How does the choice of plating affect flexible PCB manufacture?

choice of plating affect flexible PCB manufacture

The choice of plating for a PCB has important implications for its final performance. This is particularly true for flex and rigid-flex circuits, which are often subjected to a wide range of stresses during assembly and use. In particular, the copper-plating process has a direct effect on how well the board will bend. For these reasons, it’s important to work with a PCB manufacturer who understands the unique challenges of flexible and rigid-flex design rules.

During the fabrication of a flex or rigid-flex PCB, the PCB manufacturer cuts and shapes the flexible materials to match the design requirements. The conductive paths or traces are then created on the copper-clad substrates using photolithography techniques. Rigid and flexible sections are then bonded together using specialized adhesives. The plated through-holes then establish connections between layers of the rigid-flex or flexible pcb manufacture.

When it comes to the copper-plating of vias and through-holes, there are three main process options in the PCB manufacturer’s toolbox. These are panel plating, pattern plating and button plating. Pad plating is the preferred method for flex and rigid-flex circuits. This is due to the softer and more flexible copper that it uses. It’s important to note that the pad plating process combined with the copper type used (rolled annealed) must be specified in either the drawing notes or material stack up. RA copper has a specific grain structure that must be oriented in the direction of the shortest flex section for the best results.

How does the choice of plating affect flexible PCB manufacture?

Aside from the pad plating process, there are other factors that can impact the choice of plate finish for a flexible or rigid-flex circuit. For example, the thickness of the copper will have a significant effect on current carrying capability and voltage drop across the traces. In addition, the metallurgy of the copper will have an impact on mechanical properties such as stress and durability.

The cladding layer of the flexible circuit is usually made from polyimide. It’s important to ensure that the cladding material is compatible with the overall chemistry of the board, and has the capacity to remain stable when subjected to high temperatures. In addition, the cladding layer must also be capable of providing adequate protection against physical damage and environmental hazards.

For these reasons, many manufacturers will use a copper-nickel-palladium-gold (ENIG) plating material for their flex or rigid-flex circuits. This material has the advantage of being wire-bondable directly to the copper and offers a soft surface that can be damaged without exposing the nickel. It is important to understand the limitations of this type of material, however, as excessive mechanical damage could eventually expose the palladium layer.

Another consideration when choosing the plating for a flexible or rigid-flex circuit is whether or not it will require additional surface finishes, such as solder mask or hard gold. These surface finishes help to protect the conductors from oxidation during assembly and storage and improve the quality of solder joints. In addition to these surface finishes, a protective coverlay can be used to reduce the stress from thermal cycling and provide an extra level of mechanical protection for the circuit.