Plating Topics » Technical Library » What is the difference between an average, range or minimum plating thickness specification and how do I properly call out my thickness requirement on a print?

What is the difference between an average, range or minimum plating thickness specification and how do I properly call out my thickness requirement on a print?

There are five (5) methods most commonly used for defining plating thicknesses.  They are average, range, minimum, maximum and customer negotiated.  The differences between each are very distinct.  The definition of each is provided below:

Average
An Average deposit thickness requirement is given as a single number i.e. “nickel plate 0.0002”.”   An Average deposit thickness provides the target that the mean of multiple thickness readings should be within a 75uin window.  In the example given this would be 0.0002” ± 0.000075” (200±75uin).  However, it is at the plater’s discretion to choose the location where to measure the product unless the measuring location is indicated on the print.  This is a very important distinction as the plating thickness on electroplated products can vary considerably from point to point.  The thickness distribution is heavily dependent on part geometry.  On products that are drawn out such as rods or pins there can be an extremely wide range of thickness.  However, the thickness distribution can be quite minimal on spherical products such as ball bearings.

Range
A Range deposit thickness requirement is given as a range of numbers i.e. “nickel plate 0.0001-0.0003”.”   The range provided is the range within which the mean of the thickness measurements must lie.  Similarly to Average thicknesses, it is at the plater’s discretion where to measure the product unless the measuring location is indicated on the print.  If the range is ≤ 0.00015” (150uin) it is treated as a single average with the mid point of the range being the target average and the definition of average thickness above applies.

Note:  A range specification does not imply that all readings collected on all articles at any location must be within the range.  This is only designated by Minimum and Maximum thickness requirements defined below.

Minimum
A Minimum deposit thickness requirement is identified with a single number with the word minimum i.e. “nickel plate 0.0002” minimum or min.”  A Minimum thickness requirement  is defined as all readings measured on the significant surfaces must be greater than the thickness indicated.  In the example provided the thickness measured on any significant surface would have to be greater than 0.0002” (200uin).  Significant surfaces are generally defined as any portion of a part that can be touched by a 0.75” diameter sphere.  However, the manufacturer of a product can identify significant surfaces as required on the blueprint of the product.

Note:  There is no upper limit of thickness that applies in this definition. 

Maximum
A Maximum deposit thickness requirement is given as a single number with the word maximum i.e. “nickel plate 0.0002” maximum or max.”  A Maximum thickness requirement is defined as all readings measured on significant surfaces must be less than the thickness indicated.  In the example provided the thickness measured on any significant surface would have to be less than 0.0002” (200uin).  If a significant surface is not defined all readings shall be less than 0.0002” (200uin) on any area of the part that can be touched by a 0.75” diameter sphere.

Note:  There is no lower limit of thickness that applies in this definition.  Any measurable deposit thickness is acceptable.

Customer Negotiated Specifications
When a customer has a defined specification or sites commonly referenced specifications i.e. ASTM, MIL, AMS etc.  they shall be followed unless both the specification and thickness requirement are provide on the print.  In this case, the thickness otherwise specified on the print supersedes the spec referenced.  For example, specification QQ-N-290 requires minimum plating thickness requirements based on the grade of the plating (i.e. in QQ-N-290 Grade G is 0.0002” Minimum).  However, if a customer were to indicate on a print, “Nickel Plate per QQ-N-290  0.0001”-0.0003”,” this is understood as a range plating thickness requirement  because the customer has otherwise specified the thickness desired without indicating the grade.  If a customer desires the thicknesses defined within the spec, the specific grades should be cited, i.e. “Nickel Plate per QQ-N-290, Grade G.”

Customer-unique specifications can always be developed based on the wishes of our customers but they must be known upfront.  Unique specifications developed by a customer will be referenced on the appropriate process routing instructions and will be inspected to accordingly. This document will be the ruling document as to significant surfaces, thickness interpretation and target thicknesses desired.