The Chemical Connection: The Consequences of Additive Metallizing on Etching Steps
It’s Only Common Sense: Are You Really So Busy?
PCB UHDI technologist John Johnson of American Standard Circuits discusses the evolving landscape of electronics manufacturing and the critical role of innovation, specifically liquid metal ink technology, as an alternate process to traditional metallization in PCB fabrication to achieve ever finer features and tighter tolerances. The discussion highlights the benefits of reliability, efficiency, and yields as a tradeoff to any increased cost to run the process. As this technology becomes better understood and accepted, even sought out by customers and designers, John says there is a move toward mainstream incorporation.
Nolan Johnson: John, what is liquid metal ink technology?
John Johnson: It is a chemistry developed by LDQX (formerly Averatek) as part of its licensed solution for doing A-SAP™. Liquid Metal Ink (LMI™) is the heart of this process. The A-SAP process involves putting down a thin plating of electroless copper which forms the base of subsequent plate-ups for traces and so forth. You generate all your ultra-fine line circuitry with LMI. It is a non-aqueous substance that carries a palladium complex in solution. It can be coated through a dip method, a spray method, and other ways. At ASC, we use the dip method.
The beauty is that the LMI is key to the whole process. The 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 left behind if you had etched copper foil. The 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 different materials.
Nolan Johnson: If the chemical bond to copper is about a 10% contributor to adhesion, how much does the palladium affect adhesion?
John Johnson: With palladium there is no real chemical adhesion that takes place as the laminate is already cured, but it is important for adhesion in the subsequent processing.
To read this entire conversation, which appeared in the October 2024 issue of PCB007 Magazine, click here.
