How to Prevent Copper Oxidation in Flexible Printed Circuits
Copper Oxidation in Flexible Printed Circuits
Copper oxidation is one of the main challenges to a flexible printed circuit’s (FCB) performance. It happens when oxygen reaches the surface of copper and starts reacting with it, creating a chemical reaction that leaves the metal contaminated with copper oxide. The corrosion can be dangerous, especially for high-performance flex PCBs that require a lot of heat and power.
Corrosion can affect the conductivity of copper by reducing its available surface area. This can happen through a variety of mechanisms, including electrolytic corrosion, pitting corrosion, and crevice corrosion. When a contaminant like water gets into an electrical pathway between two neighboring copper traces, it can cause small slivers of metal to form, which bridge the gap and short the circuit. This can disable a functional block of the circuit and reduce its functionality, or even shut down the entire device.
To prevent this, it’s important to use conformal coatings that provide a barrier between copper and the environment. Some of the best protective materials are epoxy coatings, aerosol spray coatings, and solder mask. These can be used in combination to create a layer of protection that prevents the oxidation of copper. However, identifying the copper areas that need to be protected is often difficult because of the complex layouts and thermal demands of a flexible printed circuit.
How to Prevent Copper Oxidation in Flexible Printed Circuits
In addition, some types of copper coatings can deteriorate over time due to the environmental conditions and the nature of the fabrication process. This can lead to a build-up of copper oxide, which can degrade the conductive properties of the copper.
One way to prevent oxidation is to ensure that the conductive copper is properly fabricated and soldered before using it in a flex circuit. The best method for doing this is to choose a copper supplier that provides high-quality supplies that will last over time.
Another method is to apply a special anti-oxidation copper paste to the surface of the copper conductor. This is done by modifying the surface of the copper using a proprietary technology that incorporates antioxidant compounds such as formate anions and organic thiols. The resulting copper paste has excellent anti-oxidation and conductivity properties, making it a potential candidate for the production of low-cost flexible electronics.
Finally, it’s also important to use the right type of copper when fabricating a flex circuit. For example, some mills may coat coiled or flat copper sheet stock with an oil film that can result in dark purple or black colorations of the conductor surfaces after installation and exposure to the weather. This can make it challenging to identify which sections of the copper are the conductive paths in a flex circuit, which can impact its reliability. To avoid this, it’s recommended to use copper with a clear coating that won’t stain or discolor.