The narrow focus technology-wise as well as market-wise is keeping the manufacturer out of trouble in troubled times. ”The current economic situation hasn’t touched us at all,” Stampanoni says. ”One of our strengths is service and consulting in the design phase for products with complex circuit boards.” This position is reflected in the company’s annual growth rates of around 30% between 1998 and 2001 – just broken last year, with a very slight downward turn from its revenues of SFr 33m, which was caused in part by the move to a new facility. Not too bad for a small outfit with just 140 employees on 6,000 square meters of floor space (including a 600 sq.meter cleanroom) located 10 minutes from Zurich Airport.
Dycostrate is at the center of its worldwide market position. Introduced in 1992, it pertains to a whole set of materials and tools for the generation of microvias for fine-line, rigid-flexible PCBs in particular, and to high-density interconnects in general. Basic concept is plasma ablation as opposed to (or complementing) photovia, laser and mechanical drilling (which looses tread below 200µm anyway).
With plasma ablation, Dyconex has almost an exclusive on multilayer flex or rigid-flex of up to 16 layers with microvias between every layer. ”There may be competitors offering high-count layers for high performance,” Stampanoni concedes, ”but most are offering one- or two-layer microvia products with sequential build-up per side. For miniaturization-driven applications, only a few can produce multilayer flexible substrates with finest structures.”
Meanwhile, via/pad geometries are down to 40/100µm, and line widths and spaces down to less than 20µm. Still a bit on the extreme side for the commodity-type cell phones or PDAs, but used in ultrasound medical probes or detectors. Aside from these record-setting achievements, the company offers standard solutions for microvias and pads down to 50/200µm and lines/spaces of 50 µm. Build-ups reach from one layer to 8-N-8 rigid flex, with a thickness of 25µm. Wrap-around is offered as well, including integrated micro-coax and twisted-pair lines. This is rounded off by design consultation in regard to thermal management, mechanical problems, EMI, testability, reliability and manufacturing cost constraint analysis. Another timely service dimension is on-site layout support. Fast prototyping is another option for fast-paced customers.
Insofar, especially in performance-driven applications, the firm has proved its mettle by substituting mechanical and laser drilling in glass-reinforced materials with plasma ablation in appropriate dielectric materials such as polyimide foils. This yields high-density interconnect (HDI) solutions on flexible or rigid-flexible substrates for PCBs and MCM construction as interposers for sensible package designs.
As a particular advantage of plasma ablation, Dyconex touts the two-sided processing of boards without the need of turning and re-registering them. Compared to photochemistry, plasma ablation doesn’t require full additive Cu plating. Laser drilling, of course, is unidirectional and sequential by nature, whereas plasma ablation can be fashioned into a parallel process generating all holes simultaneously. And as such in various shapes and geometries with slots and grooves, stepped and angled vias, or in a sculptural refashioning of the substrate surface.
All in all, plasma drilling delivers a high etch rate at low substrate temperatures as well as high etch-rate uniformity across large panel areas. Another plus: there is no post-processing such as deburring or desmearing. The other process steps, such as plating and photo definition, are the same as with regular PCBs. Standard materials for the Dycostrate plasma process typically are adhesive-less polyimide foils; FR-4-buttered or resin-coated Cu foils. Sequential build-up with rigid multilayer core is also an option.
Moreover, combining UV-YAG laser drilling with microwave plasma etching can achieve new kinds of complex build-ups. We can refer to a 450µm thick, 8-layer flex containing 75µm microvias extending through 6 Cu layers. The external layers are connected by blind vias brought in by plasma etching. Such a combination build-up delivers significantly improved electrical performance and higher mechanical flexibility.
Besides polyimides, there are also other promising non-standard materials for HDI soon coming on-stream, like liquid crystalline polymers (LCP), for example. They look like good replacement candidates for polyimide. In an experimental setup yielding first prototypes with two or more layers, a double-sided, copper-clad LCP substrate has shown good manufacturability of plasma-etched and laser-drilled microvias. LCP offers good RF properties. It opens the way to gigahertz frequencies in multilayer flex build-ups – in other words for extremely miniaturized applications in the promising realm of ubiquitous wireless appliances.
Werner Schulz
