What types of electronic products are the soft-hard composite boards suitable for? What should be noted during the design and production process?

As electronic products continue to evolve towards thinner, more integrated and intelligent designs, the traditional PCB with plated-through holes connection method has become inadequate for meeting the demands of complex structural designs. The rigid-flex PCB, leveraging the integrated design advantages of "rigid board and flexible circuit", has gradually become a crucial solution in the fields of consumer electronics, medical equipment, automotive electronics and aerospace.

However, although the hybrid board has excellent performance, its design and manufacturing are much more challenging than those of ordinary PCBs. If the design is not well considered during the design stage, problems such as cracking, delamination, abnormal impedance, and assembly difficulties may occur later. Therefore, when applying the hybrid board, one should not only understand the applicable scenarios but also master the key design and production points.

What is a soft-hard hybrid board?

A soft-hard hybrid board is a special type of circuit board formed by connecting a rigid PCB and a flexible FPC through a lamination process.

Among them:

The hardboard area is used for installing components.

The soft board area is used for bending and connection.

The two parts form an integrated structure.

Compared with the traditional approach:

PCB connector, lead-out wire

The soft-hard combination board can directly achieve the connection between modules.

Having

Save space

Reduce weight

Improve reliability

Simplified assembly

The advantages.

Which electronic products are suitable for soft-hard composite boards?

1. Smartphones

Smartphones are one of the most typical application fields of soft-hard composite boards.

At present, many flagship mobile phones adopt a multi-layer structure combining soft and hard materials inside.

Mainly applied to:

Mainboard connection

Camera module

Display screen connection

Folded structure area

Antenna module

Due to the extremely limited internal space of mobile phones, the combination of soft and hard layers enables three-dimensional wiring and foldable installation, significantly enhancing the utilization of space.

II. Foldable Smartphones

Foldable products have extremely high requirements for flexible connections.

Ordinary PCBs cannot withstand repeated bending.

The soft-hard composite board can:

Achieve dynamic bending

Adapt to the opening and closing movements

Ensure stable signal transmission

Therefore, it has become an important component of foldable screen devices.

III. Smart Wearable Devices

Including:

Smartwatch

Smart bracelet

AR glasses

VR headset

These products usually require:

Small size

Light weight

High integration degree

The soft-hard combined board can be bent and arranged according to the shape of the product, better adapting to the internal space structure.

IV. Medical Electronic Equipment

Medical equipment has extremely strict requirements for reliability and miniaturization.

Typical applications include:

Endoscope

Ultrasound probe

Medical monitoring equipment

Implantable medical devices

The soft-hard combined board can reduce the number of connectors and enhance the long-term operational stability.

This is also beneficial for the miniaturization design of the equipment.

V. Automotive Electronics

The development of new energy vehicles and intelligent vehicles has driven the growth in demand for integrated circuit boards that combine both hardware and software.

Application areas include:

Vehicle-mounted camera

Compact structural design is required.

ADAS (Advanced Driver Assistance System) auxiliary driving system

Requires highly reliable signal transmission.

Intelligent cockpit system

The interior space is complex.

Instrument display system

Requires connection of multiple modules.

The combination of soft and hard materials in the board can enhance its vibration resistance and connection stability.

VI. Industrial Control Equipment

The industrial environment typically has the following characteristics:

Vibration

High temperature

Humidity variation

Traditional connectors are prone to contact problems.

After the combination of soft and hard materials reduces the connection points:

The reliability has significantly improved.

VII. Aerospace Equipment

Aerospace products emphasize:

Lightweighting

High reliability

Vibration resistance capability

The soft-hard combined board can reduce the weight of the wiring harness.

At the same time, improve the stability of the system.

Therefore, it is widely applied in avionics systems.

What should be noted during the design of the soft-hard combined board?

1. Reasonably plan the soft area and the hard area

This is the first step in the design.

The hard area is mainly used for:

Chip installation

Connector installation

Component soldering

The soft zone is mainly used for:

Fold

Transfer

Spatial extension

When designing, avoid:

Place the large-sized components in the flexible area.

Otherwise, it is likely to cause concentrated mechanical stress.

II. Design of the bending area control

The flexible area is the part that is most prone to problems.

When designing, please note:

Avoid sharp-angle wiring.

It is recommended to use circular arc wiring.

Reduce stress concentration.

The wiring direction is perpendicular to the bending direction.

This improves the bending lifespan.

Increase the bending radius

Reduce line fatigue damage.

General requirements:

The bending radius should be at least 6 to 10 times the thickness of the plate.

III. Avoid placing vias in the bending area

Vias are rigid structures.

If it is located in the bending area:

容易出现：

The copper layer has cracked.

Conduction failure

Therefore:

Flexible areas should avoid the placement of vias as much as possible.

Four. The copper sheet design should be reasonable.

Large areas of solid copper are prone to stress when bent.

During the design process, the following methods can be adopted:

Grid copper

Recessed copper

Improve the bendability of the flexible area.

V. High-speed Signal Design

If applicable:

USB4

PCIe

MIPI

LVDS

Wait for the high-speed interface.

Key points to be noted:

Impedance control

Differential line matching

Signal return path

Avoid a decline in signal quality due to structural changes.

What should be noted during the production process of soft-hard composite boards?

1. Material selection

The commonly used materials for soft-hard composite boards include:

Hardboard section:

FR-4

Soft board section:

Polyimide (PI)

The selection of materials needs to take into account:

Flexibility

Heat resistance

Reliability

II. Lamination Process Control

One of the core processes in the production of soft-hard composite boards is lamination.

Key points of control include:

Temperature

Pressure

Time

Avoid the following situations:

Stratification

Bubble

Resin loss

III. Position Control of Alignment

The connection position between the soft zone and the hard zone must be precisely controlled.

Need to control:

Graphic alignment

Drilling positioning

Position of the covering film

Ensure structural accuracy.

IV. Impedance Control

High-speed products must be strictly controlled:

Line width

Pitch

Material thickness

Ensure that the impedance meets the design requirements.

V. Reliability Testing

After the production is completed, the following tests are usually required:

Bending life test

Verify the reliability of the flexible area.

Thermal cycling test

Simulates temperature change environment.

Conduction test

Check the integrity of the circuit.

Peel strength test

Verify the interlayer bonding force.

How to choose a manufacturer of soft and hard composite boards?

When selecting a supplier, it is recommended to focus on the following aspects:

Do you have experience in mass production of combined soft and hard boards?

In particular:

Multi-layer soft-hard composite board

High-frequency soft-hard hybrid board

Project Experience.

Does it have a complete production line?

Including:

FPC production equipment

PCB production equipment

Laminating equipment

Achieve integrated manufacturing.

Does it have the ability for reliability verification?

Can it accomplish:

Dynamic bending test

Thermal shock test

Environmental reliability testing

This is more conducive to the stable mass production of the product.