PWB reliability – the next step

Abstract

Purpose

To share the findings of recent investigations of the influences of RoHS requirements on printed wire board (PWB) reliability.

Design/methodology/approach

Interconnect stress testing was used to measure the reduction in reliability of coupons that replicated high‐density multilayer circuit boards, after exposure to a simulation of the thermal excursion associated with “tin‐lead” and “lead‐free” assembly and rework. Coupons were preconditioned by exposure to tin‐lead assembly temperatures (230°C) or lead‐free assembly temperatures (245 or 260°C). Standard statistical methods were applied to the test data, which was compared between more than 20 dielectric materials.

Findings

There is a shift from copper quality being the dominant influence in reliability to copper and material quality working in concert being the major influence on PWB reliability. Delamination and crazing increases with lead‐free assembly and rework and this has the effect of artificially extending cycles to failure, frequently confounding data. Reliability testing to lead‐free temperatures requires an evaluation for delamination to ensure the cycle data are not artificially extended. A robust, well fabricated coupon's reliability is found to be reduced by 50 percent after lead‐free assembly and rework.

Research limitations/implications

There is objective evidence of a significant reduction in reliability with the thermal excursion associated with lead‐free assembly but there has been no apparent reduction in acceptance criteria or limitation on warranties. This paper does not address the influence of reliability on the solder joints, components or other structures of an assembled PWB. This paper is limited to reliability influences on the PWB. The identification of materials used in this study is protected under non‐disclosure agreements.

Originality/value

This study expands the understanding of the implications of the effect of RoHS requirements on PWB reliability. It allows companies to optimise PWB reliability with quality fabrication, using robust materials and optimised PWB designs and to make sound business decisions in order to meet the new challenges of RoHS. Meeting the challenge of RoHS is not limited to a question of compliance by getting the lead out; it is also a question of optimising PWB's reliability.

Citation

Reid, P. (2007), "PWB reliability – the next step", Circuit World, Vol. 33 No. 4, pp. 51-59. https://doi.org/10.1108/03056120710836945