ASTM B507-86(1998)

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Designation: B 507 – 86 (Reapproved 1998)
Standard Practice for
Design of Articles to Be Electroplated on Racks
This standard is issued under the fixed designation B 507; 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 electroplating baths. Table 1 lists the commonly used electro-
plating processes. They are arranged according to decreasing
1.1 This practice covers design information for parts to be
throwing power.
electroplated on racks. The recommendations contained herein
4.2 A Rochelle-type copper electroplating solution has ex-
are not mandatory, but are intended to give guidance toward
cellent throwing power compared to the poor throwing power
good practice.
of a chromic acid solution used to deposit chromium. The
1.2 This standard does not purport to address all of the
widely used Watts-type nickel bath has fair throwing power.
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro-
5. Geometric Factors Determining Deposit Distribution
priate safety and health practices and determine the applica-
5.1 Since a metal deposits preferentially at protuberances,
bility of regulatory limitations prior to use.
such as sharp corners, edges, fins, and ribs, these should be
2. Significance and Use rounded to a radius of at least 0.4 and preferably 0.8 mm to
avoid excessive buildup. Contouring a base corner in a
2.1 When an article is to be electroplated, it is necessary to
depression is also recommended to avoid thickness deficiency
consider not only the characteristics of the electroplating
at the location.
process, but also the design of the part to minimize electro-
5.2 The width-to-depth ratio of a depression or recess
plating and finishing costs and solution dragout as well as to
should be held to more than 3 as shown in Fig. 2. Otherwise,
improve appearance and functionality. It is often possible
a special auxiliary anode must be employed inside the recess to
during the design and engineering stages to make small
promote more uniform current distribution. An auxiliary anode
adjustments in shape that will result in considerable benefit
is usually made of the depositing metal and is placed close to
toward a better quality part at a lower cost.
the low-current density areas to enhance metal deposition at
2.2 The specific property of an electroplating process that
those regions.
would require some attention to the details of optional designs,
5.3 All sharp edges and base angles of a recess should be
is the throwing power of the electroplating solution. Throwing
rounded to a radius of 0.25 times or more the depth of the
power is the improvement of the coating distribution over the
recess as shown in Fig. 3. When sharp recess angles are
primary current distribution on an electrode (usually cathode)
required for a functional purpose, the electroplater cannot be
in a given solution, under specified conditions.
expected to meet a minimum thickness at those locations
3. Current Distribution and Throwing Power unless it is specifically required.
3.1 The apparent current during practical electroplating is
6. Examples of Distribution of Electrodeposited Nickel
never uniform over the surface of the product. Even parallel
on Various Shapes
plates have a nonuniform distribution of current when freely
6.1 Fig. 4 through Fig. 5 show the kind of nickel distribu-
suspended in a bath as shown in Fig. 1. In this example, the
tion that was obtained on several different cathode configura-
current lines tend to concentrate as corners, and edges (high-
tions as deposited from a Watts-type bath at normal operating
current density) of the part. Consequently more metal is
current densities. The thicknesses illustrated are exaggerated to
deposited at the high-current density areas than at the low-
emphasize the variations that were obtained. The data are
current density areas.
measurements taken from metallographic cross sections. Ref-
4. Relative Throwing Powers of Different Electrolytes erence to the figures enables similar conclusions to be drawn
with most other metals, excluding chromium. The ranges will
4.1 Throwing power is not the same for all metals and all
be smaller for metals above nickel in Table 1 and larger for
metals below nickel.
This practice is under the jurisdiction of ASTM Committee B-8 on Metallic and
6.2 Improvement in nickel distribution can be gained inside
Inorganic Coatingsand is the direct responsibility of Subcommittee B08.01 on
Ancillary Matters.
Current edition approved July 25, 1986. Published September 1986. Originally Adapted from sketches appearing in Electroplating and Engineering Hand-
e1
published as B 507 – 70. Last previous edition B 507 – 70 (1979). book, 4th ed, Durney, L. J., ed., Reinhold Publishing Corporation, New York, 1984.
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NOTICE: This standard has either been superceded and replaced by a new version or discontinued. 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. Contact ASTM International (www.astm.org) for the latest information.
B 507
FIG. 1 Current Density Distribution and Typical Electrodeposit (filled area)
TABLE 1 Relative Throwing Powers of Common Electroplating
part with the rounded corners.
Baths
6.4 Deep recesses will always have a thinner deposit than
Bath/Metal Ranking
the surrounding external areas, as shown in the cross section of
Rochell copper (cyanide based) Excellent
a concave part in Fig. 7(a). The average-to-minimum nickel
Cyanide cadmium Excellent
thickness ratio for this example was 6.6. A more uniform
Cyanide gold Good
deposit thickness can be obtained on a convex-shaped part, as
Cyanide silve
...