ASTM B765-93(2001)

NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
Designation: B 765 – 93 (Reapproved 2001)
Standard Guide for
Selection of Porosity Tests for Electrodeposits and Related
Metallic Coatings
This standard is issued under the fixed designation B 765; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope Hard-Drawn Copper Wire for Electrical Purposes
B 276 Test Method for Apparent Porosity in Cemented
1.1 This guide describes some of the available standard
Carbides
methods for the detection, identification, and measurement of
B 374 Terminology Relating to Electroplating
porosity in electrodeposited and related metallic coatings and
B 537 Practice for Rating of Electroplated Panels Subjected
provides some laboratory-type evaluations and acceptances.
to Atmospheric Exposure
Some applications of the test methods are tabulated in Table 1
B 542 Terminology Relating to Electrical Contacts and
and Table 2.
Their Use
1.2 This guide does not apply to coatings that are produced
B 545 Specification for Electrodeposited Coatings of Tin
by thermal spraying, ion bombardment, sputtering, and other
B 605 Specification for Electrodeposited Coatings of Tin-
similar techniques where the coatings are applied in the form of
Nickel Alloy
discrete particles impacting on the substrate.
B 650 Specification for Electrodeposited Engineering Chro-
1.3 This guide does not apply to beneficial or controlled
mium Coatings of Ferrous Substrates
porosity, such as that present in microdiscontinuous chromium
B 689 Specification for Electroplated Engineering Nickel
coatings.
Coatings
1.4 Porosity test results occur as chemical reaction end
B 733 Specification for Autocatalytic (Electroless) Nickel-
products. Some occur in situ, others on paper, or in a gel
Phosphorous Coatings on Metals
coating. Observations are made that are consistent with the test
B 734 Specification for Electrodeposited Copper for Engi-
method, the items being tested, and the requirements of the
neering Uses
purchaser. These may be visual inspection (unaided eye) or by
B 735 Test Method for Porosity in Gold Coatings on Metal
103 magnification (microscope). Other methods may involve
Substrates by Nitric Acid Vapor
enlarged photographs or photomicrographs.
B 741 Test Method for Porosity in Gold Coatings on Metal
1.5 The test methods are only summarized. The individual
Substrates by Paper Electrography
standards must be referred to for the instructions on how to
B 798 Test Method for Porosity in Gold or Palladium
perform the tests.
Coatings on Metal Substrates by Gel-Bulk Electrography
1.6 The values stated in SI units are to be regarded as
B 799 Test Method for Porosity in Gold and Palladium
standard. The values given in parentheses are for information
Coatings by Sulfurous Acid/Sulfur-Dioxide Vapor
only.
B 809 Test Method for Porosity in Metallic Coatings by
1.7 This standard does not purport to address all of the
Humid Sulfur Vapor (“Flowers-of-Sulfur”)
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro-
3. Terminology
priate safety and health practices and determine the applica-
3.1 Definitions—Many terms used in this guide are defined
bility of regulatory limitations prior to use.
in Terminology B 374 or B 542.
2. Referenced Documents 3.2 Definitions of Terms Specific to This Standard:
3.2.1 porosity—for the purpose of this guide, porosity in a
2.1 ASTM Standards:
coating is defined as any hole, crack, or other defect that
B 246 Specification for Tinned Hard-Drawn and Medium-
exposes the underlying metal to the environment.
3.2.2 underplate—a metallic coating layer between the
basis metal and the topmost metallic coating. The thickness of
This guide is under the jurisdiction of ASTM Committee B08 on Metallic and
Inorganic Coatings and is the direct responsibility of Subcommittee B08.10 on Test
Methods. Annual Book of ASTM Standards, Vol 02.03.
Current edition approved Jan. 15, 1993. Published March 1993. Originally Annual Book of ASTM Standards, Vol 02.05.
published as B 765 – 86. Last previous edition B 765 – 86. Annual Book of ASTM Standards, Vol 02.04.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
B 765
TABLE 1 Applications of Standard Porosity Tests to Metallic Coatings (Section 6)
A
Substrate Metal Gold Silver Nickel Tin-Nickel Tin Tin-Lead Copper Palladium Chromium
B
Copper and Copper 6.1 , 6.2, 6.3A 6.4 6.4 6.4 6.4 . 6.2, 6.3A, 6.4, .
Alloys 6.4, 6.5 6.5
B
Nickel 6.1 , 6.2, 6.5 6.3A . . . . . 6.2, 6.3A, 6.5 .
Iron or Steel 6.6 . 6.6 6.3B, 6.6 6.3B, 6.6 6.3B, 6.6 6.6 . 6.6
Silver 6.4 . 6.4 6.4 6.4 6.4 . 6.4 .
A
The substrate may be the basis metal, an underplate, or both (see Note 1).
B
Thickness restrictions may apply.
TABLE 2 Applications of Tests for Gross Defects and Mechanical Damage (Section 7)
A
Substrate Metal Gold Nickel Tin-Nickel Tin Tin-Lead Palladium Silver
Copper and Copper 7.3, 7.5 7.3, 7.4 7.3 7.3 7.3 7.3, 7.5 7.5
Alloys
Nickel 7.5 . . . . 7.5 7.5
Iron or Steel 7.1 7.1 7.1 7.1 7.1 7.1 .
Aluminum . 7.2 . . . . .
A
The substrate may be the basis metal, an underplate, or both (see Note 1).
an underplating is usually greater than 1 μm, in contrast to a ing. Examples of such defects are mechanical damage to the
strike or flash, which are usually thinner. coating through mishandling or wear. Gross defects can also be
found in undamaged coatings in the form of networks of
4. Significance and Use
microcracks and as large as-plated pores—with diameters an
4.1 Porosity tests indicate the completeness of protection or
order of magnitude (or more) greater than intrinsic porosity.
coverage offered by the coating. When a given coating is Such gross defects indicate such serious deviations from
known to be protective when properly deposited, the porosity
acceptable coating practice as dirty substrates and contami-
serves as a measure of the control of the process. The effects of
nated or out-of-balance baths.
substrate finish and preparation, plating bath, coating process,
5.2 Intrinsic porosity and most types of gross defects are too
and handling, may all affect the degree of imperfection that is
small to be seen except at magnifications so high that a realistic
measured.
assessment of the overall coating surface in the functional areas
of the part cannot be made. Instead, the presence and severity
NOTE 1—The substrate exposed by the pores may be the basis metal, an
of the porosity is normally determined by some type of
underplate, or both.
pore-corrosion test that will magnify the pore sites by produc-
4.2 The tests in this guide involve corrosion reactions in
ing visible reaction products in and around the pores or cracks.
which the products delineate pores in coatings. Since the
Tests for gross defects (Section 7), and especially for mechani-
chemistry and properties of these products may not resemble
cal damage and wear, are designed to be less severe. Such tests,
those found in service environments, these tests are not
however, may not detect a sizeable portion of the smaller
recommended for prediction of product performance unless
(intrinsic) pores in a coating. On the other hand, standard tests
correlation is first established with service experience.
for intrinsic porosity (Section 6) will easily reveal the presence
of gross defects as well.
5. Applications
5.3 Porosity tests are generally destructive in nature and are
5.1 From the viewpoint of both porosity testing and func-
designed to assess the quality of the coating process in
tional significance, it is useful to divide porosity into two broad
, conjunction with the substrate. Therefore, separate test speci-
5 6
categories, namely intrinsic porosity and gross defects.
mens are not ordinarily allowed.
5.1.1 Intrinsic or normal porosity is due primarily to small
5.4 In the tests summarized in this guide, chemicals react
deviations from ideal plating and surface preparation condi-
with the exposed substrate through the pore or channel to form
tions. As such, it will be present to some degree in all
a product that is either directly observable or that is made
commercial thin platings and will generally follow an inverse
observable by subsequent chemical development.
relationship with thickness. In addition, scanning electron
5.5 Porosity tests differ from corrosion and aging tests. A
microscope (SEM) studies have shown that the diameter of
good porosity test process must clean, depolarize, and activate
such pores at the plating surface is of the order of micrometers,
the substrate metal exposed by the pore, and attack it suffi-
so that only small areas of underlying metal are exposed to the
ciently to cause reaction products to fill the pore to the surface
environment.
of the coating. The corrosive reagent ideally does not react with
5.1.2 Gross defects, on the other hand, would result in
the coating. Reaction time is limited, particularly with thin
comparatively large areas of exposed basis metal or underplat-
coatings, since the corrosive will attack the substrate in all
directions and, in so doing, undermine the coatings so that false
Baker, R. G., Holden, C. A., and Mendizza, A., Proceedings of the American observations may be made. When the corrosion produ
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