Not all gold electroplating specs are created equal. Choosing the right one can be very confusing. Today, there are three “go to” plating specs for gold: MIL-DTL-45204D, AMS2422 and/or ASTM B488. Hopefully this guide can eliminate some of the mystery.
Let’s start with some history. MIL-G-45204C, the primary military specification for gold plating in the ‘80s and ‘90s, was canceled in 1998. It was superseded by AMS 2422 and/or ASTM B488, but with a warning, “to evaluate AMS2422 and ASTM B488 for their particular application before citing them as replacement”. Almost 20 years later, in 2007, MIL-G-45204C was essentially reinstated as MIL-DTL-45204D. However, for the revised spec, sampling to MIL-STD-105 was replaced with MIL-STD-1916, with updated restrictions on strikes and underplating.
The Underplating Process
Underplating is an important process when gold plating, as it helps maintain the integrity and longevity of the plate. In many cases, nickel underplate is used to provide a diffusion barrier when plating over copper alloy, otherwise copper will migrate through the gold. However, there are situations when nickel underplating can’t be used. In those cases the PO or part drawing should specify “no nickel underplate”.
Hardness and Purity
Hardness and purity of gold are the confusing parts of the three “go to” plating specs. As you know, gold is a soft metal and can wear quickly or smear. Its softness can also lead to high insertion forces. Nickel or cobalt are common hardeners, but they must be controlled in the gold deposit. If you have too much nickel or cobalt, they will adversely affect the purity of the deposit. When it comes to gold plating, purity is equally important to your customer as hardness.
AMS 2422 is the most forgiving of the three specs when it comes to the purity and hardness of gold. This spec calls for minimum plate purity of 99.0%, so plated parts can be pure soft gold, nickel (or cobalt) hardened, and all will comply with this spec.
ASTM B488-11, at one time, did not align with the MIL-G-45204 for gold purity and hardness. So much care needs to be given when referring to this spec. Careful consideration of the component’s end use and environment must be given.
Technical Details for the Big 3
These tables should provide some clarity, and help you determine which spec is best for your particular application: