In wearable technology, medical devices, automotive modules, and aerospace electronics, flexible PCBs (printed circuit boards) are used. The demand for thin, light, and adaptable electronics makes flex PCB assembly necessary.
At PCBONLINE, we specialize in high-precision flex PCB assembly for both PI (polyimide) and PET (polyester) substrates. Each of our four automated SMT lines for flex PCB assembly is equipped with dual AOI inspections, precision pick-and-place machines, and an industry-leading reflow oven. We provide one-stop flex PCB assembly that ensures your flexible circuits perform reliably in demanding environments.
Understanding Flex PCB Materials: PI vs. PET
Choosing the right substrate is the first step in successful flex PCB assembly. While both PI and PET offer flexibility, they have distinct thermal and mechanical properties that dictate how they are assembled.
Polyimide (PI) flexible PCBs
Polyimide is the most common material used in flex PCBs. PI flex PCBs offer better flexibility, thermal stability, and mechanical strength.
PI can withstand high temperatures, making it compatible with standard lead-free soldering processes.
PI remains flexible across a wide temperature range and is highly resistant to chemicals.
PI flexible PCBs are ideal for complex multi-layer flex circuits, aerospace, and automotive sensors.
Polyester (PET) flexible PCBs
Compared with PI, PET is fragile and can't bend arbitrarily as PI does, but it is transparent. PET flexible PCBs are used in simpler or transparent applications.
PET has a much lower melting point than PI, requiring low-temperature assembly.
Compared with PET, PI is less flexible and less resistant to repeated thermal cycling.
Challenges and Solutions in Flex PCB Assembly
Assembling components onto a flexible substrate is significantly more challenging than rigid PCB assembly. Because the material is thin, often less than 0.1mm, a flex PCB can warp, stretch, or shrink during the assembly process.
- Dimension stability: Flexible materials expand and contract with temperature changes. This can cause misalignment between the solder pads and the components.
- Handling: Unlike rigid PCBs, flex PCBs cannot be easily transported through automated tracks without support.
- Heat management: Applying too much heat can melt PET or cause PI to delaminate.
PCBONLINE's flex PCB assembly solutions
To overcome these challenges, PCBONLINE provides custom fixtures and SMT assembly with precise temperature control specifically for FPCs (flexible printed circuits).
1. Custom fixtures
Since flexible PCBs lack rigidity, we use precision-designed fixtures, which are magnetic or non-magnetic.
Magnetic fixtures include a magnetic pallet and a steel sheet. The flexible PCB is clamped between them during the entire flex PCB assembly process.
A non-magnetic fixture is only the pallet. The flexible PCB is attached to the pallet with high-temperature tapes.
Before flex PCB assembly, the pallet is placed on a base fixture with pin snags for accurately placing the FPC. When the FPC is correctly fixed on the pallet, we remove the base fixture and put the pallet that carries the flexible PCB onto the SMT line.
2. High-precision SMT
At PCBONLINE, there are 4 automated SMT lines offering flex PCB assembly. Each is equipped with dual AOI systems, precision PNP machines, and a lead-free reflow oven.
Our pick-and-place (PNP) machines are Yamaha YSM20R and YSM10, ensuring components as small as 01005 are placed with surgical precision.
We have AOI (automated optical inspection) both before and after the reflow oven. This dual-stage verification catches bridge defects or shifted components before they become permanent.
3. Low-temperature reflow control
Thermal management is where PCBONLINE excels. We operate lead-free reflow ovens with customizable temperature profiles.
- PI flex PCB reflow: For Polyimide boards, we typically maintain a reflow peak of about 180°C. This ensures a strong solder bond while protecting the integrity of the PI substrate.
- PET flex PCB reflow: PET cannot handle standard reflow temperatures. To solve this, PCBONLINE utilizes an innovative approach: we often use the residual heat from other PCB reflow runs or specialized low-temperature solder pastes to bond components to PET FPCs. This prevents the substrate from deforming or melting.
Flex PCB Assembly Process at PCBONLINE
Our flex PCB assembly workflow is designed to maximize yield and minimize the stress placed on the flexible substrate.
Step 1: Placing the flex PCB on the fixture
We place the pallet on the base fixture first, and then position the flexible PCB on the pallet. When the flex PCB is fixed correctly on the pallet, we remove the base fixture and put the pallet that loads the FPC onto the SMT line.
Step 2: Solder paste printing
In the solder paste printing machine, high-quality solder pastes are ready on the custom-designed SMT stencil. The scrapper presses the solder paste through the holes of the SMT stencil. Then the paste is deposited exactly on the pads of the FPC secured in the fixture.
Step 3: Component placement
Our PNP machines use vision systems to align components based on the FPC's fiducial marks. This compensates for any minor material stretching.
Step 4: Pre-reflow AOI
Before reflow soldering, there's an AOI machine to scan the solder paste on the FPC pads to ensure the solderability to prevent economic losses.
Step 5: Reflow soldering
The FPC passes through our 10-zone lead-free reflow oven. Each zone is meticulously monitored. The ramp-up and cooling rates are strictly controlled according to our reflow profile.
Step 6: Pro-reflow AOI
After reflow soldering, the FPC assembly is scanned by the AOI machine to ensure no soldering defects on the surface.
Step 7: Testing
After assembly, we remove the fixture from the FPC. We then perform rigorous testing, including a functional test to ensure the PCB performs its intended electrical tasks and a bending test to ensure the solder joints remain intact when the PCB is flexed in its final application.
Besides the functional test and bending test, PCBONLINE offers the tension test, button strike life test, hand sweat test, solder joint pull strength test, environmental protection test, metallographic microscope inspection, bridge test, fuse fusing test, and salt spray test.
One-stop FPC Manufacturer PCBONLINE Provides Turnkey Flex PCB Assembly
If you're looking for flexible circuit one-stop solutions, including R&D, manufacturing, and assembly, partner with PCBONLINE. Founded in 2005, PCBONLINE has an FCCL factory, an FPC manufacturing base, and a turnkey flex PCB assembly factory, with stable supply chains and an R&D team.
PCBONLINE has turnkey flex PCB fabrication and assembly capabilities. We not only fabricate and assemble FPCs, but also provide flex PCB copper-clad laminates custom for FPC fabrication.
Powerful FPC manufacturing capabilities, including transparent PET FPC, 1 to 8-layer PI FPCs with a maximum length of 200m, HDI, and rigid-flex FPCs.
PCBONLINE does comprehensive tests, such as ensuring the bend radius, the tension test, the bending test, the button strike life test, the hand sweat test, the environmental protection test, the metallographic microscope inspection, the bridge test, etc.
PCBONLINE has flex PCB R&D capabilities and can do the FPC design or take part in your project's development from the early stage.
PCBONLINE provides free DFM (design for manufacturing) and one-on-one engineering support for FPC projects, including FPC layout optimization.
High-quality flex PCB assembly certified with ISO 9001:2015, ISO 14001:2015, IATF 16949:2016, RoHS, REACH, UL, and IPC-A-610 Class 2/3.
The professional team at PCBONLINE specializes in thermal management, signal integrity, fixture design, and manufacturing process control. We ensure the flex PCB assembly is tailored to your project's custom requirements. To get a quote for your flexible circuit project, please contact info@pcbonline.com.
Conclusion
Flex PCB assembly requires custom fixtures and thermal precision in reflow soldering. Whether you require the PI or PET flex PCB assembly, PCBONLINE has the technology and the expertise to deliver turnkey services. To manufacture flexible circuits with reliability at reasonable costs, work with the one-stop flex PCB manufacturer PCBONLINE.
