Engmotion: Technical Gold Coating for Smallsat Housings. A Comparative Study with Chromate Conversion
Abstract
This paper presents the experience gained in the application of technical gold plating for smallsat housings. Unlike flash decorative gold layers (~0.1 µm), we adopted a 1 µm technical gold coating to ensure corrosion resistance, stable electrical conductivity, and compatibility with laser marking. Comparative analysis with chromate conversion (ChromitAl) is provided, focusing on advantages, drawbacks, and suitability for space hardware. Experimental results demonstrate that laser markings remain highly visible after gold deposition, contrary to initial expectations. The study also references relevant NASA and ECSS standards and discusses implications for spacecraft design.
Satellite housings, custom CNC machined by Engmotion, for smallsats (like the ones manufactured for our partner Paradigma) require protective coatings to ensure durability, electrical performance, and corrosion resistance. Gold plating is often considered a premium solution for aerospace applications due to its chemical inertness, low contact resistance, and stable long-term performance [1][2]. Alternatives such as chromate conversion coatings (ChromitAl) remain widely used for aluminum alloys [3], offering cost and weight advantages but lower electrical performance. This paper discusses the rationale behind the choice of 1 µm gold plating for smallsat housings and compares it with ChromitAl.
2. Materials and Methods
The housings were CNC machined, by Engmotion expert team, from aluminum alloys and prepared via bead blasting and polishing of functional surfaces. A nickel diffusion barrier (~5–7 µm) was applied, followed by a 1 µm gold electroplated layer. Laser markings were performed with fiber-laser technology at 1064 nm, with parameters tuned to maintain visibility post-plating. Comparative ChromitAl coatings (MIL-DTL-5541 Type II) were prepared for reference.
3. Results
Experimental findings confirmed that 1 µm gold plating provided excellent corrosion resistance and very low electrical contact resistance, as expected. Contrary to initial concerns, laser markings remained visible and in some cases exhibited increased contrast after gold plating. ChromitAl coatings provided satisfactory corrosion resistance but higher variability in electrical contact resistance.
4. Discussion
Gold plating with nickel barrier offers superior performance for bonding pads, EMI control, and corrosion resistance in spacecraft housings. However, its cost is significantly higher than ChromitAl. The latter remains valid for large structural areas where paint adhesion and low cost are prioritized. For contact-critical areas, gold plating remains the industry standard. NASA-STD-6012A [1] and ECSS-Q-ST-70-14 [2] provide guidance on coating selection. Laser marking results indicate that with correct parameter adjustment (defocus, pulse frequency, scanning strategy), high-contrast markings are compatible with gold-coated surfaces [4]. We have investigated and tested a lot in house to achieve the best results desired by our customer Paradigma Technologies.
Table 1. Comparison: Gold (1 µm) vs. ChromitAl Conversion
Attribute
Gold over Ni (1 µm Au)
ChromitAl Conversion (MIL-DTL-5541)
Corrosion resistance
Excellent, pore-limited; inert Au top layer
Good, depends on Type (I Cr⁶⁺ vs II trivalent RoHS)
Electrical contact resistance
Very low, stable; ideal for bonding & EMI
Higher and less stable; oxide re-forms
Wear/handling
Au is soft; hard-Au baths improve durability
Thin films can abrade; often painted
Cost/weight
High (gold cost, plating process)
Low cost, very light
Bonding/fastener lands
Excellent, stable torque cycles at ≥1 µm
Acceptable but resistance may increase over time
Regulatory
Ni/Au processes with wastewater controls
Type II is RoHS-compliant; Type I Cr⁶⁺ restricted
Figures
Fig. 1. Smallsat housings with 1 µm gold coating.
Fig. 2. Comparative ChromitAl coated housings.
5. Conclusions
This study confirms that technical gold plating at 1 µm thickness is suitable for smallsat housings requiring corrosion protection and reliable electrical conductivity. Laser marking compatibility enhances traceability and functionality. ChromitAl remains an effective, lower-cost alternative for non-critical areas. The combined approach ensures both performance and cost optimization for space applications.