Military Conformal Coating Testing

MIL-I-46058C, Amendment 7: Military Specification for Insulating Compound, Electrical (For Coating Printed Circuit Assemblies)

This military standard establishes qualification and conformance requirements for conformal coatings and determines which are suitable for application to printed circuit assemblies by dipping, brushing, spraying, or vacuum deposition. The status of this standard is “inactive for new design” however one can still perform testing and if successful be placed on the Qualified Products List (QPL). This list is maintained since all military manufacturers must select and use coatings from this list.

This standard outlines the qualification, retention of qualification, and quality conformance testing for a conformal coating which is intended to be listed on the Defense Logistics Agency (DLA) Qualified Products List (QPL). The conformal coating manufacturer must submit the appropriate form 19M which DLA will receive and issue a reference number. Once this is received the manufacturer will select an approved laboratory which has been audited by DLA. The coated specimens are sent to the laboratory and testing is conducted based on manufacturers submission:

  • Initial Qualification: A coating which is newly formulated and being tested for the first time and must meet the tests listed in Table I of MIL-I-46058C (page 5).
  • Retention of Qualification: In order to retain qualification the coating manufacturer shall forward reports consisting of summary of results for Groups A and B indicating number of lots either passing and/or failing and Group C indicating the number and mode of failure. This is to be report every 24 months to the qualifying activity (DLA).
  • Note: If a non-conformance is found and no corrective action is taken or deemed acceptable by DLA then the governing agency may take action to remove the product from the QPL.

  • Group A Inspection is to be performed on each lot per Table II of MIL-I-46058C (page 6).
  • Group B Inspection is to be performed on a coating which meets Group A and is to be tested in the order shown in Table III of the MIL-I-46058C (page 7) and testing shall be conducted from one production lot every 12 months.
  • Group C Inspection is to be performed on a coating which meets Group A and B and is to be tested per Table IV of the MIL-I-46058C (page 7) and testing shall be conducted from one production lot every 24 months.

Test substrates consist of glass specimens, tin panels, bare laminate, and y-patterns (either with copper or tin-lead finish). The qualification table outlines the specimens used for each test and section 4.7 (page 8) details how to prepare the test specimens prior to coating and testing. One should keep in mind that some testing results need to be obtained prior to coating.
There are five conformal coating types AR (Acrylic), ER (Epoxy), UR (Polyurethane), SR (Silicone), and XY (Paraxylylene).

Although as previously stated that the specification has been deemed inactive for new design, it should be noted that if enough interest is generated to revise this specification (its last revision was September 14, 1993) the governing agency may see fit to ultimately revise this standard.