Why gold plating on microwave equipment? - Page 1
Forum section: electronics / rf-microwave

author: mr ed
author_rank: Regular Contributor
timestamp: April 02, 2025, 02:41:30 pm
content: Skin depth always should see a higher resistance with gold plating. Corrosion resistance? I have some gold plateed mixers looking terrible.

author: jwet
author_rank: Frequent Contributor
timestamp: April 02, 2025, 05:43:48 pm
content: I don't understand your logic. Skin depth is very small at microwave frequencies, gold or silver has lower resistivity than most materials so is an effective conductor. The reason its only plated is that there is no sense in making it any thicker than a few skin depths. Is this wrong?

author: tooki
author_rank: Super Contributor
timestamp: April 02, 2025, 06:10:03 pm
content: I suppose mr ed is comparing gold to silver and copper, in which case it's a fair bit worse, but he seems to not realize that gold remains far better than most metals.Mr ed, imagine the cost if your microwave products had to be made of solid silver or solid gold. (Never mind the terrible mechanical properties of pure gold.) Copper would be effective, but tarnishes readily, and pure copper is nightmarish to machine.

author: mr ed
author_rank: Regular Contributor
timestamp: April 02, 2025, 08:51:02 pm
content: My mistake. Gold is a better conductor of electricity than brass, but not as good a pure copper. I assumed brass was like copper.Gold 2.4Copper 1.7Brass 6 to 9 x10e-8 ohm / meter cubeStill, brass can corrode underneath the gold.I wonder how big a difference gold makes for rf at 40GHz? 120GHz ? Short 2cm devices can't be worth the cost.

author: jpanhalt
author_rank: Super Contributor
timestamp: April 02, 2025, 09:08:40 pm
content: Get your tubes nice and as shiny as you want. Then make Tollen's reagent and silver plate the inside. Another use for Tollen's? Silvering telescope mirrors.

author: mr ed
author_rank: Regular Contributor
timestamp: April 02, 2025, 09:34:23 pm
content: It comes out to a few ohms per mm length for a typical brass waveguide, 122GHz, skin depth 0.2e-8. Versus a third of that for gold. Makes sense to thin plate everything gold longer than a few mm.

author: jpanhalt
author_rank: Super Contributor
timestamp: April 02, 2025, 09:44:45 pm
content: Silver is much cheaper than gold for your experiments.

author: TimFox
author_rank: Super Contributor
timestamp: April 02, 2025, 09:49:57 pm
content: Quote from: mr ed on April 02, 2025, 08:51:02 pmA pure metal (e.g. Cu) will always have a higher conductivity than an alloy containing that metal with other components: copper vs. brass, etc.

author: radiolistener
author_rank: Super Contributor
timestamp: April 02, 2025, 10:26:10 pm
content: Gold is a more reliable choice for long-term durability, as it is less prone to forming an oxide layer compared to silver. Silver oxide can negatively affect performance at microwave frequencies by increasing surface resistance in the skin layer and introducing nonlinear distortions due to its semiconducting properties. While gold has lower conductivity, its resistance to oxide formation helps maintain stable performance over time, avoiding the adverse effects associated with silver oxide.

author: TimFox
author_rank: Super Contributor
timestamp: April 02, 2025, 10:39:25 pm
content: In normal indoors atmospheres, copper develops an oxide layer but silver develops a sulfide layer.

author: mr ed
author_rank: Regular Contributor
timestamp: April 02, 2025, 11:00:20 pm
content: Thanks to all who responded.

author: radiolistener
author_rank: Super Contributor
timestamp: April 02, 2025, 11:16:49 pm
content: Quote from: TimFox on April 02, 2025, 10:39:25 pmSilver sulfide is also semiconducting material with higher resistivity than metallic silver, leading to increased surface resistance and non-linear distortions for signal.

author: TimFox
author_rank: Super Contributor
timestamp: April 02, 2025, 11:30:36 pm
content: Quote from: radiolistener on April 02, 2025, 11:16:49 pmYes: copper oxide is also a semiconductor that has been used to make rectifiers in the past. My pre-war Simpson 260 uses one for AC measurement.