ASTM_B_507_-_14.pdf

Designation:B50714Standard Practice forDesign of Articles to Be Electroplated on Racks1This standard is issued under the fixed designation B507;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon()indicates an editorial change since the last revision or reapproval.1.Scope1.1 This practice covers design information for parts to beelectroplated on racks.The recommendations contained hereinare not mandatory,but are intended to give guidance towardgood practice.1.2 The values stated in SI units are to be regarded asstandard.No other units of measurement are included in thisstandard.1.3 This standard does not purport to address all of thesafety concerns,if any,associated with its use.It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2.Significance and Use2.1 When an article is to be electroplated,it is necessary toconsider not only the characteristics of the electroplatingprocess,but also the design of the part to minimize electro-plating and finishing costs and solution dragout as well as toimprove appearance and functionality.It is often possibleduring the design and engineering stages to make smalladjustments in shape that will result in considerable benefittoward a better quality part at a lower cost.2.2 The specific property of an electroplating process thatwould require some attention to the details of optional designs,is the throwing power of the electroplating solution.This termdescribes the properties of the solution as it relates to thesolution electrical resistance and solution capacitance at thecathode and overall efficiency of the electrolyte system.Throwing power is defined as the improvement of the coatingdistribution over the primary current distribution on an elec-trode(usually cathode)in a given solution,under specifiedconditions.3.Current Distribution and Throwing Power3.1 The apparent current during practical electroplating isnever uniform over the surface of the product.Even parallelplates have a nonuniform distribution of current when freelysuspended in a bath as shown in Fig.1.In this example,thecurrent lines tend to concentrate as corners,and edges(high-current density)of the part.Consequently more metal isdeposited at the high-current density areas than at the low-current density areas.4.Relative Throwing Powers of Different Electrolytes4.1 Throwing power is not the same for all metals and allelectroplating baths.Table 1 lists the commonly used electro-plating processes.They are arranged according to decreasingthrowing power.4.2 A Rochelle-type copper electroplating solution has ex-cellent throwing power compared to the poor throwing powerof a chromic acid solution used to deposit chromium.Thewidely used Watts-type nickel bath has fair throwing power.5.Geometric Factors Determining Deposit Distribution5.1 Since a metal deposits preferentially at protuberances,such as sharp corners,edges,fins,and ribs,these should berounded to a radius of at least 0.4 and preferably 0.8 mm toavoid excessive buildup.Contouring a base corner in adepression is also recommended to avoid thickness deficiencyat the location.5.2 The width-to-depth ratio of a depression or recessshould be held to more than three as shown in Fig.2.Otherwise,a special auxiliary anode must be employed insidethe recess to promote more uniform current distribution.Anauxiliary anode is usually made of the depositing metal and isplaced close to the low-current density areas to enhance metaldeposition at those regions.5.3 All sharp edges and base angles of a recess should berounded to a radius of 0.25 times or more the depth of therecess as shown in Fig.3.When sharp recess angles arerequired for a functional purpose,the electroplater cannot beexpected to meet a minimum thickness at those locationsunless it is specifically required and optional plating techniquesare employed.NOTE1Electroplating techniques can be used to address uniformdeposition in the recess angle.These techniques include bi-polar platingand directed flow electroplating in addition to conforming anodes.1This practice is under the jurisdiction of ASTM Committee B08 on Metallicand Inorganic Coatingsand is the direct responsibility of Subcommittee B08.01 onAncillary Activities.Current edition approved May 1,2014.Published June 2014.Originallyapproved in 1970.Last previous edition approved in 2008 as B507 86(2008)1.DOI:10.1520/B0507-14.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 6.Examples of Distribution of Electrodeposited Nickelon Various Shapes6.1 Fig.4 through Fig.52show the kind of nickel distribu-tion that was obtained on several different cathode configura-tions as deposited from a Watts-type bath at normal