From smartphones and wearable devices to automotive electronics, flexible printed circuit boards (FPCs) are widely used in various intelligent electronic devices due to their bendability and lightweight characteristics.

As products evolve toward higher integration and miniaturization, component density on FPCs increases dramatically. Their inherent advantages—flexibility, low surface energy, and uneven thickness—demand even more precise dispensing processes to ensure stable performance and extended service life.

As a high-precision dispensing application expert, QUARK Industrial Research Institute has accumulated extensive case studies and experience in FPC dispensing and reinforcement processes, providing tailored solutions for diverse process requirements.

01 SMT Red Adhesive Placement and Pre‑fixation

This process is mainly used in single‑ or double‑side SMT processes on FPCs. Red adhesive is used to temporarily fix components between FPC pads, preventing displacement during subsequent soldering.

Primary application scenario: Component pre‑fixation in FPC surface mount processes
This is a foundational step in FPC assembly. The dispensing process must form consistently shaped, well‑defined adhesive dots in the gaps between designated pads to ensure component leveling and push‑off strength, while avoiding contamination of the solder pads.

Typical applications: Fixing chip resistors, capacitors, connectors, and other components on FPCs used in smartphones, tablets, wearables, and other consumer electronics.
Compatible media: Epoxy‑based red adhesive, high‑temperature SMT adhesive, etc.

Image: FPC red adhesive fixation

QUARK Process Card: Red Adhesive Component Pre‑fixation
QUARK Core Process & Metrics: The QUARK piezoelectric valve dispensing process achieves a minimum dot diameter of 200μm, meeting high‑precision requirements. Enhanced satellite‑dot suppression effectively prevents panel contamination.

02 Chip‑Level Underfill and Encapsulation Protection

In applications such as camera modules, fingerprint recognition modules, and RF chips, the interconnecting solder joints between the chip and FPC are extremely fragile. Underfill and encapsulation processes provide effective protection, enhancing impact and flex resistance.

Primary application scenario: Reinforcement of chip‑FPC interconnections and overall module protection
This is a critical process for ensuring high‑reliability FPC assembly. It requires precise control of adhesive flow, filling path, and fillet height to ensure void‑free underfill, controllable side‑fillet width, and no contamination.

Typical applications: Underfill and encapsulation for chips and components in fingerprint recognition modules, camera modules, TWS earphones, etc.
Compatible media: Capillary underfill, no‑flow underfill, low‑temperature curing epoxy encapsulants, etc.

Image: Underfill dispensing — product shown is for reference only, not a flexible board

QUARK Process Card: Board‑Level Packaging Underfill
QUARK Core Process & Metrics: Meets high‑precision underfill requirements for chip‑level devices with enhanced bubble and satellite‑dot suppression, maintaining stable accuracy over extended operation.

03 FPC Board Reinforcement and Structural Bonding Enhancement

Structures such as FPC connector roots, complex‑shaped components, and component bond wires are often located in stress‑concentrated areas. Structural reinforcement in designated areas effectively increases FPC rigidity, preventing circuit breakage or component detachment.

Primary application scenario: Reinforcement of FPC connector roots, bonding of complex‑shaped components
These applications demand high adhesive quality (no bubbles, voids, etc.) while also addressing special requirements for flexibility and adhesion in complex scenarios.

Typical applications: Reinforcement of mobile phone battery FPC protection boards, display FPC connectors, FPC bond wire reinforcement
Compatible media: High‑adhesion epoxy structural adhesives, flexible UV adhesives, thermosetting adhesives, etc.

Image: Gold wire reinforcement, chip bond wire reinforcement, FPC reinforcement

QUARK Process Card: FPC Gold Wire Reinforcement
QUARK Core Process & Metrics: Fills and reinforces a confined area of 2×6mm with thermosetting adhesive, effectively suppressing voids and bubbles while meeting structural rigidity and stability requirements.

04 Circuit and Device Structural Protection

Compared to conventional circuit board protection processes, FPC circuit and device structural protection requires greater sensitivity to adhesive layer thickness and flexibility. A thin, uniform protective layer must be formed to provide electrical isolation and protection.

Primary application scenario: Insulation covering of FPC circuits, protection of solder joints and device structures
This process demands higher coating precision and consistency. It must prevent medium overflow into other connection areas while ensuring complete coverage, uniform adhesive thickness, and no discontinuities.

Typical applications: Protective coating on flexible circuits, encapsulation of automotive electronics chip solder joints, insulation coating on rigid‑flex boards for cameras, flexible sensor packaging
Compatible media: Low‑viscosity insulating UV adhesives, conformal coatings, insulating adhesives, etc.

Image: FPC dispensing, FPC solder joint encapsulation, conformal coating on FPC

QUARK Process Card: Conformal Coating on FPC Solder Joints
QUARK Core Process & Metrics: Provides precise encapsulation of solder joints, ensuring complete coverage while enhanced satellite‑dot suppression effectively prevents board contamination.

From red adhesive pre‑fixation in the front‑end manufacturing stage, to underfill during packaging, and reinforcement for structural strengthening, precision dispensing processes run throughout the entire FPC manufacturing workflow—continually evolving toward smaller scale, higher precision, and greater reliability.

Leveraging extensive FPC application experience and a deep understanding of process principles, QUARK Industrial Research Institute helps more customers ensure consistent product quality through superior product capabilities and process expertise.