Introduction
When electronic devices become smaller, you have to pack complicated circuits into compact spaces. SMT assembly for flexible pcb is the major answer to modern electronics. With this process, you can directly mount components onto flexible circuits for products such as cameras and wearables. Let us discuss how this technology works.
What is Flexible PCB (FPC)?
A Flexible PCB (FPC) is a circuit constructed on a flexible material such as polyimide (PI) film. Instead of a rigid board, you have a circuit that can consistently bend and flex. This makes them a must in compact or uniquely shaped electronic products. FPCs provide a flexible solution for today’s designs.
FPC SMT Methods: Roll-to-Roll and Attachment with Jig
The most significant difficulty in FPC assembly is the flexibility of the board. You have to hold the circuit on a carrier to make the SMT process work effectively. That way, you can get precise placement and soldering of components. Let’s have a look at the two main approaches: roll-to-roll and using a jig.
Roll-to-Roll Method
The roll-to-roll process makes assembly of the FPC automatic using a continuous roll of material. You load the flexible circuit through the whole SMT line without separate handling. It is ideal for large-scale production runs and reduces contamination. The only drawback is the expense of specialized equipment. This makes it impractical for low-batch SMT on flex projects.
Advantages:
- You eliminate having to attach the FPC to a jig.
- You avoid creases and scratches on the circuit.
- You reduce handling contamination, perfect for cleanroom environments.
- You can meet the needs of advanced Chip-on-Flex (COF) processes.
Disadvantages:
- You need special equipment with limited application to products.
- You have a high initial investment.
- You require large-scale production; it is not economical for small quantities.
FPC SMT Using a Jig
The most popular flexible PCB assembly method employs a dedicated carrier, or jig. You attach the flexible circuit to this rigid plate, which is a temporary stiffener. It makes it easy for you to use your standard SMT equipment, and it is very cost-effective. It’s a great method for small to medium-sized production runs. The significant trade-off is more manual handling.
Advantages:
- You can easily incorporate it into your standard SMT lines.
- You enjoy the benefit of a low-cost solution for low to mid-volume production.
- You simplify the testing and inspection processes.
- You have the flexibility of reusing and converting jigs for similar FPC designs.
Disadvantages:
- You are dependent on manual loading and unloading, restricting automation.
- You have to create and produce custom jigs for every project.
- You experience increased complexity with double-sided FPC assembly.
Details of FPC SMT Process of the Attachment with Jig Method
The Jig method is the most common assembly process in flexible PCBs. The process has some very important steps to guarantee success. Let’s break down the essential information you must know, starting from jig selection up to the final inspection.
Jig Types for FPC SMT
The jig or carrier serves as a working flex pcb stiffener, holding the circuit flat during assembly. You’ll need to select something that is durable, thin, and can manage heat. Synthetic stone and aluminum are popular options. Both provide a range of advantages to your flex circuit assembly process, from cost to durability and ease of use.
Synthetic Stone (Engineering Plastics)
This material provides great stability and does not heat up, so it is easy to work with. It also has a decent service life, but is more expensive compared to aluminum.
Aluminum Jig
Aluminum jigs are cheap, durable, and deal with heat quite well. Their greatest weakness lies in the fact that they become very hot to handle and require gloves to be handled safely.
Silicone Jig
Silicone is adhesive, making it easy to attach and detach the FPC. Its tackiness, though, drops as time passes, resulting in a shorter service life.
Special High-Temperature Resistant Magnetized Steel Jig
It applies magnetism to keep the FPC flat and provides good heat insulation. It has a very long service life but has a high initial cost.
Baking FPC Before SMT Assembly
Your flexible circuits can pick up moisture from the air, a major fpc assembly issue. If not removed, this moisture turns to steam during reflow soldering and causes delamination and damage. Pre-baking of FPCs prior to assembly is an important step to avoid these defects. You need to precisely control temperature and time so that the circuits are completely dry.
Solder Paste Application
Special solder paste is not needed in the flexible PCB assembly process, but it must have very good printing performance. The paste must release cleanly from the stencil and stick well to the flexible surface. Since FPCs are not flat, you can use a softer polyurethane scraper, not a metal one. An optical positioning system is also necessary for a quality print.
Component Placement
Accurate placement of components is most important for smt assembly of flexible pcb projects. To enhance efficiency, you tend to panelize the design by mounting several FPCs on a single large jig. The SMT machine can now print the same component on every board in a single pass. This method simplifies the process and really accelerates production for your project.
Reflow Soldering
Soldering for flexible PCB involves strict control of the reflow oven settings. You will need a forced hot air convection oven to provide even distribution of the temperature. We suggest using the low end of the solder paste requirements for the temperature setting. You should also use the minimum fan speed and a stable conveyor chain so that no movement occurs.
Inspection of the FPC Assembly
After reflow, you need to test the assembly for defects. The jig containing the FPCs is processed through an automated optical inspection (AOI) machine to ensure proper placement and soldering errors. For complex or high-reliability assemblies, an X-ray inspection is performed as well. This guarantees each of your board connections is flawless.
Comparing Panel Arrays vs Singulated Carrier Assembly
When designing your flex circuit assembly, you need to determine how to handle the circuits. You can assemble them together in a large panel or on an individual carrier. This decision immediately affects your project’s speed, cost, and design capabilities. Let’s compare these two primary methods.
Efficiency and Throughput
Panel Array Assembly
This method assembles several circuits simultaneously, significantly speeding up production. It is the obvious choice for large-volume production runs.
Singulated Flex Circuit Assembly
Processing individual circuits reduces overall throughput. This method is more appropriate for prototyping or small-batch production orders.
Design Flexibility
Panel Array Assembly
Circuits must be arranged within a rigid panel configuration, potentially limiting complicated designs. This technique is best for standard, repeatable designs.
Singulated Flex Circuit Assembly
This technique provides complete freedom for irregular or complex shapes. It is ideal for custom designs that don’t fit a standard panel.
Material Handling and Stability
Panel Array Assembly
The panel’s rigid framework offers good stability during assembly. This ensures good and consistent component placement on all units.
Singulated Flex Circuit Assembly
Individual circuits are more prone to movement, presenting handling problems. You need to use a good carrier design to maintain proper alignment.
Component Density and Alignment
Panel Array Assembly
A fixed grid panel guarantees top-notch alignment for high-density circuits. This renders it a reliable option for complex designs.
Singulated Flex Circuit Assembly
Perfect alignment becomes more complicated for individual circuits. Additional caution is necessary to ensure precision for fine-pitch components.
Cost Efficiency
Panel Array Assembly
One defective circuit will require you to discard a whole section. This “X-out” risk has the potential to lead to more waste and higher expenses.
Singulated Flex Circuit Assembly
This approach isolates defects to a single unit, reducing waste. It tends to be more economical for high-quality production.
Key Considerations for Panel Arrays and Singulated Carriers
Making a decision between panels and carriers is an important step in your flexible pcb assembly process. Your choice impacts everything from the speed of production to the cost at completion. You have to balance a number of factors to choose the most effective approach. This makes your project efficient and successful.
Circuit Design (Size and Shape)
Your flexible circuit’s shape will also guide you to the best assembly technique. You’ll find panel arrays suit more basic, symmetrical designs that are simple to replicate. When you have more intricate or uniquely shaped circuits, a singulated carrier should be used. That way, you have the design flexibility that you need.
Production Volume
Take into consideration your volume of production needed when organizing your FPC assembly. If you require high-volume production, panel arrays provide higher efficiency by handling numerous boards simultaneously. For small batches, prototypes, or custom orders, singulated carriers are a more convenient and manageable approach to your requirements.
Material Handling
To avoid damage, they must follow flexible PCB assembly procedures when handling. Panel arrays’ natural rigidity reduces warping or misalignment risks during assembly. Individual circuits on carriers, however, need extremely careful handling. You will need to keep them stable and in perfect alignment during the process. For high-volume production environments, keeping cable harnesses and wiring organized on the assembly floor using bulk zip ties also helps maintain a clean, efficient workspace.
Production Versatility (Flexibility)
You must also think about how frequently your designs would shift. Singulated carriers are highly versatile and let you effortlessly switch between multiple designs or small runs. Panel arrays are not as flexible but are unbeatable for consistent, high-volume production. Select the procedure that best suits your operational requirements.
Component Density
High density of components can be among the primary FPC assembly challenges. Panel arrays offer a rigid and flat surface that ensures accurate placement for dense layouts. When you do SMT on flex with singulated circuits, you need to exercise extra caution. Accurate support is needed for precise alignment.
Alignment & Registration
Precise alignment of components is essential in successful soldering with a flexible PCB. A panel’s rigidity provides you with tighter control of registration, particularly when dealing with fine-pitch components. Singulated carriers can be more of a challenge in alignment. You will need to make sure the carrier is stable enough to prevent any placement mistakes.
Cost Considerations
You need to consider very carefully the cost of each method. With panel arrays, a single bad part can cause you to have to discard several circuits, an issue with “X-out.” This increases more material waste and is expensive. Singulated carriers keep defects isolated from one another, minimizing waste and generally being cost-effective.
One-stop SMT Assembly for Flexible PCB: MV Flex Circuit
To achieve high-quality FPC manufacturing and assembly, you require a partner with end-to-end capabilities. At MV Flex Circuit, we handle your whole project in-house. This provides you with a seamless process, from the raw material to the final assembly. We are your trusted flex PCB assembly manufacturer.
- You will enjoy the benefit of our decades of experience, producing a high yield rate on your project.
- You get top-notch FPC assembly, certified to ISO 9001, and strictly follow IPC-A-610 standards.
- You have a Design for Manufacturing (DFM) review to guarantee your product’s success.
- You get one-to-one engineering support throughout your whole project.
Need flexible PCB assembly services? Just upload your BOM to get your quote.
Conclusion
Panel arrays and singulated carriers provide distinct advantages for your flex circuit assembly. Panel arrays shine in high-volume runs, while singulated carriers provide unrivaled design flexibility. Determining the best option depends on your production objectives and budget. At MV Flex Circuit, we guide you toward the most suitable method, ensuring your process is both efficient and economical.
Contact MV Flex Circuit today to receive a quote!
