CO2 laser micromachining of optical waveguides for interconnection on circuit boards

The introduction of microvia and surface mount technologies into the manufacturing process for printed circuit boards (PCBs) has significantly improved the interconnection density. However, as the speed of signals for data communication on the board approaches and begins to exceed 10 Gb/s, the loss and crosstalk of copper interconnections increase. To resolve these problems, optical interconnections (OI) have been suggested as a viable solution. Literature reports have proved the photochemical nature of excimer laser ablation with its minimal thermal effect, and other ultra-violet lasers are also being investigated for the fabrication of polymer waveguides by laser ablation. In this paper, the authors demonstrate the fabrication of multimode optical polymer waveguides by using infra-red 10.6 μm CO2 laser micromachining to etch acrylate-based photopolymer (Truemode™). CO2 lasers offer a low cost and high speed fabrication route as CO2 lasers can be used to cut through various engineering materials including polymers and metals. The paper characterises the relationship between the laser ablation power, the fabrication speed and the resulting effect on the waveguide optical insertion loss for the first time

Experiment and Prediction of Ablation Depth in Excimer Laser Micromachining of Optical Polymer Waveguides

Extending the data transfer rates through dense interconnections at inter- and intraboard levels is a well-established technique especially in consumer electronics at the expense of more cross talk, electromagnetic interference (EMI), and power dissipation. Optical transmission using optical fibre is practically immune to the aforementioned factors. Among the manufacturing methods, UV laser ablation using an excimer laser has been repeatedly demonstrated as a suitable technique to fabricate multimode polymer waveguides. However, the main challenge is to precisely control and predict the topology of the waveguides without the need for extensive characterisation which is both time consuming and costly. In this paper, the authors present experimental results of investigation to relate the fluence, scanning speed, number of shots, and passes at varying pulse repetition rate with the depth of ablation of an acrylate-based photopolymer. The depth of ablation essentially affects total internal reflection and insertion loss, and these must be kept at minimum for a successful optical interconnection on printed circuit boards. The results are then used to predict depth of ablation for this material by means of adaptive neurofuzzy inference system (ANFIS) modelling. The predicted results, with a correlation of 0.9993, show good agreement with the experimental values. This finding will be useful in better predictions along with resource optimisation and ultimately helps in reducing cost of polymer waveguide fabrication.</jats:p

Fabrication of Polymer Waveguides by Laser Ablation Using a 355 nm Wavelength Nd:YAG Laser

The demand for optical waveguides integrated into Printed Circuit Boards (PCBs) is increasing as the limitations of copper interconnects for greater than 10 Gb/s data rates are being reached. Optical polymer materials offer a good solution due to their relatively low cost and compatibility with traditional PCB manufacturing processes. Laser ablation is one method of manufacture, for which excimer lasers have been used, but UV Nd:YAG (Neodymium-doped Yttrium Aluminium Garnet) lasers are an attractive alternative due to their widespread use within the PCB industry for drilling vias. In this paper, 355 nm, 60 ns pulse length UV Nd:YAG laser ablation of Truemode™ acrylate-based optical polymer was investigated. The UV Nd:YAG laser was found to be able to ablate the polymer efficiently and the effects of laser ablation power and pulse repetition frequency (PRF) on depth of ablation were studied and used to determine preferred settings. 45 μm × 45 μm multimode optical waveguides were fabricated to demonstrate the process and optical loss measurements were carried out. These measurements demonstrated that the structures were able to transmit light at the data communications wavelength of 850 nm (NIR), but further work is required to reduce the level of loss. The use of UV Nd:YAG as a possible alternative to excimer for laser micromachining would facilitate the rapid deployment of the optical technology within the PCB industry

Integrated optical and electronic interconnect PCB manufacturing research

Purpose – The purpose of this paper is to provide an overview of the research in a project aimed at developing manufacturing techniques for integrated optical and electronic interconnect printed circuit boards (OPCB) including the motivation for this research, the progress, the achievements and the interactions between the partners. Design/methodology/approach – Several polymer waveguide fabrication methods were developed including direct laser write, laser ablation and inkjet printing. Polymer formulations were developed to suit the fabrication methods. Computeraided design (CAD) tools were developed and waveguide layout design rules were established. The CAD tools were used to lay out a complex backplane interconnect pattern to meet practical demanding specifications for use in a system demonstrator. Findings – Novel polymer formulations for polyacrylate enable faster writing times for laser direct write fabrication. Control of the fabrication parameters enables inkjet printing of polysiloxane waveguides. Several different laser systems can be used to form waveguide structures by ablation. Establishment of waveguide layout design rules from experimental measurements and modelling enables successful first time layout of complex interconnection patterns. Research limitations/implications – The complexity and length of the waveguides in a complex backplane interconnect, beyond that achieved in this paper, is limited by the bend loss and by the propagation loss partially caused by waveguide sidewall roughness, so further research in these areas would be beneficial to give a wider range of applicability. Originality/value – The paper gives an overview of advances in polymer formulation, fabrication methods and CAD tools, for manufacturing of complex hybridintegrated OPCBs. © 2010, Emerald Group Publishing Limite