Issue link: https://iconnect007.uberflip.com/i/1527952
62 PCB007 MAGAZINE I OCTOBER 2024 e beauty is that the LMI is key to the whole process. e palladium that's created is a very dense coating. It is a very unique approach. It touches atom to atom and is several atoms thick. It is semi-aqueous so it wets well, getting down into the small micro-topography that would be le behind if you had etched copper foil. e chemical bond to the copper foil is not significant, roughly only a 10% contribution to the total adhesion. Your adhesion comes from being able to coat on that micro-topography and plate it up with the right electroless. You get very good adhesion for a variety of differ- ent materials. Nolan: If the chemical bond to copper is about a 10% contributor to adhesion, how much does the palladium affect adhesion? With palladium there is no real chemical adhe- sion that takes place as the laminate is already cured, but it is important for adhesion in the subsequent processing. Nolan: It sounds like putting down the LMI almost works like a primer before painting. In a sense, yes. What you are doing is using a much denser catalyst to allow for a stronger reaction in electroless copper, getting much better adhesion because the palladium is already there. When you look at LMI in con- trast to a process like mSAP that uses thinner foils, A-SAP allows for a much thinner base metal. With a thin foil, the best you'll get is maybe 1.5 microns. In Asia, typically, you'll see 3–5-micron foils. With A-SAP, you will create a base electroless copper that's only about two- tenths of a micron. It's really thin and works quite well from that aspect. Nolan: What are some applications where this comes into play? LMI is used in applications that require finer circuits. From what we've seen and heard, there is more of a yield issue with thin foils once you cross the 25–30-micron barrier for lines. Liquid metal link doesn't really have any barrier. It will deposit, and you can lay down extremely fine features. I've been able to cre- ate 12.5-micron features easily. Of course, you must have all the technology that goes along with that. You must have the right photoli- thography tool, be able to make small micro- vias, have excellent registration, and so on. Once you go below 10 microns, the challenge becomes keeping those lines from moving. Nolan: John, does this work in the other direction with increased performance in adhesion? Can you go back to more mainstream dimensions and get better yield, for example? You can, but the bigger issues are designs that require very tightly controlled impedance structures or with a lot of RF features. ey don't want to have the lossiness that we see when you generate a normal subtractively- etched trace that is ragged on the edge. Every- thing you hear from RF designers is that they don't like that roughness. ey want some- thing that's extremely smooth. When you look at a trace that's been created with LMI technol- ogy, it has very straight sidewalls which helps John Johnson