Printed Circuit Board Materials Research Articles

Improved thermal, mechanical, and dielectric properties of thermotropic liquid crystalline poly(ester amide)s containing lactam-derived segmental units

We prepared two different series of thermotropic liquid crystalline poly(ester amide)s (TPEAs) via bulk polycondensation reactions of 4-hydroxybenzoic acid (HBA, 75.0 mol %) and 6-hydroxy-2-naphthoic acid (HNA, 25.0–17.5 mol %) with ε-caprolactam (CL, 0.0–7.5 mol %) or γ-butyrolactam (BL, 0.0–7.5 mol %). Our investigation aimed to explore the impact of lactam-derived aliphatic amide units’ length and content on the liquid crystalline feature, microstructure, thermal transition, thermal stability, mechanical/relaxational/rheological behavior, and dielectric characteristics of TPEAs. The molecular structure and fibrillar formation of TPEAs containing aliphatic amide units were confirmed through FT-IR and SEM analysis. With increasing CL or BL-derived units from 1.0 mol % to 5.0 mol %, we observed an increase in crystallinity, glass transition temperature, melting temperature, complex melt viscosity, and storage modulus of TPEAs, attributed to the enhanced intermolecular hydrogen bonding interactions. However, at 7.5 mol % CL or BL-derived unit content, these properties decreased due to increased chain irregularity as well as lowered crystallinity. Notably, the dielectric constants (3.31–3.04 at 2 MHz) of TPEAs decreased with the increase of lactam-derived aliphatic amide units owing to the restricted chain mobility by intermolecular hydrogen bonding interactions. We believe that the TPEAs synthesized in this study hold significant potential for applications in technical plastics, superfibers, and printed circuit board materials.

Ion Mobility Separations Using Cocentric Architecture.

Ion mobility separations, especially using drift tube ion mobility spectrometers, are usually performed in linear channels, which can have a large footprint when extended to achieve higher resolving powers. In this work, we explored the performance of an ion mobility device with a curved architecture, which can have a more compact form. The cocentric ion mobility spectrometer (CoCIMS) manipulates ions between two cocentric surfaces containing a serpentine track. The mobility separation inside the CoCIMS is achieved using traveling waveforms (TWs). We initially evaluated the device using ion trajectory simulations using SIMION, which indicated that when ions traveled circularly inside the CoCIMS they resulted in similar resolving powers and transmitted m/z range as traveling in a straight path. We then performed experimental validation of the CoCIMS in conjunction with a TOF MS. The CoCIMS was made of two flexible printed circuit board materials folded into cocentric cylinders separated by a gap of 2.8 mm. The device was about 50 mm diameter ×152 mm long and provided 1.846 m of serpentine path length. Three sets of mixtures (Agilent tune mixture, tetraalkylammonium salts, and an eight-peptide mixture) and four traveling waveform profiles (square, sine, triangle, and sawtooth) were used. The sawtooth TW profile produced a slightly higher resolving power for the Agilent tuning mixture and tetraalkylammonium ions. The average resolving power for Agilent tune mixture ions ranged from 37 (using sawtooth TW) to 27 (using square TW). The average resolving powers ranged from 45 (sawtooth TW) to 31 (square TW) for tetraalkylammonium ions. The resolving power of the peptide mixture ions was similar among the four TW profiles and ranged from 51 to 56. The average percent error in TWCCS for the peptide mixture ions was about 0.4%. The new device showed promising results, but improvements are needed to further increase the resolving power.

Numerical simulation approach for consideration of ageing effects in PCB substrates by modifying viscoelastic materials properties

During operating time of electronic systems, the used materials in such devices are potentially subjected to ageing effects, which might limit the lifetime. Therefore, knowledge about the used materials and the way the materials are affected by ageing effects is of key importance to develop reliable products.In this study, a simulation approach is discussed that is able to consider ageing effects caused by oxidation at elevated temperature of a printed circuit board material, typically used for high frequency applications. The material was characterized for its thermomechanical properties with state-of-the-art techniques for different ageing durations. Ageing was accelerated by storing the samples in an oven at 175 °C for up to 1000 h.Within the simulation workflow, the thermomechanical properties of the different aged states are defined by modifying the pristine viscoelastic properties. Four exponential functions are derived modifying the initial modulus, the characteristic time constants, the shift function and the coefficient of thermal expansion, all in dependency of ageing time.To demonstrate the approach, the soldered interconnection lifetime of a theoretical chip-size-package on a printed circuit board is studied. State-of-the-art lifetime predictions of such interconnections only include thermomechanical ageing effects, for example by creep effects of the solder. By additionally considering the ageing of the printed circuit board, thermal ageing is combined with thermomechanical ageing.Results in the soldered interconnection are compared between either considering additional ageing effects of the printed circuit board or neglecting this behavior. Thus it is shown that thermal ageing plays a significant role in the development of accumulated creep strain which becomes increasingly important with increasing expected lifetime.

Ultrashort pulse ablation of printed circuit board materials using a Bessel beam

In times of digitalization, multilayer composite materials became central components in an increasing number of application fields. Thus, there is a need for optimization of the cost-intensive and time-consuming processing of multilayer composites. In this contribution, an ultrashort pulse laser-based method is presented for precise and flexible ablation of a printed circuit board base material. Therefore, an 800 nm Gaussian laser beam was transformed into a Bessel beam by an axicon to get a small spot size and an ablation result with a high aspect ratio. The influence of the average laser power, the number of exposure cycles, and the pulse duration on the geometry as well as the surface quality of ablated structures was investigated and compared to Gaussian beam ablation. Furthermore, it is shown that the results can be transferred to microdrilling processes. With the presented method, it was possible to ablate the copper top layer of the printed circuit boards as well as the FR4 layer below with a precisely adjustable depth.

Effects of Para‐ or Meta‐Aromatic Amide Units on the Microstructure, Thermal, Mechanical, Rheological, and Dielectric Properties of Thermotropic Liquid Crystalline Poly(ester amide)s

AbstractThe impact of para‐ and meta‐aromatic amide repeat units on the microstructure, thermal behavior, mechanical properties, rheological characteristics, and dielectric properties of thermotropic liquid crystalline poly(ester amide)s (TPEAs) is reported. For this purpose, two distinct series of TPEAs are synthesized using 75.0 mol% of 4‐hydroxybenzoic acid (HBA) and 25.0–17.5 mol% of 6‐hydroxy‐2‐naphtoic acid (HNA) with 0.0–7.5 mol% terephthalic acid/para‐acetylaminophenol (TPA/PAP) or isophthalic acid/para‐acetylaminophenol (IPA/PAP) are synthesized via bulk polycondensation reaction. Infrared and electron microscopic data reveal the existence of intermolecular hydrogen bonds and associated fibrillar structures of TPEAs with TPA/PAP‐ or IPA/PAP‐based aromatic amide units. Accordingly, the glass transition temperatures, dynamic storage moduli, and melt viscosities of TPEAs increased with the increment of the aromatic amide units, although they are higher for TPEAs with IPA/PAP‐derived units, compared to TPEAs with TPA/PAP‐derived units. The melting temperatures of TPEAs increase with the para‐aromatic amide unit owing to the intermolecular hydrogen bonding and the rigid linearity, whereas the melting points decrease with the meta‐aromatic amide unit due to the structural nonlinearity. Interestingly, the dielectric constants and losses of TPEAs decrease with the aromatic amide unit content, which is even dominant for TPEAs with IPA/PAP‐based repeat units. TPEAs can be thus utilized as super‐engineering plastics, industrial fibers, printed circuit board materials, etc., requiring enhanced mechanical and thermal transition properties but lower dielectric constants and losses.

Life cycle assessment of e-waste management system in Australia: Case of waste printed circuit board (PCB)

Electronic waste (e-waste) is one of the fastest-growing waste streams globally. Recycling is one of the environment-friendly waste management strategies that creates a net environmental gain in recovering valuable materials. In some countries, downstream recycling (high-value material recovery) is done overseas, and Australia is one of them. Waste printed circuit board (PCB) is a critical component of various electronic equipment, and it contains metals such as copper, tin, gold, aluminium, iron, silver, and others. Waste PCB, as apart of e-waste is mainly recycled overseas in Australia. However, the overall environmental impacts of recycling the waste stream overseas have yet to be investigated. The benefits of recovering the material in Australia have yet to be extensively understood from a supply chain perspective. This study aims to develop multiple scenarios using lifecycle assessment (LCA) methodology to identify the best possible solution for waste PCB disposal (final sink) derived from e-waste. Using SimaPro and Ecoinvent databases, four scenarios have been developed, along with a baseline scenario where waste PCB is recycled overseas. Receipe 2016 impact assessment methodology was utilized for the analysis, and results of the study showed that Scenario 2 (integrated material and energy recovery) is the best approach for waste PCB recycling in Australia, while landfill and direct incineration were the identified two worst scenarios in terms of final disposal option. When choosing local recycling over overseas recycling of waste PCB (material recovery only), it was found that impact categories such as global warming (human health) and fossil resource scarcity were reduced by 53% and 98%, respectively. In addition, the net positive environmental gain could be achieved for human non-carcinogenic toxicity by 7.16% when the waste stream is recycled in Australia. Uncertainty analysis of the study showed that in almost all major impact categories, material and energy recovery together scored high compared to scenarios when only material recovery was considered. This study is the first systematic attempt to characterize system-level lifecycle environmental impact assessment for waste PCB recycling. Future policies and regulations should focus on data transparency and availability across the value chain, local infrastructure development, and resource circularity. This study will add value to decision-making, policy on investment and future policy planning. It will also help industry and researchers develop optimized recycling-focused low-emission resource recovery supply chains.

Comparing the Measured Frequency Characteristics of PCBs with Modal Reservation Before and After Failure at Different Temperatures

Introduction . Modal reservation (MR) is a new way of reserving electrical circuits by means of strong electromagnetic coupling between their conductors, which not only increases their reliability, but also ensures their electromagnetic compatibility. Although showing much promise for critical radio electronic devices, MR has so far been studied exclusively at room temperature, without taking climatic conditions into account. Aim . Presentation of the results of an experimental study into the frequency characteristics of printed circuit boards (PCBs) with MR based on coupled microstrip lines under climatic impacts in the form of low and high temperatures to evaluate the MR effectiveness before and after failures. Materials and methods . PCB prototypes based on a microstrip line from a domestic material of the STF brand without and with MR (before and after two types of failure) were manufactured at the Polyus research and production center, Tomsk, Russia. These prototypes simulated the device operation before and after two types of failures. Using a vector network analyzer, frequency dependences of S-parameters of the prototypes were experimentally investigated in a heat-cold climatic chamber at temperatures ranging between minus 50 and 150 °С. Transmission and reflection coefficients in both directions of signal propagation were measured. Results . It is shown that for the working circuit of PCBs with MR, before and after failures, an increase in temperature from room temperature to 150 °С leads to a decrease in the transmission and reflection coefficients in both directions (to a maximum of 2 dB and 29 dB, respectively). Conversely, a decrease in temperature results in an increase in these coefficients (to a maximum of 0.8 dB and 23 dB, respectively). At low and high temperatures, a shift of resonances (up to 500 MHz) towards high and low frequencies, respectively, is observed. Conclusion . The MR effect is shown to remain after failure, having almost no influence on the useful signal, except at high temperatures, at which the operating frequency range of the useful signal can be significantly reduced. Future research should be aimed at reducing the sensitivity of the characteristics to temperature changes by means of selecting other PCB materials, as well as at investigating the radiated emissions from PCBs with MR before and after failures under the impact of climatic conditions.

Fabrication of Cost-effective Three-axis portable mini-CNC milling Machine

The utilization of Computer Numerical Control (CNC) machines in several industries are very popular for years due to the rapid growth of advanced technology. But, CNCs are inaccessible to vast communities especially students as these machines are bulky as well as expensive. The present project aims to deal with the fabrication of an automatic mini-CNC milling machine that can move in all three directions and can able to drill holes on PCB (Printed Circuit Board), wood, plastic, and other soft materials at an affordable price. The design used here is incorporated with an Arduino controller and a G-code sender library for system operation. It is also reported on the work that the qualitative development of the electronic equipment to operate a mini-CNC milling machine along with its related software. Here an attempt has been made to develop a simple three-axis mini-CNC milling in a cost-effective way, especially for educational purposes and it will also allow future research to improve process performance of different machining operations like drilling, slot cutting, etc.

Comparison of Physical and Chemical Method for Removing Copper from NonMetallic Printed Circuit Board Scrap

Printed circuit boards (PCBs) are the basic components of electrical and electronic devices. E-waste management is challenging to implement due to accompanying difficulties and danger. Valuable metals and copper (Cu) are primarily recycled through various methods in the treatment of waste PCB. A large number of non-metals materials in PCBs are disposed of through combustion or in landfill, resulting in secondary pollution and resource waste. To reduce the amount of waste non-metallic PCB (NMPCB) and the influences toward environment, recent studies focused on the usage of NMPCB as filler to replace raw material. NMPCB as filler seems to have a good interaction with the raw materials and thus can enhance the strength of the newly formed product. In our study, we focused on developing new NMPCB added with waste NMPCB. Commercial NMPCBs are often a flat laminated composite comprising non-conductive substrate materials. Hence, pre-treatment methods to remove metals, especially Cu, must be investigated. The present study attempted to remove the Cu layer on PCB by using chemical and physical methods. The untreated and Cu removed PCB residues were characterized using X-ray diffraction (XRD), scanning electron microscopy, and infrared spectroscopy (FTIR) for the determination of structural and functional groups and hydrophobicity test. XRD analysis indicated that the Cu in untreated PCB was successfully removed using physical and chemical methods.

Ultrashort Pulsed Laser Drilling of Printed Circuit Board Materials

We report on a comprehensive study of laser percussion microvia drilling of FR-4 printed circuit board material using ultrashort pulse lasers with emission in the green spectral region. Laser pulse durations in the pico- and femtosecond regime, laser pulse repetition rates up to 400 kHz and laser fluences up to 11.5 J/cm are applied to optimize the quality of microvias, as being evaluated by the generated taper, the extension of glass fiber protrusions and damage of inner lying copper layers using materialography. The results are discussed in terms of the ablation threshold for FR-4 and copper, heat accumulation and pulse shielding effects as a result of pulse to pulse interactions. As a specific result, using a laser pulse duration of 2 ps appears beneficial, resulting in small glass fiber protrusions and high precision in the stopping process at inner copper layer. If laser pulse repetition rates larger than 100 kHz are applied, we find that the processing quality can be increased by heat accumulation effects.

Femtosecond Laser Ablation Assisted NFC Antenna Fabrication for Smart Contact Lenses

AbstractSmart contact lenses (SCLs) have drawn substantial interest for continuous health monitoring applications. Even though most of the reported works utilize near‐field communication (NFC) or inductive coupling for wireless powering and data transmission, developing a scalable and rapid fabrication technique for annular ring antennas confined in a small contact lens area is still an unsolved challenge. Here, femtosecond laser ablation is employed for the first time as a simple, single‐step, and highly precise fabrication technique for NFC antennas using conventional flexible printed circuit board materials. Antenna lines with depth and width of 9 and 35 μm are achieved, respectively. The antenna with a footprint of 19.5 mm2 is characterized in biological solution followed by aging, and bending tests, and a frequency deviation of less than %1 is recorded. A real‐life application is demonstrated by fabricating an SCL embedded with the antenna, an NFC chip, and an electrochemical sensor for wireless monitoring of glucose in artificial tear solution by a smartphone. The device could successfully quantify biologically relevant glucose concentrations ranging from 0.2 to 1 mM with a limit‐of‐detection of 66 μM. In addition, device response to interfering molecules is less than ±1 nA, and the spike‐and‐recovery test is successfully demonstrated.

Wireless Low-Power Transfer for Galvanically Isolated High-Voltage Applications

For various applications, such as gate drivers for transistors, wireless chargers for mobile devices and cars, and isolated measurement equipment, an isolated DC power supply for electronic components is required. In this work, a new concept for an isolated power supply with insulation strength of 50 kV and power transmission of up to 60 W to supply measurement equipment with 12 or 24 V is presented. Furthermore, high overall efficiency of 82.5% at 55 W is achieved. Feasibility is demonstrated in a real application powering data acquisition electronics at high reference potential. Our new concept uses a coreless printed circuit board (PCB) transformer (15 cm × 10 cm × 4 cm and a weight of 480 g) designed for maximum efficiency via a coil layout and close proximity of adjacent coils on one PCB while reaching high isolation strength via the PCB material and potted coils. To increase efficiency, we investigated different coil geometries at different frequencies. A low-cost design consisting of two Qi charging coils mounted on one PCB is compared with our integrated PCB transformers manufactured from a four-layer PCB with ferrites applied on the outside. With this new design, high isolation voltages are possible while reaching high transformer efficiency of up to 90%.

Innovative process for material separation of printed circuit boards (PCB) with laser technology

In the last years, the worldwide amount of electronic waste has increased, according to a report of the United Nations University. Our society urgently needs new solutions for the recycling of electronic waste, which is often not recycled in an environmentally friendly way. However, the electronic waste contains a large quantity of noble metals. They are excellent for reuse and can be melted and reshaped several times. For this purpose, they must be separated into their components before recycling. The laser technology has a great potential for an environmentally friendly, cost-effective and at the same time material-appropriate separation of the individual materials from different hybrid components. The possibility of using a laser to mechanically and physically separate the individual layers of a printed circuit board was studied for this paper. The first tests have shown that it is possible to separate the individual PCB materials to facilitate optimal reuse of them.

Flexible Liquid Crystal Polymer Technologies from Microwave to Terahertz Frequencies.

With the emergence of fifth-generation (5G) cellular networks, millimeter-wave (mmW) and terahertz (THz) frequencies have attracted ever-growing interest for advanced wireless applications. The traditional printed circuit board materials have become uncompetitive at such high frequencies due to their high dielectric loss and large water absorption rates. As a promising high-frequency alternative, liquid crystal polymers (LCPs) have been widely investigated for use in circuit devices, chip integration, and module packaging over the last decade due to their low loss tangent up to 1.8 THz and good hermeticity. The previous review articles have summarized the chemical properties of LCP films, flexible LCP antennas, and LCP-based antenna-in-package and system-in-package technologies for 5G applications, although these articles did not discuss synthetic LCP technologies. In addition to wireless applications, the attractive mechanical, chemical, and thermal properties of LCP films enable interesting applications in micro-electro-mechanical systems (MEMS), biomedical electronics, and microfluidics, which have not been summarized to date. Here, a comprehensive review of flexible LCP technologies covering electric circuits, antennas, integration and packaging technologies, front-end modules, MEMS, biomedical devices, and microfluidics from microwave to THz frequencies is presented for the first time, which gives a broad introduction for those outside or just entering the field and provides perspective and breadth for those who are well established in the field.

Evaluation of PCB materials for high frequency power applications using MOORA method

One of the first and foremost steps in design is the material selection. The selection of the best available material is quite important for the product as it influence the final quality and performance of the product. The materials used generally for printed circuit board (PCB) similarly requires shortlisting based on several factors which affect the durability and the functionality of the PCB assembly. Selecting the correct PCB material requires a knowledge of the available materials and their physical characteristics and how they align with the required functionality of the board. In the current research work, four factors namely, thermal conductivity, dissipation factor, moisture absorption and dielectric constant are used to evaluate nine PCB materials under consideration for high frequency applications. The evaluation of the nine PCB materials under consideration based on the four factors listed above is done using MOORA method (Multi-objective optimization on the basis of ratio analysis). The analytical tool used here makes a comprehensive list of PCB materials while considering the multi-conflicting material selection attributes. The assessment value of the alternatives with respect to all the criteria is calculated and compared for all the nine materials chosen. The final ranking is done, based on the assessment values of the nine alternatives for high frequency applications. The alternative with the highest assessment value is ranked one and is the most obvious choice while the one with the least assessment value is the least preferred material and is to be avoided.

Pilot-scale combined pyrolysis and decoupling biomass gasification for energy and metal recovery from discarded printed circuit board and waste cable

This paper aims to the design innovation concept of e-waste pyrolysis and decoupling biomass gasification in pilot-scale for e-waste recycling and metal recovery. The syngas product and exhaust gas from decoupling gasification were injected to the pyrolysis burner for fuel reduction in sustaining the pyrolysis process. Results showed that the PCB (printed circuit board) and WC (waste cable) materials had pyrolysis oil yield of 20% and 27.3%, respectively, and pyrolysis char yield of 48% and 42%wt, respectively. Single ring compounds were the major compositions of the pyrolysis oil. The main composition of the synthesis gas product was 10.91%vol (H2), 23.4%vol (CO), and 5.68%vol (CH4). The methane content of the decoupling process was higher than that of conventional gasification. Precious metal content in the PCB char comprised Au, Ag, and Cu. Metal recovery from PCB char and ash via ultrasonication was 83.8–89.8%. The combined pyrolysis and decoupling gasification process offered a reduction in LPG (liquefied petroleum gas) consumption (36.1–41.7%), and high energy recovery from the pyrolysis products (53.4–81.6%). This could save the cost of e-waste recycling by about 25.7–28.7% compared to traditional pyrolysis. Therefore, the combined pyrolysis and decoupling gasification has a very good potential for e-waste conversion and metal recovery.

Novel PMMA based 96-well microelectrode arrays for bioelectronic high throughput monitoring of cells in a live mode

Microelectrode arrays (MEA) are widely used for bioelectronic monitoring of alterations in cells and tissues. MEAs are based on a substrate that is structured with electrodes and conducting paths. While cheap substrates like printed circuit board materials offers easy production and flexible contacting, there are limitations regarding microstructure resolution, optical transparency and biocompatibility. In contrast, glass substrates are favored due to its biocompatibility, chemical resistance and optical transparency. Drawbacks are high substrate costs and limited flexibility for routing of conducting paths. To overcome these limitations, we wanted to use optical transparent polymer-based substrates. Therefore, we identified the polymer poly-methyl-methacrylate (PMMA) as a promising substrate material, due to its good optical and mechanical properties as well as biocompatibility. To achieve sufficient chemical resistance for high resolution photolithographic structuring a novel process had to be developed involving a protection coating. After optimization of the structuring process, we achieved a comparable resolution and thus, microelectrodes with diameter of less than 100 μm. Moreover, the use of PMMA allowed the simple integration of more than 400 vias directly into the substrate for contacting of the microelectrode array from the bottom without the need of complex and error prone redirecting adapters with hundreds of additional bonding sides. In order to show that the PMMA based MEA is comparable to glass based MEA in terms of signal quality and sensitivity as well as optical and surface properties, we cultivated different cell models on the MEAs and validated our 96-well PMMA MEAs by different bioelectronic monitoring techniques.

Effect of high-frequency PCB laminate on thermal cycling behavior of electronic packaging structures

PurposeAs the solution to improve fatigue life and mechanical reliability of packaging structure, the material selection in PCB stack-up and partitioning design on PCB to eliminate the electromagnetic interference by keeping all circuit functions separate are suggested to be optimized from the mechanical stress point of view.Design/methodology/approachThe present paper investigated the effect of RO4350B and RT5880 printed circuit board (PCB) laminates on fatigue life of the QFN (quad flat no-lead) packaging structure for high-frequency applications. During accelerated thermal cycling between −50 °C and 100 °C, the mismatched coefficients of thermal expansion (CTE) between packaging and PCB materials, initial PCB warping deformation and locally concentrated stress states significantly affected the fatigue life of the packaging structure. The intermetallics layer and mechanical strength of solder joints were examined to ensure the satisfactorily soldering quality prior to the thermal cycling process. The failure mechanism was investigated by the metallographic observations using a scanning electron microscope.FindingsTypical fatigue behavior was revealed by grain coarsening due to cyclic stress, while at critical locations of packaging structures, the crack propagations were confirmed to be accompanied with coarsened grains by dye penetration tests. It is confirmed that the cyclic stress induced fatigue deformation is dominant in the deformation history of both PCB laminates. Due to the greater CTE differences in the RT5880 PCB laminate with those of the packaging materials, the thermally induced strains among different layered materials were more mismatched and led to the initiation and propagation of fatigue cracks in solder joints subjected to more severe stress states.Originality/valueIn addition to the electrical insulation and thermal dissipation, electronic packaging structures play a key role in mechanical connections between IC chips and PCB.

Fabrication, tribological properties and cutting performances of high-quality multilayer graded MCD/NCD/UNCD coated PCB end mills

Ultrananocrystalline diamond (UNCD) coating possessing low surface roughness was innovatively deposited on printed circuit board (PCB) end mills in order to improve the surface smoothness and prolong the tool duration while machining 5G PCB material. Six types of diamond coatings, involving microcrystalline diamond (MCD), nanocrystalline diamond (NCD), ultrananocrystalline diamond (UNCD), microcrystalline diamond/nanocrystalline diamond (MCD/NCD), microcrystalline diamond/ultrananocrystalline diamond (MCD/UNCD), microcrystalline diamond/nanocrystalline diamond/ultrananocrystalline diamond (MCD/NCD/UNCD), were synthesized on PCB end mills. The Raman spectrum of diamond coatings were obtained to characterize the phase composition, illustrating that Raman spectra of UNCD, MCD/UNCD and MCD/NCD/UNCD present “M” shape, including dominant D peak and G peak. The adhesion levels were assessed, showing that the bottom MCD layer helps to improve the adhesion of MCD/NCD, MCD/UNCD and MCD/NCD/UNCD on WC-Co substrates and MCD/NCD/UNCD can suppress effectively the crack propagation. Moreover, the tribological properties and wear performances of these diamond coatings were compared. The comparison results of friction coefficients are in good accordance with those of surface roughness. The superior adhesion of bottom MCD, the elegant transition of middle NCD and the low friction coefficient of the top UNCD lead to the outstanding wear performances of MCD/NCD/UNCD coated end mill while machining PCB slots.

DDR4 BER Degradation Due to Crack in FBGA Package Solder Ball

This paper measures bit error rate degradation in DDR4 due to crack in fine pitch ball grid array (FBGA) package solder ball. Thermal coefficient mismatch between the package and printed circuit board material causes cracks to occur in solder balls. These cracks change the electrical model of the solder ball and introduce parallel capacitance in the electrical model. The capacitance causes higher frequency attenuation and closes the data eye. As the data rate of the DDR4 increases there are more data eye closures. The data eye closure causes bit error rate (BER) degradation as the timing margin and voltage margin decreases. This degradation reduces the reliability of the system and causes more intermittent errors. DDR4 data line is loaded with a parallel capacitive element to mimic a crack in solder ball. The measured data eye shows a decrease in eye width. Bathtub plots are created for comparison of cracked solder ball and intact solder ball. The bathtub plots show the BER degradation due to crack in solder ball.