Complete Flexible PCB Manufacturing Process Flow

The relentless pursuit of the ultimate technological experience has been an ongoing endeavor, and a notable advancement in this regard is miniaturization, closely tied to the development of flexible circuit technology. In contrast to traditional circuits, flexible PCB (FPCB) made from materials like polyimide, offer compatibility with the internal space of electronic devices. While they bring numerous benefits, it’s crucial to recognize the greater manufacturing complexity. In this article, TechSparks will delve into each step of the flexible PCB manufacturing process to better assist you in realizing your projects.

Table of Contents

Step 1: Design and Layout

Flexible PCB Design Layout

Circuit design is always at the initial stages of a project. At this stage, designers can specify materials, thickness, patterns, layouts, and layering—essentially everything related to manufacturing. Flexible PCB commonly categorized as dynamic and static, share the same underlying principle of meeting three-dimensional spatial layouts, despite their inherent differences. 

It’s crucial to note that constructing multilayer flex PCB is challenging, and manufacturers capable of achieving a 20-layer layout are scarce. Therefore, during the design phase, it’s imperative not to deviate from practical considerations to avoid increased manufacturing costs. Once the design is complete, you need to export the relevant files and send them to the manufacturer for review.

Further Reading: Complete Flexible PCB Design Guide

Step 2: Materials Selection

Select Flex PCB Material

While various materials play a role in FPC manufacturing, the spotlight often falls on substrate when discussing material selection. Substrate materials ensure that the board can withstand various mechanical stresses during application and provide electrical performance. For flexible substrate materials may include polyimide, polyester film, liquid crystal polymers, and more. The key is to recognize the flexibility, dielectric constant, tensile strength, and other properties of substrate materials, ensuring your choice aligns with your requirements.

Further Reading: Which Flexible PCB Material is Best Suited for Your Project

Step 3: Printed Circuit

Flexible PCB circuit pattern printing

To facilitate the flow of current, the first step is to transfer the designed circuit pattern onto the surface of the substrate. This process begins by covering the clean copper foil layer onto the substrate surface and bonding them together through chemical methods. Next, the entire board surface is coated with a photosensitive material, and the circuit pattern’s graphics are exposed using a photolithography machine. Then, chemical substances are used to remove the unexposed photosensitive material, exposing the copper foil to form the circuit pattern. Finally, the board is placed into an etching tank, where a chemical solution is used to remove the copper foil not protected by photolithography, forming the conductors and connections of the flexible PCB circuit pattern.

Step 4: Drilling

Flexible PCB Drilling

Drilling is carried out to create holes on the board for assembling and soldering, forming a flexible PCBA board. However, due to the characteristics of flexibility, bending may occur during the CNC, leading to potential defects. To address this issue, additional fixing measures need to be taken.

For more complex projects, using laser is an ideal choice. This helps achieve precise control over the position and size of the holes, reducing deformation issues during the manufacturing process. After drilling is completed, it is essential to clean the remaining debris to prevent adverse effects during component installation and soldering.

Further Reading: All You Need to Know About Flexible PCB Via Holes

Step 5: Plating

Flex PCB Plated Through Hole

Electroplating is employed to deposit a thin layer of copper within the plated through-holes, allowing the flow of current from one layer of the flexible PCB to another, and facilitating the connection between layers. This process involves coating the surface of the through-holes with an activator to enhance its reaction with the electroplating solution. Subsequently, the through-holes are immersed in the electroplating bath, and an electric current is applied, causing the metal to deposit on the inner walls of the through-holes.

Step 6: Cover Layer

Flexible Circuit Overlays

The cover layer is a polymer film designed to protect the circuit pattern on a flexible PCB from physical damage and oxidation, which is similar to solder mask. Before application, it needs to be cut according to the size of the board, then positioned on the flexible PCB and firmly secured to its surface through methods like heating or pressure.

Further Reading: Flex PCB Coverlay Guide to Assist You Apply It Better

Step 7: Lamination

Flexible PCB Lamination

The lamination process involves placing the stacked materials into a lamination machine, where the internal adhesive melts under pressure and high temperature. After cooling, the layers are tightly bonded together.

Further Reading: Comprehensive Introduction to PCB Lamination Process

Step 8: Surface Finish

Surface finish is a process designed to apply a thin film on board, enhancing its performance, corrosion resistance, and soldering characteristics. Various surface finish methods are used for flexible circuits, and the processes for these treatments can differ slightly. Such as:

ENIG involves depositing a layer of nickel onto the copper surface, followed by a layer of gold on top of the nickel.

OSP applies an organic protective layer onto the copper surface to improve adhesion and prevent oxidation.

Step 9: Testing

Flexible PCB Bending Test

To ensure manufacturing quality, testing must be conducted during and after the production process to validate its performance. Because flexible PCB are thinner and may require frequent bending, testing efforts may need to be intensified during this phase. For example, bend testing should be added to the items to verify their bending performance and ensure they can withstand repeated folding or bending. Additionally, due to the finer traces, the current load capacity of individual boards should be tested when facing certain high-power applications to ensure they can withstand normal loads and avoid problems such as wire breakage due to overload.

Further Reading: Flexible PCB Testing Guide

Step 10: Cutting

Cutting flexible PCB

In commercial projects, flexible PCB are often present in the form of panels or arrays to reduce production costs. Once the entire panel production is complete, they are loaded onto a cutting machine for slicing. This process is machine-driven and requires only alignment, with the key focus on ensuring smooth edges of the boards.

Further Reading: Optimizing Flexible PCB Panelization to Reduce Costs

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