Destructive Physical Analysis (DPA) Testing for Crystals

Microelectronic devices, assemblies and systems requiring stable clock signals utilize crystals as timing devices. The primary crystal blank material used for oscillators and resonators is quartz. Quartz is a piezoelectric material that resonates under an applied electric field. Crystal shape or geometry as well as orientation are varied to achieve a desired frequency value required for the application. The benefit of a crystal resonator relative to RLC circuits is the high Q-value, an essential property for many systems. Metal electrodes are deposited onto the crystal surface to orient the electrical field. The electrode/crystal metal is then used as attachment contacts for support pins that suspend the resonator within the package. The mass of the electrode metal influences the resonant frequency. Fine tuning of a crystal is achieved by laser trimming or deposition referred to as mass loading, depending on design. Due to the wide-ranging applications multiple package construction configurations exist.

Variations in environmental conditions, including vibrations, will influence the resonant frequency. Crystal packages are primarily hermetic to mitigate these environmental factures. Various construction designs that form hermetic packages would include metal and ceramic materials with glass bead-sealed pins and seam-welded or solder-sealed lids. Aerospace, military and automotive systems use hermetic packages that are subject to qualification requirements, including military performance specifications and DPA methods, to ensure performance and reliability. Crystal device construction variations require specific test methods in a DPA test flow. Crystals are tested to MIL-STD-1580 Requirement 12 for DPA and qualification requirements of MIL-STD-202 per MIL-PRF-3098.

Crystals included in microcircuits or oscillators impose additional testing requirements within the context of those assemblies.