Circuit Board Assembly Research Articles

Influence of thermal cycling on reliability of solder joints executed on long and metal core PCBs

Purpose – The purpose of this paper is to evaluate the reliability of solder joints made on long FR-4 and metal core printed circuit boards using the accelerated thermal cycling. Design/methodology/approach – Solder joints of diodes and resistors samples made on long FR-4 and aluminum (Al) core printed circuit boards were examined. Two kinds of solder pastes were used for the samples preparation. All samples were subjected to temperature aging cycles (−40°C – 3 hours/+85°C – 3 hours). Solder joints resistance, X-Ray inspection and metallographic cross-sections for samples as received and after 100, 500 and 1,000 hours of thermal cycles were utilized for solder joints assessment. Findings – It was stated that 1,000 hours of thermal cycles were enough to show reliability problems in solder joints on long and/or AL core printed circuit board assembly (PCBA). The solder joints of R1206 components were the most sensitive reliability elements. The solder joints of LED diodes are more reliable than solder joints of R1206 resistors. Solder joints made on FR-4 substrate were about two times more reliable than ones on AL core substrate. Cracks in solder joints were the visible reason of solder joints failures. Originality/value – The influence of thermal cycles on the reliability of solder joints on long, FR-4 and metal core printed circuit boards were presented. Findings from this paper can be used for planning of reliability trials during validation of reflow processes of products containing long or long metal core printed circuit boards (PCBs).

Solder Flux Residues and Humidity-Related Failures in Electronics: Relative Effects of Weak Organic Acids Used in No-Clean Flux Systems

This paper presents the results of humidity testing of weak organic acids (WOAs), namely adipic, succinic, glutaric, dl-malic, and palmitic acids, which are commonly used as activators in no-clean solder fluxes. The study was performed under humidity conditions varying from 60% relative humidity (RH) to ∼99%RH at 25°C. The following parameters were used for characterization of WOAs: mass gain due to water adsorption and deliquescence of the WOA (by quartz crystal microbalance), resistivity of the water layer formed on the printed circuit board (by impedance spectroscopy), and leakage current measured using the surface insulation resistance pattern in the potential range from 0 V to 10 V. The combined results indicate the importance of the WOA chemical structure for the water adsorption and therefore conductive water layer formation on the printed circuit board assembly (PCBA). A substantial increase of leakage currents and probability of electrochemical migration was observed at humidity levels above the RH corresponding to the deliquescence point of WOAs present as contaminants on the printed circuit boards. The results suggest that use of solder fluxes with WOAs having higher deliquescence point could improve the reliability of electronics operating under circumstances in which exposure to high humidity is likely to occur.

Optimized High Power GaN Transistors

GaN transistors intended for use at 600–900 V and that are capable of providing of 30–100 A are being introduced this year. These devices have a substantially better switching Figure-of-Merit (FOM) than silicon power switches. Rapid market acceptance is expected leading to compound annual growth rates of 85 %. However these devices present new packaging challenges. Their high speed combined with the very high current being switched demands that very low inductance packaging must be combined with highly controlled drive circuitry. While convention, and the usually vertical power device die structure, has largely determined power transistor package formats in the past, the lateral nature of the today GaN devices requires the use of new package types. The new packages have to operate at high temperatures while providing effective heat removal, low inductance, and low series resistance. Because GaN devices are lateral they require the package metal tracks to be integrated within the on-chip tracks to carry the current away from the thin on-chip metal tracks. The new GaN devices are available in two formats: one for use in embedded modular assemblies and the other for use mounted upon conventional circuit board systems. The package intended for discrete printed circuit board (PCB) assemblies has a top side cooling option that simplifies the thermal interface to the heat sink. The paper describes the die layout including the added copper tracks. The corresponding package elements that interface directly with the surface of the die play a vital role in terms of the current handling. They also provide the interface to the external busbars that allow the package to be mounted within, or on PCB. The assembly has been subject to extensive thermal analysis and the performance of a 30 A, 650 V transistor is described.

Scheduling of printed circuit board (PCB) assembly systems with heterogeneous processors using simulation-based intelligent optimization methods

The complexity of printed circuit boards (PCBs), as an important sector of the electronics manufacturing industry, has increased over the last three decades. This paper focuses on a practical application observed at a PCB assembly line of electronics manufacturing facility. It is shown that this problem is equivalent to a flowshop scheduling with multiple heterogeneous batch processors where processors can perform multiple tasks as long as the sizes of jobs in a batch do not violate the processors' capacity. The equivalent problem is mathematically formulated as a mixed integer programming model. Then, a Monte Carlo simulation is incorporated into high-level genetic algorithm-based intelligent optimization techniques to assess the performance of makespan-oriented system under uncertain processing times. At each iteration of algorithm, the output of simulator is used by optimizers to provide online feedbacks on the progress of the search and direct the search toward a promising solution zone. Furthermore, various parameters and operators of the algorithm are discussed and calibrated by means of Taguchi statistical technique. The result of extensive computational experiments shows that the solution approach gives high-quality solutions in reasonable computational time.

Direct printing and assembly of FM radio at the user end via liquid metal printer

Purpose – This paper aims to demonstrate the practicability of the liquid metal printer, developed in the authors’ laboratory, in the direct manufacture and assembly of circuit boards at the end customer side using GaIn24.5 alloy as printing ink at room temperature. Design/methodology/approach – A practical procedure for printing a real designed frequency modulation (FM) radio circuit on flexible and transparent substrate using liquid metal printer was established. Necessary electronic components are then assembled on this circuit board. To enhance the mechanical stability of the FM radio circuit board, we further package the circuit board using room temperature vulcanizing silicone rubber. Finally, an efficient way to recycle the liquid metal ink and electronic components is presented at the end of circuit board’s life cycle. Findings – Methods of designing the circuit patterns that are applicable to liquid metal printer are similar to the conventional printed circuit board (PCB) designing strategies. The procedure of applying liquid metal printer for printing the circuits is entirely automatic, cost-effective and highly time-saving, which allows the user to print out desired device in a moment. Through appropriate packaging, the FM radio circuit board can be flexibly used. These PCBs own many outstanding merits including easy modification and stretchability. Nearly all liquid metal ink and components can be recycled. Originality/value – The present end-customer-oriented liquid metal printing opens the way for large-scale personal electronics manufacture which is expected to initiate many emerging applications in education, design, industry, entertainment and more maker targets.

Lean transformation in a high mix low volume electronics assembly environment

Purpose – This paper aims to focus on integrating a lean framework in a high-mix-low-volume (HMLV) printed circuit board assembly (PCBA) environment to enhance current assembly processes and facility layouts. An HMLV PCBA environment is characterized by stochastic demands, a variety of products in terms of shapes and sizes and different sequences of assembly and test operations, in addition to long cycle times and high fall-out rates. Design/methodology/approach – Preliminary analysis indicates that the push inventory control system led to the longer cycle times, such that various lean methodologies have been applied to enhance the assembly operations. In this research, Kanban sizes for different assembly lines are also estimated to integrate and implement a “pull-system” into the lean framework. In addition, material movement and facility layout have been studied to minimize work-in-process travel time. An “iterative-MAIC” approach has been applied to implement lean principles. Findings – As a result, a lean manufacturing pilot line has been implemented to evaluate the effectiveness of the lean principles before rolling them out across the manufacturing floor. It has been shown that the cycle times of the pilot line products are decreased by 40 per cent and the number of defects decreased by 10-30 per cent, depending on different assembly processes, after the lean implementation. Originality/value – There is limited literature that addresses lean transformation in an HMLV electronics manufacturing service provider handling several product types with different testing methodologies, frequent product revision changes and higher fall-out rates. Hence, in this research, lean manufacturing has been implemented in an HMLV PCBA environment, which has the challenges of varying demand with a mix of assembly and test operations for different product families.

Fretting corrosion: Analysis of the failure mechanism for low voltage drives applications

In many power electronics products, such as low voltage LV motor drives, the mechanical and electrical connection between printed circuit board assemblies (PCBAs) is obtained though board-to-board connectors. A common failure mechanism for these components is fretting corrosion. This failure mechanism results from mechanical micro-motion of two parts with respect to each other and causes a wear damage at the asperities of the contact surface resulting in an increase of the ohmic resistance which finally triggers various device failures. Failures resulting from interrupted communication path may create different effects at the product level depending on the power electronic circuit diagram. In this paper investigation on fretting corrosion on board-to-board connectors was performed. The chemical composition and microstructural analysis at the junction part of the connectors were performed for as new samples and after aging testing which includes stressors like humidity, temperature, temperature cycling and vibration. Scanning Electron Microscopy (SEM) and energy dispersive X-ray analysis (EDX) showed aging effect on the intermetallic compound (IMC) material correlated to intermetallic growth and oxidation.

Contamination profile on typical printed circuit board assemblies vs soldering process

Purpose – The purpose of this paper was to analyse typical printed circuit board assemblies (PCBAs) processed by reflow, wave or selective wave soldering for typical levels of process-related residues, resulting from a specific or combination of soldering processes. Typical solder flux residue distribution pattern, composition and concentration are profiled and reported. The effect of such contaminants on conformal coating was tested. Design/methodology/approach – Presence of localized flux residues was visualized using a commercial residue reliability assessment testing gel test and chemical structure was identified by Fourier transform infrared spectroscopy, while the concentration was measured using ion chromatography, and the electrical properties of the extracts were determined by measuring the leak current using a twin platinum electrode set-up. Localized extraction of residue was carried out using a commercial critical contamination control extraction system. Findings – Results clearly show that the amount and distribution of flux residues are a function of the soldering process, and the level can be reduced by an appropriate cleaning. Selective soldering process generates significantly higher levels of residues compared to the wave and reflow process. For conformal coated PCBAs, the contamination levels generated from the tested wave and selective soldering process are found to be enough to generate blisters under exposure to high humidity levels. Originality/value – Although it is generally known that different soldering processes can introduce contamination on the PCBA surface, compromising its cleanliness, no systematic work is reported investigating the relative levels of residue introduced by various soldering processes and its effect on corrosion reliability.

Pollution profiles and health risk assessment of VOCs emitted during e-waste dismantling processes associated with different dismantling methods

Pollution profiles of typical volatile organic compounds (VOCs) emitted during dismantling of various printed circuit board assemblies (PCBAs) of e-wastes using different methods were comparatively investigated in the real e-waste dismantling workshops in South China in April 2013. Similar pollution profiles and concentrations of VOCs were observed between dismantling mobile phone and hard disk PCBAs by using electric blowers and between dismantling television and power supplier PCBAs using electric heating furnaces. Aromatic hydrocarbons (accounting for >60% of the sum of VOCs) were the dominant group during using electric blowers, while aromatic (accounting for >44% of the sum of VOCs) and halogenated hydrocarbons (accounting for >48% of the sum of VOCs) were the two dominant groups which contributed equally using electric heating furnaces. However, the distribution profiles of VOCs emitted during dismantling of televisions, hard disks and micro motors using rotary incinerators varied greatly, though aromatic hydrocarbons were still the dominant group. The combustion of e-wastes led to the most severe contamination of VOCs, with total VOCs (3.3×104μgm−3) using rotary incinerators about 190, 180, 139, and 40 times higher than those using mechanical cutting, electric soldering iron, electric blower, and electric heating furnace, respectively. Both cancer and non-cancer risks existed for workers due to exposure to on-site emitted VOCs in all workshops especially in those using rotary incinerators according to the USEPA methodology, whereas only cancer risks existed in rotary incinerator workshops according to the American Conference of Industrial Hygienists methodology.

Doubling‐resolution analog‐to‐digital conversion based on PIC18F45K80

Aiming at the analog signal being converted into the digital with a higher precision, a method to improve the analog-to-digital converter (ADC) resolution is proposed and described. Based on the microcomputer PIC18F45K80 in which the internal ADC modules are embedded, a circuit is designed for doubling the resolution of ADC. According to the circuit diagram, the mathematical formula for calculating this resolution is derived. The corresponding software and print circuit board assembly is also prepared. With the experiment, a 13 bit ADC is achieved based on the 12 bit ADC module predesigned in the PIC18F45K80.

A 5 Giga Samples Per Second 8-Bit Analog to Digital Printed Circuit Board for Radio Astronomy

We have designed, manufactured, and characterized an 8-bit 5 Giga samples per second (Gsps) ADC printed circuit board assembly (PCBA). An e2v EV8AQ160 ADC chip was used in the design and the board is plug compatible with the field programmable gate array (FPGA) board developed by the Collaboration for Astronomy Signal Processing and Electronics Research (CASPER) community. Astronomical interference fringes were demonstrated across a single baseline pair of antennas using two ADC boards on the Yuan Tseh Lee Array for Microwave Background Anisotropy (AMiBA) telescope. Several radio interferometers are using this board for bandwidth expansion, such as Submillimeter Array; also, several experimental telescopes are building new spectrometers using the same board. The ADC boards were attached directly to the Reconfigurable Open Architecture Computing Hardware (ROACH-2) FPGA board for processing of the digital output signals. This ADC board provides the capability of digitizing radio frequency signals from DC to 2 GHz (3 dB bandwidth), and to an extended bandwidth of 2.5 GHz (5 dB) with derated performance. The following worst-case performance parameters were obtained over 2 GHz: spur free dynamic range (SFDR) of 44 dB, signal-to-noise and distortion (SINAD) of 35 dB, and effective number of bits (ENOB) of 5.5.

A Simplified Branch-and-Price Mechanism for a Three-Machine Dynamic PCB Assembly

A dynamic Printed Circuit Board (PCB) assembly system along with the most complete form of setup time in this assembly is introduced in this paper. An effective Branch-and-Price mechanism is employed to develop a lower bound for the three-machine problem. However, solving the sub problems remains computationally difficult because of their NP-hard nature. An optimal approach is established, which makes solving the sub problems computationally feasible.

Applying weakest t-norm based approximate intuitionistic fuzzy arithmetic operations on different types of intuitionistic fuzzy numbers to evaluate reliability of PCBA fault

This research addresses system reliability analysis using weakest t-norm based approximate intuitionistic fuzzy arithmetic operations, where failure probabilities of all components are represented by different types of intuitionistic fuzzy numbers. Due to the incomplete, imprecise, vague and conflicting information about the component of system, the present study evaluates the reliability of system in terms of membership function and non-membership function by using weakest t-norm (Tw) based approximate intuitionistic fuzzy arithmetic operations on different types of intuitionistic fuzzy numbers. In general, interval arithmetic (α-cut arithmetic) operations have been used to analyze the fuzzy system reliability. In complicated systems, interval arithmetic operations may occur the accumulating phenomenon of fuzziness. In order to overcome the accumulating phenomenon of fuzziness, this research adopts approximate intuitionistic fuzzy arithmetic operations under the weakest t-norm arithmetic operations (Tw) to analyze fuzzy system reliability. The approximate intuitionistic fuzzy arithmetic operations employ principle of interval arithmetic under the weakest t-norm arithmetic operations. The proposed novel fuzzy arithmetic operations may obtain fitter decision values, which have smaller fuzziness accumulating and successfully analyze the system reliability. Also weakest t-norm arithmetic operations provide more exact fuzzy results and effectively reduce fuzzy spreads (fuzzy intervals). Using proposed approach, fuzzy reliability of series system and parallel system are also constructed. For numerical verification of proposed approach, a malfunction of printed circuit board assembly (PCBA) is presented as a numerical example. The result of the proposed method is compared with the listing approaches of reliability analysis methods.

An improved Shuffled Frog-leaping Algorithm to optimize component pick-and-place sequencing optimization problem

The component pick-and-place sequence is one of the key factors to affect the working efficiency of the surface mounting machine in the printed circuit board assembly. In this paper, an improved Shuffled Frog-leaping Algorithm was presented by improving the basic Shuffled Frog-leaping Algorithm (SFLA) with the strategy of letting all frogs taking part in memetic evolution and adding the self-variation behavior to the frog. The objective function of component pick-and-place sequence of the gantry multi-head component surface mounting machine was established. Parameters selection is critical for SFLA. In this study, Three-way ANOVA was used in parameters analyzing of the new improved SFLA. The parameters like memeplex numbers m, the frogs’ number P and local evolution numbers iPart were found having notable effects on the mounting time (time spent for components picking and placing), but the interactions among these parameters were not obvious. Multiple comparison procedures were adopted to determine the best parameter settings. In order to test the performance of the new algorithm, several experiments were carried out to compare the performance of improved SFLA with the basic SFLA and the genetic algorithm (GA) in solving the component pick-and-place sequence optimization problems. The experiment results indicate that improved SFLA can solve the optimization problem efficiently and outperforms SFLA and GA in terms of convergence accuracy, although more CPU time is undeniably needed.

A New Approach to Calibration of Printed Circuit Board Coordinates: 2D-Depth Sensor Applied to Robotic Screwdrivers Assembly Systems

We consider the parts screwing problems, which of automatic assembly robotic screwdrivers system required precisely depth and tilt-angle at each insertion point. However, commonly computer vision inspection tools which obtain tilt-angle on clamping printed circuit board is a challenging problem. Further, even if given a depth senor, that still to consider inspection target size. Thus, we present an approach for screwing angle measurement of printed circuit board assembly in Consumer electronics production lines. The methods involved using 2D-Depth sensor to identify screwing angle, and measuring depth information near the hole of printed circuit board. Our method successfully conform to screwdrivers system requirement, tilt angle under three degree and sampling small area target under 10mm^2,which obtains measurement results will be applied to refer on robotic positioning and assembling.

Estimating the production time of a PCB assembly job without solving the optimised machine control

Production planning and control of the printed circuit board (PCB) assembly includes several decisions dealing with, for example, grouping of PCB jobs, allocation of PCB batches to machine lines, sequencing of batches and load balancing of lines. The production time of a PCB job for a given placement machine is a key factor in this context and it must be quickly and accurately estimated, possibly millions of times in a single planning task, to avoid erroneous decisions. The commonly used nominal tact time-based estimators are very rough and the machine simulators too slow. Therefore, the purpose of this study is to give better machine-specific estimators that avoid the construction the actual machine control program. Two new estimators are proposed for gantry machines, one based on the information given by the manufacturer about the operations of the placement head, and the other on the regularised least-squares regression method trained with a set of PCB placement jobs. In practical evaluation with 95 PCB jobs, the mean absolute percentage error of the first and second methods are 3.75% and 6.52%, respectively, while that of the tact time-based approach is more than 17%. This indicates a great potential of the proposed methods as production time estimators.

Life cycle assessment of a domestic induction hob: electronic boards

Abstract This study analyzes the environmental performance of the electronic boards used in the current generation of induction hob designed and assembled in Spain. A Life Cycle Assessment (LCA) has been performed, defining the functional unit as the electronic boards used in an induction cooktop with 4 hobs and 7.2 kW of nominal power. The electronic boards are two power electronic boards (ELIN PCBAs -Printed Circuit Board Assembly-), and one touch control electronic board (Touch Control PCBA). Each one has been thoroughly analysed having into account every electronic component. The software used to create the LCA model was SimaPro 7.3.3, using two databases Ecoinvent v2.2 and Chalmers CPM LCA Database. The most relevant environmental impact in every category is caused by the two ELIN PCBAs. Touch Control PCBA has significant impact in Ozone Layer Depletion, although its value is four times lower than the emissions of one ELIN PCBA. Both ELIN PCBAs show similar environmental impact distribution. Components create between 70 and 85% of the total impact in most categories. Touch Control PCBA has a different environmental impact distribution from both ELIN PCBA. This analysis of the environmental impact of the ELIN PCBAs and the Touch Control PCBA used in an induction hob has revealed that there are several clear areas for improvement, such as reducing the environmental impact of the components and improving its end-of-life treatment.

Experiment and Simulation of Board Level Drop Tests With Intentional Board Slap at High Impact Accelerations

This paper explores multiple impacts generated through fixture design to induce high accelerations in board level drop testing. Drop tests were conducted at accelerations as high as 30000 G using mechanical accelerators. Finite element analysis simulations were used to determine impact locations and acceleration magnitude. Wafer level chip scale package components were tested at the board level at accelerations ranging from 10000 to 30000 G. The clearance between the printed circuit board assembly and the fixture are parametrically varied in the investigation to understand the effects of the clearance. Experiments and simulation show interesting results due to dynamic modal interaction.

Impact of NaCl Contamination and Climatic Conditions on the Reliability of Printed Circuit Board Assemblies

The effect of climatic conditions and ionic contamination on the reliability of printed circuit board assembly has been investigated in terms of leakage current (LC) and electrochemical migration susceptibility. The change in LC as a function of relative humidity (RH) and temperature was measured using single components (size 0805) and surface insulation resistance comb patterns precontaminated with sodium chloride at levels adjacent to levels used in the IPC J-STD-001 standard. The potential bias of 5-10 V was applied during experiments, and the climatic conditions were in the range 60%-98% RH and 15 °C-65 °C. The variation of RH at the surface of the test specimens was imposed by 1) increasing the RH of the surrounding air and 2) reducing the temperature of the printed circuit boards using a cooling stage, while maintaining a constant climatic condition in the chamber. A considerable increase in LC was observed at sodium chloride concentrations above 1.56 μg·cm-2, as the RH on the surface was close to the critical RH for sodium chloride. Prolonged exposure to conditions close to condensation resulted in the formation of tin whiskers and hillocks growing from the component electrodes due to corrosion of the electrodes freeing the whisker growth.

Probability increment based swarm optimization for combinatorial optimization with application to printed circuit board assembly

AbstractA novel swarm intelligence approach for combinatorial optimization is proposed, which we call probability increment based swarm optimization (PIBSO). The population evolution mechanism of PIBSO is depicted. Each state in search space has a probability to be chosen. The rule of increasing the probabilities of states is established. Incremental factor is proposed to update probability of a state, and its value is determined by the fitness of the state. It lets the states with better fitness have higher probabilities. Usual roulette wheel selection is employed to select states. Population evolution is impelled by roulette wheel selection and state probability updating. The most distinctive feature of PIBSO is because roulette wheel selection and probability updating produce a trade-off between global and local search; when PIBSO is applied to solve the printed circuit board assembly optimization problem (PCBAOP), it performs superiorly over existing genetic algorithm and adaptive particle swarm optimization on length of tour and CPU running time, respectively. The reason for having such advantages is analyzed in detail. The success of PCBAOP application verifies the effectiveness and efficiency of PIBSO and shows that it is a good method for combinatorial optimization in engineering.