ICT Evening Seminar - "High Density Interconnect".
16th February 2005

Bill Wilkie, ICT Technical Director, welcomed everyone to the seminar and thanked the sponsor, Artetch Circuits Ltd. Bill then introduced the speakers for the evening, Sue Critcher, Kerry Hewlett and Ashley Luxton, both from Graphic Plc.

Sue gave a spirited paper covering at the start a little history of pcb design and her background. Sue is currently working at Roke Manor Research in Romsey.

Sue moved on swiftly to blind and buried vias and stressed the cost consciousness in this field of genuine designers; this technology should be used sparingly and only when necessary. Pitch and pin dimensions are reducing fast with smaller and smaller pads and gaps. Microvia technology carries down to only the next layer and is of a fixed size; aspect ratio of 1:1 is rather limiting.

In impedence matching the h dimension is fixed and only possible to vary the track width, w. There are options such as z axis controlled drilling. One company example cited a smaller pad on the outside layer to aid registration in drilling. Designing with the process in mind is key and over all is the cost discipline.

The next presentation, "HDI Manufacture", was given by Kerry Hewlett & Ashley Luxton both from Graphic Plc.

HDI techniques enable small dimensions to be achieved with optimisation of “real estate”. However microvias are just one aspect.

Thin substrate quality and reproduceability are key in this area of technology. The use of very thin materials requires special equipment and handling techniques. Imaging and image quality is another critical area. Laser drilling enables < 0.15mm hole dimensions with CO2 TAG equipment – in any substrate and variable aspect ratios at 1:1 or better. Copper filled hole technology lends itself to the stacked via approach.

Frank Coultard

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