With the emergence of flexible PCB technology, modern electronic products have come a long way. They exist in the core of many sensitive and precise electronic products. Even your smartphones, cameras, laptops, calculators and many electronic products are using this technology.
What is a flexible PCB?
It is made of polyimide substrate material. This material is both natural and synthetic, and is used in various industries such as automobile and clothing. Compared with traditional rigid printed circuit boards, the compactness and high electrical connection density of flexible circuits provide us with considerable weight, space and savings. When connected to the right application, this technology can reduce the total cost of electrical interconnection by up to 70% and reduce the use of cabling by up to 75%.
Progressive manufacturing process of flexible circuit board
The manufacturing method is programmed and structured. Let's understand three important manufacturing steps:
Step 1: Flexible PCB construction
This is the main stage, with the main focus on the preservation of basic materials. The main material used for flexible circuits is polyimide. Compared with FR-4, this material is expensive and needs to be used correctly. In order to properly use polyimide, you need to use nesting technology to make the circuit as close as possible. Prototype PCB manufacturing includes the following processes:
Circulation: It is acceptable to add a small amount of additional materials beyond the designer's limit. This extra material is called service loop, which can realize service length and circuit assembly.
Adjust conductor size: it provides maximum flexibility, so you need to select the thinnest copper, especially when you want to use the circuit for dynamic applications.
Etching: This process is used to compensate for any isotropic loss in the manufacturing process. In this process, the line width loss is almost twice the thickness of copper foil. Several factors will affect the linewidth, such as different types of copper, etching masks, conductors, etc.
Wiring: The wiring of conductors can be easily completed. Just fold in the vertical position of bending. This will improve folding and bending by reducing stress.
Grounding plane: If the electrical distribution is sufficient, the grounding area of cross hatches is created. This helps to improve the flexibility of the circuit by reducing the weight of the circuit board.
Step 2: Manufacturing process of flexible printed circuit board (PCB)
Now, let's focus on the board of directors. It starts with conductor spacing and width. The polymer film requires a standard conductor width of 375 microns. At the same time, the nominal polymer thick film and silver-based polymer film carry the required percentage of circuit current. The diameter of holes in flexible PCBs may vary depending on design and application.
Hole size: The manufacturer can create small holes, and can also flexibly layout the PCB to tilt it. With advanced technology, you can make the hole as small as possible (i.e. 25 μ m）。
Fillet: Fillet is a technology, you can multiply the area of the pad and divide the stress. Fillets are required for all pads and pad termination points on flexible circuits. Electroplated through holes are suitable for creating reliable solder joints.
Button electroplating: here, you can create an alternative electroplating through hole. Today, manufacturers use copper to prepare through holes and through holes.
Step 3: Focus on physical constraints
In this process, the manufacturer deals with the covering layer and the covering coating. We have brought you some common overlays used in this process:
Adhesive film: suitable for dynamic flexible circuit applications because it is composed of raw materials. The backing film is mainly used for recoating customized PCBs.
Screen-printable liquid outer coating: Screen-printable liquid outer coating is easy to carry and is usually used for thick polymer film.
Imaginable liquid and film polymer: it is the most advanced coating method and has some surprising functions, such as:
It acts as a solder mask and prevents solder from forming circuit traces.
It protects the printed circuit from external and internal damage.
It can prevent external electrification of the circuit.