In the manufacturing and design of TFT LCD display modules, one of the most significant cost-driving components is the Flexible Printed Circuit Assembly (FPCA). The FPCA serves as a critical bridge between the TFT panel and the mainboard, and its design intricacies directly influence not only functionality but also overall production cost. Due to the wide variety of factors that influence FPCA costs, this article focuses on how design elements impact those costs.

FPCA External Dimensions and Tolerance

The size of an FPCA directly impacts the number of units that can be produced from a single sheet during panel layout, thereby affecting per-unit cost. For example, larger FPCAs reduce yield per panel and increase material waste. Additionally, tighter tolerances such as ±0.05±0.07mm require slow wire-cutting molds, which are more expensive than medium wire-cutting molds used for looser tolerances like ±0.1±0.15mm. Thus, unless high-precision is necessary, designing with standard tolerances can significantly lower manufacturing expenses.

FPCA Connection Methods

The method by which an FPCA connects to a motherboard also plays a crucial role in cost determination. There are typically three types: latch-style, plug-in style, and soldered connections. Among these options, the cost ranking from highest to lowest is: latch-style > plug-in > soldered. However, soldered types are less commonly used due to their lower efficiency and poor connection repeatability. To reduce costs without compromising performance, plug-in style connections are generally preferred if no special requirement exists.

FPCA Bending Area and Component Area Covering Processes

The coverage processes for FPCA’s bending area and component area (such as component and connector areas) are typically: coverage film process and thermosetting green oil process for the bending area, and windowing film process and photosensitive ink process for the component area.

Bending Area:

As the frames of TFT-LCD display modules are getting narrower and the thickness of the LCD panels is reducing, the rebound stress requirements for the FPCA bending area are increasing. Using a coverage film process for the bending area may lead to higher rebound stress compared to the thermosetting green oil process, which increases the risk of hotspots at the BLU lamp holes.

The cost of using the thermosetting green oil process for the bending area is higher than the coverage film process due to the additional screen printing process.

In general, if the frame width is wider and there are no special customer requirements, the coverage film process can be preferred for cost considerations.

Component Area:

The component area can be divided into two parts: the component region and the connector region. The most common coverage process for the component area is the photosensitive ink coverage process. This is because small components, such as 0201 and 01005, cannot meet the accuracy requirements for window film process and SMT placement accuracy.

For the connector region, the coverage film windowing process can be selected flexibly based on the project requirements, but the spacing and width of the windowing pads should meet the process capabilities of FPCA manufacturers.

Generally, the coverage film windowing process is cost-effective compared to photosensitive ink coverage.

FPCA Steel Reinforcement Grounding Requirements

There are two main types of steel reinforcement grounding requirements for FPCA: grounded steel reinforcement and non-grounded steel reinforcement. Whether or not the steel reinforcement is grounded affects the cost of FPCA.

If grounding is required, the grounding impedance is typically required to be ≤5Ω. If grounding is not required, there is no control over impedance.

Generally, for cost consideration, if the customer does not specify grounding requirements, non-grounded steel reinforcement should be used. If grounding is required but impedance is not specified, the impedance should be controlled at <5Ω.

FPCA Component Potting Requirements

To avoid issues like pad peeling or delamination in the component area during bending, potting treatment is usually required to protect the component pads and enhance the strength of the pads.

There are two main types of potting processes in the industry: full encapsulation and partial encapsulation.

In general, the full encapsulation process is more costly than the partial encapsulation process. For cost considerations, if there are no special customer requirements, the partial encapsulation process is preferred.

FPCA Exposed Copper Area and Count

Exposed copper pads on FPCAs serve primarily for grounding or ESD protection. However, each pad increases material usage during surface treatment processes like ENIG (Electroless Nickel Immersion Gold). More exposed copper means higher consumption of gold and nickel—both costly materials—especially as gold prices have surged in recent years. Therefore, designers should aim to minimize both area and count of exposed copper while still meeting functional requirements.

FPCA EMI Shielding Design Requirements

Electromagnetic interference (EMI) shielding is essential in many applications but contributes significantly to cost depending on implementation:

• Double-sided shielding is more expensive than single-sided

• Full-surface coverage costs more than localized shielding over component areas

If EMI shielding is required, it’s advisable to apply it only where necessary using a single-sided approach with minimal surface area. Avoid segmented designs that require multiple attachment steps.

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