PCB technology - today and tomorrow
26 August 2008
EMTww asked Tim Dennis Price of Merlin Circuit Technology to outline a technology roadmap for the next few years…
Predicting future PCB technological requirements has always been a precarious business. Generally current “state of the art” products are designed with 100 micron track & gap and are typically between four and sixteen layers, fabricated on high-end epoxy laminates. Impedance controlled tracking is invariably required along with through via holes drilled at 0.20 mm diameter.
Merlin Circuit Technology Ltd has installed a Laser Direct Imaging (LDI) exposure machine to accommodate the predicted reduction in track & gap requirements of 50 microns (see Fig.1). This is required to pin-out BGA devices below 0.50 mm pitch and maximise component real estate.
Other predicted changes over the next two to three years are the development of 3D interconnects structures with associated thermal management. To accommodate lead-free assembly, the recent curing agent changes to FR4 epoxy products have resulted in improvements in Tg, Td and CAF resistance but have caused problems with reduced Copper peel strengths and lower resin ductility.
Ever decreasing electronic device contact pitches have resulted in the increased use of buried, blind and micro-via technologies. This is predicted to increase significantly as designers find that they can reduce layer counts by adding high density interconnect (HDI) layers.
To maximise both wiring density and electrical performance, the increased use of embedded passive components will continue. This will be complemented by embedded silicon devices, which Merlin are already providing prototype development products for a leading OEM.
The world market for flexible and flexi-rigid circuits will continue to grow with the increased use of printed electronics, rather than the normal subtractive method of etching away copper foil. Cost effective semi-flex products are becoming more popular especially in automotive electronics.
Surface finishes are typically electroless Nickel / immersion Gold (ENIG), immersion Tin, immersion Silver, OSP or lead-free hot air solder level (HASL) depending on board complexity and working environment. Merlin are currently evaluating the new autocatalytic Silver / immersion Gold finish and copper filled micro-vias (see Fig.2), which we believe will be specified in standard products by designers in the very near future
Developing and perfecting these techniques will be demanding but required to ensure fabricators maintain their capability levels to produce cost effective products.
The Author is Merlin’s Business Development Director
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