Thomas, O; Wickham, M; Hunt, C (2012) Obtaining the moisture content of printed circuit boards from capacitance measurements. Circuit World, 38 (2). pp. 68-74.

Full text not available from this repository.

Abstract

Purpose - To present work on the incorporation of capacitors into Printed Circuit Boards (PCB) as a method to measure moisture content and follow moisture diffusion under ground planes.
Design/methodology/approach - PCBs of FR-4 were manufactured which incorporated different arrangements and sizes of capacitors formed between the tracks on adjacent layers of the PCB. The boards have been placed in damp, 85ºC & 85%RH environments to absorb moisture and baked at temperatures of 80, 110 or 125ºC with the capacitance periodically measured. The effect of ground planes with different densities of plated and non-plated through holes (PTH) has been studied by placing capacitors between ground planes.
Findings - Parallel plate capacitors embedded within a PCB show a 10% capacitance increase going from a dry state to being saturated with moisture in a 85ºC & 85%RH environment. Due to the slow ingression of moisture under the capacitance planes, the capacitance only reflected the average moisture content within the capacitor and did not reflect the board as a whole. Capacitor plates with slots for the moisture to penetrate were also investigated with the increase in capacitance correlating well with increase in the board mass. In investigating moisture under ground planes, either decreasing the hole density or plating the holes are observed to increase to the diffusion time due to the lower area of exposed PCB.
Originality/value - This work has illustrated a method that can be applied the PCB manufacture to assess moisture content of the board prior to reflow.

Item Type:	Article
Subjects:	Advanced Materials Advanced Materials > Electronics Interconnection
Identification number/DOI:	10.1108/03056121211222282
Last Modified:	02 Feb 2018 13:14
URI:	http://eprintspublications.npl.co.uk/id/eprint/5521

Actions (login required)

View Item