Agfa on Revolutionary Inkjet Solder Mask Applications

Estimated reading time: 11 minutes

Van Dam: I like this QR code (Figure 3). It works—you can scan it with your phone! It is very difficult to make with the traditional solder mask process.

Louwet: This QR code is full copper with the soldermask printed on top, followed by nickel-gold finishing. If you do the nickel-gold process, it is important that the adhesion is good every time. You need to be able to guarantee 100% yield in that respect. We have quite good confidence.

Starkey: With UV curing, are there preferred wavelengths for your photoinitiators? I see exposure equipment now that has either a broad wavelength or a series of wavelengths with different peaks in various areas of the spectrum. Some will cure the surface, and others will provide a through-cure or guarantee a good cure against the surface, so you get good adhesion.

Louwet: It's all LED-curing. In some cases you use two wavelengths, like 395nm and 365nm, that you combine into one machine to achieve the surface cure and the through cure.

Starkey: Again, these are really important; the nickel-gold process is a very aggressive chemical process and can harm the solder resist and reduce its resistance at subsequent stages. If you consider this as a production process with good industry standard inkjet-printing machines, what sort of throughput could you expect?

Louwet: It all depends on the printer itself, and it comes down to the number of heads. For instance, we are working with a Chinese printer integrator. At the moment he's concentrating on mass production legend-ink printers. His next step is solder mask. What you see in China is that companies are replacing their complete screen-printing lines with inkjet. It's growing massively. The latest machines that they have for flex applications can do up to 400 panels per hour. So that's the kind of throughput that they're thinking of.

Starkey: Does inkjet solder mask have a future as a production process rather than just a prototyping process?

Louwet: Certainly. When I see how fast it goes with the legend ink in China, I’m convinced that it will. And there is a big pull from the market; it's not that you have to push this technology.

Starkey: The market has been waiting for it for a long time, maybe even 15 years. I think that the market has been promised products before they’ve been fully developed, perfected, or qualified. There have been so many false dawns and promises that have never been realized.

Louwet: The market is indeed waiting and pulling for some time. Also distributors and dealers are saying "Let's start selling this." We really have to slow them down.

Starkey: The worst thing you can do at this stage in the development is go too fast.

Van Dam: Absolutely. You have to study the whole process, and it takes time before we can fully go to the market.

Starkey: I think some suppliers have been guilty of being too eager to hit the market. They haven't fully resolved all of the problems or gained all of the knowledge, and then the process starts poorly and garners a bad reputation.

Van Dam: Agreed.

Starkey: You mentioned earlier your developments in etch resist. What's the situation there?

Louwet: We developed an ink for etching copper for inner- and outer layers. But that as a technology is not flying as well as we expected. Also from the hardware side, there's more interest in developing something first for solder mask rather than for etch resist. And for inner layers, LDI is progressing very fast and is becoming the accepted technology. So the window of opportunity for inkjet imaging of innerlayers is getting smaller.

But for etch resist there are still some very interesting applications, like decorative etching and chemical milling. We have several very nice projects and some good volumes.

Starkey: The chemical milling market has been around for a long time. It doesn’t have high visibility, but if you are a supplier of the right process into this industry, it can be a good market sector.

Louwet: Yes, so far we have great success with die cutting, embossing and decorative applications.

Van Dam: For cutting dies, inkjet is really interesting. If you use dry film, you must cover the whole surface just for a few lines! With inkjet you need only a small amount of ink, so it is the perfect method for this kind of product.

Starkey: Yes, I'm looking at a stainless steel die (Figure 4), which is in three dimensions and the actual cutting edges are standing a millimeter above the surface. So the pattern has been defined by inkjet printing, and then by etching. If you had to make that tool by machining, that would be very expensive!

Louwet: Yes, and those types of companies may make hundreds of different designs on a weekly or monthly basis. For them, the digital way of working is very important.

Van Dam: Metal decoration is also interesting. For instance, in China you have the decorated elevator doors, that also can be done with an inkjet etch resist. With all those different designs, it's great to have the digital solution.

Louwet: Next to this, we have also a plating resist which is a kind of derivative of our etch resist. In this instance we’re not talking about pattern plating as such. It is used in the post processing, in the nickel gold finishing. For some boards, they want to have, for instance, nickel-gold here, but over there they want OSP or something else. So it's an ink that is printed to protect that part while you do the nickel-gold on the other part. Then you strip the ink, and put the OSP on the remaining areas.

Starkey: Now I understand. You're not really using the resist to define the pattern. You're using it to protect areas of the pattern. The solder resist has already defined the pattern that you're going to plate.

Louwet:  Yes. It's also different from just printing on copper, because now you have not only to strip from the copper, but also from the solder mask. So you need a different ink that can be removed without damaging the mask.

Starkey: I have learned a lot, Mariana and Frank. Thank you very much for your very clear answers to my questions.

Van Dam: Thank you, Pete.

Louwet: It has been a pleasure.

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