"Good quality and high reliability are not an accident: They are there by design!" These were the opening words of Artetch Circuits' Managing Director Martin Morrell as he introduced the SMART Group seminar on high-technology, high-reliability PCBs at the UK's National Physical Laboratory (NPL) on November 17, 2009. "Understanding your product, the materials used in its production and how it is manufactured are crucial in designing cost-effective products with high reliability," he continued, addressing an attentive audience of PCB designers. 

Speakers at the SMART Group seminar (left to right): Dennis Price, Martin Wickham, Neil Chamberlain, Terry Bateman, Alun Morgan, Chris Hunt, Martin Morrell, Neil Stanton and Paul Comer.

Morrell highlighted SMART Group's role in facilitating the sharing of knowledge and understanding of products, materials and processes in the electronics industry, and the support of NPL in partnering industry through research and studio projects. He referred, in particular, to the establishment of the NPL Defect Data Base, an open resource enabling the electronics industry to gather and categorise data on process defects and field failures, to monitor their frequency and to assist in their elimination.

The well-balanced seminar programme covered many aspects relevant to printed circuit design and included presentations on materials for high-end PCBs, specifying PCBs in fabricators' language, finishes for wire-bonding and soldering, specifications and approvals, PCBs for military and aerospace applications, the outcome of reliability testing projects, and methods of calculating, specifying and testing electrical impedance characteristics of PCBs.

The first presentation came from Alun Morgan, Director of OEM Marketing at Isola, who described the influence of the three component materials--glass, resin and foil--on the thermal and electrical properties of laminates. He made some interesting observations on the effects of foil treatment on signal loss at high frequencies. At 10GHz, the signal is carried not in the bulk cross-section of a copper trace, but in a layer less than one micron deep in the "skin" of the conductor. The comparative roughness of the bonding treatment on conventional foil led to substantial loss, and drum-side-treated foil was now preferred in high-frequency applications. Dielectric losses had also been reduced by improvements in the manufacture of glass fabric to give a more uniform distribution of glass filaments,

On the subject of thermal reliability, particularly in a lead-free soldering context, Morgan referred to thermo-mechanical and thermo-gravimetric analysis techniques for determining glass transition and decomposition temperatures, and pointed out that a high Tg did not, in itself, infer high thermal reliability. There had been a wholesale adoption of phenolic curing systems for epoxy laminates since the advent of lead-free soldering, and these gave enormous improvements in thermal stability over conventional dicyandiamide systems.