Beyond Prepreg: The Glassless ‘Revolution’

Estimated reading time: 2 minutes

As our industry rallies around the call to action for HDI and UHDI, we find unparalleled and myriad laminate options. This abundance is rivaled only by the question surrounding them: Can they measure up to the high technology packaging demands required in our near future? Unsurprisingly, recent developments in FR-4-esque materials for high-speed and high-density designs, as well as newer, glassless technology for replacing traditional glass-impregnated laminates and prepreg, are garnering much interest. I caught up with Alun Morgan, technology ambassador for Ventec International Group, to ask about the impending “glassless revolution” and how it’s poised to solve some of our manufacturing challenges.

Marcy LaRont: Alun, can you explain glassless epoxy filler? Is it liquid?

Alun Morgan: It's not liquid; it’s a rubber-like unreinforced dielectric material. The industry vernacular for this is bondply. It is a non-glass reinforced resin that can be delivered in two standard formats: resin-coated copper foil (RCC) or resin-coated film (RCF).

There are many ways of delivering resin into a circuit board. The standard way is to use prepreg, which is a resin-impregnated fiber, and usually a glass fabric. Another option is to screen-print the resin onto the printed circuit board material, which has been available for years. Then there is the bondply technique, which has a few specific advantages.

LaRont: We heard about this at a recent UHDI conference. Please explain bondply.

Morgan: It's a dielectric layer used in multilayer stackups where you want to build bonding in sequential layers. Imagine you have a circuit, and you want to make HDI layers on the outside with very thin dielectrics, 25–50 microns, just one or two mils. You take the board, which has copper on one side and laminate a layer of bondply onto it. In this case, that could be resin-coated copper foil. You form a pattern on the copper and laser drill through that layer to connect down to the layer beneath. You can build up layers that way, adding one layer after another. This is a standard technique for making multilayer, high density circuits, typically with microvias on the outside using such standard constructions as 2+4+2 or 2+8+2, etc. That is one area where these bondply films can be used and it is a standard method of forming thin layers.

Continue reading the rest of this interview which was originally published in the June 2024 issue of PCB007 Magazine.