The electronics interconnection group at National Physical Laboratory (NPL, Teddington, UK) is making progress in its current research projects.

The use of AC signals instead of DC in surface monitoring of process residues, such as flux, is yielding startling results. The new methods, dubbed surface insulation impedance (SII), show that some fluxes appear to provide variations in loss of signal in an AC environment orders of magnitude higher than predicted by traditional DC surface insulation resistance (SIR) techniques. Ongoing work continues to validate the findings, which could have important implications for AC circuit reliability. For more information, contact: alan.brewin@npl.co.uk.

Over 170,000 electronic component joints have been built with two isotropic conductive adhesive materials at NPL. These samples are now in seven different accelerated environments comprising damp heat, dry heat and thermal cycling. The next steps will involve analysis of joint conductivity, shear and drop test data to compare the reliability performance of the adhesive joints to that achievable with solder. Contact martin.wickham@ntlworld.com for further information.

Work to improve solderability wetting balance tests by including a pre-heating process for the component is showing significant rewards. The use of pre-heat with focused IR energy allows for a lower solder globule or bath temperature and better representation in the test to the reality of wave of reflow soldering conditions. The improved method is likely to reward users with a better prediction of defect rates if parts are used in production. For more information, contact: alan.brewin@npl.co.uk.

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