355 nm UV laser patterning and post-processing of FR4 PCB for fine pitch components integration

In this paper, the performance of a complete halogen-free (HF) board assembled with five ball grid array components using daisy chains on an 8-layer high density interconnection printed circuit board (PCB) was examined using bending tests. The solder joint was composed of the SAC405 solder ball melted with the SAC105 solder paste on the Cu pad surface of either organic solderable preservative (OSP) or electroless nickel immersion gold (ENIG), and was tested to examine the extent of intermetallic compound (IMC) formed. A board-level cyclic bending test was executed to the as-reflowed assemblies according to the JESD22-B113 standard to evaluate the reliability of various surface finished HF PCB assemblies under a recommended load condition. By Weibull analyzes the characteristic lives of the assemblies were 99098 and 130290 cycles on OSP soldering system and ENIG system respectively, indicating that the ENIG had a higher bending fatigue endurance as compared to the OSP. The dominant failure mode was the fracture of Cu trace within the micro-via caused by the crack of the resin coated copper layer. At the interface of the solder joint, the IMC formed on both OSP and ENIG was with various Ni contents of 3.9 and 20.1 at%, and different thicknesses of 5.6 and 1.1 , respectively. Numerical simulations showed that both composition and thickness of IMC influenced the stress concentrations and characteristic life of the HF test vehicle as they could slightly increase localized solder joint rigidity and result in more serious pull and drag behaviors at the corner joint. Although the on the ENIG was stiffer than that on the OSP, the thicker IMC layer instead increased the stress on the OSP system due to size effect, and resulted in a lower characteristic life.

Ball grid array (BGA) component packages challenge the circuit board design with signal routing and layout, creating in some cases extra board layers and added vias all resulting in increased costs for the printed circuit board (PCB). As component densities increase and microBGA (μBGA) and other fine pitch components become more common, microvia‐in‐pad technology will ease the transition to these fine pitch components. This paper presents and profiles a cost‐effective solution to interconnecting BGAs on PCBs using laser drilled blind vias connecting the outer three or more layers of a multilayer circuit board. Following a discussion on the design advantages, a comprehensive outline of the PCB fabrication process explores a new procedure for the rapid production of via‐in‐pad multi‐depth blind via laser drilling.

The iNEMI technical subcommittee on creep corrosion has developed a flowers-of-sulfur (FOS) based qualification test for creep corrosion on printed-circuit boards (PCBs). In phase 1 of the project, the performances of FOS chambers of two designs were evaluated by measuring the corrosion rates of copper and silver foils. In the 1 st and 2 nd test runs of phase 2 of the project, PCBs with immersion silver (ImAg) and lead-free hot-air-surface-level (HASL) finishes soldered with rosin and organic acid fluxes were tested. The ImAg PCBs soldered with organic acid flux suffered the most creep corrosion in agreement with the generally expected field experience. There were fewer instances of creep corrosion on ImAg PCBs soldered with rosin flux and on Pb-free HASL PCBs. The 3 rd test of phase 2 discovered that contaminating the test PCBs with ammonium salts contributed to more creep corrosion but made the test less discriminatory in that even test PCBs with HASL finish soldered with rosin flux suffered creep corrosion. The results of the 4 th through 6 th test runs of phase 2 of the iNEMI project are reported in this paper. The test condition changes included the introduction of chlorine using household Clorox and of pre-baking the test PCBs. The test chambers were maintained at 50°C. In the 4 th and 5 th test runs the relative humidity was maintained at 81% using KCl saturated salt solution. Pre-baking the test PCBs at 100°C for one day under nitrogen gas cover was found to be necessary to generate creep corrosion. The creep corrosion on ImAg PCBs was in general more than that on HASL and OSP PCBs. Creep corrosion was most severe on ENIG (electroless nickel immersion gold) PCBs, independent of the flux used. The 6 th test run studied the effect of relative humidity on creep corrosion. A surprising result was that the iNEMI prepared ENIG PCBs suffered creep corrosion even at the relatively low relative humidity of 60%. The test is now sufficiently developed for consideration by the industry as a qualification test for creep corrosion on PCBs.

Corrosion on automobile printed circuit broad

Integration of shape memory alloys (SMA) into actuator systems is still challenging, since mechanically and electrically anchoring are needed to provide stroke and trigger the shape memory effect (SME) in a controlled manner. A direct connection of SMA wires with printed circuit boards (PCBs) would offer many advantages. No additional material (e.g. crimps, clamp connections) and no additional steps for the electrical connection would be required. This would facilitate the engineering for new actuator systems because key integration challenges would be addressed through the use of the nickel-titanium (NiTi) PCB assembly. Soldering is traditionally used for bonding components with PCBs, but due to the poor wettability of the natural passivation layer, NiTi can only be soldered by using aggressive fluxes. In addition, soldered connections withstand mechanical loads to a limited extent. A stronger connection can be achieved using micro laser welding to create a joint, which provides mechanical and electrical connection for actuators. Controlling the heat input yield by laser radiation is especially important for this purpose. On the one hand, too intense heat input causes delamination processes due to excessive temperatures at the interface layer between copper layer and the PCB substrate. On the other hand, insufficient heat input leads to a weak connection that lacks mechanical strength, most importantly tensile and cyclic strength. In this work, the influence of laser power on the welded joint is investigated. In this context, tensile tests, lifetime tests, and microsections of the joint area are used for characterisation.

This study is part three in a series of papers on voiding in solder joints and methods for mitigation of voids. In this study several new variables were tested and compared to previous data on voiding. A new circuit board design was used which is different than the circuit board used in previous studies. The new circuit board design includes two sizes of QFNs (Quad Flat No Lead), BGA's (Ball Grid Array), and LGA (Land Grid Array) components which are susceptible to voiding. The following variables were evaluated with respect to voiding: Solder powder size was varied using a no-clean lead-free solder paste and IPC Type 3, Type 4 and Type 5 SAC305 solder powders. Solder alloy was studied using SAC305 alloy, SN100C® alloy, SN100CV® alloy and a mixture of SAC305/SN100C alloys. Surface finish on the circuit board is thought to have an impact on voiding. Organic solderability preservative (OSP) surface finish is more difficult to wet with solder than other surface finishes and in theory should produce higher voiding levels, and this was evaluated with multiple solder pastes. The performance of a new “low voiding” no clean solder paste was compared to other industry standard no clean solder pastes. Several new stencil designs on QFN thermal pads were tested. Data was gathered and statistical analysis performed to compare and contrast the voiding data. What was learned from this work is summarized below: Solder powder particle size affects voiding for some solder pastes. Voiding tends to decrease as solder powder size becomes smaller. Solder alloy affects voiding and seems to follow a trend with melting range. Wider melting ranges tend to generate lower voiding levels. Organic solderability preservative (OSP) surface finish gave higher voiding than electroless nickel immersion gold (ENIG) surface finish for a no clean lead free solder paste that was tested. Two different water soluble lead free solder pastes showed similar voiding levels for OSP and ENIG finishes. New “low voiding” solder pastes are becoming more common in our industry. In this work, low voiding solder paste F showed lower voiding than an industry standard solder paste C. Stencil design has an impact on voiding. In this study, area of printed solder paste coverage was varied. Voiding levels were much higher for 50 to 60% solder paste coverage than for 70 to 80% solder paste coverage. Based on the results of this work, the following recommendations were made to reduce voiding. Use of smaller solder powder sizes can reduce voiding with certain types of solder paste. Use of specific solder alloys may help mitigate voiding. Use a solder paste that works well with the surface finish to minimize voiding. Use “low voiding” solder pastes to reduce the overall potential for voiding. Optimize the stencil design for the components to allow for complete wetting and gas escape routes. Applying these recommendations may create issues on the printed circuit board assembly (PCBA). For example, use of smaller solder powder particle sizes may lead to increased random solder balling and/or graping. Increasing the volume of printed solder paste may lead to bridging for micro BGA and ultra-fine pitch components. Reduction of voiding may be important enough to risk these potential issues. This is left to the reader's judgement. It is the intent of this work to analyze general trends in voiding and give recommendations to help the reader to “Fill the Void.

Designed and manufactured set of measuring test fixtures for printed circuit board (PCB) materials research and characterization is described in this article. Attention is paid to special designed test vehicle “General board” which includes six types of transmission lines that are used for PCB materials characterization by two measurement methods. Measurements of the frequency dependencies of the dielectric constant and dielectric loss for a number of the most widely used PCB substrates are presented. The comparison of the measurement results made by two measurement methods is also shown. The influence of the inhomogeneities of the PCB dielectric and some differences in the extracted material parameters data correlated with electro-magnetic fields structure in different transmission lines is demonstrated. In addition it is shown that measurements performed using “General board” can be used for characterization of the losses due to PCB surface plating.

Plasma treatment of printed circuit board (PCB) is a common step in the electronic packaging processes in order to modify the surface and enhance its adhesion to molding compound. In this paper, PCB surface modifications resulting from plasma treatment were investigated by chemical and mechanical analysis methods. The PCB substrate in consideration was for multichip package, consisting of a core layer sandwiched by solder resist (SR) material, which in turn was composed of epoxy, acryl resins, and several kinds of fillers. Argon was employed as a plasma gas and the number of times that the plasma treatment was applied was chosen as a variable to estimate the effect of repeated exposure to the SR surface during the manufacturing process. The resulting surface conditions were analyzed using roughness measurement, water contact angle measurement, X-ray photoelectron spectroscopy (XPS), nano-indentation, and nano-scratch test method. Comprehensive analyses made it possible to understand the characteristics of the effect of plasma on the PCB surface, i.e., SR material. It was found that the surface roughness after the one-time plasma treatment increased from ~ 62 to ~ 90nm, then decreased more or less to the initial level after three and eight times of repeated treatments. These roughness trends were explained by cleaning out contaminants accumulated in the surface crevices and then preferentially removing or melting away a thin resin layer from the peaks on the surface. The plasma treatment decreased the contact angle significantly and increased work of adhesion. Chemical analysis of these surfaces by XPS showed that the C-C bonds in SR were broken, the population of the polar groups such as O-H, C=O, and COOH increased, and the oxygen content increased. The polar groups increased surface energy, and resulted in increased PCB adhesion with the epoxy molding compound (EMC). Mechanical analysis by nano-indentation and nano-scratch test showed that the surface became soft and weak if plasma treatment was too excessive. In this case, a plasma affected zone corresponding to the severe C-C bond breakage was formed near the surface and the adhesion with EMC suffered. Therefore, caution should be exercised in determining the degree of plasma treatment needed.

The printed circuit board (PCB) is the core control unit of electromechanical equipment. In order to determine the influence of the coupling vibration caused by vehicle–road interaction on the PCB reliability of roadside electromechanical equipment, first, the dynamic load of the vehicle tire is solved by establishing the dynamic model of a vehicle road. Then, the acceleration response data generated by road vibration are obtained by solving the road finite element model. Finally, the power density spectrum of the acceleration response is taken as input excitation, and the deformation response of the PCB under vehicle–road coupling vibration is analyzed. The experimental results show that when the vehicle is driving close to the roadside, the vibration caused by vehicle–road coupling will lead to a large deformation of the PCB, and the deformation value reaches 0.170 mm, which can cause structural damage to the PCB. This shows that the vehicle–road coupling vibration can affect the reliability of the roadside electromechanical equipment; thus, the optimal design of the PCB layout is created. After optimization, the first-order modal frequency of the PCB is increase by 5.4%, which reduces the risk of the components breaking away from the PCB substrate.

Chip-scale package (CSP) is commonly seen on high density boards as it minimizes the foot print while packed more functionality into one component. Board level reliability concern over CSPs is that finer pitch limits the solder ball size attached and the stencil thickness used in assembly which leads to much smaller joint volume and standoff while larger die-to-package ratio typically means higher stress level caused by the CTE mismatch. Prior studies have shown that the grain orientation may impact SnAgCu solder joint reliability. With less solder volume, the joint reliability of fine pitch SnAgCu solder may be more sensitive to the grain size, grain orientation, and IMC formation within the bulk solder. The purpose of the study is to evaluate the board level reliability of Pb-free ball grid array (BGA) packages with ball pitch smaller than 0.5mm under different packaging and assembly conditions. Based on a test vehicle with 0.4mm pitch daisy-chained CVBGA, the impact on solder joint reliability from a wide spectrum of variables such as PCB thickness, SMT configuration, die size, package pad finish, and mini cycle profiling has been investigated. The results of this study enable us to better understand the Pb-free fine pitch joint behaviors under different conditions and the factors that have significant impact on joint reliability. Isothermal aging effect has also been studied, will be presented in a separated paper, which demonstrated that isothermal aging could significantly degrade joint reliability for fine pitch packages. The ATC results proved that the fine pitch packages may underperform the components with regular 0.8-1.0mm pitch therefore extra attention needs to be paid on fine pitch components while converting high reliability products to Pb-free.

Board level drop testing is an effective method to characterize the solder joint reliability performance of miniature handheld products. In this study, drop test of printed circuit boards (PCB) with four-screw support condition was conducted for a 15 mm /spl times/ 15 mm fine-pitch ball grid array (FBGA) package assembly with solder ball compositions of 36Pb-62Sn-2Ag and Sn-4Ag-0.5Cu on PCB surface finishes of organic solderability preservative, electroless nickel immersion gold and immersion tin. The results revealed a strong influence of different intermetallic compound formation on soldered assemblies drop durability. The lead-based solder supersedes the lead-free composition regardless of the types of surface finish. Joints on organic solderability preservative were found to be strongest for each solder type. Other factors affecting drop reliability such as component location on the board and thermal aging effects are reported.

Board-level drop testing is an effective method to characterize the solder joint reliability performance of miniature handheld products. In this study, drop test of printed circuit boards (PCBs) with a four-screw support condition was conducted for a 15 mm times 15 mm fine-pitch ball grid array (FBGA) package assembly with solder ball compositions of 36Pb-62Sn-2Ag and Sn-4Ag-0.5Cu on printed circuit board (PCB) surface finishes of organic solderability preservative, electroless nickel immersion gold, and immersion tin. Finite element modeling of the FBGA assembly was performed to study the stress-strain behavior of the solder joints during drop test. The drop test results revealed a strong influence of different intermetallic compound formation on soldered assemblies drop durability. The lead-based solder supersedes the lead-free composition regardless of the types of surface finish. Joints on organic solderability preservative were found to be strongest for each solder type. Other factors affecting drop reliability such as component location on the board and thermal cycling aging effects are reported. Finite element modeling results showed that a solder joint is more prone to failure on the PCB side, and the predicted solder joint stresses are location dependent. Predicted failure sites based on simulation results are consistent with experimental observations.

Waste electrical and electronic equipment is a significant source of material that can contribute to reduce environmental impacts associated to extraction and discard stages; therefore, it is necessary to develop efficient recycling processes for components such as Printed Circuit Boards (PCBs). Current methods for PCB recycling may be optimized by previous disassembly of such components. In the work reported here, an especially designed and manufactured centrifuge was employed to disassemble PCBs from power supplies (PS-PCBs) and memory chips (ME-PCBs) of personal computers (PCs), through combination of hot air flow and centrifugal force. The results showed that the device was capable of separating tin solder, electronic components (EC) and PCB substrate, as long as hazardous components and plastic parts are previously removed. A scanning electron microscope (SEM) with combined energy dispersive X-ray (EDX) analyzer showed that the recovered solder had under 3%wt of contamination; therefore, it can be employed in the production of new soldering material, replacing the more commonly used solder dross. EC recovery rates were up to 94%wt for PS-PCBs and 32%wt for ME-PCBs, and once components such as inductors were not visibly damaged in the process, possibilities of reusing recovered components may be further investigated.

This paper compares natural and controlled soil composting, in which the degradation of flax-fiber reinforced, flame-retarded polylactic acid (PLA) composite printed circuit board (PCB) samples are monitored. We aim to investigate the structural alterations that occur over a prolonged degradation process of these biodegradable laminates, utilized as environmentally friendly substitutes for PCB substrates. The experiment involves the degradation of functional blinker circuits with surface-mounted components and blank substrate boards without a conductive copper layer. During the long-term storage, we registered the composition of the surface with Fourier-transform infrared spectroscopy (FTIR) and inspected the changes in structure with scanning electron microscopy (SEM). Compared to traditional epoxy-based (FR4) references, significant changes (at both microscopic and visible levels) and the susceptibility to natural organisms can be observed, key elements in developing a greener and more sustainable approach for future PCB designs. After 40 weeks, the FTIR analysis showed the dominant presence of PLA in the naturally degraded samples. Cellulose, which acts as a reinforcement component, could be seen at specific locations within the cracks. The SEM study revealed contaminations and microbiological remnants on the boards’ surface, along with a growing number of cracks and slight PLA deterioration. The FTIR and SEM results also highlighted the efficiency of the controlled degradation, as a significant loss of resin in the composite started after 6 weeks.

Laminating screen-printed, flexible transfers is a reliable method of creating electronic connections across a textile. However, their limited resolution means that it is not possible to solder on fine-pitched components. An alternative substrate, etched copper on polyimide is compatible with fine pitch components, but is unsuitable for use over large areas. This work examines methods of combining the two systems to produce e-textiles that combine both their benefits. Tensiometer tests showed that 3M 9087 double-sided tape was the most robust for attaching the polyimide, and electrical interconnects formed by overlapping the transfer on top of the polyimide circuit gave the most stable and lowest resistance connections.