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Flying Tail Structure PCB

  • Flying-tail-structure-pcb

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OVERVIEW

Item Rigid-Flex PCB
Max Layer 36L
Inner Layer Min Trace/Space 3/3mil
Out Layer Min Trace/Space 3.5/4mil
Inner Layer Max Copper 6oz
Out Layer Max Copper 3oz
Min Mechanical Drilling 0.15mm
Min Laser Drilling 0.1mm
Aspect Ratio(Mechanical Drilling) 12:1
Aspect Ratio(Laser Drilling) 1:1
Press Fit Hole Ttolerance ±0.05mm
PTH Tolerance ±0.075mm
NPTH Tolerance ±0.15mm
Countersink Tolerance ±0.15mm
Board Thickness 0.4-3mm
Board Thickness Tolerance(<1.0mm) ±0.1mm
Board Thickness Tolerance(≥1.0mm) ±10%
Impedance Tolerance Single-Ended:±5Ω(≤50Ω),±10%(>50Ω)
Differential:±5Ω(≤50Ω),±10%(>50Ω)
Min Board Size 10*10mm
Max Board Size 22.5*30inch
Contour Tolerance ±0.1mm
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,Black,Blue,Red,Matt Green
Min Solder Mask Clearance 1.5mil
Min Solder Mask Dam 3mil
Legend White,Black,Red,Yellow
Min Legend Width/Height 4/23mil
Strain Fillet Width 1.5±0.5mm
Bow & Twist 0.05%
Table of Contents
Primary Item (H2)

Flying tail PCB is a rigid-flex printed circuit board structure. The various rigid and flexible portions of the printed board are connected via traces instead of holes. Flying tail structure PCBs are not commonly used; however, they overcome the limitations of conventional PCBs. 

For instance, they can be created as a hybrid structure layer stacked up together. An eight-layer rigid-flex PCB can have a 1+6+1 stack up with a flying tail structure. The first two layers may be rigid, with other inner layers flexible and connected with a flexible flying tail structure. 

These are ideal for specific device designs with modern designs. In this article, we’ll discuss all about rigid-flex flying tail structure PCBs. 

What are Flying Tail PCBs?

Rigid-flex circuit boards with flying tails are advanced PCB designs that combine rigid and flexible substrates for fitting into smaller devices. This can be useful in increasing the reliability and functionality of the devices. The stack-up design brings better heat dissipation and airflow, considering rigid-flex PCBs. 

The flying tail structure of PCBs extends from the ends of the board and connects the two adjacent boards in some designs. Moreover, a part of the trace extends instead of vias being used for connecting two layers of the boards. 

In case you wish to eliminate or minimize the use of vias, flying tale structure is a good idea. It can save space while also reducing manufacturing costs in raw materials. Another benefit is that it can enhance the signal integrity of the devices.

Applications of Flying Tail PCBs

Here are the major applications of flying tail PCBs:

  • Mobile phones 
  • Computers 
  • Miniature wearables 
  • Communication devices 
  • Medical devices 
  • Aerospace electronics
Flying-tail-structure-pcb

Fabrication of Tail Structure PCB 

The flying tail structure PCB is fairly new in the market. It can be made in a rigid-flexible printed circuit board time. The same principles apply when fabricating rigid-flex flying tail PCB. A base material substrate is used to add the first inner circuit pattern over it. 

Circuit Pattern Etching on Both Ends 

Both sides can be used to print the circuit pattern using a photoresist. A single circuit layer from the laminated substrate is extended beyond the rigid region of the PCB. After the insulation is done, some part of the substrate that extends beyond the rigid region is removed from the circuit using laser cutting

Layering of PCB

The first layer of the flying tail type PCB can be made using an insulated rigid substrate. On the other hand, the second layer is usually a flexible insulator. This second layer is usually a non-cured prepreg.

Via and Hole Fabrication

To make blinds via holes over the first insulating layers, a CO2 laser can be used. The first layer is not in contact with the coverlay as it is not laminated. After this, a through-hole can be fabricated by penetrating the first insulating layer as well as the base substrate. This can be fashioned using a CNC drill. 

Circuit Over Tail

A circuit pattern layer is formed over the rigid-flex part of the tail structure. The second layer of PCB is insulated and laminated. Besides, manufacturers may choose to use a cured insulator as a go-to material. 

The usual methods of forming a flying tail PCB include an etching process to get rid of the excess circuit print and the metal layer plating. Once the PCB is fabricated, a cover laid with solder resist is added to enhance its bendability and functioning. 

Globalwell Flying Tail Structure PCB

What are the Advantages of Flying Tail Structure PCBs?

Here are the advantages of flying tail PCBs: 

Lower Impedance

The elimination of vias for connecting layers in flying tail PCBs ensures that the impedance is low at all times. This also reduces the unnecessary parasitic electrical current in the holes. Moreover, trace geometries using microstrips can also be used to minimize impedance. 

Signal Integrity

Flying tail boards enhance signal transmission and reduce the risk of electromagnetic interference (EMI) with their unique structure. This makes them ideal for high-speed and high-frequency applications where data transmission and integrity are critical.

Reduced Crosstalk

Flying tail PCBs have reduced crosstalk as components are placed uniformly within the layers. The absence of too many vias and holes also diminishes crosstalk. Besides, better spacing and shielding techniques may also be used to reduce crosstalk even more. 

Improved Device Life

Flying tail structure PCBs have rigid layers outside and flexible layers in the middle. This type of structure allows heat dissipation even when the devices are working for long hours. As a result, they can be used in high-performance devices without the fear of failure. 

The improved mechanical stability and resistance to mechanical stress and vibration make flying tail structure PCBs suitable for use in challenging environments. So, industries can rely on flying-tail PCBs in custom-designed devices.

Design Flexibility

For the manufacturing of space-restricted and weight-limit devices, flying-tail PCBs are usually preferable. Their unique structure in rigid-flex PCBs can manage to deliver the right electrical support. 

Devices such as medical wearables and aerospace electronics rely on unique flying tail circuit boards for function. The flexibility and high performance of these PCBs are one advantage when it comes to data transmission.

Structural impact

The flying tail rigid-flex PCB has high mechanical strength as an insulating layer is embedded in the rigid domain. At the same time, the flex side offers connectivity and elasticity in restricted spaces.

Are There Any Limitations for Flying Tale PCBs?

The devices that require dense components may not benefit from using flying tail PCBs. They cannot accommodate large component density due to less space available. 

Moreover, the mechanical and electrical limitations of the flying tail structures should be considered. The unique design of the flying tail PCBs may not allow complicated device designs or may not work with conventionally designed electronic devices. 

Globalwell Flying Tail Structure PCB 1

What to Avoid When Designing Flying Tail Structure PCBs?

Avoid the following when designing flying tail PCBs:

Ignoring the Whole Design

Don’t make the mistake of ignoring the entire system of the PCB. Pay attention to each layer subsystem. Make sure you add high-grade components to the PCB that work at an optimal state at all times. 

Cost of Flex Tails

A unique design of PCB will cost more than the usual circuit boards. As a result, you have to factor in the cost of both the flex and rigid regions of the PCB. Make sure you allot extra space to the flex tail of the PCB right from the beginning. Create a three-dimensional model to ensure no errors occur when fabricating the flex tail. 

Incorrect Layer Stack

The stack-up of the tail structure PCB will be different whether the number of layers is 8 or 12. Moreover, you must include asymmetry in the design due to the presence of flexor layers, traces, and metal vias. Usually, PCB with 6 or higher layers is suggested for flex tail structures so that the overall design is sturdy and able to work well with asymmetry. 

ZIF connectors

Zero insertion force(ZIF) Connectors are added to the IC socket so that the installation of the PCB is easier. The connector design may be designed while the fabrication process is going as there is no standard design set for the connectors. So you may choose the best available one based on the technical data collection needs.

Make sure the connector has a specific thickness and is precise to fit the PCB. Consider the type of contact surface and rigid area length for connector choice. 

Delivery Panels

The flying tail PCB has a unique shape, which is why it is important to pay attention to the delivery panels. They should not be filled with electrical components, considering the space restriction. 

Another important thing to consider is the rise in cost when you include too many components on the delivery panel. This may be avoided by making adjustments during the design and manufacturing stages. Focus on assembly and testing to ensure the PCB works reliably even in harsh conditions such as humidity change or high temperatures.  

Choosing the Right Manufacturer

When designing and fabricating printed circuit boards, it is important to connect with professionals to ensure seamless manufacturing. PCBs require prior designing and the use of the right software, such as CAD, Altium Designer, and Cadence, to stack up the layers and components. 

When it comes to flying structure PCBs, the design is even more complex. This complicated design can only be done with advanced tools and experienced technicians. Only cutting-edge technology can fabricate flying tail PCBs. 

Moreover, look for a facility that can handle custom orders and deliver them for testing before bulk ordering. There is an additional cost involved in flying tail structures as their design requires advanced tools and skills. 

These PCBs may have to be designed with smaller components, so there should always be room for improving the design. It can only be possible with a reliable manufacturing team.

Wrapping Up

Flying tail PCBs are unique in their structure as well as functioning. Their rigid-flex structure makes it easier to connect with other electrical parts in the device. Due to minimal vias, the signal integrity is high. 

On the other hand, space taken by these PCBs is less, so they can fit well into miniature devices. Consult a professional when designing flying tail PCBs for accurate component layout and fabrication. 

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