Condensation Testing to Predict Multilayer Ceramic Capacitors Reliability

The assembly of miniature components on Printed Circuit Boards (PCBs) poses numerous challenges to each process step. The 0201 components are miniature components which are 0.020” in length and 0.010” in width. The assembly of 0201s using process settings that are currently in-place may result in defects including bridging, tombstoning and solderballing. The objectives of this research are to evaluate two no-clean eutectic solder pastes, determine ‘optimum’ print parameters, and develop good reflow profiles to eliminate defects that are commonly observed during the assembly of 0201 components. The two no-clean solder pastes are evaluated and the ‘optimum’ print parameters were determined through a full factorial experiment. Statistical tests, such as the paired t-test and the calculation of the coefficient of variation of the volume of the solder paste deposited, helped to evaluate the two solder pastes. A comprehensive literature review was conducted to arrive at the initial reflow parameters. The solder paste printing and reflow processes were modified as per the findings and were implemented to assemble several PCBs (test vehicles) with 0201s on them. The assemblies were inspected for defects, both visually and using a 10X microscope. In addition, the assemblies were also inspected using automated optical inspection equipment. No defects were observed during these inspections. Consequently, it can be concluded that the recommended changes to the printing and reflow soldering processes have resulted in the successful development of a viable ‘drop in’ process for the assembly of 0201 components.

With lead-free legislation impacting printed circuit board (PCB) manufacturing, immersion silver (ImAg) finish is adapted as the top finish of copper trace on PCB due to its many advantages. However, it is easy for silver to form electrochemical migration (ECM) in high humid environment, so that the potential bias and spacing between adjacent circuits are limited. In addition, since the thickness of ImAg finish is usually less than 0.15µm restrained by the electroless plating process, the copper trace under the silver finish cannot be fully covered, which causes the complexity of corrosion and electrochemical migration. In this paper, water drop test was used to induce the electrochemical migration on ImAg finished “Y” pattern circuits on PCB. The surface insulation resistance was detected by a picoammeter and the growth of dendrite deposit between two electrodes was monitored by a video system. The electrolytic reaction and galvanic reaction on the electrodes formed by bimetal couples was analyzed theoretically. The mechanism of electrochemical migration of copper driven by immersion silver finish was discussed. The effects of potential bias, spacing and electric field intensity between adjacent circuits on electrochemical migration were discussed.

Multilayer ceramic capacitors (MLCC) play a vital role in electronic systems, and their reliability is of critical importance. The ongoing advancement in MLCC manufacturing has improved capacitive volumetric density for both low and high voltage devices; however, concerns about long-term stability under higher fields and temperatures are always a concern, which impact their reliability and lifespan. Consequently, predicting the mean time to failure (MTTF) for MLCCs remains a challenge due to the limitations of existing models. In this study, we develop a physics-based machine learning approach using the eXtreme Gradient Boosting method to predict the MTTF of X7R MLCCs under various temperature and voltage conditions. We employ a transfer learning framework to improve prediction accuracy for test conditions with limited data and to provide predictions for test conditions where no experimental data exists. We compare our model with the conventional Eyring model (EM) and, more recently, the tipping point model (TPM) in terms of accuracy and performance. Our results show that the machine learning model consistently outperforms both the EM and TPM, demonstrating superior accuracy and stability across different conditions. Our model also exhibits a reliable performance for untested voltage and temperature conditions, making it a promising approach for predicting MTTF in MLCCs.

The rapid growth of the global electronics manufacture environment has brought about the onset of a variety of new, untested materials and processing chemicals. The interactions between substrates and processing chemicals that can occur during manufacture, storage and use must be assessed in order to determine long-term reliability. Surface insulation resistance (SIR) testing is a standard industry technique used to assess the interactions between processing chemicals (e.g., soldering fluxes) and substrates. SIR test method conditions vary in terms of the temperature and the humidity used to accelerate the normal failure modes. Typically, a 45 to 50 volt bias is applied to an interdigitated comb pattern, and periodic SIR measurements are made using a 100 volt test. Pass/fail criteria based solely on SIR electrical values, (e.g., 100 MΩ) however are inadequate. Often the electrical measurement fails to reveal the presence of surface dendrites due to contaminants related to processing chemicals. This failure occurs because the dendrite burns out between electrical readings when the circuit continues to be biased at 50 volts. A new “linear test circuit” has been developed to overcome this deficiency. The circuit uses an operational amplifier to detect the formation of a surface dendrite between electrodes on the comb pattern. When the dendrite shorts the circuit, voltage to the comb pattern is removed. Thus, the presence of the dendrite is captured electrically, and the dendrite is preserved for further analysis. This paper will present the circuit used and data showing its’ effectiveness at detecting both surface dendrites and subsurface conductive anodic filament formation.

With the miniaturization of the electronic devices, the spacing among the circuit traces on printed circuit boards (PCB) keeps reducing, which increases the risk of insulation failure based on electrochemical migration (ECM), especially for immersion silver (ImAg) plated PCB. Meanwhile, due to the severe air pollution in developing countries, airborne dust can deposit on the PCBs in electronic devices. The soluble salts in the dust can decrease critical humidity and increase the ion concentration in the moisture condensed on the PCB surfaces, so that the failure mechanism based on ECM may be changed and the time to failure (TTF) can be shorten. In this paper, the effect of the soluble salt with various concentrations on the ECM failure on PCB was investigated. The life model of ECM was built up based on the electrochemical reactions on electrodes. Then the ECM of PCB under sodium chloride (NaCl) solution with various concentrations was simulated on Y- pattern PCB by water drop (WD) test method. The failure characteristics of ECM during various stages of migration and under various concentrations of salt solution were analyzed by the morphology and element compositions of dendrite products, as well as real time monitoring of surface insulation resistance (SIR). The TTF of ECM was extracted to fit the life model. Finally, the mechanism and performance of ECM of PCB under salt solution was analyzed. And the application of the life model of the ECM failure of PCB contaminated by soluble salts was discussed.

Miniaturization and increasing voltage for e-mobility solutions both are a big challenge for the design of robust electronic devices in the automotive industry considering the harsh environmental conditions that they work in. The operation of electronic control units (ECU) in humid environments can lead to electrochemical migration (ECM) that can cause unpredictable electrical failures in cases where unsuitable materials, processes, or housing concepts are used. Due to the variety of components, materials, and assembly steps, following the common no-clean approach in the automotive industry, a complex mixture of materials with a specific ionic load and hygroscopic behavior is combined on a printed circuit board assembly (PCBA) in a way that the electrochemical reliability is not easily predictable. The simple measurement of ionic contaminants on PCBAs, as widely assumed, does not predict the reliability of the unit in the end-use-environment. Therefore, reliability testing by measurement of the surface insulation resistance (SIR) of the combination of materials that are used and processed on high volume electronic assembly lines is a fundamental task for the automotive industry. Robert Bosch GmbH has established the B52 test board (IPC-9202) and developed it further in a way that it can be used as a base for material and process release on an ECU-platform level. SIR-results from long-term testing (constant climate conditions) and from damp heat testing (environmental testing following IEC60068-3-4) with B52 test boards are presented. The results show that even under high humidity load reliable electronic devices can be achieved with the benefit of no-clean fluxes, if suitable materials and processes are chosen and controlled. The approach and results confirm that the B52 test board and content of the IPC-9202 can be successfully transferred and applied to the requirements of the automotive industry if improvements are considered. These should become part of further international standardization.

This paper is in English and Chinese languages. Conformal coatings have been used for many years in markets requiring high reliability like automotive, military, aerospace and energy, to protect Printed Circuit Board Assemblies (PCBAs) operating under harsh environmental conditions such as high humidity, vibrations, presence of solvents, corrosive atmosphere... Use of conformal coating will increase in the coming years due to the demand to improve performance and lifetime of electronics, also to increase reliability of circuits due to miniaturization, and the growth of some markets including inverters, electronics in automotive, etc To ensure an optimal performance of a coating over a PCBA, cleaning the flux residues as well as all the contaminants before coating is a must. However, due to the additional costs of this cleaning step, sometimes it is not considered as an option in several markets (i.e, Automotive, Energy) using today no clean materials. This paper describes the performance of several kinds of conformal coatings (acrylics, polyurethanes, UV cured) over no-clean lead free solder paste residues. The physical and chemical compatibility will be assessed using several techniques. After a description of the coatings and pastes chemistries used in the study, the compatibility before curing will be investigated (influence of viscosity, surface tension, thickness … ) Second, the adhesion properties of the coatings after curing on different surfaces including lead free solder paste residues will be evaluated. Finally, Surface Insulation Resistance (SIR), Electrochemical Migration (ECM) tests and Bono corrosion test - which has been proven to better differentiate the nature of solder pastes residues- will be used for the chemical compatibility. It will be shown that several tools are necessary and complementary to anticipate the performance of conformal coatings with no-clean pastes residues due to the different kinds of coatings and pastes chemistries.

A century of diligent R&D has resulted in a wide range of ceramic dielectrics and processing technologies. The technology used to manufacture an MLCC (multilayer ceramic capacitors) that costs pennies was unimaginable 30 years ago. The present trends of enhanced mobility, connectivity, and reliability in consumer, industrial, and military electronics will continue to drive future innovations in ceramic capacitor technology. In addition, power electronics applications are an emerging market in which ceramic capacitors will play an increasing role through improved breakdown strength, enhanced dielectric stability in harsh environments, and innovative packaging. The investment made by the US government to develop high energy density and high temperature capacitor technology will also contribute to the advancement of dielectric materials technology for pulse and power electronic capacitors.

Multilayer ceramic capacitors are prone to mechanical defects and damage because of the fragility of the ceramic dielectric. Because these faults are often not recognized by visual or electrical inspection, a nondestructive fast way of detecting these defects would be very useful. Ceramic capacitors are known to generate acoustic emissions, caused by mechanical vibration of the capacitor body. Physical defects alter the mechanical properties of the capacitor, which, in turn, affect the acoustic signature of the capacitor. In this paper, acoustic information is acquired directly from both pristine and damaged capacitors. An experiment was conducted where capacitors were driven with a voltage chirp over a wide range of frequencies, and subsequent acoustic emissions were measured with a piezoelectric point contact sensor. Test boards were bent to cause flex cracks to the soldered capacitors, which were measured acoustically before and after bending. A comparison of these measurements showed that printed circuit board bending causes characteristic changes to the capacitor acoustic response, which can be correlated with the resulted damage.

Acoustic noise induced by multilayer ceramic capacitors (MLCCs) in power distribution network (PDN) is a critical issue regarding product user experience. In this work, design guidelines for decoupling capacitor selection, layout geometries are proposed targeting the acoustic noise, through analysis of the acoustic noise generation mechanism in printed circuit board (PCB). A test board is designed to validate the proposed design guidelines. With sound pressure level measurement of the test vehicle, the effectiveness of the proposed design guidelines is confirmed. In general, the decoupling capacitor layout design guidelines for acoustic noise consideration are consistent with the requirements for PDN to achieve high electrical performance.

Flux consumption for wave soldering tends to decrease, mainly due to its gradual replacement by reflow soldering methods (i.e. pin-in-paste) in many electronics applications. However, in several cases, wave soldering still remains a must, with an increasing share of “selective” soldering processes, either using wave frames with dedicated apertures or solder fountains. Such processes are more challenging for the fluxes in terms of reliability under operation, since some chemistries remaining on the printed circuit boards after soldering may promote corrosion. Thus, flux manufacturers had to adapt their formulations to minimize such issues while keeping an efficient activation level, with several types of alloys (tin-lead, tin-silver-copper and low/no-silver) and associated with the numerous types of finishes encountered. The paper will cover the types of flux used in the electronic industry according to their chemistry and activation level (rosin-based, halides, alcohol-based or water-based flux…), and their characteristics with reference to standards. The limits of current standards will be discussed in regards to the last generation solder fluxes. Then, the development of two low-residue new generation fluxes, an alcohol-based flux and a true VOC-free flux, will be described, according to requirements: the lab tests results (surface tension, spread tests, wettability tests…) will be presented and discussed. Reliability will be especially investigated through surface insulation resistance, electro-chemical migration test, ionic contamination as well as Bono tests to determine the candidates able to provide high processability combined with chemical inertness of residues. Finally, the performance of flux will be assessed through customer tests, involving several types of boards, finishes and different solder alloys and wave equipment.

There are several methods accepted by the industry for determining the electrochemical reliability for electronic assemblies. These methods are typically designed to either simulate humid environments in accelerated lifetime testing, or assess the species of ionic residues present on surfaces. Some can be used to test prototypes or test boards; others are more applicable for quality and consistency testing in a production environment. The increasing complexity of high density assemblies, along with low standoff components, imposes greater associated challenges related to assessing electrochemical reliability. This has led to development and adoption of new methods for testing ionic residues that can lead to electrochemical migration. This paper will review traditional and emerging methods to characterize flux residues and cleanliness of finished assemblies, including surface insulation resistance, electrochemical migration, ROSE extraction, and other emerging test methods. Data will be shared showing how different methods can detect process variations in different ways, results will be compared.

A study of conductive adhesive joining technology on printed circuit boards (PCB) was conducted. Six different isotropically conductive, silver-loaded epoxies were evaluated for the surface mount process. These adhesives were used to attach electrically and mechanically 160-lead, 25-mil pitch, quad flat package (QFP) and 0805 chip components on PCB's with hash gold, passivated copper, and tin/lead metallization. The reliability of the conductive adhesive joints was evaluated in two types of environmental test: constant humidity at 60/spl deg/C and 90% RH for 1000 h, and temperature cycling for 1000 h from -40/spl deg/C to 85/spl deg/C. Under these conditions, both the electrical performance, in terms of contact resistance and surface insulation resistance (SIR), and the mechanical strength of the adhesive bonds were evaluated. The results show that reliable conductive adhesive joining can be achieved for both chip components and QFP components on PCB's with all three metallizations tested. Under well-controlled conditions, and with the right choice of adhesive for the application in mind, no significant increase or variation in electrical resistance during the temperature cycling test was encountered. The humidity exposure test was found to have a minor impact on both contact resistance and adhesion strength of most adhesives tested. In general. There was little difference between the different PCB metallizations used (except for SIR measurements). No evidence of silver migration could be observed after the humidity exposure for any of the adhesives tested.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

With the rapid development of electronic technology, electronic components are increasingly widely applied in modern technology, ranging from robots to spacecraft, and from wearable devices to marine equipment. Their reliability is directly related to the stable operation of the entire system. However, metallic tin (Sn) and its alloys, which are the key materials in electronic components, are facing severe corrosion challenges, with tin corrosion being one of the critical factors for component failure. This paper reviews the corrosion mechanisms and protective measures for metallic tin in typical electronic components. Firstly, the structural characteristics, functional roles, and failure modes associated with tin in multilayer ceramic capacitors (MLCCs), hermetically sealed surface-mounted devices, and surface-mounted crystal oscillators are first analyzed. Subsequently, the corrosion behavior of tin under diverse complex environmental conditions is systematically elaborated, including atmospheric environments, marine atmospheres, hygrothermal environments, PVC fume environments, PE fume environments, mold environments, H<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf>S environments, and SO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> environments. The findings reveal that tin corrosion is influenced by a combination of environmental factors, material properties, and component design. Finally, addressing the corrosion issues of tin and its alloys, this paper systematically outlines effective protective measures from multiple perspectives, including tin alloy modification, conformal coating technologies, and microenvironment control. Approaches such as the addition of rare-earth elements, the use of nanocomposite protective coatings, and dynamic micro-environment monitoring are shown to significantly reduce corrosion risks. This study not only establishes a theoretical foundation for the reliability design and corrosion protection of electronic components but also provides practical solutions for mitigating corrosion challenges in real-world engineering applications. It aims to enhance the stability and service life of electronic components in harsh environments, thereby ensuring the reliable operation of electronic devices.

Acoustic noises in the audible range produced by ceramic capacitors has become an increasingly important concern in consumer electronics. The audible noises deteriorate the consumer experience. In order to locate the ceramic capacitors on a printed circuit board (PCB) that cause acoustic noises, we proposed a three-dimensional (3-D) simulation methodology, which is based on the finite element method. The proposed simulation methodology takes into account the product design, the board design, and the detailed component information. The simulation methodology accurately models the board vibrations, which is considered as the primary and the direct cause of acoustic noises. We conduct sound pressure level and laser Doppler vibrometer measurements to benchmark the accuracy and capability of the proposed simulation methodology. On a testing board, the velocity distributions obtained from the proposed simulation agree very well with the measurement results. Through the proposed simulation methodology, we can characterize the board vibrations and extrapolate design guidelines in order to prevent acoustic noise in the early design stage.