Automated visual inspection for microdrills in printed circuit board production

The rapid growth in printed circuit board production has led to the growing importance of microdrilling. Owing to the trend for high-density circuits on printed circuit boards, the diameter of a microdrill has to be much finer than ever before. The inspection for microdrills becomes more difficult and the detection of defects is harder. An automated visual inspection scheme for detecting the major defects of microdrills is proposed. The colour images of microdrills are first derived, and the boundary of the lip relief plane is extracted. A robust K-curvature corner detection algorithm is then used to detect the corners on the blade boundaries and to split boundaries into segments. The least-squares linear regression method is used to fit the segments into linear equations. With the fitted equations, the intersections on the boundaries of two facets are located and their distances (gap or overlap) are measured. In addition, the defects of taper and flare are identified by comparing the angle measurements with predefined specifications. Two types of microdrills are used to verify the proposed inspection process. Experimental results show that the proposed scheme reliably achieves precise inspection.     

Development and comparative analysis of fluxgate magnetic sensor structures in PCB technology

In this paper, we present a family of fluxgate magnetic sensors on printed circuit boards (PCBs), suitable for an electronic compass. This fabrication process is simple and inexpensive and uses commercially available thin ferromagnetic materials. We developed and analyzed the prototype sensors with software tools based on the finite-element method. We developed both singleand double-axis planar fluxgate magnetic sensors as well as front-end circuitry based on second-harmonic detection. Two amorphous magnetic materials, Vitrovac 6025X (25 /spl mu/m thick) and Vitrovac 6025Z (20 /spl mu/m thick), were used as the ferromagnetic core. We found that the same structures can be made with Metglas ferromagnetic core. The double-axis fluxgate magnetic sensor has a sensitivity of about 1.25 mV//spl mu/T with a linearity error of 1.5% full scale, which is suitable for detecting Earth's magnetic field (/spl plusmn/60 /spl mu/T full-scale) in an electronic compass.     

基于动态特性的印制板结构改进

印制板的动态特性对电子设备的可靠性有较大的影响。本文结合计算方法和实验方法对印制板的动态特性进行研究 ,对二种方法所得结果进行比较 ,证实了本文所采用的印制板有限元模型成型技术的有效性。一般地 ,船舶运行时外界环境所引起的激励频率范围为几Hz至几百Hz ,为了避免印制板共振引起的产品失效 ,希望印刷板的基频越高越好。通过计算 ,证明了本文提出的二种结构改进设计方法不同程度地提高了印制板基频     

Improving the reliability of ball grid arrays under random vibration by optimization of module design

Abstract

In this work, three different arrangements of circuit board in an electronic device were designed and the effects of random vibration frequencies on the reliability of ball grid arrays (BGA) in these arrangements were evaluated. The failure criterion in solder balls was the root mean square of peeling stress exerted during the dynamical loadings. According to the finite element method (FEM) results, the uttermost stress concentration was generated at the interface of printed circuit board (PCB) and the solder balls. It was also revealed that the increase of input power spectral density (PSD) decreased the fatigue life of solder joint in all the arrangements. Considering the arrangements of circuit boards, it was found that the maximum domain of peeling stress had a minimum effect on the solder balls when the heat sinks were away from the packages. The microstructural characterization of critical zone in solder balls indicated that with the increase of maximum peeling stress, the crack initiated and propagated along the interface.     

用新型包装方法实现某电子设备印制板的长期储存

对于某系统电子设备来说,产品的设计已逐步模块化,印制板作为模块化设备中的重要元素被大量使用和备份.简述了某系统电子设备的特点和防护包装要求,重点介绍了应用综合储存包装技术,对某电子设备中的印制板进行包装并确保其长期储存的方法.实际应用证明此方法是切实可行的,解决了此类设备中印制板长期储存的问题.     

废旧印刷电路板中电子元器件回收处理技术进展

电子元器件广泛应用于电子电器设备中,但由于产品更新换代和电子电器产业市场的膨胀,大量的电子元器件被丢弃。对电子元器件的资源性和危害性进行分析,综合评述了电子元器件回收利用的最新研究进展和成果,主要包括电子元器件的拆卸技术(解锡方法和分离方法)和回收技术。在此基础上,提出了废旧印刷电路板中电子元器件的无害化和资源化回收研究新动向及发展建议。     

Dielectric response of an epoxy resin when exposed to high temperatures

Epoxy resins are popular insulators that are used for the encapsulation of integrated circuits and for the fabrication of printed circuits boards. As such, it is important to evaluate their reliability when exposed to an environmental stress. This work reports on the influence of a high-temperature thermal stress (400 ^∘C) on the dielectric properties of an acid-anhydride cured DGEBA resin. Gold/epoxy/gold capacitors are used as a test structure. The studied electrical properties are the dielectric constant and the loss factor in the 10⁻¹ Hz100 kHz range, and the DC resistivity. It is found that cycling the sample for several minutes to temperatures as high as 400 ^∘C has almost no effect on its dielectric properties. It is believed that the gold electrodes prevent the thermo-oxidative degradation of the underlying epoxy. Electrical properties are also studied at high temperatures in the 200 ^∘C-400 ^∘C range. Above 200 ^∘C the DC resistivity is considerably increased, as well as the loss in the low-frequency part of the spectrum (< 1kHz). At high frequencies (> 1kHz) the epoxy maintains good dielectric performances up to 400 ^∘C.     

Progress Report on “From Printed Electrolyte‐Gated Metal‐Oxide Devices to Circuits”

Printed electrolyte‐gated oxide electronics is an emerging electronic technology in the low voltage regime (≤1 V). Whereas in the past mainly dielectrics have been used for gating the transistors, many recent approaches employ the advantages of solution processable, solid polymer electrolytes, or ion gels that provide high gate capacitances produced by a Helmholtz double layer, allowing for low‐voltage operation. Herein, with special focus on work performed at KIT recent advances in building electronic circuits based on indium oxide, n‐type electrolyte‐gated field‐effect transistors (EGFETs) are reviewed. When integrated into ring oscillator circuits a digital performance ranging from 250 Hz at 1 V up to 1 kHz is achieved. Sequential circuits such as memory cells are also demonstrated. More complex circuits are feasible but remain challenging also because of the high variability of the printed devices. However, the device inherent variability can be even exploited in security circuits such as physically unclonable functions (PUFs), which output a reliable and unique, device specific, digital response signal. As an overall advantage of the technology all the presented circuits can operate at very low supply voltages (0.6 V), which is crucial for low‐power printed electronics applications.     

Application of matrix-assisted laser desorption/ionization mass spectrometric imaging for photolithographic structuring

The aim of this contribution is the application of matrix-assisted laser desorption/ionization mass spectrometric imaging (MALDI-MSI) in the area of photolithographic structuring. As proof of concept, this method was used to image an UV exposed negative photoresist layer, which is generally used to manufacture printed circuit boards (PCB) for electronic components. The negative photoresist layer consisting of the main component novolac, benzophenone as the active component, and the solvent tetrahydrofuran was mixed with the matrix dithranol and the salt additive LiTFA and spin-coated onto an ITO-conductive glass slide. To imprint an image on the created surface, a transparency with a printed wiring diagram was placed on top of it and irradiated by UV light for 15 min. The inspection of the efficient imprinting of the microstructure onto the photoresist layer was performed by MALDI-MSI. This unique application represents a further step toward the surface analysis of polymer films by this emerging life science imaging technique.     

An improved measure of quality loss for notching processes

Nowadays, electronic products are progressively becoming thinner, lighter, and more convenient for people to use. Printed circuit boards, and especially integrated circuit (IC) substrates, are among the essential component of these products. The IC substrate not only protects circuits, fixes lines, and conducts heat, but is also the critical component that provides signal connectivity between the chip, the printed circuit boards, and other crucial parts during the packaging process. The process capability index C_pm is commonly used to assess the product quality loss for decision making in modern semiconductor packaging manufacturing. For high-definition products, packaging processes often have very strict quality requirements and thus the quality inspection procedure is time-consuming and complicated. Therefore, because of the limitation of manpower and capacity of the inspection instruments, the collected sample for quality assessment may be with small to moderate sample sizes. In this paper, we introduce an unbiased estimator for C_pm and provide a step-by-step parametric bootstrap procedure for obtaining a composite lower confidence bound on C_pm . To compare with the approaches discussed in the literature, numerical simulations are conducted under various process parameter settings. The results show that for small to moderate sample sizes, the proposed method applying the unbiased estimator has more accurate coverage rates than the existing methods. At the end of this paper, an application of quality loss assessment in notching processes is demonstrated.     

Study of Photosensitive Dry Films Absorption for Printed Circuit Boards by Photoacoustic Technique

In this work, the study of photosensitive dry-type films by photoacoustic technique is proposed. The dry film photoresist is resistant to chemical etching for printed circuit boards such as ferric chloride, sodium persulfate or ammonium, hydrochloric acid. It is capable of faithfully reproducing circuit pattern exposed to ultraviolet light (UV) through a negative. Once recorded, the uncured portion is removed with alkaline solution. It is possible to obtain good results in surface mount circuits with tracks of 5 mm. Furthermore, the solid resin films are formed by three layers, two protective layers and a UV-sensitive optical absorption layer in the range of 325 nm to 405 nm. By means of optical absorption of UV–visible rays emitted by a low-power Xe lamp, the films transform this energy into thermal waves generated by the absorption of optical radiation and subsequently no-radiative de-excitation occurs. The photoacoustic spectroscopy is a useful technique to measure the transmittance and absorption directly. In this study, the optical absorption spectra of the three layers of photosensitive dry-type films were obtained as a function of the wavelength, in order to have a knowledge of the absorber layer and the protective layers. These analyses will give us the physical properties of the photosensitive film, which are very important in curing the dry film for applications in printed circuit boards.     

Humidity Threshold Model of Numerical Control Multilayer Printed Circuit Board for Electrochemical Migration

In this paper, numerical control finished boards are employed as test samples to evaluate the effects of the environment and bias voltage on the surface insulation resistance of printed circuit boards. The results indicate that the surface insulation resistance degradation processes leading to failure exhibit a relative humidity threshold value, which is mostly related to temperature, test patterns, and bias voltage. Then, a humidity threshold model is built on the basis of electrochemical migration to quantify the relationship between the relative humidity threshold and conductor spacing and bias voltage under the controlled environments. Finally, experiments and tests have been carried out to validate the effectiveness and practicability of the model. Furthermore, the residual analysis is applied to check the fitting effect of the proposed model. According to the new model, the humidity threshold value can be obtained to provide the guidance for reliability problems in application. It is crucial to the design and deployment of reliable printed circuit boards. Copyright © 2014 John Wiley & Sons, Ltd.     

An overview of recycling and treatment of scrap computers

In order to recover valuable materials and to minimize the adverse effects of hazardous materials contained in scrap computers, a dismantling practice is commonly adopted to treat scrap computers. By using the dismantling process, both useful and hazardous materials can be manually separated and retrieved. On the basis of the properties of the retrieved materials, they can be sent to appropriate facilities for further recycling or treatment. Among the retrieved materials, the treatment of hazardous materials from cathode ray tubes (CRT) and printed circuit boards with integrated circuits have drawn considerable attention, thus implying that the proper treatment of such materials can greatly assure the successful recycling of scrap computers. For this reason, this study reviews the available technologies which can be applied to treat and recycle cathode ray tube components and printed circuit boards with integrated circuits. Actual recycling data from a scrap computer recycling plant located in Taiwan are also introduced. The data show that this recycling plant can recover 94.75 wt. % and 45.99 wt. % of useful materials from the main machines (i.e., CPU, power supplier, fan, IC boards, DVD drive, CD drive, hard disk, soft disk, shell casing, etc.) and monitors of scrap computers, respectively.     

吸湿对印制电路板层压板热膨胀系数的影响

水分对印制电路板的可靠性有重要影响.电路板中的水分子可以改变电路基板的热性能及热力学性能,从而影响电路板及元器件的正常功能.研究了吸湿对两种无卤PCB及两种含卤PCB层压板热膨胀系数的影响,评价了IPC-TM-650 2.4.24测试方法中预处理方法对吸湿样品的适用性.结果表明,PCB层压板中的水分对PCB层压板的热膨胀曲线有明显影响,但传统的热膨胀系数计算方法并不能显示这种影响,对此作了详细分析并提出了改进建议.同时,IPC测试方法中的预处理可以降低湿度对样品热膨胀曲线的影响,但不能完全消除.     

Group set-up for printed circuit board assembly

The current practice in the assembly of electronic components on printed circuit boards (PCBs) is serial production, a process characterized by very long set-up times. However, with the advent of efficient on-line process information, new production control methods are now possible. This paper proposes a different production method, called the group set-up (GSU) method, which can significantly reduce set-up times. The traditional and the GSU production methods are compared, and it is shown that the GSU always performs better than the traditional method in terms of total production flow (throughput) and labour time. However, the traditional method performs better than the GSU in terms of work in process (WIP) inventory; and in some cases, in terms of makespan (lead time). A detailed analysis for a small number of PCBs is presented.     

Near-Field Electromagnetic Characterization and Perturbation of Logic Circuits

We propose here a nondestructive electromagnetic (EM) near-field test bench for both EM compatibility and susceptibility of circuits. This setup permits both the collection of the near field and injection without contact of a disturbing EM field, all through a probe. Exhaustive characterizations of probes are undertaken via simulations and experiments. According to their design, they are supposedly linked more to the electric or the magnetic field. Simulations of their EM behavior are undergone to fix their optimal geometries, leading to the best measurement performances. It is shown by both the simulations and the S-parameter measurements that their presence does not interfere with the electric behavior of the device under test. Then, logic circuits are characterized from the EM point of view, with the help of this test bench. Circuits are placed on three different printed boards: one double-sided low-frequency board without a ground plane and two single-sided boards with a ground plane and a design that is more or less optimized. EM near-field mappings highlight the strong field areas of the circuits. The need for a ground plane is highlighted. Field patterns on the traces are linked with those observed on microstrip lines. Then, an EM aggression is injected over a supposed sensitive zone of the circuit. Whichever printed board is considered, a parasitic signal superimposes itself on the output signal of the gates. Deepened studies are undergone to exhaustively explain the phenomena observed.     

Role of similarity measures in PCB grouping procedures

The problem of grouping printed circuit boards (PCBs) for simultaneous assembly on electronic assembly machines is an extension of the set-covering problem. A general approach based on cluster analysis and measure of similarity between PCBs is suggested as a basis of PCB grouping. The approach is independent of the specific similarity measure used. We show that, due to the analogy between this problem and the problem of machine cell formation in group technology, similarity measures developed for the second problem are useful as building blocks in a general framework that solves the PCB grouping problem.     

A novel hybrid network optimization model for printed circuit boards recycling: a circular economy perspective

Clean Technologies and Environmental Policy - The recycling of printed circuit boards, which accounts for a considerable monetary value in waste electrical and electronic equipment, has long been...     

Insulation reliability of fine-pitch through-vias in glass fiber reinforced halogen-free epoxy substrates

Insulation failures from electrochemical migration is a major reliability concern for achieving reliable small conductor spacings in glass fiber reinforced substrates in the presence of humidity and DC bias voltage. In this study, insulation reliability of fine-pitch copper plated-through-vias in two different halogen-free epoxy substrates was investigated using accelerated testing condition (85 °C, 85 % RH and 100 V DC). The test vehicles included two different conductor geometry: (1) through-via to through-via (spacing: 100 and 150 μm) and (2) through-via to surface-trace (spacing: 75 μm). In accelerated testing, the through-via to through-via test vehicles exhibited insulation failures (failure criterion: 1 MΩ) with a strong dependence on via spacing with through-via spacing of 100 μm showing significantly shorter time to failures compared to test vehicles with spacing of 150 μm. Failure analysis revealed cracking in resin-glass fiber interfaces and within the resin matrix between the failed through-vias. The through-via to surface-trace test vehicles, on the other hand, did not exhibit failures based on the 1 MΩ criterion. However, occurrence of electrochemical migration was visible after optical inspection of the test vehicles. Elemental characterization revealed the presence of copper and chlorine in the resin-glass fiber interface, similar to the previously reported chloride-containing conductive anodic filament compound in printed wiring boards. Accelerating testing and failure analysis in this study indicates a strong dependence of insulation reliability on conductor spacing, geometry and substrate material properties.     

Recovery of copper from printed circuit boards scraps by mechanical processing and electrometallurgy

The constant growth in generation of solid wastes stimulates studies of recycling processes. The electronic scrap is part of this universe of obsolete and/or defective materials that need to be disposed of more appropriately, or then recycled. In this work, printed circuit boards, that are part of electronic scrap and are found in almost all electro-electronic equipments, were studied. Printed circuit boards were collected in obsolete or defective personal computers that are the largest source of this kind of waste. Printed circuit boards are composed of different materials such as polymers, ceramics and metals, which makes the process more difficult. However, the presence of metals, such as copper and precious metals encourage recycling studies. Also the presence of heavy metals, as Pb and Cd turns this scrap into dangerous residues. This demonstrates the need to search for solutions of this kind of residue, in order to have it disposed in a proper way, without harming the environment. At the first stage of this work, mechanical processing was used, as comminution followed by size, magnetic and electrostatic separation. By this process it was possible to obtain a concentrated fraction in metals (mainly Cu, Pb and Sn) and another fraction containing polymers and ceramics. The copper content reached more than 50% in mass in most of the conductive fractions and significant content of Pb and Sn. At the second stage, the fraction concentrated in metals was dissolved with acids and treated in an electrochemical process in order to recover the metals separately, especially copper. The results demonstrate the technical viability of recovering copper using mechanical processing followed by an electrometallurgical technique. The copper content in solution decayed quickly in all the experiments and the copper obtained by electrowinning is above 98% in most of the tests.