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On the specification sheet of single conductive copper foil tape, it is usually stated that the surface resistivity is ≤ 0.05 Ω/sq and the shielding effectiveness is 60-100 dB (30 MHz -1 GHz). During the incoming material inspection, a multimeter was used to measure the copper foil surface, and the conductivity was found to be normal; Applied to the inside of the shielding cover, the initial EMC test also passed.
But after two years of service and several temperature cycles, the shielding effectiveness of the product may have quietly decreased by an order of magnitude, and there is no apparent abnormality in its appearance. The problem is not that the tape is "broken", but that its performance has undergone a gradual implicit decay over time and under repeated environmental influences. There are two main sources of this attenuation: the roughness loss of the copper foil surface at high frequencies, and the continuous increase in contact impedance of the adhesive layer at high temperatures.
The first source of high-frequency loss: skin effect turns "surface roughness" into resistance
In the low frequency range, the current is evenly distributed on the cross-section of the copper foil, and the purity of the copper foil dominates the conductivity performance. But when the frequency enters the GHz range, the skin effect concentrates the current on a very thin layer on the surface of the copper foil. At this point, the actual path through which the current flows is no longer a geometric straight line, but rather "crawls" along the microscopic undulations of the surface. The rougher the surface, the longer the current path, the greater the equivalent resistance, and the insertion loss increases accordingly.
The magnitude of this effect is not small. Research data shows that at 10 GHz, the losses caused by rough surfaces can be more than 20% higher than those caused by smooth surfaces. For grounding and shielding applications near 77 GHz radar or high-speed SerDes interfaces, this difference is sufficient to affect signal integrity.
There are systematic differences in the roughness of copper foils produced by different processes. The typical surface roughness of electrolytic copper foil is relatively high, and the Ra of some conventional products is above 0.9 μ m; The surface roughness of rolled copper foil can be controlled in the range of 0.14-0.35 μ m, which is closer to the skin depth at high frequencies. In the transmission loss test at 5 GHz, the electrolytic copper foil with higher roughness has a loss of about -35.0 dB, while the rolled copper foil with lower roughness has significantly lower loss. There is a measurable correlation between surface roughness and transmission loss. The cost of rolled copper foil is higher than that of electrolytic copper foil, but its skin loss in the millimeter wave frequency band is lower. This gap is shifting from an "optional advantage" to a "must-have" in high-end millimeter wave scenarios.
For single conductive copper foil tape, the meaning of this mechanism is that if only low-frequency shielding effectiveness and DC resistance are considered during selection, the insertion loss of the tape in the frequency band above GHz may be much higher than expected, and this loss will not disappear due to the "right" placement process. It is an inherent property of the surface morphology of copper foil.
The second source of high-frequency loss: the dielectric properties of the adhesive layer participate in impedance formation
The adhesive surface of single conductive tape is insulated, but this does not mean that the adhesive layer is completely "electrically transparent" at high frequencies. The adhesive layer serves as a dielectric layer between the copper foil and the substrate, and its dielectric constant (Dk) and loss factor (Df) can affect the parasitic capacitance near the grounding structure, thereby changing the characteristic impedance of the transmission line.
For double conductive tape, the conductive particles in the adhesive layer and the resin matrix together form a non ideal conductor dielectric hybrid system, and the stability of its high-frequency Dk/Df directly affects impedance consistency. Although single conductive tape does not have conductive particles, if the dielectric constant of the insulating adhesive layer fluctuates with temperature or frequency, it will still modulate the equivalent impedance of the grounding circuit. Frontier products control the high-frequency dielectric fluctuation of the adhesive layer within 5% by optimizing the resin system and filler dispersion, but this indicator is usually not provided in ordinary specifications. This means that the actual insertion loss of single conductive copper foil tape in high-frequency scenarios is the result of the combined effect of "copper foil surface roughness" and "adhesive layer dielectric properties". Optimizing only one of them is not enough to control overall performance.
Gradual degradation at high temperatures: why contact impedance increases over time
More concealed than high-frequency losses is the degradation of contact impedance in high-temperature environments.
A study on conductive tape under high temperature storage at 110 ° C provided a clear degradation path: the tape was used as a signal return path in microstrip lines, and after 2400 hours of high temperature storage, both contact resistance and contact capacitance significantly increased, resulting in a 30 dB decrease in magnetic field shielding effectiveness below 500 MHz. The degradation mechanism was attributed to the aging of the adhesive at high temperatures, causing a change in the interface impedance between the ground plane and the tape.
This data point reveals a failure mode that cannot be detected during incoming material inspection at room temperature. 2400 hours is approximately equivalent to working continuously at 110 ° C for 100 days, or a longer service time calculated based on temperature cycling. Such levels of thermal exposure are not uncommon in automotive electronics, base station RF units, and industrial equipment. When the contact resistance increases and the contact capacitance increases, the grounding of the shielding cavity is no longer low impedance, and high-frequency currents cannot find a smooth return path, resulting in a decrease in shielding effectiveness. Degradation occurs at the interface rather than the copper foil itself, making it difficult to capture through visual inspection and DC resistance sampling.
For single copper foil tape, the aging of the adhesive layer also affects the contact pressure between the copper foil surface and the exposed copper area. Pressure sensitive adhesives may soften or creep under sustained high temperatures, resulting in a decrease in the adhesion between copper foil and substrate, a reduction in effective contact area, and an increase in contact resistance. This process is consistent in direction with the degradation mechanism of double conductive tape, except that the conductivity of single conductive tape depends on the direct bonding between the copper foil surface and the conductive area, and the aging of the adhesive layer has a more direct impact on the contact pressure.
Selection and judgment of shifting from "initial indicators" to "service life retention rate"
Firstly, select the copper foil process based on the target frequency band, rather than choosing based on whether it is copper or not
If the operating frequency of the application scenario is below 1 GHz, the influence of the roughness of electrolytic copper foil on shielding effectiveness is relatively limited, and cost and processability may be more practical considerations. If the grounding or shielding path involves signals above 3 GHz, especially in the millimeter wave frequency band, preference should be given to using rolled copper foil or ultra-low profile electrolytic copper foil, and suppliers should be required to provide insertion loss or surface roughness (Ra/Rz) data at the target frequency band, rather than just providing DC resistance and low-frequency shielding effectiveness.
Secondly, in high-temperature or long-life scenarios, the "contact impedance after high-temperature storage" is used as an independent verification term
The initial contact resistance on the specification sheet cannot represent the state after 2400 hours. For on-board, outdoor, or continuously operating equipment, suppliers should be required to provide contact resistance change data after high-temperature storage (such as 110 ° C, 1000-2400 hours), or at least provide a long-term temperature resistance level and aging mechanism explanation of the adhesive layer. If the supplier is unable to provide such data, a larger impedance margin should be reserved for the interface during selection, or mechanical compression measures should be added to the structure to compensate for the contact pressure loss caused by adhesive aging.
Thirdly, distinguish between the two degradation pathways of "copper foil oxidation" and "adhesive layer aging", and address them separately
The oxidation of copper foil affects the conductivity of the copper foil surface, and tin plating or anti-corrosion coating can delay this process; The aging of the adhesive layer affects the interface contact pressure, and when selecting, attention should be paid to the glass transition temperature and long-term temperature resistance level of the adhesive, rather than just looking at the short-term temperature resistance peak. Two types of degradation may occur simultaneously, and solving only one of them is not enough to maintain long-term grounding reliability.
Advanced Institute (Shenzhen) Technology Co., LtdThe single conductive copper foil tape product line covers electrolytic copper foil and rolled copper foil substrates, providing options for different surface roughness levels. The surface resistivity of the copper foil surface is controlled at the level of ≤ 0.05 Ω/sq, and the adhesive surface is an insulating pressure-sensitive adhesive structure.
The product can provide options for tin plated copper foil to delay oxidation, and the temperature resistance level of the adhesive layer can be matched according to the target service temperature range. It also supports sampling and evaluation of contact resistance changes after high-temperature storage. Suitable for single point grounding in exposed copper areas of PCB, lining of plastic shielding covers, and partial shielding of FPC. For more technical information, please visithttp://www.avanzado.cn/.