The engineer applied a double conductive copper foil tape between the PCB grounding pad and the metal frame. Measured with a multimeter, there is indeed conductivity between the adhesive surface and the copper foil surface, and the reading is normal. But after the equipment was assembled, the ESD test still failed and the grounding resistance was much higher than expected.

2、 Structure and Z-axis conduction mechanism of double conductive copper foil tape

The double conductive copper foil tape consists of three layers: high-purity electrolytic copper foil layer, conductive acrylic pressure-sensitive adhesive layer, and release layer. The copper foil surface is conductive, and the adhesive surface is also conductive due to the addition of conductive particles such as nickel.

The implementation path of Z-axis conduction is that when the adhesive tape is attached between the surfaces of two conductors, the conductive pressure-sensitive adhesive layer is compressed, and the nickel particles in the adhesive layer approach each other. When the pressure is sufficient to overcome the elastic resistance of the adhesive layer, physical contact is formed between particles, constructing a vertical conductive path from the adhesive surface to the copper foil. This mechanism is similar to the Z-axis conduction principle of anisotropic conductive adhesive (ACF) - the conductive path is only established in the direction of pressure, rather than randomly diffusing within the plane of the adhesive layer.

3、 How does pressure determine vertical resistance

Vertical resistance is the most crucial but easily misread parameter of double conductive copper foil tape. The "≤ 0.03 Ω" on the specification sheet is usually measured under standard pressure conditions - for example, after reciprocating rolling with a roller of a specified weight. In actual construction, if only lightly pressing with fingers or not applying sufficient pressure after bonding, the vertical resistance may significantly increase.

Three key variables that affect vertical resistance:

4、 Dual conductivity and single conductivity: the fundamental difference in Z-axis conductivity

The adhesive surface of the single conductive copper foil tape is insulated, and current can only be conducted along the X-Y direction within the copper foil surface. The adhesive surface of the double conductive copper foil tape is conductive, and current can pass through the adhesive layer to reach the object being pasted, forming X-Y-Z three-way conduction.

The core application scenarios of dual conductive copper foil tape include: bridging the gap between two conductive casings, and the adhesive surface contacts the two casings to form a bridging path; The PCB grounding pad is connected to the metal frame to release static electricity, and Z-axis conduction completes grounding; The conductive connection between the cable shielding layer and the metal connector housing; Maintain electrical continuity at the seams between the components of the shielding cover.

5、 Key performance parameters and correct construction points

The three steps of correct construction:

• Clean the surface.Wipe the surface of the sticker with alcohol or isopropanol to remove oil stains, dust, and oxide layers. Surface contamination is the most common cause of increased contact resistance.
• Apply pressure.After bonding, use a scraper or roller to evenly press and compact the surface of the tape. The pressure needs to be sufficient to compress the adhesive layer and bring the nickel particles into contact with each other. For scenarios with strict requirements for grounding resistance, it is recommended to measure the vertical resistance after bonding for verification.
• Avoid touching the adhesive surface.The grease on the fingers can contaminate the adhesive surface, reducing adhesion and conductivity. During construction, the edge of the tape should be pinched or tweezers should be used for operation.

6. Conclusion

The value of double conductive copper foil tape lies in its provision of a detachable and field repairable Z-axis conductivity solution - no welding equipment or high-temperature processes are required, only surface cleaning and pressure application are needed to establish an electrical connection between two conductors. But the premise of this convenience is to understand the pressure dependent mechanism of its Z-axis conduction: it is not a switch that "conducts when attached", but a pressure contact interface that "conducts when pressed".

Understanding the relationship between vertical resistance and bonding pressure, the influence of adhesive layer thickness on conductivity, and the decisive role of correct construction in the reliability of Z-axis conductivity - these are the key to upgrading double conductive copper foil tape from a "roll of tape" to an "engineering decision".