Gold plating
Selecting and specifying gold deposits by application, underplate, purity, hardness, thickness and qualified performance.
Tags: processes, finishing, electroplating, gold
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At Technic's reported 17.5–18.5 g/cm³ density for Oroscene 80RC, a hypothetical 1.00 µm deposit over 10 cm² weighs 17.5–18.5 mg. Use the deposit-specific density and local thickness. Specify the stack and qualify performance for sliding contact, soldering or wire bonding. Technic Oroscene deposit data
Specify the complete electrodeposited stack and intended function. ASTM B488-18(2025) classifies electrodeposits by purity and hardness, covers inspection and excludes immersion, autocatalytic and vapor-deposited gold.
Soft gold, hard gold and joining surfaces
“Soft” and “hard” describe deposit behavior, not simply thickness. Technic's undated Precious Metals brochure gives these bounded examples, both with hardness measured using a 25 g Knoop load:
| Named process | Published deposit properties | Stated application |
|---|---|---|
| Oroscene 80RC | Purity >99.7%; hardness 140–170 Knoop; density 17.5–18.5 g/cm³ | Touch and sliding contacts; also supplier-described soldered connections |
| Technic 434 HS | Purity >99.9%; hardness 80–90 Knoop, as plated | High-purity deposits for wire bonding |
These are supplier product data, not universal boundaries separating every soft and hard gold. The brochure's historical military-specification reference also does not establish compliance with a current procurement document. Confirm the selected product, current technical sheet, deposit state and required standard edition with the plater. Technic, Precious Metals, page 2
Wire bonding requires control of the actual bonding surface. Technic's separate 434 HS reel-to-reel application note, marked “New 0222”, discusses minimizing alloy-metal carryover to maintain deposit purity and acceptable wire-bond properties, including a strike following nickel. This is a product-specific process-control example; it does not prescribe a universal strike sequence for other substrates or chemistries. Specify bond qualification using the intended wire, pad finish and assembly process rather than accepting the word “gold” as sufficient. Technic 434 HS application note
For soldered terminals, identify the soldering area separately from the mating area. Samtec explains that gold dissolves into molten solder, and its connector guidance discusses cobalt-hardened gold for mating contacts. A contact finish therefore does not, by itself, qualify the eventual solder joint. Review finish quantity and the intended soldering process together. Samtec, connector plating FAQs
Underplates and surface condition
The underplate is part of the functional system. Samtec describes nickel beneath gold as a barrier against migration from copper-based contacts and gives 50 microinches minimum nickel for its practice. It also cautions that thick nickel can crack when leads are bent after plating. That supplier example is not a minimum for every gold-plated part: substrate, forming sequence and required flexibility must be resolved for the actual component. Samtec, connector plating FAQs
Underplate quality matters as well as its nominal thickness. Bell Labs' 1 February 1979 research description explains how exposed base metal can develop films that raise contact resistance, and discusses diffusion and corrosion through pores. It also reports that nickel underplates do not improve wear in every case; poor adhesion or nodular finishes can worsen behavior. Treat this as evidence for evaluating the whole contact system, not a modern qualification specification or a fixed service-life prediction. Bell Labs, Wear of Gold Electrodeposits: Effect of Substrate and of Nickel Underplate
For a drawing handoff, identify permitted preparation, significant surfaces, masking boundaries and any post-plating forming. Ask the supplier to resolve substrate activation and adhesion for the named alloy. Keep rack or electrical-contact marks away from functional areas by agreement. Include surface appearance requirements separately from electrical or bonding acceptance so that a cosmetic sample cannot substitute for a performance test.
Thickness, porosity and contact life
Thickness must have units, a location and an acceptance basis. Distinguish a minimum on the mating track from an average over a whole part, and identify whether a quoted value describes gold alone or the complete stack. Selective plating can intentionally give different finishes to a contact and its solder tail.
Samtec's June 2025 guide illustrates selective options of 3, 10 and 30 microinches gold, including options with matte-tin tails. Crucially, its mating-cycle figures depend on contact style and were not tested to failure; it directs readers to the particular series' drawings and test reports. Do not turn such a table into a general rule that a chosen gold thickness guarantees a number of operations, or transfer qualification from one connector geometry to another. Samtec, Gold Plating: Worth its Weight?
Inspection methods also have boundaries. ASTM B866-24 detects gross defects exposing copper or copper alloy; it does not detect exposed nickel and is explicitly unsuitable as a general small-pore test. Its destructive test specimens must not enter service, and the result is not a field-life prediction. Specify a suitable porosity or environmental method and acceptance criteria for the actual stack rather than writing only “porosity tested.” ASTM B866-24, significance and use
Original thickness and material estimate
Assume an ideal flat plated area of 10 cm², uniform 1.00 µm gold-alloy thickness and the Oroscene brochure's 17.5–18.5 g/cm³ deposit density. The thickness is an illustrative design assumption, not Technic's recommendation.
- Volume = 10 cm² × 0.000100 cm = 0.00100 cm³.
- Deposit mass = volume × density = 17.5–18.5 mg.
- For comparison, 30 microinches = 0.762 µm; at the same assumed area and density this gives 13.335–14.097 mg.
This estimates deposited alloy mass only. It excludes underplates, edges, thickness distribution, fixtures, process losses and recovery; it is neither pure-gold mass nor purchased chemical consumption. Density input: Technic brochure
Specification and release handoff
Record the base alloy and condition; deposition route; standard and edition where applicable; purity and hardness requirements; underplate materials; local minimum thickness; significant surfaces; masking; dimensional allowance; and appearance criteria. Then identify the actual function and its verification: mating wear and contact resistance, bond tests, soldering qualification, or a controlled cosmetic reference.
For acceptance, agree on measurement locations, sample quantities, test methods, limits and treatment of tested parts before production. Require approval for changes to the stack or plating process where qualification depends on them. Retain the connection between the drawing revision, supplier process and tested assembly: a certificate naming gold plating is only useful when it corresponds to the specified finish and its intended service.