Printed circuit boards for lead‐free soldering: materials and failure mechanisms

Abstract

Purpose

This paper aims to evaluate the influence of previous exposure to moisture on delamination and formation of CAF (conductive anodic filament) in printed circuit boards used for lead‐free soldering.

Design/methodology/approach

The moisture absorption and desorption characteristics of printed circuit boards were evaluated according to the IPC/JEDEC J‐STD‐020C standard for handling of moisture sensitive components. The CAF test was performed according to IPC‐TM‐650, Test Method 2.6.25.

Findings

Printed circuit boards used for lead‐free soldering must be treated as moisture sensitive components. Severe delamination occurred on test boards that had been exposed to JEDEC level 1 conditions prior to soldering, while no delamination was observed on boards exposed to level 3. Furthermore, previous moisture and thermal exposure had a strong influence on CAF formation. The insulation resistance dropped three decades in less than 15 h in the worst case.

Research limitations/implications

There are considerable stresses on printed circuit boards in lead‐free soldering processes. The influence from materials and processes is very large on the CAF formation. Therefore, a useful strategy is to evaluate the CAF properties for each supplier and material.

Originality/value

The paper pin‐points previous moisture exposure as a very important factor for delamination and CAF formation and confirms that printed circuit boards must be treated as moisture sensitive components.

Citation

Johander, P., Tegehall, P., Ahmed Osman, A., Wetter, G. and Andersson, D. (2007), "Printed circuit boards for lead‐free soldering: materials and failure mechanisms", Circuit World, Vol. 33 No. 2, pp. 10-16. https://doi.org/10.1108/03056120710750210