ASTM B735-16
Standard Test Method for Porosity in Gold Coatings on Metal Substrates by Nitric Acid Vapor

Standard No.

ASTM B735-16

Release Date

2016

Published By

American Society for Testing and Materials (ASTM)

Status

Be replaced

Replace By

ASTM B735-16(2022)

Latest

ASTM B735-16(2022)

Scope

5.1 Gold coatings are often specified for the contacts of separable electrical connectors and other devices. Electrodeposits are the form of gold that is most used on contacts, although it is also employed as clad metal and as weldments on the contact surface. The intrinsic nobility of gold enables it to resist the formation of insulating oxide films that could interfere with reliable contact operation.

5.2 In order that the nobility of gold be assured, porosity, cracks, and other defects in the coating that expose base-metal substrates and underplates must be minimal or absent, except in those cases where it is feasible to use the contacts in structures that shield the surface from the environment or where corrosion inhibiting surface treatments for the deposit are employed. The level of porosity in the coating that may be tolerable depends on the severity of the environment to the underplate or substrate, design factors for the contact device like the force with which it is mated, circuit parameters, and the reliability of contact operation that it is necessary to maintain. Also, when present, the location of pores on the surface is important. If the pores are few in number and are outside of the zone of contact of the mating surfaces, their presence can often be tolerated.

5.3 Methods for determining pores on a contact surface are most suitable if they enable their precise location and numbers to be determined. Contact surfaces are often curved or irregular in shape, and testing methods should be suitable for them. In addition, the severity of porosity-determining tests may vary. This test method is regarded as severe.

5.4 The relationship of porosity levels revealed by particular tests to contact behavior must be made by the user of these tests through practical experience or by judgement. Thus, absence of porosity in the coating may be a requirement for some applications, while a few pores on the critical surfaces may be acceptable for another. Such acceptance (or pass-fail) criteria should be part of the product specification for the particular product or part requiring the porosity test.

5.5 This test method is highly sensitive and is capable of detecting virtually all porosity or other defects in gold coatings that could participate in substrate corrosion reactions. The test is rapid, simple, and inexpensive. In addition, it can be used on contacts having complex geometry such as pin-socket contacts. However, it is preferred that deeply recessed sockets be opened to expose their critical surfaces prior to testing.

5.6 This test method is considered destructive in that it reveals the presence of porosity by contaminating the surface with corrosion products and by undercutting the coating at pore sites or at the boundaries of unplated areas. Any parts exposed to these tests shall not be placed in service.

5.7 This test method is intended to be used for quantitative descriptions of porosity (such as number of pores per unit area or per contact) only on coatings that have a pore density sufficiently low that the corrosion sites are well separated and can be readily resolved. As a general guideline this can be achieved for pore densities up to about 100/cm² or per 100 contacts. Above this value the ......

ASTM B735-16 Referenced Document

• ASTM B374 Standard Terminology Relating to Electroplating
• ASTM B542 Standard Terminology Relating to Electrical Contacts and Their Use
• ASTM B741 Standard Test Method for Porosity In Gold Coatings On Metal Substrates By Paper Electrography
• ASTM B765 Standard Guide for Selection of Porosity Tests for Electrodeposits and Related Metallic Coatings
• ASTM B798 Standard Test Method for Porosity in Gold or Palladium Coatings on Metal Substrates by Gel-Bulk Electrography
• ASTM B799 Standard Test Method for Porosity in Gold and Palladium Coatings by Sulfurous Acid/Sulfur-Dioxide Vapor
• ASTM B809 Standard Test Method for Porosity in Metallic Coatings by Humid Sulfur Vapor ("Flowers-of-Sulfur")*， 2024-04-20 Update

ASTM B735-16 history

• 2022 ASTM B735-16(2022) Standard Test Method for Porosity in Gold Coatings on Metal Substrates by Nitric Acid Vapor
• 2016 ASTM B735-16 Standard Test Method for Porosity in Gold Coatings on Metal Substrates by Nitric Acid Vapor
• 2006 ASTM B735-06(2011) Standard Test Method for Porosity in Gold Coatings on Metal Substrates by Nitric Acid Vapor
• 2006 ASTM B735-06 Standard Test Method for Porosity in Gold Coatings on Metal Substrates by Nitric Acid Vapor
• 2005 ASTM B735-05 Standard Test Method for Porosity in Gold Coatings on Metal Substrates by Nitric Acid Vapor
• 1995 ASTM B735-95(2000) Standard Test Method for Porosity in Gold Coatings on Metal Substrates by Nitric Acid Vapor