Are you tired of using the traditional rigid boards in your projects? Do you need flexible circuitry in your life? If that is so, you must be looking for something that can be bent, shaped, folded, and even twisted into numerous shapes. Your origami creativity will offer the only limitation.
As an electronics designer or packaging engineer, you would no longer to use the inflexible printed circuit boards. This article is all about what is flexible circuitry and how it can help you in fulfilling your dream designs: many problems, One solution. Buckle up!
1.1 What is a flexible circuitry?
In simplest terms, flexible circuitry is a grid of conductive paths that connects on a flexible substrate. So, it is a solution for packaging your electronics projects. Globally, it is also known as flexible printed circuits, flex circuits, flexible circuits, and flexible PCBs.
You can also think of flexible circuitry as a printed circuit board that can bend. However, there are main differences between them while designing and fabricating them. You cannot use the same rules as you use while creating a PCB layout.
In flexible circuitry, a dielectric layer, connects with a metallic coating of traces. Copper is a popular choice for conductive material. However, it can get oxidized easily, so solder or gold are often used to protect it. And, polyester or polyimide is mostly for the dielectric layer. Figure 1 shows the details on a flexible printed circuit board.
Image 1: A flexible printed circuit board
1.2 Why do you need it?
You need it to fulfil your requirements of a flexible circuit board. You would need them when you are looking for reliability and durability. Don’t worry, if you don’t know where you can use such boards. Let us help you with that.
You can use flexible circuitry in many different areas. You can use them in antennas, laptops, cell phones, and LCD televisions. You can even use them in the aviation field. That is not it; they are also popular in calculators, cameras, hearing aids, satellites, and printers.
In this section, we defined flexible circuitry and its usage. In the next section, we will tell you about the five basic types of flexible circuits.
2、Fundamental types of Flexible Circuitry
Flexible circuitry can be classified based on their size, configuration, and functionality. However, its circuits are known for one of the following classes.
Single-sided flexible printed circuit boards have a single layer of metal trace arranged on only one side of a dielectric layer. In other words, a flexible polyimide film bonds to a metallic copper sheet. After that, you would need to chemically etch the copper layer to develop your desired circuit pattern. Later, the polyimide dielectric layer bonds for environmental protection and insulation of the circuit.
2.2Dual access Single-sided
Single-sided flexible circuitry with dual access manufactures in such a way that copper is accessible from both sides. Special laser techniques and processes skive open the dielectric layer to get dual access of the single conductive layer.
Double-sided flexible circuits have a single dielectric layer with metal layers on both of its sides. Conductive copper layers mostly affix to substrate film via metalized thru-holes. You can create trace patterns according to your requirements on both sides of the polyimide film. After that, you should connect it to two copper layers using plated through-holes.
Multi-layered flexible circuitry has many conductive layers that are encapsulated and separated by dielectric layers. Overall, it combines many complex double-sided or single-sided circuits in a multi-layer fashion. These multiple layers may or may not have laminations throughout its structure.
If you want to provide maximum flexibility to your design, then continuous lamination may not be the best choice. If you are facing the following design challenges, then multi-layer circuits are your design solution.
1. Specific impedance requirements
2. Unavoidable crossovers
3. Elimination of crosstalk
4. High component density, and
5. Additional shielding.
‘We Go Where Others Will Not,’ you could think of multi-layer flexible circuitry like that.
Image 2: Surface Mount Device (SMD) placed on a flexible circuit board
2.5 Rigid Flexible Circuitry
Rigid-flexible circuits have multiple layers which can be both flexible and rigid. You will observe that they have inner layers connected through an epoxy pre-preg bonding film, like in multi-layer flex circuit. The board can be incorporated internally, externally, or both as per your requirement.
In this section, we described the five main types of flexible circuitry. The next part we will explain the benefits of these circuits.
3、Benefits of These Circuits
As these devices are connecting devices, we will write down their advantages compared to standard rigid and cabling boards.
1. Decreased Assembly Costs and Time:
Flexible circuitry reduces the expenses of wrapping, routing, and soldering wires. Also, they need minimal manual labour for assembly and eliminates any production errors. They have inherited the property of functioning correctly.
2. Error Reduction during Assembly:
Automatic production and precise designs reduce man errors resulting from building the wire harnesses by hand.
3. Design Liberty:
Flexible circuitry is not limited to two dimensions like the rigid boards. They are flexible, so they provide endless design options. You can design them to fulfil unimaginable and complicated configurations; they will still operate against all the odds.
Image 3: Flexible printed circuit board attached to its application
4. Installation Flexibility:
Flex circuits can connect with two or more planes during installation, so they provide a third dimension. They can be deployed several times during execution and installation without any electronic faults.
5. Enhanced Air Flow:
The modernised designs allow fresh air to flow through the electronic components.
6. High-Density Uses:
High-density devices can be easily made using the flexible circuitry.
7. Improved dissipation of Heat:
Flexible circuitry has a compact design and large surface-to-volume ratio, which allows it to provide a short thermal path. The slim designs also permit heat to dissipate from both sides of the circuit.
8. Durability and Reliability:
In designs with moving parts, you can bend or move your flexible circuit up to 500 million times without worrying about any fiasco. Polyimide is thermally stable that permits the circuit to withstand high-temperature applications.
9. Repeatable Routings:
The wiring errors gets eliminated as these circuits work as a substitute for hand wiring and solder.
10. Reduced Weight and Size of Package:
In traditional rigid boards, many systems add weight to the overall product in addition to covering more space. However, flexible circuitry has thinnest polyimide substrates, which result in lightweight and small products.
We will tell you about the common errors that shall not be there while making their designs in the next section.
4、Common Errors in Designs of Flexible Circuitry Boards
Here, we are about to tell you about the common errors that are made by designers while designing the layout of flexible circuitry.
Coverfilm openings or solder mask:
Flexible circuitry can show a change in dimension during fabrication. That is after going through procedures like copper plating, pumice scrubbing, and etching. So, its design rules need larger tolerances to take into account stiffness, cover film, or die cutting. You should design the openings in the cover film to permit more room in the design.
Spacing among adjacent traces and solder pads:
It is the design compromise which depends upon the error as mentioned above. While larger openings of the cover film could expose the edges of the adjacent traces if they are near the solder pad. So, this can result in short circuits. Hence, you should add more space among a nearby trace and a solder pad.
Conductors’ Stress points:
Traces of conductors with acute junctures and sharp corners are natural “stress points” when you try to bend their nearby area. So, the trace can break or delaminate. Therefore, you should make a smooth radius for turning points of the conductor while designing the layout.
You should not directly “stack” together traces on opposite sides of the substrate film. Hence there is a chance that they break when you flex the circuit if they are in parallel with the other side trace. So you can place the copper in the neutral axis of flex by making it a single conductive layer. Or, you can “stagger” the traces among the bottom and top conductive layers.
Soldered joints near the flex point:
The copper trace that is soldered gets inflexible and very rigid. If you flex the dielectric close to the soldered joint, it can break or delaminate.
Furthermore, the last word is that designing the layout of flexible circuitry can cause some severe reliability and manufacturing problems. So, it is recommended to contact an expert in flexible circuits. Figure 4 shows a flexible circuitry layout in the hand of an expert.
Image 4: An expert is showing the layout of flexible circuitry
In this section, we told you about the common design errors of flexible circuits. In the next section, we will notify you about common misconceptions related to it.
5、Common Misbeliefs about Flexible Circuitry
We know that people must be telling you about things related to flexible circuitry that are not true. Therefore, as a beginner, you may look for a second think that they are exact and can become double-minded. Let us walk you through the common misbeliefs of flexible circuitry.
1. Flexible Circuitry is a new-fangled Tech: That is not true. And this concept has been revolving around since the idea of a rigid printed circuit. Albert Hanson filed a patent in 1902 for conductive patterns of a flex substrate film.
2. Flexible Circuitry is Costly: Traditional printed circuit boards are usually cheaper than flex circuits but only as a standalone product. But people don’t buy them as a standalone product. Because flexible circuitry saves the cost of wire harnesses, connectors, and more circuit boards. You need to look at the whole picture to decide which one is cheap.
3. Rigid boards and Flex circuits follow the same design rules: That is also not at all true.
4. Flexible circuitry is less durable than hardboards: A adequately designed flex circuit will last for long. It is one of its benefits.
5. Surface Mount Devices are better on rigid boards: Studies have shown that flex circuits are equally or more reliable than hardboards in this case too.
Image 5: Flex circuit with SMD
In conclusion, if you want to reduce wiring errors, eliminate mechanical connectors, get higher circuit density, have stronger signal quality and reduce the size and weight of their printed circuit boards, then you seriously need to learn about flexible circuitry.
In this article, we have added all the details that you need to know about flexible circuitry. What is it? How is it beneficial for you. Why and when to use it? And much more!
Still, if you need any help, you can contact us right away. We are here to help you 24-7.