Selective Solder Mask Deposition by Inkjet
At IPC APEX EXPO 2019, I spoke with Joost Valeton, product manager for PiXDRO inkjet printing equipment with Meyer Burger, about their newly configured inkjet printer for PCB applications, and bringing awareness to opportunities using selective solder mask deposition.
Pete Starkey: I’m here at IPC APEX EXPO 2019 in San Diego, California, with Joost Valeton from Meyer Burger. Joost, you're launching a new inkjet printer. Is it specifically aimed at the PCB market?
Joost Valeton: In this configuration, yes.
Starkey: Can you give us a brief description of the equipment?
Valeton: Absolutely. At Meyer Burger, we have our JETx platform for volume production. For this specific application—solder mask printing for rigid PCBs—we have defined a configuration for an 18-inch x 24-inch panel size. It comes with the number of print heads and the ink supply we believe is required for this application. It's a new configuration from our well-established product family (Figure 1).
Figure 1: PiXDRO JETx-M, an IPC APEX EXPO 2019 award-winning product.
Starkey: So, this equipment is not new to Meyer Burger. You are experts in producing inkjet equipment and have chosen the characteristics of this particular machine to suit printed circuit application?
Valeton: Exactly. We identified the benefits of doing digital additive manufacturing production of solder mask, and we've looked at the requirements for such a tool in terms of resolution, feature sizes, product size, etc. We've come up with this configuration as a first launching tool in this market. This solution is suited for fast product adjustments and prototyping for PCB manufacturers serving high-tech industries, such as automotive, medical, and aerospace.
Starkey: From your position, are you an equipment supplier and have you cooperated with manufacturers of the consumable materials?
Valeton: Yes. The ink is a huge part of course. As you know, solder mask has specific requirements for the material it has to conform to—not just in color—and for that reason, we work with material suppliers. We mostly work with Agfa from Belgium—who is very close to us, which is convenient—to develop so that we match the performance of the print heads, which for us are also a consumable. We don't build those ourselves; we integrate them. In this case, we have integrated print heads of a well-known supplier. Together with Agfa, we have developed a formulation that matches very well with the characteristics of these print heads.
Starkey: I have been following the development of the market for inkjet printing technology in printed circuit manufacturing for many years. I think that the most difficult objective to realize has been solder mask mainly because solder mask is subject to so many qualifications and standards, customer, and OEM approvals. In my experience, two properties have tended to mutually exclusive. If a formulation were to jet successfully, it would be unlikely to meet qualification requirements. Meanwhile, if it were to meet qualification requirements, it would be unlikely to jet successfully. In the past, a lot of very optimistic claims had been made and then not realized, which made the market a bit apprehensive. But I feel that in the last five years, we've seen a gradual building of confidence in this technology. We have seen several inks reach the stage both of being processable with the equipment and of qualifying to the acceptance standards.
Valeton: Print-head technology has evolved enormously in recent years. Now, with the emergence of silicon MEMS print-head technology, we are finally getting the performance required for demanding applications like solder mask. You're absolutely right that material development has taken a large leap, and we now have a material that can be printed very well and also meets IPC standards on outgassing and all others. The new PiXDRO JETx-M inkjet printer offers unbeatable benefits very specific to these stringent requirements, as smallest droplets of two pL for best-in-class resolution and accuracy eliminate photo and development processes. PiXDRO JETx-M is also environmentally friendly, drastically reducing energy consumption and chemical waste while also conserving water usage (Figure 2).
Figure 2: PiXDRO solder mask best-in-class with smallest droplets.
Starkey: Now that I have the opportunity to see some examples of PCBs that have been coated with solder mask using your equipment, perhaps I had been a little complacent in presuming that I understood the current state-of-the-art technology. I've seen examples where you can selectively print in various areas of the PCB while some areas have been left uncoated, with various thicknesses for different purposes, or very fine and high-resolution features.
Valeton: Of course, the benefit of an additive process is the ability to apply the material only where you need it to be. Traditional processes would cover the entire board and remove it just where you don't want it to be. In an additive process, you can apply only where you want it, realizing substantial material savings. As a further bonus of inkjet, by changing the resolution, you can apply various amounts of material across a board in a single print job. For example, if you have a high-voltage application with a high breakdown voltage requirement for your solder mask, you can do that as opposed to the opportunity to save material by printing on other parts of the board where you don't have such stringent requirements. In older techniques, you would need to coat a uniform thickness all over the board (Figure 3).
Furthermore, it gives new possibilities where also I think the industry needs to get an understanding of what this new technology can mean for them such as including different functionalities with a QR code in the solder mask layer for product tracking. Before, it required a separate step because it was not a digital technique. You could not apply it. You would apply solder mask over the entire board so you couldn't even do it in that respect.
Figure 3: Selective deposition of solder mask.
Starkey: I’ve enjoyed listening to what you've been saying and seeing some examples of what you have been able to achieve with this equipment and the materials that you've effectively helped develop. It's opened up a whole new area of thinking for me in terms of realizing what is achievable by not presuming, “This is the way we've always done it, so this is the way we'll always do it.”
Valeton: And that kind of change in thinking is what we need to push into the market this vanguard technology until everybody starts understanding, including making sure that designers recognize the possibilities offered by our inkjet solder mask printing solution.
Starkey: In my experience, most designers only know about putting solder mask down in the places where they traditionally put solder mask down—things like the benefits of inkjets being able to stop mask going into holes where you don't want it. The ability to deposit selectively in different areas and thicknesses is where we need to bring it to their attention. If I were a designer, I would produce my printed circuit layout and as part of that data package and supply you with the solder mask information. Have you spoken with the suppliers of the CAD systems to make them aware of what you can achieve with the equipment such that they can build those features and facilities into their CAD software? Or if you want to do selective deposition of different thicknesses, is that something that you have to write your own program to achieve, or can that be part of the manufacturing data package?
Valeton: It would have to be part of the entire package. Whereas the designer defines an image, the printer will always print a bitmap. One thing we must be careful about is if the designer makes a very small feature in the rasterizing process to transfer that image to a bitmap, we must ensure that it does not get lost because if you have a very thin dam, it has to be always there. And that's a part we have taken care of in working together with software companies that have these kinds of programs. Hopefully, it points towards a completely integrated CAD/CAM interface where the designers say, “This design is going to be printed with an inkjet printer,” and that program knows exactly where to extract specific information. Then, it's automatically sent to the printer. The printer knows from a barcode on the PCB that it must print a particular product with a certain process, so there's little to no operator intervention needed as long as the CAD designer knows how to output it and the CAD suite offers that possibility.
Starkey: This opens up a whole new opportunity for looking at things from a slightly different angle. Forget about the standard practice of the past, and look at what opportunity exists for the future.
Valeton: Absolutely. Generally, I think you will see a change in many applications from an analog to a digital technique. We see that the PCB industry tends to be somewhat conservative in this, and changes may be slow. But once we get more and more people convinced of the possibilities, then we have a very good position to work from.
Starkey: If we can help in bringing the potential capability of this sort of system to the attention of people, then you're achieving something.
Valeton: Also, from the customer perspective, they may have to understand and hopefully accept that the product may look slightly different, but that doesn't mean the functionality is any different.
Starkey: In many cases, I think the functionality will be improved.
Valeton: Yes, and the cost will be reduced. One of the many comments we get from the customer’s OEM clients is, “Yes, but it is different,” and that's something that we need to manage. That is the sort of thinking that we need to change.
Starkey: Change people's perception of it. Get people not to look back but to look forward and see what can be achieved.
Valeton: Absolutely. Thanks, Pete.
Starkey: Thank you, Joost. It has been a very interesting conversation.