Facilitated by the development of various direct-write techniques and functional polymeric materials including polymer based conductors and semiconductors, printed electronics are flourishing both commercially and as a research topic. This is not only because of their simpler manufacturing routes and lower cost, but also as a result of lower processing temperatures and better compatibility with flexible substrates, compared with conventional electronics. The development of conventional electronics has been guided by Moore s Law, the driver for which lies in the demand for electronic devices with better performance and portability at lower prices. Therefore, one can expect a similar trend for printed electronics to guide its development. Multi-layered printing can be adopted in printed electronics to achieve higher density integration, so that this development trend can be maintained. In such circumstances, creation of electrical connections between multiple layers emerges as an important issue for printed electronics. Inkjet-etched via holes are one potential solution to providing such electrical interconnections, and which can provide good integration with other inkjet-printed features simply by switching nozzles. This thesis aims to elicit a better understanding of the physics involved in inkjet etching and investigate the capability of the inkjet etching technique. In the thesis, the factors that can affect the size of via holes produced by inkjet etching are evaluated, which is significant for evaluating the capability of this technique to deliver industrially relevant features. Identified factors include droplet ejection frequency, droplet diameter, solvent properties and substrate temperature. Droplet ejection frequency, i.e. the reciprocal of the time interval between drops, determines the extent of evaporation of the solvent between two consecutive drop impacts. Droplet diameter determines the radius of the wetted area after the droplet I impacts on the surface and spreads into a sessile drop. Solvents with different evaporation properties result in different size evolution with the number of drops dispensed, as does droplet ejection frequency. Higher substrate temperatures can reduce the drop diameter during flight and decrease the evaporation time on polymer surfaces, which can shrink the size of via holes. Another important issue is achieving complete polymer penetration as residual polymer creates an electrical conduction barrier after such holes are subsequently filled with conductive materials or act as a barrier to filling by electroplating. Experiments have been carried out to test the effect of outer diameter and polymer thickness on polymer penetration. Electroplating is utilised to test the completeness of via hole penetration. A mechanism using the Marangoni effect to explain the protrusion drying pattern other than a hole in the polymer layer is proposed.

Electromagnetic compatibility remains an important topic in the design and manufacturing of printed circuit boards (PCBs). Compatibility of these devices with their surroundings is becoming increasingly difficult as a modern PCB can have hundreds or thousands of parts, operating on many layers, and all at high speed. One such part is a via and its clearance, or via hole, commonly required in multilayer circuits where vertical connections between layers are used. The via hole may be exposed to large electromagnetic fields within the PCB. Although electrically small, the via hole provides a pathway for the fields to excite the exterior, either directly or through coupling to adjacent structures. To quantify this process, the near fields and radiation of an excited via hole are analysed, and are the focus of this thesis. The near fields of the via hole are first decoupled into electric and magnetic fields of the 'static' type. In both cases a series solution for two regions, one outside, and one inside the layers is constructed. The coefficients of the terms of the series are chosen to best satisfy the boundary behaviour of the fields on the conducting surfaces and across the hole. The criteria for assessing quality of the solution is based on the least squares method (LSM). Linear equation systems for both models are derived, and as no numerical integration or discretisation is required, an efficient and robust implementation to find the near fields is developed. Transformation into the far field is then achieved through surface integration of relevant field quantities close to the via hole. The far fields are best viewed as that due to two dipoles, of the magnetic and electric type, with strength and orientation depending on how the via hole is excited. It is shown that the two dipole model is sufficient to find the radiation from a 1mm diameter via hole at a frequency up to 8 GHz. Of further interest is how the choice of via hole dimensions affects the dipole moments and the near fields solved earlier are a key to this understanding.