Don't know how to select parameters for FPC board making? A mind map will teach you!

嘉立创FPC

Don't know how to select parameters for FPC board making? A mind map will teach you! [Copy link]

Although FPC flexible printed circuit boards are widely used in consumer electronics, wearable devices, robot AI, medical equipment and other fields, they are still relatively unfamiliar to many students.

This also causes many students to be confused when they encounter parameters such as copper thickness, minimum line width/line spacing, minimum aperture, via opening, via cover oil, and reinforcement when making boards.

Today, I will use a mind map to teach you how to choose FPC parameters , so that you don’t have to chase the engineer to ask questions when making boards in the future!

1. Number of boards/board size

The number of boards is easy to understand, it is how many boards you want to make.

The board size refers to the size of the board. The maximum size of the Jialichuang FPC board is 234X490mm (limit 250X500mm) , and there is no limit on the minimum size , but if it is smaller than 20X20mm, it is recommended to splice the board.

2. Number of board layers

The number of layers is usually determined during the design, so you can simply select the corresponding number of layers based on the design requirements.

FPC can be divided into single-layer boards, double-layer boards and multi-layer boards according to the number of layers .

Single-layer boards are the simplest flexible boards and are generally used in fields such as industrial control and electronic instruments where the circuits are relatively simple.

The biggest difference between double-layer FPC and single-layer FPC is that it has more vias to connect two layers of copper foil to form a conductive path. It is generally used in mobile phones, automotive instruments and other products.

Multilayer boards are made by pressing multiple layers of single-sided or double-sided FPC together, forming metalized holes through drilling and electroplating to form conductive paths between different layers. They are generally used in high-end consumer electronic products such as smartphones.

1. Solder mask color

The solder mask colors of FPC are yellow, black and white. Yellow is recommended .

Yellow film is suitable for most products, such as various types of cable products.

Black film is often used in high-end products or products that need to absorb light, such as automobiles, mobile phones, LED displays, etc.

The white film has an extra layer of white coating compared to the yellow film and is often used on products that require reflection, such as lighting fixtures, LED screens, medical beauty products, etc.

2. Board thickness

The board thickness refers to the thickness of the FPC soft board, excluding the thickness of the reinforcing material.

If there is no copper or covering film in the measurement area, the finished product thickness will be reduced accordingly.

If white cover film is used, the thickness of single-sided board will increase by 18um, and that of double-sided board will increase by 36um.

3. Copper foil thickness

Refers to the thickness of the copper foil of the FPC circuit layer, which must correspond to the board thickness.

The single-sided board can be selected as 18um (0.5oz), 35um (1oz); the double-sided board can be selected as 12um (0.33oz), 18um (0.5oz), 35um (1oz).

4. Minimum line width/line gap

Normally, the smaller the size, the higher the difficulty. Generally, it is recommended to be above 3/3mil , and the limit of Jiali Chuang is around 2/2mil, but it is recommended not to design it as much as possible.

5. Minimum via/pad

The via's outer diameter must be 0.2mm larger than the inner diameter, and it is recommended to be 0.25mm or larger. Generally speaking, the smaller the hole, the more expensive it is. It is recommended that the via's inner diameter be 0.3mm and the outer diameter be 0.55mm.

6. Solder mask coverage

FPC uses a cover film as the solder mask. There are two main types of solder mask covering: via opening and via cover oil.

Via window: It means that the via pad of the finished board will be exposed, but the via window of FPC may cause oxidation in the hole and breakage of the copper in the hole.

Via cover oil: refers to the finished board via pads covered with solder mask, which can protect the copper from oxidation and from breaking when bending. Jiali Chuang has done via cover oil by default. If you need to open a via window, you need to make special remarks when placing an order!

7. Minimum solder bridge width

The minimum solder resist bridge width is 0.5mm, that is, the pad spacing must be ≥0.5mm to ensure the bridge . If the value is less than this, Jiali Chuang will open the window by default.

8. Reinforcement

There are five main types of reinforcement: PI, FR4, steel sheet, 3M double-sided tape, electromagnetic shielding film, etc.

PI reinforcement is often used in gold finger plug-in products.

FR4 is suitable for component hole area reinforcement.

The price of steel sheets is relatively high, but they have good flatness and will not deform. They are suitable for products that require chip mounting (steel sheets have weak magnetism and are not recommended for products similar to Hall elements)

3M glue is generally used to fix FPC boards during assembly

Electromagnetic shielding film is used to solve EMC problems. It is generally recommended to add grounding windows in the solder mask layer to make the electromagnetic shielding film and the ground copper conductive and increase the shielding effect. (Note: Be sure to make a sample first for verification. The electromagnetic film has a greater impact on impedance. Improper design will cause signal abnormality.)

The total thickness of the reinforcement area = FPC board thickness + reinforcement thickness, but it is not a direct addition. The thickness of the solder mask and whether there is copper covering on the back of the finger must be considered.

9. Make-up

The maximum size of the panel is 234X490mm; the recommended spacing is 2mm. If there is steel reinforcement, the spacing is designed to be 3mm .

Attention! Many FPC frames are of special shapes. If the layout is not done properly, the utilization rate of the board will be low, which will not only increase the cost, but also make production more troublesome. If you don't know how to layout, you can also ask Jiali Chuang engineers to help you.

In addition to the above conventional parameters, the production of FPC also involves gold fingers, impedance, half holes and other processes.