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24 The PCB Magazine • February 2017 INDUSTRY 4.0—INKJET TECHNOLOGY IS CHANGING THE WORLD OF PCB MANUFACTURING Utilizing state of the art digital inkjet print- ing for the application of solder mask on PCB boards, the number of process steps can be re- duced: 1. Pre-treatment of the PCB 2. Digital inkjet printing including in-situ UV curing 3. Post cure The benefits of this simplified manufactur- ing process are obvious. Besides the reduction in required capital equipment and associated la- bor, the digital process also significantly reduces the use of process chemicals and therefore also the related handling and disposal cost. Overall, the environmental benefits are enormous. Last but not least is the reduction in manufacturing turn-around time—an important asset in to- day's fast moving electronics business. Unique Characteristics of Inkjet Inkjet technology is widely used in homes and offices all over the world for traditional printing applications. Although the fundamen- tal concept of modern industrial inkjet applica- tions is comparable to those printers, there are significant differences. Industrial use of inkjet technology is characterized to a large degree by the type of materials which are deposited. In- stead of traditional ink, materials such as resists, adhesives, conductive inks, polymers and their likes are deposited. Inkjet is a selective coating technology. This means that material is only deposited where it is needed. In the case of solder mask printing, this not only reduces material consumption, but also avoids solder mask material in via holes and other areas where it is difficult to remove or simply not desired. Flushing uncured solder mask material from high aspect ratio holes in the development step is a known challenge in the PCB industry and is completely avoided by inkjet printing. The use of inkjet technology to directly pat- tern solder mask material renders the use of a photo-lithography patterning process unnec- essary. Hence, post exposure development be- comes obsolete as well—a great benefit as the risk of removing small solder dams between IC contacts during this step is completely elimi- nated. Another unique characteristic of inkjet is its flexibility. Not only can it cope with differ- ent surfaces, but it also enables the creation of different surface finishes. In addition, different layer thicknesses can be accomplished and even different materials can be deposited. The digital nature of inkjet technology also offers critical benefits in regards to pattern alignment and scaling: The digital print image can not only be accurately aligned to the un- derlying pattern, it can also be scaled as needed. Especially in tough manufacturing conditions with varying process requirements, this flexibil- ity is critical for cost efficient production. Figure 2: The process flow when using a digital inkjet printer to directly apply the patterned solder mask. Figure 3: Example of a board with inkjet printed solder mask layer.