VCM Flexible PCB: Key Design and Manufacturing Requirements for Voice Coil Motors

A voice coil motor (VCM) is widely used in compact camera modules for functions, such as autofocus (AF) and optical image stabilization (OIS). Although the VCM itself is small, the flexible PCB inside the module has to meet surprisingly tight mechanical and dimensional requirements.

The flexible PCB isn’t simply used to connect the VCM to the main board. It also needs to accommodate movement, provide connections for ICs and sensors, and fit accurately into a very limited space.

For this reason, VCM flex PCB manufacturing requires tighter control than many conventional flexible circuit applications.

How Is Flexible PCB Used in a VCM?

In a VCM module, it provides the electrical connection between the motor, sensors, ICs, and the external circuit.

At the same time, the flexible PCB may need to follow the small movements generated by the VCM during operation. This is particularly important in camera modules using OIS, where the actuator continuously makes small movements to compensate for camera shake.

Precision Is Critical in VCM flexible PCB Manufacturing

One of the biggest differences between VCM flexible PCBs and general-purpose flexible PCBs is dimensional accuracy.

The available space inside a camera module is extremely limited. A small positional error in the flexible PCB can affect the assembly of the VCM, IC, sensor, or other components.

Double-Sided Circuit Alignment

For double-sided VCM flexible PCBs, the relative position between the front and back circuits needs to be carefully controlled.

Depending on the design, a typical production target may be around ±0.05 mm, while more demanding structures may require control approaching ±0.03 mm.

This alignment affects not only the circuit itself, but also the position of pads, vias, coverlay openings, and other features. The actual tolerance should always be determined by the customer's drawing and assembly requirements.

Flexible PCB Flatness

VCM flex PCBs may require SMT, IC attachment, stiffener bonding, or other assembly processes. Excessive warpage can make accurate placement more difficult.

For small precision flexible PCBs, a flatness target of approximately 0.10 mm or better can be considered, with some applications requiring around 0.05 mm, depending on the flexible PCB size and structure.

Component-to-Outline Positioning

Controlling the distance between components and the flexible PCB outline can be just as important as controlling the outline itself.

A component may technically be within its own dimensional tolerance but still interfere with the surrounding mechanical structure if its position relative to the flex PCB edge is incorrect.

For precision applications, a component-to-outline positional tolerance of approximately ±0.10 mm may be used as a production target.

Steel Stiffener Alignment

Many VCM flexible PCBs use a steel stiffener on the back side. 

A typical target for steel stiffener positioning may be around ±0.10 mm, with high-precision applications potentially requiring approximately ±0.05 mm. The positioning reference should ideally be based on defined datum points, holes, or edges.

Dynamic Bending Reliability

OIS applications make dynamic bending one of the most important considerations for VCM flexible PCBs.

The flexible circuit board may experience repeated small movements rather than a single static bend. Over time, repeated mechanical stress can cause copper fatigue, especially if the circuit structure concentrates stress in one area.

The following factors can affect bending reliability:

• Copper type

• Copper thickness

• Bend radius

• Circuit width

• Number of copper layers

• Coverlay structure

• Copper distribution

• Transition design

The goal is to keep the flexible section flexible while avoiding unnecessary stress concentration.

IC Underfill for Additional Reliability

Some VCM FPC assemblies include ICs that require underfill.

Underfill fills the space beneath the IC and helps distribute mechanical stress between the component and the flexible PCB. This can be useful when the assembly experiences vibration, thermal cycling, or repeated mechanical movement.

From a manufacturing perspective, the process needs to control:

Dispensing volume → Flow → Coverage → Overflow → Curing

Excessive glue can contaminate nearby pads or flexible areas, while insufficient filling may leave voids and reduce mechanical support. For compact VCM assemblies, controlling the flow area is very important.

Packaging Is Part of VCM flexible PCB Quality

Because VCM flexible PCBs are typically small and thin, and may include steel stiffeners or assembled ICs, improper packaging can cause deformation or component damage during transportation.

Packaging should therefore consider:

• Flexible PCB deformation

• Surface scratches

• IC protection

• Steel stiffener protection

• ESD protection

• Moisture control

• Cleanliness

• Separation between individual parts

For high-precision VCM flexible PCBs, packaging is not simply a transportation step. It is part of the overall quality-control process.

Conclusion

Flexible PCBs play an important role in VCMs used for compact camera modules. They provide electrical connections while allowing the module to remain small and accommodate the movement required for AF and OIS.

The challenge is not simply making the flexible PCB smaller or thinner. The real challenge is maintaining dimensional accuracy while keeping the FPC flexible and reliable.

Circuit alignment, flatness, component positioning, steel stiffener placement, dynamic bending, IC underfill, and packaging can all affect the final VCM assembly.

For VCM applications, reliable flexible PCB manufacturing is therefore a process of controlling small tolerances across multiple manufacturing steps.