Introduction
Flex PCBs can fold and bend, but they have their limitations. It is called the bend radius, which is the tightest you would be able to bend the circuit without causing damage. So if your design requires transparency and flexibility, the PET flex PCB is your solution. It is the best to use for producing innovative see-through electronic devices.
What is PET Flexible PCB
PET flex PCB is a circuit built on a clear polyester film. Consider the polyester flexible circuit to be a transparent, flexible board for your electronics. We use polyethylene terephthalate (PET) as the base material, insulation, and protective coverlay. We laminate a thin copper foil layer onto the PET film and then etch it to produce your exact circuit paths.
This construction technique supports designs ranging from the basic single-layer to the more complicated six-layer board. As a low-cost, popular, flexible PCB, the end product is an incredibly light and flexible circuit. It’s perfect for applications in which weight and space are important. Aside from these characteristics, PET has special features such as food safety, biocompatibility, and recyclability, making it a smart choice.
PET Flexible PCBs and High Temperatures
The major drawback of a PET flex PCB is its limited heat resistance, making it a dedicated low-temperature flex PCB. This feature heavily influences the manufacturing procedures, particularly soldering. You need to consider material selection very carefully to allow successful assembly and a reliable final product.
The following are the main things you should know about temperature and PET flexible circuits:
- Soldering Process: You need to use low-temperature reflow soldering, with the peak temperature below 150°C. Standard wave soldering is not an option since this involves a special low-temperature solder paste, usually a tin-bismuth (SnBi) alloy with a melting point of about 138°C.
- Conductive Through-Holes: A PET FPC uses non-plated through-holes (NPTH) rather than the standard plated ones. To achieve a conductive path between layers, we fill such holes with materials such as silver conductive ink or a specific conductive adhesive.
- Surface Finishes: For parts you will be soldering, we suggest OSP or ENIG as a surface finish. Do not use silver plating since silver ions will migrate at lower temperatures. For conductive pads that won’t be soldered, such as in a membrane switch PCB material, use carbon ink.
- Connection Alternatives: Soldering is not your only choice. On many designs, you can connect components with ZIF (Zero Insertion Force) connectors, which form an effective connection by simply pressing the circuit into place.
- Operating Temperature: A polyester flexible circuit works at a temperature range of -25 °C to +75 °C. This means it is not suitable for high-power applications such as LED lighting, where a metal-core or ceramic PCB would be a better choice.
Fabrication of PET Flex PCBs
As your PET flex PCB manufacturer, we use a precise process to manufacture your circuits. We begin with the underlying PET film for printed electronics and take care of each step to handle these unique, low-temperature materials. From lamination and etching through assembly and testing, our process provides you with a high-quality, dependable polyester flexible circuit.
The Core Fabrication Steps
- Material Prep: We start by prepping the PET film, adhesive, and thin copper foil layer.
- Circuit Etching: Next, we print your circuit pattern on the copper and etch out the unwanted material, leaving behind only the exact traces you created.
- Initial Inspection: The board then undergoes an automated optical inspection (AOI) to ensure that the circuit is flawless.
- Via Creation: If your design involves connections through the board, we drill using lasers and fill the holes with conductive silver ink.
- Final Lamination: Then, we laminate over the protective coverlay to protect the finished circuitry.
Specialized SMT Assembly
Assembling a PET FPC involves special care because it is flexible. To avoid warping, we attach your flexible circuit to a carrier board that is rigid for the entire SMT process. In case of a time lag between fabrication and assembly, we dry out the circuits by baking off moisture. The most sensitive operation is low-temperature reflow soldering. We carefully control this operation, keeping temperatures below 150°C, to preserve the integrity of the PET material.
Final Quality and Testing
Once the components are assembled, a second AOI pass ensures each solder joint and component is flawless. Our job doesn’t end there. To ensure your finished product is prepared for its use, we also offer post-assembly services. These include functional testing, thermal aging, programming, and even full box-build assembly to provide a finished, market-ready product.
PET Flex PCB vs PI Flex PCB
When deciding which flexible circuit to use, you will most frequently compare PET vs Polyimide. Although they have some similar characteristics, their differences in heat tolerance and durability are important. Learning about the PET vs Polyimide helps you to choose the proper material for your use and manufacturing requirements.
Similarities
Both PET and Polyimide (PI) boards share the same core advantages for your design. Both are light materials that enable small, flexible electronics. You can create them as one or multi-layered boards. For assembly, both need a flat, rigid jig to hold them in place, and surface finishes such as OSP and ENIG are common for both.
Differences
Differences between a PET FPC and a PI board are essential to your application’s success. The most important distinction is heat resistance, which determines what soldering process you can use. Other factors of importance are their physical appearance, ability to handle repeated bending, and overall cost, so each material is best suited for very different products.
Appearance
The material you use will have a direct effect on how the circuit will look. The major difference is that one is totally transparent, unlike the other, which is opaque.
Polyethylene Terephthalate (PET)
This is a transparent material, and it is therefore perfect for see-through applications such as overlays and displays.
Polyimide (PI)
It can be yellow (amber), black, or white (depending on your coverlay color).
Physical Properties
The most obvious physical difference is their form and mechanical durability. Your selection will be based on whether you require transparency or repeated, dynamic flexing.
Polyethylene Terephthalate (PET) Physical Properties
PET is transparent in nature but not suitable for cases that need repeated bending.
Polyimide (PI) Physical Properties
Polyimide is opaque and best suited for dynamic applications where the circuit will be repeatedly flexed or bent.
Chemical Properties
While both materials offer some chemical resistance, one is more durable. This is an important consideration, especially in harsh conditions that are anticipated.
Polyethylene Terephthalate (PET)
This material offers good chemical resistance for general use in consumer and commercial applications.
Polyimide (PI)
Polyimide has excellent chemical resistance, which makes it the preferred option for industrial or automotive environments.
Production Processes
The way we create the conductive traces is very different for these two materials. This affects the materials involved, from copper foil to conductive inks.
Polyethylene Terephthalate (PET)
We produce PET circuits by printing a conductive substance, such as silver conductive ink, onto the PET film.
Polyimide (PI)
We produce PI circuits by applying a standard etching process to remove unwanted copper, similar to a rigid PCB.
Cost
When you weigh PET vs Polyimide, cost is a determining factor. The difference in price depends on the conductive material used, and this margin can increase dramatically based on how large your circuit is.
Polyethylene Terephthalate (PET)
PET is your lower-cost option, so it is a great, low-cost, flexible PCB. It uses printed conductive inks, which are less costly than copper, particularly for large surface areas such as in a membrane switch.
Polyimide (PI)
Polyimide circuits are more costly because they use etched copper foil for their conductive traces. The cost rises quite significantly as the board size increases, due to the greater volume of copper needed.
Trace Width Benefits
When your design requires extremely fine traces and close spacings, the decision is easy. The production process of each material has a direct bearing on how dense your circuit layout will be.
Polyethylene Terephthalate (PET)
Traces printed on a PET circuit are naturally wider. This makes PET not an option for high-density designs or components that require ultra-fine pitch connectors.
Polyimide (PI)
Polyimide’s etched copper process enables much finer trace widths. This enables you to place more components into a smaller area and use fine-pitch connectors with confidence, such as a 0.5mm ZIF tail.
For a quick side-by-side comparison, refer to the table below for a summary of the key differences between PET and PI flexible PCBs.
| Feature Comparison | PET Flexible PCB | Polyimide (PI) Flexible PCB |
| Cost-Effectiveness | More economical, especially for larger designs. | Higher cost due to copper-based construction. |
| Visual Appearance | Transparent. | Opaque (typically amber, white, or black). |
| Environmental Durability | Good chemical resistance for most applications. | Excellent chemical resistance for harsh environments. |
| Mechanical Flexibility | Good for “flex-to-install” uses; not for repeated bending. | Excellent for dynamic, high-cycle flexing applications. |
| Design Complexity | Supports designs with 1 to 6 circuit layers. | Supports more complex designs with 1 to 8 layers. |
| Assembly Heat Tolerance | Requires a low-temperature process (below 150°C). | Withstands standard reflow soldering (up to 210°C). |
| Operating Temperature | Reliable performance from -25°C to +75°C. | A wider operating range of -20°C to +80°C. |
| Ideal Applications | Transparent displays, wearables, and lighting overlays. | Smartphones, medical devices, and automotive systems. |
Properties and Benefits of PET Flexible PCB
If you choose a PET flex PCB, you can benefit from many important advantages for your product. This material provides a unique blend of physical characteristics and affordability. A polyester flexible circuit is thin and light, with the ability to withstand moderate bending. These advantages allow it to be a superior option for numerous electronic applications.
Lightweight and Thin Profile
With the use of a PET film for printed electronics, you significantly cut the weight of your final product. These circuits are significantly lighter and thinner compared to rigid boards. You can create smaller, more portable devices through design. You can save precious space and produce a slimmer, more modern product profile.
Moderate Flexibility
PET provides moderate flexibility, which makes it ideal for “flex-to-install” applications. It is simple to bend and form the circuit to fit into small or uniquely shaped enclosures. Although not intended for dynamic constant flexing, it has sufficient pliability for complex assembly. This allows for a good fit within your final product.
Good Environmental Resistance
Your PET flexible PCB is reliable for use in any environment. It can handle temperatures of -40°C to 85°C and provides sufficient moisture resistance. This makes it stable for use in consumer and commercial settings. You can rely on it to perform consistently in electronic equipment for daily use.
Cost-Effective Solution
One of the best things about PET is how affordable it is. This material offers you a high-performance, low-cost flexible PCB solution when compared to other films such as Polyimide. With PET, you can achieve your technical specifications and considerably lower your overall cost of production. It’s the best option for cost-effective projects without compromising on quality.
Typical Applications
Due to its exclusive combination of price and performance, the PET FPC is used in most of the new electronics. It is made transparent, flexible, and thin, and this suits small devices best. You can find the technology widely employed in user interfaces, automotive screens, and wearable devices.
Touchscreens and Mobile Devices
PET is one of the favorite materials used for touch screen circuits on tablets and smartphones. Since the material is transparent, it won’t disrupt the visibility of the display. With its flexible and thin design, it can easily find a place in the compact, sleek designs of today’s mobile phones. This produces a responsive, durable user interface.
Automotive Display Systems
You will frequently encounter a polyester flexible circuit in modern automotive displays. The material easily bends around the curved dashboards and intricate shapes of central control screens. This flexibility makes it easier to wire advanced in-car infotainment and instrument clusters. It assists in presenting a seamless and integrated appearance for the interior of the vehicle.
Smart Wearable Technology
The compact and lightweight form of PET makes it ideal for intelligent wearable devices. It is present in smartwatches, fitness trackers, and health monitoring sensors. The shape of the circuit can fit comfortably against the body. This enables you to design highly integrated and compact products with no unwanted weight or bulk.
Conclusion
PET flex PCBs empower you to build the next generation of transparent and flexible electronics. To succeed with this special material, you need a manufacturer that understands its unique low-temperature assembly needs and material handling. When your design is ready, you require an expert manufacturer.
MV Flex Circuit specializes in the fabrication of high-quality PET flexible PCBs to your precise needs. In addition to producing the bare boards, we also offer complete turnkey assembly services. Our group will source the appropriate low-temperature components and make sure that all PET FPC devices are compliant with IPC Class 2/3 and with RoHS/REACH standards.
Your boards will go through thorough quality inspections, such as AOI and functionality testing, to ensure performance.
If you are searching for a professional PET flex PCB manufacturer for your next project, please forward your Gerber Files and Bill of Materials (BOM) to sales@flexiblepcbboard.com to receive a quick quote and a complimentary DFM/DFA review.
