Thermo-mechanical coupled separation of high-value BGA components from waste mobile-phone printed circuit boards.

Abstract

Discarded smartphone printed circuit boards (PCBs) contain high-value CPU and ROM components with reuse potential. This study investigated a thermally assisted separation strategy integrating thermal-process evaluation, mechanical analysis, and VOC characterization. A purposive set of 20 used smartphone models was examined. Under the tested conditions, air-convection heating provided a more controllable thermal response than contact-conduction heating. A programmed heating rate of 3 ℃/s with a 170 ℃ preheating plateau for 90 s shortened the heating period and produced favorable macroscopic separation quality with comparatively low solder residue. A simplified force model, copper-plate validation experiments, and complementary finite element analysis were used to compare horizontal and vertical removal. In the simplified system without underfill, the complete horizontal detachment force was lower than the corresponding vertical force, whereas underfilled components required removal forces of approximately 2.8-3.9 N. Near-source PID measurements showed that VOC concentrations increased from 0.4 mg/m3 at 215 ℃ to 7.0 mg/m3 at 265 ℃. GC-MS and Py-GC-MS were used to characterize VOC composition and thermal degradation products. Because target BGA components were generally separated at actual component temperatures of approximately 215-235 ℃, 245 ℃ was tentatively proposed as a conservative upper process-control temperature under the tested conditions, rather than as a regulatory, toxicological, or directly measured thermal-degradation threshold.