Español
Français
Português
In the specification book of conductive cloth tape, the corrosion resistance usually appears in the form of "salt spray test for XX hours". This value describes the "tolerance of the coating itself in salt spray environment", but in actual assembly, conductive cloth tape rarely exists alone - it is attached to the fiber coating on one side and contacts another metal through conductive adhesive or direct pressing on the other side. Copper, aluminum, stainless steel, tin plated surfaces, and gold-plated solder pads may all become its "neighbors".
When two different metals come into contact at the interface where an electrolyte is present, they form an electric couple. The potential difference drives electrons to flow from more reactive metals to more inert metals, and the more reactive metals become anodes, accelerating dissolution. This mechanism does not require an external power supply, only moisture and potential difference.
Electric couple sequence: who protects whom, who corrodes whom
The position of the metal in the thermocouple sequence determines whether it is the anode or cathode in the thermocouple pair. In the galvanic sequence in seawater, the potential of nickel is approximately -0.05 to -0.15 V (vs SCE), copper is about -0.20 V, aluminum is about -0.75 V, zinc is about -1.00 V, and carbon steel is about -0.60 V. The more negative the potential, the easier it is to corrode the anode.
The nickel plating layer of conductive cloth tape acts as the cathode when in contact with aluminum, zinc, and carbon steel, while the more active substrate becomes the anode, with corrosion concentrated on one side of the substrate. The products of anodic corrosion may accumulate at the interface, forming a high resistance oxide layer or salt deposition. More importantly, the dissolution of the anode metal will form micro pits at the interface, reducing the effective contact area and increasing the contact resistance.
The situation is reversed when in contact with copper. The potential of nickel is slightly higher than that of copper, with the nickel layer serving as the anode and copper as the cathode. The nickel layer is accelerated to dissolve in humid and hot environments, causing the coating to become thinner and even partially expose fibers. The fiber itself is non-conductive, and the conductive path in the exposed area is cut off, resulting in an increase in both surface resistance and contact resistance.
When in contact with the tin plated surface, the potential of tin is about -0.14 V, which is close to that of nickel. The potential difference between the two is small, and the driving force for galvanic corrosion is weak. This is also why tin plated surfaces are usually more "friendly" than aluminum or bare copper in conductive cloth grounding - not because tin does not corrode, but because the potential difference between nickel tin couples is not sufficient to drive strong accelerated corrosion.
A humid and hot environment is a catalyst, not the only condition
Electrochemical corrosion requires the presence of electrolytes. In a dry environment, there is no continuous electrolytic liquid film on the metal surface, ion migration is hindered, and the electric current is very small. But in humid and hot environments, the thin water film that condenses on the surface (even if only a few tens of micrometers thick) is already sufficient to dissolve CO ₂ and pollutants in the air, forming a conductive electrolyte. When the relative humidity exceeds 60% -70%, most metal surfaces begin to form a continuous water film; If there is salt spray, sweat, or acidic gases in the environment, the conductivity of the electrolyte is higher and the corrosion rate further increases.
For conductive tape, there are several accelerating factors for galvanic corrosion in humid and hot environments. The fiber network of conductive cloth has capillary effect, and water easily penetrates deep into the interface along the fiber gaps, making the electrolyte stay at the interface for a longer time. The hydrophilic groups in the conductive adhesive layer may also absorb moisture and form a localized electrolytic liquid film at the adhesive metal interface. These factors combined may result in a higher galvanic corrosion rate for conductive cloth grounding compared to flat plate contact with the same metal.
Die cutting edge and overlapping interface: concentrated location of localized corrosion
The distribution of galvanic corrosion on conductive cloth tape is not uniform. The die-cutting edge is the most concentrated location where the coating is exposed - the fibers are cut, the metal coating forms a cross-section at the incision, and the interface between the coating and the substrate is directly exposed to the environment. If the die-cutting edge comes into contact with different metals, the galvanic corrosion rate at the cutting edge will be significantly higher than that in the fabric surface area.
The overlapping interface is another centralized location. When conductive tape is used to bridge two metal structures, the fiber network of the tape contacts two different metals simultaneously. If there is a potential difference between these two metals, the tape itself becomes part of the thermocouple pair, and the current distribution in the fiber network becomes complex. At the overlapping edge, the current density is higher and corrosion may be more concentrated.
Selection judgment based on "substrate coating thermocouple pair"
Firstly, confirm all metal types at the grounding interface of the conductive cloth tape, not just 'what is the surface being pasted'
Galvanic corrosion is the interaction between two metals, not a property of a single material. When selecting, all the metals that the tape actually comes into contact with during assembly should be listed: copper foil, aluminum shell, stainless steel screws, tin plated solder pads, and gold-plated connectors. Each metal and nickel plating pair has a different potential difference and corrosion risk.
Secondly, in the grounding interface of more active metals such as aluminum and carbon steel, priority should be given to the compatibility of the coating system
The potential difference between nickel aluminum thermocouple pairs is large, and aluminum becomes the anode and is accelerated to corrode. If the grounding interface is an aluminum shell, the nickel coating on the conductive cloth tape may accelerate the corrosion of the aluminum surface, causing corrosion products to accumulate at the interface and increase the contact resistance. In this scenario, tin plated conductive cloth or conductive cloth with anti-corrosion coating may be a more suitable choice - the potential difference of tin aluminum thermocouple pairs is smaller than that of nickel aluminum, and the corrosion driving force is weaker.
Thirdly, in humid or high humidity environments, incorporate "thermocouple pairs" into reliability verification instead of conducting salt spray testing on a single material
The salt spray test describes the corrosion resistance of the conductive cloth itself, and does not reflect its galvanic corrosion when in contact with dissimilar metals. For in car, outdoor, or high humidity scenarios, suppliers should be required to provide contact resistance change data of the "conductive fabric target substrate" combination under wet and hot conditions, or at least complete wet and hot aging testing of the lap interface at the sample stage.
Fourthly, in the die-cutting and assembly process, control the exposure of the cutting edge and interface sealing
The coating section at the edge of the die-cutting is the concentrated location of galvanic corrosion. If the application scenario involves humid and hot environments, it can be considered to perform edge sealing treatment on the die-cutting edge or cover the non-contact area with insulating tape to reduce the exposed area. The sealing of the overlapping interface is equally important - if moisture cannot reach the interface, the electrolyte conditions for galvanic corrosion will not be established.
Advanced Institute (Shenzhen) Technology Co., LtdThe conductive cloth tape product line covers nickel plating, tin plating, and composite coating solutions, providing galvanic corrosion assessment data for different coating systems combined with common substrates (copper, aluminum, stainless steel, tin plated surfaces).
The product supports edge sealing treatment for die-cutting and sealing solutions for overlapping interfaces, suitable for scenarios that require reliable grounding in humid and hot environments. For more technical information, please visithttp://www.avanzado.cn/.