Material composition trends in printed circuit boards of mobile phones

• Mobile phones became heavier with transition to smartphones. • Simultaneously, PCBs became smaller over time, decreasing on average 6.9 mass % per year. • Only three elements, Cu, Ni, and Sn, constitute up to 65 % of the total smartphone PCB mass. • The median concentration of elements Pb, Au, Pd, As, and Cd decreased significantly over time. • The median concentration of Au decreased from 1244 ppm in Feature phone PBCs to 428 ppm in Smartphone PCBs. In this research, we have investigated 45 mobile phones manufactured between 1998 and 2021. After dismantling, the resulting Printed Circuit Boards (PCBs) have been mechanically processed and homogenised. From each PCB, three sample pellets were created and analysed with a portable X-Ray Fluorescence (pXRF). In addition, a post-hoc calibration was performed to correct element and sample-specific biases. This approach allowed us to analyse a large sample size and to identify element mass value trends over time. The results for precious metals show an average annual decrease -2.49 mg/PCB for Ag, -1.14 mg/PCB for Au, and -0.13 mg/PCB for Pd. By contrast, the concentrations of Cu and Ni were increasing, but due to the decreasing mass of PCBs, the overall trends remained constant. Ultimately, the applied methodological approach was effective for analysing large number of samples and provided unique insights into the material trends across different generations of mobile phones.