Flexible printed circuit boards (FPCBs) offer lightweight, thin, and flexible properties but lack rigidity. To enhance thickness and stiffness in specific areas for easier subsequent installation or assembly, FPCB assemblies typically require reinforcement plates to increase strength.
In FPCB manufacturing, reinforcement costs account for approximately 5% to 10% of total expenses. Therefore, reducing reinforcement costs is one method to control overall FPCB expenses. This paper explores cost-reduction approaches for different reinforcement plate manufacturing processes by examining the impact of reinforcement plates on FPCBs.
1. Introduction to Reinforcement Types and Processing Techniques
The primary reinforcement materials for FPCBs are steel foil, polyimide (PI), and epoxy glass fiber laminate (FR-4), as shown in Figure 1. Considering actual manufacturing costs, we analyze these three reinforcement materials. Steel reinforcement is the most widely used but also the highest in material cost. PI reinforcement follows in usage and cost, while FR-4 is the lowest. The characteristics of each reinforcement processing method are as follows.
1.1 Steel Reinforcement Processing
Steel plate reinforcement typically refers to 303 stainless steel reinforcement. As a metal, it offers superior stability and provides grounding functionality, making it the preferred choice for applications requiring grounding. However, steel plate reinforcement cannot be drilled using computer numerical control (CNC) machines nor cut with lasers. It is generally formed through chemical etching or die-cutting.
1.2 PI Reinforcement Processing
As a specialty engineering material, PI offers flame retardancy alongside high and low temperature resistance, with a long-term operating range of −200 to 426°C. In FPCB manufacturing, PI reinforcement plates are applied to the rear area of the FPCB board edge connector. Different thicknesses of PI reinforcement sheets are selected based on design drawings and the operating environment.
1.3 FR-4 Reinforcement Processing
As a flame-retardant material, FR-4 offers excellent electrical properties, minimal environmental impact on its performance, and lower cost. However, its abrasion resistance is relatively inferior to PI. Therefore, in FPCB manufacturing, it is generally not used for reinforcing board edge connectors.
2. Exploration of Reinforcement Cost Reduction Methods
The scientific and rational nature of product design and process flows significantly determines production technology, quality levels, and cost consumption. It also impacts production efficiency and product performance. Improving product design enables optimization of production processes while ensuring quality and performance, thereby achieving the goal of reducing processing costs.
2.1 Cost Optimization for Steel Plate Reinforcement
2.1.1 Comparison of Two Steel Plate Reinforcement Processing Methods
Steel plate reinforcement board processing involves two methods: etching and punching. A comparison of these two methods is shown in Table 1.
As indicated by Table 1: ① The etching process involves multiple steps and complex procedures, requiring investments in etching, manual adhesive backing (with an additional step of inward retraction for adhesive tape relative to steel plate holes), and adhesive tape mold costs. Consequently, it incurs higher expenses but offers superior processing precision compared to die-cutting, making it applicable to a broader range of scenarios. As shown in Figure 2.
When the product is designed as a prototype or when processing capabilities cannot meet die-cutting requirements, the etching process can be selected. ② Die-cutting eliminates the etching process, manual adhesive backing, and mold/processing costs, offering higher efficiency. However, it imposes stricter requirements on hole-to-hole spacing and hole-to-outline clearance for manufacturable products.
Therefore, in practical applications, die-cutting should be prioritized over etching when product designs meet die-cutting requirements and involve mass production.