1. When the end user specifies the copper thickness of the flexible circuit board, there are likely several reasons behind this choice. For instance, current carrying capacity is a key factor, but copper thickness also significantly influences thermal performance and impedance. All these aspects are critical characteristics that greatly affect the functionality and reliability of the flexible circuit.
2. At this point, understanding the functional requirements that dictate the copper thickness is essential. Some typical functional requirements may include:
1. A minimum thickness in the connector area to guarantee a secure contact.
2. The current-carrying capacity is directly related to the cross-sectional area of the trace.
3. The appropriate conductivity depends on the cross-sectional area of the wire and the type of metal used.
4. The suitable impedance in high-speed circuits is influenced by the copper wire’s cross-sectional area, the surrounding dielectric constant, and the distance from the signal trace to the ground plane.
5. The thermal properties are directly linked to both the type of metal and the trace profile.
In the industry, copper weight is commonly used to indicate “thickness.” Flexible printed circuit (FPC) manufacturers typically purchase copper foils labeled as ½ ounce, 1 ounce, 2 ounces, etc. This weight reflects the amount of copper per square foot of foil. Similarly, material suppliers maintain a tolerance of +/- 10% for copper foil thickness.
Drawing specifications often utilize weight to define the thickness of flexible PCB copper. For instance, stating “the circuit uses 1 ounce of copper” can lead to some confusion, as the copper plating on a double-sided circuit may easily add an additional ounce to the surface of the trace. Therefore, it is unclear whether this figure represents the final or the initial thickness. Additionally, controlled impedance designs are most effective when copper plating is restricted to the through holes, avoiding copper plating on the trace surface. This minimizes variations in trace thickness and indicates specific product categories. This process is referred to as “pad plating only” or “button plating.” For controlled impedance design, one of these terms should be included in the drawing notes.
Several manufacturing processes can affect the final copper thickness, either increasing or decreasing it. Micro-etching is a common “clean” process used to prepare surfaces for electroplating or coating, and this process removes a small amount of copper. Conversely, copper plating will increase thickness. The circuit manufacturer will measure the thickness change directly in mils (1 mil = .001″) or microns (25μm = .001″).
The most precise method to determine thickness is through microdissection, a destructive test that typically utilizes coupons from unused areas of the processing panel. The location and size of these samples should accurately represent the copper thickness of the circuit. Variations in copper thickness across the panel can occur due to the current density generated during electroplating, which may vary based on the copper trace pattern, resulting in differences among individual part numbers. Generally, the copper plating layer is thinner at the outer edges of the panel and thicker towards the center.
In summary, when defining the specific copper thickness for a given application, it is highly advisable to discuss the various functional requirements beforehand. Additionally, FPC manufacturers can provide valuable recommendations regarding copper thickness, tolerances, and the most effective measurement methods.
2. At this point, understanding the functional requirements that dictate the copper thickness is essential. Some typical functional requirements may include:
1. A minimum thickness in the connector area to guarantee a secure contact.
2. The current-carrying capacity is directly related to the cross-sectional area of the trace.
3. The appropriate conductivity depends on the cross-sectional area of the wire and the type of metal used.
4. The suitable impedance in high-speed circuits is influenced by the copper wire’s cross-sectional area, the surrounding dielectric constant, and the distance from the signal trace to the ground plane.
5. The thermal properties are directly linked to both the type of metal and the trace profile.
In the industry, copper weight is commonly used to indicate “thickness.” Flexible printed circuit (FPC) manufacturers typically purchase copper foils labeled as ½ ounce, 1 ounce, 2 ounces, etc. This weight reflects the amount of copper per square foot of foil. Similarly, material suppliers maintain a tolerance of +/- 10% for copper foil thickness.
Drawing specifications often utilize weight to define the thickness of flexible PCB copper. For instance, stating “the circuit uses 1 ounce of copper” can lead to some confusion, as the copper plating on a double-sided circuit may easily add an additional ounce to the surface of the trace. Therefore, it is unclear whether this figure represents the final or the initial thickness. Additionally, controlled impedance designs are most effective when copper plating is restricted to the through holes, avoiding copper plating on the trace surface. This minimizes variations in trace thickness and indicates specific product categories. This process is referred to as “pad plating only” or “button plating.” For controlled impedance design, one of these terms should be included in the drawing notes.
Several manufacturing processes can affect the final copper thickness, either increasing or decreasing it. Micro-etching is a common “clean” process used to prepare surfaces for electroplating or coating, and this process removes a small amount of copper. Conversely, copper plating will increase thickness. The circuit manufacturer will measure the thickness change directly in mils (1 mil = .001″) or microns (25μm = .001″).
The most precise method to determine thickness is through microdissection, a destructive test that typically utilizes coupons from unused areas of the processing panel. The location and size of these samples should accurately represent the copper thickness of the circuit. Variations in copper thickness across the panel can occur due to the current density generated during electroplating, which may vary based on the copper trace pattern, resulting in differences among individual part numbers. Generally, the copper plating layer is thinner at the outer edges of the panel and thicker towards the center.
In summary, when defining the specific copper thickness for a given application, it is highly advisable to discuss the various functional requirements beforehand. Additionally, FPC manufacturers can provide valuable recommendations regarding copper thickness, tolerances, and the most effective measurement methods.
