were coated with a ROHS - and WEEE - compliant super hydro- and oleophobic low pressure plasma conformal nanocoating. These electronic devices were then subjected to splash-proof testing according to IEC60529. IP ratings from IPX2 to IPX4 were obtained,depending on the device’s design. Acoustic performance was tested on microphones and speakers by measuring the sensitivity for a frequency range from 20 Hz to 20 kHz,and showed that the coating does not impact the acoustic performance. The coatings are z-axis conductive and thus obviate the use of masking and allow for flexible integration in the manufacturing process. Waterproof and sweatproof case study: Electronic components were coated with a 1-3 µm low pressure plasma barrier coating and were then assembled into the electronic device. A thin conformal nanocoating can be applied on the assembled product to reduce the ingress of water. These coated devices were then subjected to waterproof testing according to IEC60529. IP ratings from IPX5 to IPX8 were obtained,depending on the device’s design. Short circuit testing was performed on SIR-like PCBs,measuring the current of the circuit when the powered PCB is submersed in water,salt water or artificial sweat. The short circuit current values stayed below 0.1mA,indicating no corrosion on the PCBs (4.7 V,15 minutes submersion time). One of the key drivers of low pressure plasma is the reduced environmental impact compared to traditional wet chemical processes and to the use of more harmful metals. The dry and clean technology has a zero-water consumption,a minimal chemical consumption and a reduced energy consumption,because no heating,drying or curing is needed. This leads to innovative low-pressure plasma coatings that can be used in many applications. The system design and size is adaptable to the dimensions of the products to be coated. In most cases there exists a suited low-pressure plasma treatment with well-dimensioned equipment to help improve protection of electronics.

Conformal coating formulators are developing two-component solutions that improve protection,adhesion,and cure speed. Multi-component coatings are not new to the industry. Some of the oldest conformal coating formulations available are of the two-component variety. While there are some similarities between past and present,the range of possibilities these new formulations provide has not been seen in the industry prior to now. Demand for increased performance and faster cure times are driving manufacturers to revisit these chemistries. New application technologies and techniques have been developed for use in production while focusing on ease of setup,cleaning,and performance. Along with developments in spray technology,a number of process improvements have been found. Today the majority of conformal coatings applied in high volume are done using a selective coating machine where a single wet layer of coating is applied only in desired areas of a PCB. When using traditional single part coatings there can be some challenges in developing a successful process. The properties found in some of the new coatings have provided process benefits such as: improved thickness/coverage on leads and edges,minimal underfilling of sensitive components by the coating,complete cure in shadowed areas,and offers a wide range of flexibility for target application thickness. Descriptions will follow of the benefits found with two-component coatings and how they can potentially enhance the protection of electronic circuits. Examples of applicator technology developed for these materials and the corresponding fluid delivery systems will also be described.

Solder paste is one of the most common materials used in surface mount technology (SMT) processes. Typical methods for applying solder paste to devices are needle dispensing or screen printing,each one has specific benefits and drawbacks. The process of jet printing of solder pastes and other functional materials enable higher throughput than needle dispensing while eliminating the material waste generated by screen printing. Volumetric repeatability of the jetted solder paste is a critical property that must be ensured for any deposition technology to be considered as mature for real SMT production. According to the 2016 iNEMI roadmap placement accuracy for these kinds of components will reach 6 sigma placement accuracy in X and Y of 30 um by 2023 [1]. This level of placement accuracy for components must be accompanied by a related accuracy for the deposit of solder paste and related fluids in order to fulfill the related increasing demands on interconnect reliability in increasingly demanding environments with respect to temperature extremes,mechanical stresses and/or production limitations. Data will be presented demonstrating equipment accuracy for jet printing solder paste,jetted process capability for a given output and jet printing process capability for varying outputs within a single board. Throughput comparisons will be presented to understand how jet printing fares against both needle dispensing and screen printing.

Components are still shrinking in the SMT world and the next evolution of the passive components are the m03015 (009005) and m0201 (008004). Today it is seen that the 01005 component is still relatively unused in most of today’s printed circuit board assemblies. Usage is mainly seen on module assemblies and smart products. It has been a slow adoption rate for other product technologies. For most assemblies 0402 components are still common but the 0201s are still rising in usage as there is a movement to use these in server,network,base station products. The m03015 and the m0201 will see primary adoption in the products that require more miniaturization which would be system in packages (modules). These modules would then be assembled into products either through attachment to another assembly or via other interconnect methods. This paper will explore the development of an assembly process (SMT only) for the m03015 component. Solder paste and stencil type will be discussed with results from the evaluations,as well as the placement and reflow of these components. Component to component spacing down to 0.100mm spacing will be discussed as well. AOI and the challenges around this area will be presented in a separate paper and rework will not be discussed at this time. At the time of this writing,an investigation is being started on the m0201 and results at the time of the paper will be briefly touched on as well.

In Power Electronics,increasing attention are drawn to silver sinter materials as an attractive interconnect material for its properties and also as a lead replacement solution. New property demands are longer lifetime,better performance,higher efficiency,lower manufacturing cost and crucially non-lead containing. Specifically,for T0220 application,non-pressure sinter pastes are dispensed on the lead frame followed by die placement. Sintering process is performed in a programmable oven under nitrogen or air atmosphere. Typical non-pressure sintering profile takes approximately 4hrs long to complete,which if shortened,increases attractiveness to adopt non-pressure sintering. In this study,the objective was to investigate using IR radiation to reduce the total sintering profile. A 2-step profile was to reduce sintering defects and encourage maximum diffusion properties. Larger dies would be recommended to hold longer than 30mins to achieve homogenous drying. From our investigations using IR radiation,comparable non-pressure sintered results were achieved with 25% of the standard convection oven profile. In the convection oven,non-pressure sintering is achievable up to typically 25mm² die dimension. Above this,risk of sinter defects increases. With IR radiation,cross section of die sizes above 25mm² did not detect channeling nor voids. From our temperature profiling analysis,the uniform heat distribution within the specimen was a critical improvement,which encourages homogeneous densification of the sintered layer. For dies above 25mm2,young modulus difference between the die’s center and edge reduces to improve reliability. Our analysis also reported increases in die shear strength and higher thermal conductivity. The paper will show the detailed results with this new sintering process.

A production process free from defects,with every production step being reproducible and traceable,is the target of quality assurance in electronics production worldwide. In many cases manual rework processes are not allowed,due to quality related reasons and cost issues. Manual rework is time consuming and cost-intensive,and hidden costs such as productivity rates or personnel training need to be considered. Because of this,assemblies with defects often go through the production process a second time. However,in this case the entire board is exposed to the thermal load,not only the faulty solder connections,which can affect the overall product reliability. An automated zero-fault production concept can provide a cost-effective solution. Automated process control and integrated automated rework enable a soldering process free from defects and completely documented. Process Challenges: Compared to other automated processes,selective soldering is considered as particularly demanding. Structures with small pitches result in a small process window,variable parameters such as flux quantity,temperatures or wetting time play a decisive role in terms of solder joint quality and reliability. In addition,material-related influences have to be considered. The Zero-Fault Production Concept: A controlled and reliable process is a basic requirement for approaching a zero-fault production. Besides the selective mini-wave soldering process with monitoring and control functions for all process steps,the zero-fault production concept incorporates integrated automated optical inspection (AOI) of the solder joints as well as a defined and automated rework soldering process at the fault coordinates,corresponding to the fault classification. This is an advantage from the technical processing point of view as only defective solder joints go through the process again,not the entire board. As all work stations are linked with a bi-directional data transfer,all process steps are completely traceable and reproducible. In addition,analysis of trend and series faults allows process optimization at an early stage. This particularly applies for component placement and the soldering process,however,design faults can quickly be identified as well. With a focus on the critical issues in a selective soldering process,this paper will describe all process steps that need to be controlled to ensure consistently high product quality. In addition,it will describe a production concept enabling automated rework with minimal thermal exposure for the assemblies.

Aerospace Defense High Performance (ADHP) electronics products primarily use tin-lead solders,but electrical and electronic component finishes (i.e.,platings) increasingly are designed for lead-free solders. The knowledge-gap on tin-lead integrity with new component finishes is growing over time. Also,the reworking of components to make them tin-lead compatible presents a component reliability risk. Therefore,it is important to understand and overcome the interfacial reliability risk for every combination of solder alloy and component finish used in ADHP products. The intermetallic compounds,which nucleate and grow during the soldering and use environments of electronics hardware,are of two general types. These are,1) Precipitation Compounds and 2) Diffusion Compounds. The precipitation compounds occur during the soldering process. The diffusion compounds can begin during the soldering process,and can grow during the environmental exposure of the solder connection to the product application (time at temperature,temperature cycling). We report numerous material combinations of soldering alloys and plating metals,where a common finding is that the growth of the diffusion compounds,at the solder-to-plating interface,is a precursor indicator of solder connection interfacial failure. The precursor is associated with vacancy accumulation and observation of Kirkendall voiding. Diffusion between the plating and the precipitation compounds leads to connection separation because the vacancy content of the plating can be up to twenty percent,and that vacancy content accumulates into area voids as the diffusion compounds grow. The diffusion compounds occur concurrent with,or subsequent to,the precipitation compounds. So the precipitation compounds are called first compounds. The diffusion compounds are called second compounds. The second (diffusion) compounds are stoichiometrically richer in the plating metal than are the first (precipitation) compounds. Technical examples show cross-sectional microstructures,and compound chemistry identifications,from the following solder-to-plating systems: tin-lead-to-gold,tin-lead-to-copper,indium-lead-to-gold,gold-germanium-to-nickel,tin-lead-to-iron-nickel and tin-lead-to-palladium. The influence of the first compounds on the mechanical properties of the solder connection can be characterized with predictability equations. However,the second compounds need to be avoided or minimized,by means of material selection (solder alloy,volume),plating design (metal,thickness,area) and processing parameters (plating,soldering). Lead-free solder connections to copper and iron-nickel finishes indicate qualification testing is needed,for lead-free solder alloys,showing their failure precursor compounds and voids are minimized.

Printed circuit assemblies have become more susceptible to a failure mode known as “pad cratering” due to the implementation of several material restrictions. Pad cratering is defined as mechanically-induced fracture between the copper pad/trace and printed circuit board (PCB)laminate. If left undetected during manufacturing,pad cratering can significantly reduce the reliable life of electronic products. The industry needs a fast,precise,non-destructive method to assess pad cratering,as it increasingly moves toward thinner,more mobile products. There are several methods being used in the electronics industry,both destructive and non-destructive,but all have significant limitations. Acoustic emission detection is a broad-area,non-destructive technique that has the potential to detect solder joint fractures. Passive acoustic emission detection (AED) records the sound waves emitted by fracture events during structural loading. This technique typically employs an array of piezoelectric transducers to measure sound waves at the surface; the location of the fracture event is calculated using the positions of the sensors,the time delay between the arrival of the events at the sensors,and the sonic velocity through the medium. This article discusses the development work performed to date by the authors in both transient bend and shock. The general test and data analysis methods are discussed. Transient bend and shock tests,results,and validation are described. Finally,further potential for the application of these methods to the electronics industryIPC-9709are presented.