Heat treatment effects on the physical property changes and liberation characteristics of waste printed circuit board (PCB)

Abstract

Copper liberation is one of the most important unit operations of PCB (printed circuit board) grinding process. It is known that the free copper particles are acquired only if the PCB is ground under 500um, which requires overgrinding and high energy consumption. In this research, the heat treatment for PCB prior to size reduction was investigated to improve copper liberation from the board. Personal computer PCB assemblies were acquired from a recycling center in Korea. The ECs, which are soldered on PCB, were disassembled from the boards manually. The thermogravimetric analysis of the bared boards was conducted in the atmosphere of air and N2 at the temperature range from 200 to 325 celsius degree in order to inspect thermal behavior of PCB. The bending strengths of PCB at each thermal treatment conditions were also examined to confirm specifying the optimal heat conditions. Size reduction by 2-stage crushing process was done to obtain PCB grind products and their size distribution, density distribution and morphology analysis were conducted in order to investigate copper liberation improvements. Observation of the particle shape through an electron microscope revealed that copper was liberated in the range of -4000+2800 um. It was confirmed that the physical characteristics of the crushed products were changed before and after heat treatment. As a result, it was found that the copper liberation was significantly improved by introducing heat treatment prior to crushing and/or grinding process.