Slash Sheets and Material Selection

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In a recent I-Connect007 survey to PCB designers, about one third of respondents said they consult IPC's so-called slash sheets, such as IPC-4101/126, that contain a variety of information about PCB materials. But many designers say these specs don't contain enough information. Some ask their fabricator to pick a material, and still others say, "It's an RF board, and I always use supplier X for RF." What's the best process for selecting your PCB materials?

Doug Sober helped pioneer the development of IPC's first slash sheets in 1996 for IPC-4101 Specification for Base Materials for Rigid and Multilayer Printed Boards and we asked him to discuss slash sheets—what they are, what they are not, and why PCB designers might benefit from an IPC materials guide developed specifically for designers.

Andy Shaughnessy: Doug, let's start with your work with IPC and slash sheet development.

Doug Sober: I started in the laminate and prepreg business in 1978 for General Electric and was sent to my first IPC meeting in 1980. I got heavily involved right away with the task groups regarding specifications for laminates, prepregs, copper foils, glass fabric, resin coated foil, etc. The first standard we did was IPC-4101, but it did not just come out of thin air. We had a document from the military called MIL-S-13949H that had requirements for base materials. The requirements were physical such as flex strength and peel strength, electrical such as Dk and Df, thermal such as Tg and solder float, and environmental such as moisture absorption and fungus resistance. After IPC-4101 was all finished, it had specification sheets for simple FR-4s and polyimide base materials of various types.

The military had these specification sheets which described specific base materials and, as laminate and prepreg producers, we had to qualify our products to the requirements of the sheets. With specification sheet 21, for example, a bevy of lab tests proved that we met the requirements. Then the Defense Electronics Supply Center (DESC) would list our product by commercial name on their qualified product list (QPL). For example, Westinghouse's FR-4 product 65M38 as listed on the QPL for specification sheet 21. Once a year, Lowell Sherman or Dave Corbett from DESC came to audit each base material supplier. When the 3-11 subcommittee created IPC-4101, we duplicated MIL-S-13949 because we wanted the military to sign off on it, discontinue their document, and use IPC-4101 in its place. In 1996, with the help of Dave Bergman negotiating with the military higher-ups, IPC-4101 was launched and Mil-S-13949 was discontinued.

To read this entire conversation, which appeared in the May 2023 issue of Design007 Magazine, click here.