MacDermid’s Research Team Talks New Cyanide-free Immersion Gold at SMTAI
While at SMTAI in Chicago recently, I met with two of MacDermid’s research team, Jun Nable, research project manager, who has been with MacDermid since 2007, and Cherry Santos, associate research fellow responsible for formulation work for metal plating solutions. We talked about the posters they were presenting and why they chose SMTAI.
Patty Goldman: I understand that you both presented posters here at SMTA, so why don’t you tell us a little about them.
Jun Nable: The poster that I presented is about a new cyanide-free immersion gold that's suitable for PCB surface finishes. What makes this different is it is cyanide-free. It's more environmentally-friendly, it's easier to handle, and has the advantage of simplified operating parameters. The majority of conventional immersion gold in use right now contains cyanide. When you hear the word cyanide, you know it's toxic. We need to take special precautions when handling it.
Santos: And there are requirements for waste treatment.
Nable: Right, like waste permits and things like that. So, that's the conventional immersion gold generally in use in the industry. We are providing an alternative to that without compromising the performance of the surface finish.
Goldman: That's very important. There must be a lot of interest in cyanide-free. How thick is the final gold finish?
Nable: For ENIG purposes, the target is around two micro-inches. In terms of plating performance like plating rate, the cyanide-free immersion gold is comparable to the conventional immersion gold. It's comparable, if not better in solderability, appearance and uniformity.
Goldman: And how about the controls and lifetime of the bath, things like that?
Nable: I mentioned earlier about simplifying the operating parameters. The advantage of this cyanide-free immersion gold is we can operate at 40°C. Conventional immersion gold operates at a much higher temperature of 80°C. Also the pH is near neutral for this cyanide-free bath. So, it's much more simplified. Not to mention the energy savings as well, by not having to get to that high temperature.
Goldman: That has got to be a nice selling point. A lot of people here are with EMS companies. Has there been a lot of interest in your new process?
Nable: There has been some interest. Every time you give an alternative that has new features, of course, it has to be further qualified.
Santos: There's always that skepticism with any new finish. It has to go through a rigorous qualification process.
Goldman: So, in order for a PCB fabricator to begin using this, it still has to be qualified by their customers?
Santos: Yes, it has to go to trial production and get OEM approval. The customer needs to assess the performance and ensure that it meets the specified standard for their target application. Does the alternative finish perform similarly or better than the current finish?
Goldman: That's a good reason to present it here, so they know what's new and coming down the road.
Nable: Exactly. We put it out there to show it to the industry and say, “Yes, we do have an alternative. If you're willing to work with us, come and talk to us in person.”
Goldman: That helps, especially if they ask their PCB supplier, "Could you use this?" I think that would be beneficial for you and MacDermid.
Nable: We've done our rigorous testing, but of course, everything can’t be done in our labs. We need to get out into the real world and qualify it there. That hasn't happened just yet, but there is interest and there have been talks, but in the very early stages.
Santos: We're in the stage of marketing it and letting the customer know the benefits and performance similarities with the existing cyanide-based finish.
Goldman: A chance to work with them and see what questions they have about it. About how long does it take to get the proper amount of thickness?
Nable: Just to give you a perspective, for ENIG applications it deposits about two micro-inches of gold in about ten minutes, which is similar to that with cyanide versions.
Goldman: So, it's not a time-saver, not that it would be, but with the reduced waste treatment, improved safety, and the lower temperature—these are all important things. And even their customers would be interested in the cyanide-free part, I would think.
Santos: Yes, because they pay a lot of money for the waste treatment, permit application, etc.
Goldman: We talk about value-add processes and, of course, waste treatment is not considered value-add. It's an extra expense. So, to reduce the extra expense is very important. And Cherry, you have your own poster?
Santos: Yes, I have a poster on immersion tin. Immersion tin is not a new process. It's been around for years and has been successfully used as a final finish for the automotive industry.
Goldman: Not as glamorous. Not as pretty as gold.
Santos: No (laughs). The challenge for immersion tin is the deterioration of solderability performance after heat treatment. As it goes through heat treatment, it loses thickness due to the formation of copper-tin intermetallic compound between the tin finish and the Cu metal substrate. For this to be solderable, there has to be a free tin layer left after the heat process because the copper-tin IMC has inferior solder wetting. We just listened to a talk that discussed the different final finishes, and there is no ideal finish. There is no perfect finish.
Goldman: There is no universal finish.
Santos: There is none that fits everything. It depends on the application, the end-use environment, which finish you need for a specific application. The talk also mentioned that there should be at least 0.1 micron of metallic tin after the reflow cycle, which is a pre-treatment process that the immersion tin goes through. So, that is exactly my poster: The reflow effect on the immersion tin solder wetting.
We also went to another talk given by George Milad about IPC thickness requirements. He mentioned that for the tin finish to be solderable after two reflow cycles, you need at least one micron of immersion tin to begin with to have free-tin at the end of the reflow cycle, so that it would still be solderable.
Goldman: And your immersion tin achieves that?
Santos: Yes. So, it's comparable to what competitors have.
Nable: This study also contributes to the understanding of how the immersion tin finish changes with thermal exposure. We wanted to dig a little bit deeper into the mechanism of how immersion tin changes.
Goldman: Surface finishes are of interest to the audience here.
Nable: Right. And that's what we do at MacDermid. We both work in the electronics solutions division and our projects particularly are more focused on final finish, surface finish type of projects. But we're not limited to that.
Goldman: Anything else going on?
Nable: I also want to share that I am a volunteer officer for our local chapter in Connecticut for SMTA, so this is really nice to be able to participate in SMTAI and meet people, and meet the other chapter officers as well. This is the international conference, so this is where all chapters might come together.
Santos: Jun is actually the president of the SMTA Connecticut chapter.
Nable: I am. We try to organize activities or meetings that would be of benefit and relevant to our members that we can all learn from. We get ideas from SMTAI, having these technical talks to gauge the current issues and level of interest in certain topics. We try to bring that back to our local chapter because not all of our members can come to SMTAI.
Santos: The venue of previous SMTA Connecticut chapter expo and forum is just five minutes’ walk from our Waterbury, Connecticut site and fairly accessible to all local members.
Goldman: I hear there are new acquisitions at MacDermid. You probably don't get involved in that. You certainly hear about it, but it probably has no effect on you. It's got to be an exciting time for MacDermid. You work for a great company.
Nable: Every day is exciting. All we know is also what’s been publicly announced. As far as technical people like us are concerned, before or after the announcements, it doesn't change our daily responsibilities. We still work on solving technical problems. We try to come up with innovative solutions for our customers.
Goldman: It doesn't change what you're doing. You might just have a broader audience later on. As researchers, do you get out in the field much to work with customers?
Nable: Not so much. On occasion, if needed, we do go out in the field to provide support.
Santos: It's mostly the process specialists that go into the field. Once in a while, if the formulator needs to be in the field, then we may be called upon.
Goldman: Now, when your new processes first go to a customer, will you go with them for the very first tests and all that?
Santos: If necessary, we do provide support. The process specialist takes over when the product goes to the field. Bringing a product to the field is a long process. It starts with the researcher working on the formulation. If the formula is ready for scale up, let’s say from a liter beaker to a 50-liter tank, the process specialist then becomes heavily involved. When we scale up at our Waterbury site, both researcher and process specialist work together. We assess the performance and resolve issues we encounter until we meet all the requirements. When the product is brought to the field, the process specialist already has an idea and background of the requirements, performance, etc.
Goldman: Thanks so much for your time, and best of luck with both of your projects going forward.
Nable: Thank you.