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Understanding Flexible PCB: Designing & Manufacturing

OVERVIEW

Item Flexible PCB
Max Layer 8L
Inner Layer Min Trace/Space 3/3mil
Out Layer Min Trace/Space 3.5/4mil
Inner Layer Max Copper 2oz
Out Layer Max Copper 2oz
Min Mechanical Drilling 0.1mm
Min Laser Drilling 0.1mm
Aspect Ratio(Mechanical Drilling) 10:1
Aspect Ratio(Laser Drilling) /
Press Fit Hole Ttolerance ±0.05mm
PTH Tolerance ±0.075mm
NPTH Tolerance ±0.05mm
Countersink Tolerance ±0.15mm
Board Thickness 0.1-0.5mm
Board Thickness Tolerance(<1.0mm) ±0.05mm
Board Thickness Tolerance(≥1.0mm) /
Impedance Tolerance Single-Ended:±5Ω(≤50Ω),±10%(>50Ω)
Differential:±5Ω(≤50Ω),±10%(>50Ω)
Min Board Size 5*10mm
Max Board Size 9*14inch
Contour Tolerance ±0.05mm
Min BGA 7mil
Min SMT 7*10mil
Surface Treatment ENIG,Gold Finger,Immersion Silver,Immersion Tin,HASL(LF),OSP,ENEPIG,Flash Gold;Hard gold plating
Solder Mask Green Solder Mask/Black PI/Yellow PI
Min Solder Mask Clearance 3mil
Min Solder Mask Dam 8mil
Legend White,Black,Red,Yellow
Min Legend Width/Height 4/23mil
Strain Fillet Width 1.5+0.5mil
Bow & Twist /
Table of Contents
Primary Item (H2)

Different Types of Flexible PCB Provided By GlobalWellPCBA

Simply select your Flexible PCB below to access the guide.

Introduction

Flexible PCBs are among the common types of industrial PCBs that have vast applications in electronics. Over the years, we have been able to see many upgrades in these PCBs so that they can meet future standards easily. 

There is no doubt that today, we can see many appliances performing at their best due to flexible PCBs. Things are different when we are developing flexible PCBs because of their different nature. It means it will be better to have accurate information regarding flexible PCBs to avoid all sorts of confusion. 

There have been many cases when people were unaware of developing appropriate PCBs and were unable to derive the desired results. If you don't know much about Flexible PCBs, then it's time to hop onto this discussion and shed light on different aspects of flexible PCBs in detail. Here we go!

Flexible PCB

Flexible PCBs are bendable types of PCBs due to their flexible substrate. Due to this reason, we can easily identify these PCBs based on their nature. Particularly, those appliances that work on high density and high temperature use these PCBs. We use polyamide and polyester to construct flexible PCBs due to their excellent heat-resistant properties. 

Other than this, these substrates are also crucial for seamless component mounting. Like all PCBs, flexible PCBs are conductive, and we use copper traces in these PCBs for better performance. The thickness of dielectric materials and these layers is variable based on the size of PCBs. 

There is also a special adhesive material needed to build strong bonds between the boards and their counterparts. There is a wide spectrum of materials that we can use to develop flexible PCBS. But we cannot use them as it is since we have to weigh down these materials based on these factors. We use flexible PCBs for less solder joints and contact crimps. Therefore, these are space-efficient types of PCBs and can also come in handy for portable devices. 

Manufacturing Procedure of Flexible PCB

Polyimide is an important substrate for flexible PCBs. One thing to remember here is that flexible PCBs are expensive because of this substrate. Polyimide is more valuable than FR4, which is used for rigid PCBs. Therefore, there is no margin to be reckless with polyimide since negligence can waste it and topple the producer’s budget as well. 

It is clear that to save polyimide substrate, you need to stick to an accurate production process. Here, we are going to learn about the breakdown of developing fine, flexible PCBs. 

  • Looping

The role of the service loop is to regulate the servicing length and circuit assembly so that we can see how much material we have to use for the development. 

  • Sizing Conductor

Only a thin layer of copper is reliable for making the whole setup conductive. Due to less thickness, we can use this copper to add to the flexibility so that it can empower versatile appliances and electronics in the market. 

  • Etching

The etching process is for taking care of isotropic losses that are crucial for the production process. We carefully etch the copper foil that we don't need so that working with the rest becomes easier. However, we have to consider line width, etch mask, and the conductor type for etching. 

  • Routing

Routing is not a time-consuming process; instead, it is quite basic. The purpose of routing is to lower the stress on the boards and make them more flexible for some specific electronics. 

  • Ground Planes

We also need to work on ground planes so that it can reduce the overall weight of the boards, which is also beneficial for making the setup flexible. After these, we will drill holes that are crucial for expanding the pad area and stress distribution. Also, adhesive films are necessary for these boards so that they can perform better in the long run. Next, we will add screen printable liquid overcoats that mimic the functions of a solder mask. The benefit here will be that the solder mask will protect the board from possible damage easily. 

Flexible PCB: Materials

Using fiberglass as the metallic base is common in the PCB industry. But in the case of a flexible circuit, we use a flexible polymer. This is why it is a standard distinction between flexible and rigid PCBs. By far, you know that we cannot develop flexible PCBs without a polyimide substrate, which means we have to acquire high-quality polyimide for developing industrial-grade flex PCBs. However, there are some downsides of polyimide, and less resistance to humidity and moisture is common. This is common when you are not relying on high-end polyimide. Adhesive bases are integral for binding flexible PCBs together. Due to this reason, we can make flexible PCBs more reliable for usage in the long run. The purpose of adhesives is to join the copper layer to them to reduce the thickness of PCBs on the whole. Therefore, after doing this, there will be fewer chances of board breakage and damage. 

Considerations for Designing Flexible PCB

Developing a flexible PCB is not a simple job. Therefore, you have to consider some important points while you are proceeding with the development. Let’s take a quick look!

Through Hole Position

You should not compromise vias while you are modifying flexible PCBs. The reason is that these vias can get damaged due to negligence. Also, you should avoid altering the combination area while you are designing flexible PCBs since there are higher chances of damage. Also, when you are punching holes, make sure not to go to the periphery where there are sensitive components mounted. Experts believe that suitable distance is crucial to maintain while you are designing these PCBs. The optimum size of vias is 30 mil in general development cases. Therefore, you have to know the right thickness to save vias and boards from undergoing potential damage. 

Designing of Pads & Vias

Flexible PCBs can give you a hard time in terms of design pads and vias. Since the substrate we are using here is flexible, we can twist and turn flexible PCBs without compromising them at all. Due to this reason, we have to be careful with the designs of pads and vias since these can easily undergo damage while we are twisting PCBs. The shapes of these pads and vias can also be unique based on the nature and performance of the boards. With efficient designs of pads and vias, we can also reduce the mechanical strain on PCBs. Therefore, the designs of pads and vias should be immaculate to enhance the performance of PCBs on all counts. 

Routing Design

When you are developing flexible PCBs, you should know that if you are working with more than one line in the flex area, then you do not need to overlap the paths of the top and bottom layers in the boards. If you do this, then there will be unnecessary strain on the setup. It can later hamper the performance of PCBs as well. Also, the layers can be misaligned, and it can ruin the structure of PCBs. Try to maintain a circular arc while you are protecting the lines of PCBs. So that there will be less interruption with these lines. A teardrop shape is crucial for both thick and thin lines so that these will not break at all. 

Designing of Copper Layer

Another important thing to consider here is the copper layer design. The reason is that copper is the most crucial aspect of flex PCBs, and it is the core of these boards. Therefore, it is beneficial that we introduce a copper plane layer in the PCBs so that it can support their function. A crucial role of designers here is to carefully determine the components and the copper sheet. We also need to rely on solid copper so that it cannot only protect the PCBs but also strengthen their core to ensure great performance. 

Drilling Hole & Copper Sheet

We can develop large distances in flexible PCBs between the holes we drill and the copper part of the flex PCBs. The reason is that these PCBs have flexible substrates that give more freedom to the designers for desired details. Therefore, it is possible to bring out more space within the setup on all counts. 

Bending Radius

It will be better that we use the bending radius of flex PCBs. The reason is that it has a direct impact on the performance of PCBs. The purpose is to detect the pressure on the PCBs exerted by its components. Therefore, working with a bending radius will give you an edge to easily utilize the space of the boards without compromising these. 

Conclusion

Here, you have a detailed overview of flexible PCBs. You were able to identify the key aspects of flexible PCBs and industrial procedures to develop them as well. Also, we have tried to elaborate on the important considerations to develop flexible PCBs that can help you develop such boards that meet the industrial standards on all counts. Hopefully, now you can develop flexible PCBs with great confidence and leverage your creativity to enhance their performance as well.

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