Comparative measurement of residual stresses with the method based on the magnetic Barkhausen noise and the relaxation method
For an efficient prediction of residual stresses in a material or a machine part the non-destructive method based on the magnetic Barkhausen noise is, among others, employed in practice. An experimental system developed at home and including measuring and assessment units has proved to be very efficient in various applications of surface hardening or cold hardening, and heat treatment.
The influence of product thickness on the measurements by Barkhausen Noise method
Purpose: The aim of this paper is to show how varying cross section thickness of tested product and calibration sample can depend on results of the residual stress measurements by the Barkhausen Noise method. Design/methodology/approach: The Barkhausen noise parameters as RMS value and total number of Barkhausen pulses in samples with different thickness was measured and compared. Also influence of the frequency and intensity of the magnetization current was analysing. Findings: The significant indirect influence of various cross-section thicknesses on Barkhausen Noise level was pointed. The equations describing influence of the thickness on Barkhausen noise at different magnetization current parameters were found. Research limitations/implications: Also the influence of the differences in width of the calibration sample and tested product was observed but in this research was not analysed. Practical implications: Taking into consideration obtained results lets compensate analytically indirect influence of geometrical factors and magnetization parameters on Barkhausen noise parameters. Originality/value: Original value of this paper is demonstrating significant source of error during residual stress measurements by Barkhausen method. For this moment this fact were not taken into consideration.
Failure analysis for poor solderability of Au surface of PCB
Nonwetting is one of the common problems and is always rejected in electronic assemblies. ENIG pads of a PCBA exhibited nonwetting after lead-free reflow soldering. With the aid of stereomicroscope, SEM&EDS and XRF, a series of analysis was performed. And after visual inspection, surface and cross section analysis, thickness measurement and solderability test, it can be inferred that oxidation of plating surface was the main reason for nonwetting, and corrosion in Ni plating caused an adverse impact on solderalibity.