Material Matters and Tribal Knowledge

Estimated reading time: 1 minute

At a recent IPC Laminate/Prepreg Materials Subcommittee meeting, I made two observations: It was very well-chaired and managed, and despite a full attendance of very knowledgeable materials experts, none could remember the rationale for several of the specification sheet descriptions—slash sheets—that comprise IPC-4101E, “Specification for Base Materials for Rigid and Multilayer Printed Boards.”

The thought naturally followed that if a comprehensive cross-section of materials experts struggled with this, what hope do PCB designers have of making sense of it?

It was a revelation to learn at a previous materials subcommittee that the headings for each specification sheet do not form part of the specification. These headings include reference definitions for the material, including any reinforcements, resin systems, flame retardants, and fillers that may be used, as well as its other known identifications and the glass transition temperature. However, the requirements for the material are solely defined by the ensuing specific line items within the specification sheets. Bearing in mind that the specification sheets are organized according to the reinforcement type, resin system, and/or construction—although these do not form part of the specification requirements—one could be forgiven for wondering what value this classification system has.

Hypothetically, it would be possible for a materials manufacturer supplying a glass-reinforced polyimide laminate material, which would ordinarily be classified as IPC-4101/40, as an IPC-4101/126 material which would ordinarily be classified as an epoxy woven-glass material. There would be nothing to stop this from happening if the material satisfies the specification sheet requirements. Clearly absurd, but possible under the classification system.

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