The future of inkjet processes<br>for PCB manufacturing

Legend ink is already up and running, solder mask is on the way, but etch resist for inkjet is not yet available for production scale PCBs, and conductives, the ultimate goal. AT&S is looking for the ultimate low cost PCB, and here they are pursuing new technologies, they do not to buy in a fixed system, but to devise one that suits them. Ink Print Head Machine and the Process are the key elements. The application has been identified, the business plan and cost calculation has been done, now they are tackling the technical problems, partnering with Printed Electronics Ltd. They meet every 1-2 weeks, and have short communication paths. An ink formulation is almost in place; they have to integrate a machine, the process will be developed by PEL, and AT&S will be the beta site for it. Dr. Steve Jones spoke on behalf of Printed Electronic Industries, of Cambridge. PEL now have an industrial process – it has been designed to work in a rugged environment, can print at industrial speeds, this is an iTi machine, which can take 6 different heads, Xaar heads mainly, for high speed printing with a small number of heads. Using high speed photography, they can see how the ink is leaving the head and how it is forming on the substrate, PEL know the PCB business and thus are a suitable partner for AT&S. They have an etch resist, and the initial work looks most encouraging. The future includes nano-conductive inks, multilayer dielectronic structures, and components. A panel per second is the goal. Uwe Altmann from Orbotech said Orbothech is now firmly into the inkjet field, and DoD (drop on demand) is the future, a process which Uwe described. Drops come in a continuous stream, the viscosity is controlled by temperature, (solvent evaporation), and the system boasts lower consumable and maintenance costs than before. Inkjet resolution is 1440 dpi. UV inks are attractive, no solvents, and with them you can create 3D structures. They also cure easily and quickly. The advantages of inkjet versus screen were clearly shown, and probably already well known. Conventional solder mask process steps against ink jet application were also shown, and here the speed of UV assists greatly in the drying process for legend inks. Legend inks exist now, to come will be etch resists, chemical milling, solder masks and solder dams using inks only. Conformal masks and conductives are also in the future. They have done some work on 100µm lines and spaces using inkjet. They need 1440 dpi for this. Gregory Blake from Printar’s US operation talked about advanced inkjet technology. Cost pressures are enormous on PCB production, so inkjet technology offers potentially attractive cost advantages for certain kinds of circuitry, but not all. Printar have 50 systems installed worldwide, and have 70 staff employed, dedicated to inkjet and nothing else. Having their ink approved is a key element here. Legend printing was the start, and here they have been successful; the advantages of inkjet v screen printing were underlined once more, including the availability of ‘serialisation’, of on-line numbering. Gregory highlighted some of the problems with conventional solder masks, and the potential advantages of ink jet solder mask; here inkjet replaces lots of machines, people, and saves a lot of time – a 2 minute cycle time against 133 minutes. One the face of it, it sounds good, but one must ask the question, given the need for approvals and the meeting of specifications - will it work with all solder masks? Ashok Sridhar from the University of Twente in The Netherlands is working on his PhD researching the interface between inkjet printed semi-conducting components and the substrates used in the PCB industry. His technical paper covered inkjet printing using functional inks such as PEDOT and a silver nano-particle ink, on pcb substrates and glass. They have characterised adhesion between printed layer and substrate. Using a Microfab JetLab4 inkjet printer, Mr. Sridhar clearly showed how the droplet size can be strongly affected by temperature and humidity. They have also used a silver ink on FR4. The problems and challenges are not a few. One is the absorption of the ink into the substrate, so they have measured this with an autoperosity measurement system, and they can see how problems might occur where two lines meet inside the substrate. Future work looks extensive, and the results so far look most encouraging. Rob Haslett is the CEO of Patterning Technologies Limited showed the shopping list that is required: a system that produces high quality at low cost, is fast, handles complex materials, in small batch sizes and with full traceability. Here inkjet technology can be of real assistance. If offers minimal set up time, minimal operator skills, fewer processes, lower cost, and with variable data. Getting rid of the wet processing is desirable, but how do you go down that route? With inkjet there are many parameters – ink, print heads, print platforms, and print strategy - they all have to be balanced. Factors to be considered are adhesion-surface wetting; viscosity and jetability, coalescence; resolution, reliability, speed and accuracy. There is 10 years experience at PTL, a technical consultancy that is experienced in the bio-medical and flat panel displays, and etching applications as well as PCB. They have partnered with KLG in Germany, who know all about X Y positioning, and together they have launched JetRite® as a system. PTL are looking at the marketing, KLG are producing the printing platform, and the manufacturing and sales and support, which is now in place. Unsurprisingly, the printing platform is very similar to a drilling machine. PTL are providing the printing head, the ink, managing the suppliers, and notifying the end users. So far they have a machine that has one printing speed at very high quality – a 17 second print time. With a 14picolitre drop size, they are obtaining 100 micron lines and spaces. There are two self-aligning print heads, one for white and one for yellow (legend inks). It is a compatible partnership and doubtless destined for great things - interesting to see how his company has arrived at the same place, but via a rather different route.