B. Y. Wu

Assessment of toxicity potential of metallic elements in discarded electronics: A case study of mobile phones in China

The electronic waste (e-waste) is increasingly flooding Asia, especially China. E-waste could precipitate a growing volume of toxic input to the local environment if it was not handed properly. This makes the evaluation of environmental impact from electronics an essentially important task for the life cycle assessment (LCA) and the end-of-life management of electronic products. This study presented a quantitative investigation on the environmental performance of typical electronics. Two types of disposed mobile phones (MPs), as a representative of consumer electronics, were evaluated in terms of toxicity potential indicator (TPI) with an assumption of worst-case scenario. It is found that the composition and the percentages of constituents in MPs are similar. More than 20 metallic elements make up 35 wt.%-40 wt.% of the total weight, of which 12 elements are identified to be highly hazardous and 12 are less harmful. With the TPI technique, the environmental performance of Pb is attributed to be 20.8 mg(-1). The total TPIs of metallic elements in the old and new type MP is 255,403 and 127,639 units, respectively, which is equivalent to the effect of releasing 6.14 and 12.28 g Pb into the environment. The average TPI of the old and new type MP is 4.1 and 4.5 mg(-1), respectively, which suggests a similar eco-efficiency per unit mass. The new model of MP is more eco-effective than the old one, which is not due to a reduction in the type of hazardous elements, but rather due to a significant miniaturization of the package with less weight. A single MP can have a considerable toxicity to the environment as referred to Pb, which suggests a major concern for the environmental impact of the total e-waste with a huge quantity and a heavy mass in China.

Microstructural evolution and atomic transport by thermomigration in eutectic tin-lead flip chip solder joints

The thermomigration of eutectic tin-lead flip chip solder joints under ambient temperatures of 20 degC, 100degC and 150degC was investigated in terms of microstructural evolution. No significant thermomigration occurred after 100 h at 20degC and at 100degC. Only microstructural coarsening was observed in solder joints for these cases. However, Pb thermomigration and phase segregation were observed in solder joints after only 50 h at 150degC. Measurements showed that the temperature difference between the chip side and the substrate side reached 8.1degC (a temperature gradient of about 2700degC/cm across the solder joints) at an ambient temperature of 150degC. It is believed that Pb atoms migrated from the chip side (the hot side) to the substrate side (the cold side) under a temperature gradient of 2700 degC/cm

The determination of hexavalent chromium (Cr6+) in electronic and electrical components and products to comply with RoHS regulations.

Toxicity of hexavalent chromium (Cr(6+)) was focused on with a publication of EU RoHS directive, a novel method to determine hexavalent chromium is developed. It is a combination of energy dispersion X-ray fluorescence spectrometry (EDXRF), spot test, alkali digestion and UV-vis spectrophotometric analysis. First, by EDXRF screening, the presence or absence of element Cr was established. Spot test was followed to identify the valent state of chromium because Cr(6+) and Cr(3+) normally coexist. After alkali digestion, Cr(VI) was separated without an undersired Cr(VI)-Cr(III) interconversions. With a color reagent (DPC) to chelated with Cr(VI), the solution was finally detected by a UV-vis spectrophotometer at a wavelength of 540 nm which is the basis of analyzing Cr(VI) quantitatively. Some parameters affecting analyses were studied. It was found that when pH in the final solution was 2.0, the extraction time was 60 min, the extraction temperature was 90 degrees C, pH during the extraction process was 7.5-8.5, and a mixed buffer solution (0.5M K(2)HPO(4)/0.5M KH(2)PO(4)) was added up to 1 ml, colorimetric reagent was added to 2 ml, it is optimal for extraction. Under this condition, interferences from Fe(3+), Pb(2+), Ag(+), etc., were overcome. It was also found that the curves are rectilinear in the range of 0-500 microg l(-1), the correlation coefficient is up to 0.999924, and the recovery rates are more than 85%, the Cr(III)-DPCO complex can be kept stable for 24h with a relative humidity (RH) range of 60-90%, and a temperature range of 5-40 degrees C. So it can be concluded that the proposed method has a good sensitivity and high precision. It is a more convincing and reliable method due to its relative standard deviation (R.S.D.) <1% after six replicate determinations of Cr(VI) in an Fe-Ni alloy sample.

Effects of electromigration on the growth of intermetallic compounds in Cu/SnBi/Cu solder joints

In this study, the effects of electromigration (EM) on the growth of Cu–Sn intermetallic compounds (IMCs) in Cu/SnBi/Cu solder joints under 5 × 10 A/cm direct current stressing at 308, 328, and 348 K were investigated. For each Cu/SnBi/Cu solder joint under current stressing, the IMCs at the cathode side grew faster than that at the anode side. The growth of these IMCs at the anode side and the cathode side were enhanced by electric current. The growth of these IMCs at the cathode followed a parabolic growth law. The kinetics parameters of the growth of the IMCs were calculated from the thickness data of the IMCs at the cathode side at different ambient temperatures. The calculated intrinsic diffusivity (D0) of the Cu–Sn IMCs was 9.91 × 10 m/s, and the activation energy of the growth of the total Cu–Sn IMC layer was 89.2 kJ/mol (0.92 eV).

Study of the thermal stress in a Pb-free half-bump solder joint under current stressing

The thermal stress in a Sn3.5Ag1Cu half-bump solder joint under a 3.82×108A∕m2 current stressing was analyzed using a coupled-field simulation. Substantial thermal stress accumulated around the Al-to-solder interface, especially in the Ni+(Ni,Cu)3Sn4 layer, where a maximal stress of 138MPa was identified. The stress gradient in the Ni layer was about 1.67×1013Pa∕m, resulting in a stress migration force of 1.82×10−16N, which is comparable to the electromigration force, 2.82×10−16N. Dissolution of the Ni+(Ni,Cu)3Sn4 layer, void formation with cracks at the anode side, and extrusions at the cathode side were observed.

Shear Strength Analysis of Ball Grid Array (BGA) Solder Interfaces

Ball shear test is the most common test method used to assess the reliability of bond strength for ball grid array (BGA) packages. In this work, a combined experimental and numerical study was carried out to realize of BGA solder interface strength. Solder mask defined bond pads on the BGA substrate were used for BGA ball bonding. Different bond pad metallizations and solder alloys were used. Solid state aging at 150degC up to 1000 h has been carried out to change the interfacial microstructure. Cross-sectional studies of the solder-to-bond pad interfaces was conducted by scanning electron microscopy (SEM) equipped with an energy dispersive X-ray (EDX) analyzer to investigate the interfacial reaction phenomena. Ball shear tests have been carried out to obtain the mechanical strength of the solder joints and to correlate shear behaviour with the interfacial reaction products. An attempt has been taken to realize experimental findings by Finite Element Analysis (FEA). It was found that intermetallic compound (IMC) formation at the solder interface plays an important role in the BGA solder bond strength. By changing the morphology and the microchemistry of IMCs, the fracture propagation path could be changed and hence, reliability could be improved.

High Current Density induced Damage Mechanisms in Electronic Solder Joints: A State-of-the-Art Review

High current density induced damages such as electromigration in the on-chip interconnection /metallization of Al or Cu has been the subject of intense study over the last 40 years. Recently, because of the increasing trend of miniaturization of the electronic packaging that encloses the chip, electromigration as well as other high current density induced damages are becoming a growing concern for off-chip interconnection where low melting point solder joints are commonly used. Before long, a huge number of publications have been explored on the electromigration issue of solder joints. However, a wide spectrum of findings might confuse electronic companies/designers. Thus, a review of the high current induced damages in solder joints is timely right this moment. We have selected 6 major phenomena to review in this paper. They are (i) electromigration (mass transfer due electron bombardment), (ii) thermomigration (mass transfer due to thermal gradient), (iii) enhanced intermetallic compound growth, (iv) enhanced current crowding, (v) enhanced under bump metallisation dissolution and (vi) high Joule heating and (vii) solder melting. the damage mechanisms under high current stressing in the tiny solder joint, mentioned in the review article, are significant roadblocks to further miniaturization of electronics. Without through understanding of these failure mechanisms by experiments coupled with mathematical modeling work, further miniaturization in electronics will be jeopardized.

Effect of Carbon Inclusion in the Ni-P Coating on Shearing Behavior of Sn4Ag0.5Cu Ball Grid Array Solder Joints

This study employed an electroless Ni-P-carbon nanotubes (Ni-P-CNTs) composite coating as a pad finish for electronic packaging. It aimed at investigating the effect of carbon on the mechanical behavior and microstructure of ball grid array (BGA) solder joints after multiple reflows. Electroless Ni-P and electroless Ni-P-CNTs composite coatings with the same P-content were prepared for comparison. It was found that the carbon in the coating increased the brittleness of solder joints and weakened their shear strength. After shearing tests, more brittle fractures occurred in the intermetallic compound (IMC) layer in the Sn-4Ag-0.5Cu/Ni-P-CNTs (SAC/Ni-P-CNTs) solder joints. After multiple reflows, a Ni3Sn4 IMC layer and a P-rich layer were formed in the solder joints on both coatings. The IMC layers in the SAC/Ni-P solder joints were found to be compact with chunky-shaped grains, whilst the IMC layers in the SAC/Ni-P-CNTs solder joints were porous with needle-shaped grains.

Evaluation of the Potential Toxicity of Metals in Discarded Electronics: A Case Study of Mobile Phones in P. R. China

The e-waste is increasingly flooding Asia, especially China, which could precipitate a growing volume of toxic input to the local environment if not handled properly. This makes the assessment of environmental impact from discarded electronics an essentially important task for end-of-life (EOL) management. Tins paper presents a quantitative investigation of the toxicity of metals in mobile phones under a worst-case scenario using the toxicity potential indicator (TPI) module in the Fraunhofer Institute for Reliability and Microintegration (IZM)-EE Toolbox.

The Determinations of Pb, Cd, Hg, Cr 6+ , PBBs/PBDEs to Comply with RoHS Directive

For RoHS compliance, a method coupled inductively coupled plasma-optical emission spectrometry (ICP-OES), gas chromatography-mass spectrometry (GC-MS), and UV-visible spectrophotometry with microwave technology was developed to determine trace Cd, Hg, Pb, Cr6+, PBBs/PBDEs in electronic and electrical products (EEP). Elements were screened by Energy dispersion X-ray fluorescence spectrometry (EDXRF). In order to achieve good performance, other methods such as colorific test, inter-element correction (IEC) and standard addition techniques etc. were performed. By this study, it showed that analyses of Hg, Cd, Pb by ICP-OES and Cr6+ by UV-visible spectrophotometry had a RSD <5%, and a RSD <1% for PBBs/PBDEs by GC-MS analyzer. UV-visible spectrophotometry offered a good alternative for Cr6+ determination with alkali digestion, the inferences from Fe3+, Pb2+ etc. were eliminated by K2HPO4 buffer. The ramifications from monoBB/BDE to DecaBB/BDE were distinctly separated and successfully determined in the optimized condition. Furthermore, microwave system did an excellent job of consistently putting solid samples into solutions and had a moderate compatibility with spectrometric analyzer due to good recoveries. Though RSD of XRF screening was larger than 10%, it proved to be an easier, cheaper, faster technique. Because of the combination of multiple methodologies, the restricted substances can be determined with good precision and high reliability. It provides a prominent project for EE industries to comply with RoHS compliance.