4.1 The term reference as employed in this practice implies that both the glass and the metal of the reference glass-metal seal will be a standard reference material such as those supplied for other physical tests by the National Institute of Standards and Technology, or a secondary reference material whose sealing characteristics have been determined by seals to a standard reference material (see NIST Special Publication 260).4 Until standard reference materials for seals are established by the NIST, secondary reference materials may be agreed upon between producer and user.5

1.1 This practice covers procedures for preparing and testing reference glass-to-metal bead-seals for determining the magnitude of thermal expansion (or contraction) mismatch between the glass and metal. Tests are in accordance with Test Method F218 (2).

1.2 This practice applies to all glass-metal combinations, established or experimental, particularly those intended for electronic components.

1.3 The practical limit of the test in devising mismatch is approximately 300 ppm, above which the glass is likely to fracture.

1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.