Metals In Printed Circuit Boards Research Articles

Leaching of base metals in PCBs and copper cementation by iron powder

When dealing with electronic waste, printed circuit boards (PCBs) are some of the most important materials in terms of recovery possibilities, because of their high content of precious metals and base metals, notably copper (> 20% w/w), in addition to organic resins and ceramic materials. Efficient hydrometallurgical metals recovery from electronic waste is an important on-going research topic, and the present study consisted in the development of a process for the concentration of precious metals by leaching and recovery of major base metals mainly copper.A fraction of crushed PCBs concentrated in metals with more than 50 % copper was used for the leaching tests for two types of components: processor cards and mobile phone cards. For the leaching process, two steps were carried out. A first step consisted in leaching the concentrate three times with sulfuric acid and hydrogen peroxide, a second step consisted in lead removal by nitric acid leaching.The obtained results exhibit that, for processor cards, the first stage of leaching allowed the extraction of about 98 % of copper. Other base metals, zinc (99.8 %) and nickel (96 %) were also significantly leached. Precious metals were less leached except Ag with 88 % of release. The second stage of leaching with nitric acid allowed significant removal of lead (66 %). For mobile phone cards, the first stage of leaching led to an almost complete extraction of Cu (>98 %) and some other base metals (Fe, Ni, Sn, and Zn > 90 %). Al, Co and Mn were also extracted at 76 %, 78 % and 81 % respectively. Precious metals remained in the residue, except Pd which was leached at 16 %. The second stage of leaching with dilute nitric acid solution was not necessary for mobile phone cards, as it was responsible of an important Ag release from residue (80 %).

Biological extraction of Cu and Ni from printed circuit boards via redoxolysis with concomitant material characterization

Among the different types of secondary post-consumption wastes, E-wastes or waste electrical and electronic equipment represent the fastest growing and most problematic waste stream with printed circuit boards (PCBs) constituting its major ingredient. Results from the extraction of Cu and Ni from PCBs using biogenic Fe2(SO4)3 obtained from the original isolate Acidithiobacillus ferrooxidans 61 (KM819692) are presented. At. ferrooxidans 61 was grown at a temperature of 30 °C in a modified 9 K medium supplemented with ferrous iron. Two-stage bioleaching was carried out at 600 rpm and 40 °C. Experiments were performed at 10% of pulp density (PD) with 48-h duration (each stage of 24 h), under pH 1 and 20 g/L Fe3+. Under these conditions, overall recovery of Cu and Ni of 95% and 87% respectively was achieved. The obtained results indicate that non-ferrous metals in PCBs may be efficiently leached within two-stage bioleaching coupling bio-oxidation to subsequent redoxolysis. Scanning electron microscope (SEM) images acquisition and elemental mapping were performed to assess the liberation degree of essential phases after size-reduction steps and their implication on bioleaching efficiency.

Two-stage catalytic pyrolysis and debromination of printed circuit boards: Effect of zero-valent Fe and Ni metals

The non-metallic fraction of waste printed circuit boards (PCBs) has received extensive attention for material recycling, due to the potential risk of brominated flame retardants and heavy metals in PCBs. Here, the catalytic pyrolysis of PCBs was performed at 400–600 °C in a two-stage fixed bed reactor. Low-cost Fe and Ni metals were investigated for their catalytic effect on the product yields and bromine removal from the pyrolysis products. In the absence of additives, the maximum oil yield of 50.1 wt% was obtained at 500 °C from the PCBs pyrolysis. The addition of Ni particles decreased the oil yield to 29.1 wt%, and increased the gas yield to 9.6 wt% at 600 °C. The Fe/Ni mixture had a synergistic effect on the product yields, which depended on different pyrolysis temperatures. The composition of the oils from the PCBs pyrolysis was dominated by phenol derivatives. The presence of Fe or Ni particles promoted the formation of phenol and other aromatic compounds, such as benzene and toluene. Moreover, the transformation of bromine species was exhaustively investigated. The higher temperature promoted the conversion of brominated compounds into HBr. Fe particles exhibited excellent debromination performance, which not only reduced the formation of organobromine compounds, but also captured some of the evolved bromine.

Preliminary Investigation of the Influence of Potentiodynamic Electrosynthesis of Polyaniline@Carbon Fiber on the Formation of Charge Carriers and Their Effects on Double Layer

Aerospace systems contain a number of electronic devices responsible for data acquisition and transmission, device control, and power storage. Resistant structural materials, and light electronics are of strong interest to the aerospace industry. Thus, it is possible to aggregate these properties in a single electroactive composite material for application in new aeronautical structures of panels, circuits, de-icing and anti-icing systems, and sensor integration. The combination of carbon fiber with conductive polymer results in a material that can replace printed circuit board metal with improvements in the properties of thermal and mechanical resistance, and density resulting in a lighter material and electric conductor. The most suitable forms of electrodeposited polyaniline in carbon fiber structural cables were tested, through analysis of number of electrochemical cycles influence. In general, the electrochemical cell can be described as carbon fiber (CF) used as work electrode, against platinum electrode, using cyclic voltammetry in the region of -0.50 V to +1.05 V vs. Ag/AgCl at variable sweep rate from 5 mV/s, and different numbers of voltammetric cycles, 2, 4, 6 and 9, in a 0.5 mol/L aniline and H2SO4 0.5 mol/L solution The cyclic voltammetry shown in Figure 1 shows the anode peak of interest around 0.25 V, which is the potential for maximum formation of emeraldine in the fiber, used as the final potential of each process of obtaining.. Morphological (Scanning Electron Microscopy), structural (X-ray Diffraction) and chemical (Infrared Spectroscopy by Fourier Transform) analyzes were performed. It is possible to observe that the morphology advances for more intense deposition of polyaniline on carbon fibers. Noticeable forms: “coral reef”, alveoli, nanofibers. The diffractograms have polyaniline@Carbon fiber peaks, showing that polyaniline (001) is oriented by the carbon fiber (002) for the first cycles, close to 10°. In addition, polyaniline grown to cycle 2 exhibits a relatively small population of structures growing in the directions associated with 2Θ = 12°, 17°, and 34°, most common in the case of chemical synthesis. In the diffractogram of polyaniline grown up to cycle 4, there is a significant contribution obtained in 6,2° competing with the growth of orthorhombic structures around 9°, as it had been presented in 2 cycles. For the polymer obtained after 6 and 9 cycles, the peaks 17° and 25° show higher incidence. These new orientations indicate that growth does not occur on both the fiber surface and on the previously formed polyaniline itself. The identification of functional groups was useful for confirming the formation of emeraldine and its conductive, saline, more or less protonated form. However, all samples present bands related to the C=C stretch in the structure of the quinoid and benzenoid ring, proving the presence of polyaniline. The proximity of the height of these bands, between 1565 and 1490 cm-1, indicates the obtaining of the emeraldine form, which is the most susceptible to electric charge accommodation. However, there are no bands expressing between 1240-1255 cm-1 relative to the assignment of the C-N stretch in the BBB sequence (which does not favor electroactivity), indicating that there are no long sequences of benzenoid groups in the polymer, which does not have definitively insulating chain branches , since the BBB sequence is insulating. According to the literature, the degree of oxidation of PAni is calculated by Equation 1, the ratio of the presence of quinoids. Equation 2 shows how to calculate the S ratio of protonated C-N groups. The higher the value of S, the greater the number of protons accommodated, and therefore, the greater the electroactivity. Through Bode Plot, it is possible to calculate the relaxation time (t) of each sample. Table 1 presents the values of y, S and t, as they enabled quantification of the spectra of Figures 3, 4 and 5. Being y ~ 0.5 (emeraldine) for all samples, the electroactivity is favored, with slight variations in the degree of protonation . However, for 6 cycles, only 76% of the species are protonated. In this case, the electrochemical relaxation time was higher, indicating that the shortage of accommodated load allows for greater storage, making it difficult to release them, being less suitable for the aforementioned circuits (Table 1). The Polyaniline@carbon fiber most suitable for this purpose should be closer to that obtained with 4 cycles. Figure 1

Recycling Tin from Electronic Waste: A Problem That Needs More Attention

The rapid generation of electronic waste (e-waste) has become a global problem owing to its potential environmental pollution and human-health risk, especially from informal recycling in developing countries. In 2014, however, only ∼15.5% of the total global e-waste was formally treated by national take-back programs. Waste printed circuit boards (PCBs) are an integral part of e-waste, and they contain many valuable metal resources. Most recycling from waste PCBs has focused on metals like Au, platinum group metals, and Cu, which have high economic value, but tin also makes up a large proportion of the metal in waste PCBs. Over the past decade, ∼44% of the refined tin has been used as solder in the electronics industry each year. Although current global tin reserves can meet the short-term demand, for long-term sustainable development, recycling tin from secondary resources, especially from e-waste, is essential. For addressing the shortage of mineral resources and conserving energy, tin recycling from e-...

Erratum: "Printed circuit board metal powder filters for low electron temperatures" [Rev. Sci. Instrum. 84, 044706 (2013)

Erratum: "Printed circuit board metal powder filters for low electron temperatures" [Rev. Sci. Instrum. 84, 044706 (2013)

Concentration of precious metals during their recovery from electronic waste

The rapid growth of electronic devices, their subsequent obsolescence and disposal has resulted in electronic waste (e-waste) being one of the fastest increasing waste streams worldwide. The main component of e-waste is printed circuit boards (PCBs), which contain substantial quantities of precious metals in concentrations significantly higher than those typically found in corresponding ores. The high value and limited reserves of minerals containing these metals makes urban mining of precious metals very attractive. This article is focused on the concentration and recovery of precious metals during pyro-metallurgical recycling of waste PCBs. High temperature pyrolysis was carried out for ten minutes in a horizontal tube furnace in the temperature range 800–1350°C under Argon gas flowing at 1L/min. These temperatures were chosen to lie below and above the melting point (1084.87°C) of copper, the main metal in PCBs, to study the influence of its physical state on the recovery of precious metals. The heat treatment of waste PCBs resulted in two different types of solid products, namely a carbonaceous non-metallic fraction (NMFs) and metallic products, composed of copper rich foils and/or droplets and tin–lead rich droplets and some wires. Significant proportions of Ag, Au, Pd and Pt were found concentrated within two types of metallic phases, with very limited quantities retained by the NMFs. This process was successful in concentrating several precious metals such as Ag, Au, Pd and Pt in a small volume fraction, and reduced volumes for further processing/refinement by up to 75%. The amounts of secondary wastes produced were also minimised to a great extent. The generation of precious metals rich metallic phases demonstrates high temperature pyrolysis as a viable approach towards the recovery of precious metals from e-waste.

Thermal characteristics for chip on metal package of LED lighting module

The insulator of the metal printed circuit board (PCB) area layer, where a chip is packaged in the metal PCB structure of the chip on board (COB) package, is removed in order to propose a chip on metal (COM) package that allows the direct packaging of the chip to the PCB metal layer. In order to analyze the thermal characteristics from the chip, both COB and COM packages were fabricated during the operation to measure the chip junction temperatures (Tj) and thermal resistances of both specimens. According to the Tj measurement result, Tj=34.64°C for the COM package with the removed insulator and Tj=45.28°C for the COB package, showing that the COM package had an approximately 10°C less thermal distribution. Similarly, the thermal resistance of the COM package was 0.7°C/W, which was about 1°C/W less than the COB package thermal resistance of 1.67°C/W. Also, by comparatively analyzing the changes in the spectrum, color coordinates, and speed of light according to the driving time, it was found that luminous color stabilization may have contributed to the luminescence properties of the COM package, which has lower thermal resistance, and the degradation of the chip and packaging material can be minimized.

Generation of copper rich metallic phases from waste printed circuit boards

The rapid consumption and obsolescence of electronics have resulted in e-waste being one of the fastest growing waste streams worldwide. Printed circuit boards (PCBs) are among the most complex e-waste, containing significant quantities of hazardous and toxic materials leading to high levels of pollution if landfilled or processed inappropriately. However, PCBs are also an important resource of metals including copper, tin, lead and precious metals; their recycling is appealing especially as the concentration of these metals in PCBs is considerably higher than in their ores. This article is focused on a novel approach to recover copper rich phases from waste PCBs. Crushed PCBs were heat treated at 1150°C under argon gas flowing at 1L/min into a horizontal tube furnace. Samples were placed into an alumina crucible and positioned in the cold zone of the furnace for 5min to avoid thermal shock, and then pushed into the hot zone, with specimens exposed to high temperatures for 10 and 20min. After treatment, residues were pulled back to the cold zone and kept there for 5min to avoid thermal cracking and re-oxidation. This process resulted in the generation of a metallic phase in the form of droplets and a carbonaceous residue. The metallic phase was formed of copper-rich red droplets and tin-rich white droplets along with the presence of several precious metals. The carbonaceous residue was found to consist of slag and ∼30% carbon. The process conditions led to the segregation of hazardous lead and tin clusters in the metallic phase. The heat treatment temperature was chosen to be above the melting point of copper; molten copper helped to concentrate metallic constituents and their separation from the carbonaceous residue and the slag. Inert atmosphere prevented the re-oxidation of metals and the loss of carbon in the gaseous fraction. Recycling e-waste is expected to lead to enhanced metal recovery, conserving natural resources and providing an environmentally sustainable solution to the management of waste products.

Printed circuit board metal powder filters for low electron temperatures

We report the characterisation of printed circuit boards (PCB) metal powder filters and their influence on the effective electron temperature which is as low as 22 mK for a quantum dot in a silicon MOSFET structure in a dilution refrigerator. We investigate the attenuation behaviour (10 MHz-20 GHz) of filter made of four metal powders with a grain size below 50 μm. The room-temperature attenuation of a stainless steel powder filter is more than 80 dB at frequencies above 1.5 GHz. In all metal powder filters, the attenuation increases with temperature. Compared to classical powder filters, the design presented here is much less laborious to fabricate and specifically the copper powder PCB-filters deliver an equal or even better performance than their classical counterparts.

Characterization and recovery of polymers from mobile phone scrap

Electronic scrap is part of a universally wide range of obsolete, defective, or used materials that need to be disposed of or recycled in an ecologically friendly manner. The present study focused on the polymers present in mobile phone scrap. In mobile phones, polymers are found in frames and in printed circuit boards (PCBs). The frames are mainly made of polymers whereas PCBs use a variety of material (polymers, ceramics, and metals) which makes recycling more difficult. As a first step, mobile phones were collected, separated by manufacturer/model, and weighed, and the principal polymer types identified. The frames and PCBs were processed separately. The metals in PCBs were separated out by an electrostatic separation process. The resulting polymeric material was identified and mixed with the polymers of frames to fabricate the samples. Two types of samples were made: one with polymeric frames, and the other with a mixture of frames and polymeric fraction from the PCBs. Both kinds of sample were fabricated by injection moulding. The samples were evaluated by mechanical tests (tensile, impact, and hardness) to verify the feasibility of recycling the polymers present in mobile phone scrap. The results demonstrated the technical viability of recovering polymers using mechanical processing followed by an injection process.