Flexible PCBs are becoming increasingly popular in our daily devices like smartwatches, foldable phones, and even medical equipment. Two main manufacturing processes for making these flex PCB boards are additive and subtractive. While it sounds technical, it’s actually easy to understand.
Subtractive process of flex PCB fabrication
The subtractive process starts with a copper-clad substrate, where excess copper is removed through etching, leaving only the desired circuit patterns. This traditional approach is widely used due to its reliability and scalability.
Key steps in subtractive flex PCB fabrication:
Copper Clad Laminate Preparation: A flexible polyimide substrate is coated with a uniform layer of copper.
Photoresist Application and Exposure: A light-sensitive material is applied and patterned using UV light to define the circuit layout.
Etching: Unwanted copper is chemically etched away, leaving only the desired conductive traces.
Final Processing: Layers are laminated, and protective coatings are added.
Advantages:
Established Process: Well-suited for mass production with consistent results.
Cost-Effective: Lower production costs for standard designs.
Scalability: Easily adapted to various project sizes.
Additive manufacturing process
The additive process builds the circuit by layering conductive materials (like copper) directly onto the flexible substrate where the conductive traces are required. This method minimizes material waste, making it an eco-friendly option for flex PCB fabrication.
A simple example to understand additive manufacturing
Imagine you want to draw a circuit pattern on a transparent plastic film. Traditional subtractive processes are like painting the entire film with color and then erasing the unwanted areas to leave the desired pattern. In contrast, the additive process is like directly “drawing” the circuit lines only where they’re needed, without wasting any material.
In the additive process, conductive materials like copper are “grown” or “printed” directly onto a flexible substrate, such as polyimide. A great example is inkjet printing technology: much like a printer creating text on paper, the printer head deposits copper ink precisely in the required locations. The final circuit perfectly matches the design, while the rest of the substrate remains untouched.
Key steps in additive flex PCB fabrication:
Substrate Preparation: The flexible base material, such as polyimide, is cleaned and treated to ensure adhesion.
Patterning: Conductive traces are deposited precisely where needed using techniques like screen printing or additive plating.
Lamination and Finishing: Protective layers are applied to ensure circuit integrity and flexibility.
Advantages:
Material Efficiency: No excess copper is etched away, reducing waste.
High Precision: Ideal for intricate designs with fine lines and spacing.
Eco-Friendly: Lower chemical use and reduced environmental impact.
Conclusion
The subtractive process is like "sculpting," where you remove excess material to reveal the desired pattern—simple, efficient, and cost-effective. The additive process is like "drawing," where you build the circuit by adding material in a controlled way—more material-efficient but also more complex and slower. That’s why subtractive is the go-to method for most flexible PCBs, while additive is reserved for more niche applications where precision is crucial. After all, in everyday life, we often prefer things to be "useful and affordable," right?
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