1 Scope

1.1 These requirements apply to single layer, multilayer, and multilayer rigid-flex composite flexible materials interconnect printed wiring board constructions (FMIC’s) for use as components in flexible, flex-to-install, and/or rigid, and multilayer rigid-flex composite applications with and without stiffener and adhesive materials in devices or appliances.

1.2 Together with the Standards mentioned in the Supplementary Test Procedures, Section 3, these requirements provide data with respect to the physical, electrical, flammability, thermal, and other properties of the FMIC under consideration and are intended to provide guidance to the fabricator, end product manufacturer, safety engineers and other interested parties.

1.3 Compliance with these requirements does not indicate the product is acceptable for use as a component of an end product without further investigation.

1.4 The single layer, and multilayer, flexible, flex-to-install, and multilayer rigid-flex composite constructions addressed by these requirements consist of conductors affixed to base material, with mid-board interconnections, and cover materials.

1.5 The suitability of additional stiffener and adhesive materials, not evaluated in accordance with Stiffener and adhesive (external bonding) materials, 10, the Stiffener bond strength test, 12, and Flammability tests, 15, are subject to the applicable end-use product construction and performance requirements. See Additional stiffener and adhesive (external bonding) materials, 12, for marking requirements for FMIC’s provided with additional stiffener and adhesive materials not investigated.

1.6 The requirements for rigid printed wiring boards, not utilizing flexible materials, are in the Standard for Printed Wiring Boards, UL 796.

Summary of Topics

This revision of ANSI/UL 796F dated November 17, 2025 includes the following:

– Clarification of FMIC construction type versus sub-category application; 1.1, 1.4, 1.6, and 5.5 – 5.8.

– Updates to multiple terms and definitions in Glossary, Section 6; 6.4, 6.14, 6.15, 6.17, 6.47, 6.80 – 6.82, 6.87, 6.101, 6.117, 6.134 (deleted), 6.135, 6.137, 6.143, 6.148, 6.162, and 6.174.

– Clarification of Polyimide ANSI-like flammability program requirements in 8.2; 8.2.2

– Clarification of metal requirements for conductors; 8.4.5, 8.4.8 – 8.4.12, and 8.4.24.

– Clarification of multilayer constructions and silver conductors requirements in 8.4; 8.4.19, 8.4.22, and 8.4.25.

– Clarification of conductive coin size determination in 8.4.22A.

– Clarification of flammability testing for cover material, solder resist, and plugged hole materials clarification in Sections 8.6, 8.7, and 8.8; 8.6.3, 8.7.4, 8.7.11, and 8.8.2.

– Clarification of HDI material in 8.9.2 to include reference to build-up materials; 8.9.2, 8.9.11, and Table 8.6 (deleted).

– Clarification of alternate stiffener requirements in Section 8.10; 8.10.2, 8.10.3, and 8.10.11.

– Clarification of construction type and sub-category application in FMIC Constructions, Parameter Profile Indices and Tests in Sections 9, 11, and 12; 9.1.3 – 9.1.7, 9.1.9, 9.1.10 (deleted), 9.3.1, 9.3.2, 9.3.5, 9.3.8, Section 9.3A, 9.4.2, 9.4.5, 9.4.6, 9.6.2, 9.6.5A, 9.6.6, 9.7.2, 9.7.5A, 9.7.6, 9.8.2, 9.8.4A, Section 9.9 (deleted), 9.10.2 – 9.10.4A, 9.11.2 – 9.11.7, 11.1.2, 11.3.2, 11.5.7, 12.1.3.1.6, 12.1.3.2.1, 12.1.3.2.3, 12.1.3.3.1 – 12.1.3.3.5, 12.1.6.8, 12.4.3.6, Figure 12.8, 12.8.3.1, 12.9.2.1, 12.10.2.1, 12.11.2.1, 12.11.3.5, 12.12.1.1, Figure 12.14, 12.12.3.3, 12.12.3.7, 12.12.3.8, 12.12.3.10, 12.13.1.1, 12.13.3.11, 12.14.3.6, Section 13.5.