Issue link: https://iconnect007.uberflip.com/i/1498723
12 DESIGN007 MAGAZINE I MAY 2023 ished, it had specification sheets for simple FR-4s and polyimide base materials of various types. e 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 exam- ple, a bevy of lab tests proved that we met the requirements. en 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 speci- fication sheet 21. Once a year, Lowell Sherman or Dave Corbett from DESC came to audit each base material supplier. When the 3-11 subcom- mittee 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. In the IPC-4101, a simple FR-4 would also be qualified to specification sheet 21. It was called out the same as it was in MIL-S-13949 as IPC-4101/21. is is how the industry got to calling each specification sheet a "slash" sheet /24, /99, /126 and so forth. But a slash sheet, as we called it, was never intended to be a design guide. It is only there to make mini- mum requirements for base materials so each could be bought and sold. Each specification sheet had some generic chemistry commonal- ity in the header section with other descriptive words. For example, IPC-4101/21 would say "majority epoxy resin" no filler, woven fiber- glass reinforcement and a minimum Tg. So, when you hear, "With slash sheets, it's hard for the designers to decide what to use," remember that's not what it was intended for. Once a designer has the product they want in terms of the characteristics, it goes through the purchasing department which uses that to make their purchases. We use the terms "slash sheet" and "specification sheet" interchangeably. For a specification sheet like 4101/126, there might be 10 to 20 different laminate and pre- preg suppliers that have materials to fit that. You should be able to buy those and they would reasonably interchange with one another. Now, since we have so many low-Dk , low-Df, and ultra-high-Tg materials, I think it's time for us to create a design guide for the rigid materials that come from 4101. at is my thought process having looked at what the 3-11 Subcommittee has done since 1996. We have released a lot of base material specifications with specification sheets, but there should be a design guide to help the designers. We have design guides for flexible printed boards and high-speed/high-frequency pr inted boards. There should be one for standard rigid boards. is concept would make a really good proj- ect: Put together a Tiger Team consisting of 6 to 8 designers along with some base materials experts and, using one of those other design guides as a pattern, we could devise a design guide for these materials fairly easily. Doug Sober