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34 PCB007 MAGAZINE I FEBRUARY 2020 in iron chloride or copper chloride and alkali stripping. It strips in flakes and works in the same etching and stripping lines that are used with dry film. We have also added a new series of materials that are soluble in the stripping so- lution for some industries where that is impor- tant. I have to admit that the main application today is not in PCB, but more in products like chemical milling, photochemical machining, decorative etching of metals, etc. It's a good market that is developing nicely. Starkey: Is this an acid-etch resist? Louwet: Yes, both inks are for acid-etch. The newest materials in our portfolio are plating resists. There's an interest from the market to do selective ENIG plating. For that reason, they cover part of the PCB with a plating resist through the ENIG process and then strip away the resist for applying a different finish, such as OSP on the rest of the board. Starkey: We're not looking for critical edge definition; effectively, we're using the solder mask as the pattern-defining resist, but we're using your plating resist to mask the already- patterned areas that we don't want to plate with ENIG. Louwet: Exactly. It's not an easy process (Fig- ure 1)! Starkey: You have to resist the ENIG process, which can be very aggressive chemistry, and then strip the plating resist without damaging the solder mask? Louwet: We are succeeding in that, but the challenge has been to find the right balance. On the side of the solder mask ink, we have commercialized our green solder mask, SMG01. Last year, we put in the hard work to optimize the ecosystem, including what kind of pre-treat- ments can be used, which printing and curing Figure 1: DiPaMAT PR01 plating resist.

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