Printing as an Alternative Manufacturing Process for Printed Circuit Boards

Abstract

The use of printing techniques as a manufacturing process for physical products is well established in the form of 3D rapid prototyping printing systems. Additive methods of manufacturing of this form are being considered as environmentally friendly as less material is wasted and the number of processes needed for the finished product is reduced. Printed manufacturing is also being established in the electronics industries as conductive inks and electrical conductive adhesives have been developed (Gomatam & Mittal 2008). This has allowed for the creation of printed circuit boards, on various substrates using screen printing methods and developments towards the use of desktop printing for circuit design (Ryan & Lewis 2007). Coupled with this, a range of printing methods can now be used to produce components such as transistors, diodes, sensors and RFID tags, and batteries (www.plasticelectronics.org 2009). Mass printing processes fall into approximately 6 main types (Table 1), with the properties of each analysed in Table 2. All of the processes excluding inkjet printing require some form of stencil or impression plate on which the required pattern is formed. Ink is either forced through the stencil in the case of screen printing, or is held within the impression plate for other processes. The ink is deposited onto the substrate surface when the impression plate and substrate come into contact. The means of inking the plates vary depending on the process. Printing systems offer high resolution and speeds, and are thus suited to Mass manufacture. The resolution of the patterns formed depend on the process and the substrate, with roller based systems being able to repeatedly print lines at 50μm, screen printing to approximately 75μm, and pad printing to 10μm. The speed of printing ranges from 50 m/min to 250m/min using the roller based lithography, rotogravure and flexography methods, with screen, pad and inkjet printing up to 75K units an hour on high speed machines. Printing processes by their very nature apply thin layers of ink/resin onto a substrate (16 microns) (Raghu et al 2008), which can be built up to form the required shape or pattern. This inherently involves the over printing of existing patterns to develop the required thicknesses. Hence two problems occur, the alignment of the substrate for subsequent printing, and the amount of time required to continually over print to get a defined thickness. For rapid prototype systems, the alignment is held by keeping the component in