Failure of Printed Circuit Boards during Storage and Service: Leaked Capacitors and White Residue
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JMEPEG https://doi.org/10.1007/s11665-020-05148-3
Failure of Printed Circuit Boards during Storage and Service: Leaked Capacitors and White Residue A. Ravi Shankar, K. Praveen, S.R. Polaki, S.C. Vanithakumari, Nanda Gopala Krishna, L. Srivani, R.P. George, and John Philip (Submitted May 11, 2020; in revised form August 24, 2020) Failure of electronic components of printed circuit boards (PCBs) is a major concern, especially during storage. In the present study, we analyzed different modes of damages noticed on PCBs stored in coastal atmosphere such as leaking capacitors, white residues and attack around soldered joints. Fourier transform infrared spectroscopy, and pH measurements of the electrolyte from good and leaked capacitors indicated that the degraded electrolyte can cause capacitor leakage and subsequent failure. Scanning electron microscopy, energy dispersive x-ray analysis and x-ray photoelectron spectroscopy analysis of the white residue on PCB board showed the presence of phosphorus and oxygen as dendrites, formed due to the leaked electrolyte from capacitors on PCB. PCBs in continuous service with capacitor leak and white residue were also characterized. In this PCB, white residue was predominantly consisting of tin, oxygen and chlorine, which was formed due to corrosion of flux residue under high humid conditions. The damage around soldered joints of stored PCB board was found to be due to re-soldering, over heating which caused damage to the conformal coating and subsequent corrosion due to contaminants from flux residues. Based on the analysis of results, the probable mechanisms for the failure of PCBs are evolved, and the consequences for PCBs on prolonged storage and subsequent operation are also discussed. Keywords
corrosion, FTIR, printed circuit board, SEM, white residue, XPS
1. Introduction Reliability of electronic components of printed circuit boards (PCBs) is a major concern. The most common reason for failure of electronic components is the presence of corrosive environmental conditions and contaminants. Corrosion of electronic components affects the service life of PCBs, and, the expenses incurred due to replacement and downtime, results in huge economic losses. Electrochemical corrosion of electronic components occurs in a localized region on PCBs based on the presence of potential bias, contaminants/corrosive species, susceptible metal/alloy and humid/corrosive environment. Potential bias can occur by galvanic coupling of dissimilar metals or from the power supply of the electronic device (Ref 1). During manufacture and assembly of PCBs, residues can be deposited on PCBs which are corrosive. Contaminants which are hygroscopic, lead to corrosion in humid atmosphere thus affecting the service life of PCBs. The well-known corrosion failure modes under humid atmospheric
A. Ravi Shankar, S.C. Vanithakumari, Nanda Gopala Krishna, R.P. George, and John Philip, Corrosion Science and Technology Division, Indira Gandhi Centre for Atomic Research, Kalpakkam, Tamil Nadu 603102, India; K. Praveen a
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