FPC Coverlay Opening FAQ

Since electronic products tend to be shorter, smaller, lighter and thinner, flex pcb is more and more popular with people and the demand is increasing.

FPC coverlay is a functional film normally used in PCB industry, and it is used to protect copper foil from oxidation, cover for surface treatment subsequently and play the role of solder mask in SMT process.

flex pcb
flex pcb

Speaking of fpc coverlay opening, that is, at bare copper foil point, open a hole in coverlay according to the shape of design solder pad, so that fpc traces or traces at golden finger or solder pad can be exposed, which contributes to subsequent surface treatment by connection and placement.

flex pcb
flex pcb

We often adopt 2 ways for fpc coverlay opening. One is to open a tool. This is the first choice, very suitable for production in large batch. The other is uv laser cutting, very suitable for prototyping and production in small batch.

These are what we have sorted out about fpc coverlay opening. Hope it is helpful to you. If you are still confused, please contact us, we have professional staff who can answer your inquires for 24 hours a whole day.  

FPC Flexibility Influencing Factors

During PCB design, FPC flexibility plays an important part and FPC flexibility is influenced by the followings:

(1)From the perspective of FPC material itself, FPC flexibility is influenced by the followings:

First, molecular structure and direction of copper foil(i.e. copper foil types);

Folding strength of RA copper is obviously superior to ED copper.

Second, thickness of copper foil;

In terms of the same type, the thinner the copper foil, the better the folding strength.

Third, types of adhesive used by substrate;

flex pcb
flex pcb

As a general rule, the flexibility of epoxy glue is better than that of acrylic adhesive. So, if high flexible material is required, epoxy glue is recommended. Moreover, the adhesive with high tensile modules can improve flexibility.

Fourthly, the thickness of adhesive;

The thinner the adhesive, the softer the material. Thin adhesive can improve FPC flexibility.

Fifth, insulation substrate.

flex pcb
flex pcb

The thinner the insulation substrate(PI), the softer the material. Thin insulation substrate can improve FPC flexibility. And FPC flexibility will get better if PI with low tensile modules is used.

In conclusion, for material, type and thickness are the most important 2 factors influencing FPC flexibility.

(2)From the perspective of FPC technology, FPC flexibility is influenced by the followings

First, symmetry of FPC combination;

After substrate is pasted with coverlay, good symmetry of material on both sides of copper foil can improve flexibility. This is because they bear the same stress when bending. PI thickness on both sides of PCB tends to be the same, and thickness of adhesive on both sides of PCB tends to be the same.

Second, control of lamination technology.

During coverlay lamination, the adhesive is required to be completely filled into the middle of the trace, and there can be no delamination. If there is delamination, it is equivalent to bare copper bending, which will reduce the number of bending.

If you have any queries, comments or suggestions on FPC flexibility, feel free to contact us, and we have 24-hour online customer services.

How to calculate bending radius of fpc?

 The most frequently asked question we received regarding fpc is “how much can I bend a fpc?” So, we would like to share how to calculate bending radius of fpc with you today.

fpc
fpc

When fpc is bending, the stress borne by both sides of center line is different. Pressure is inside of bending face, while tension is outside. The stress has something to do with thickness and bending radius of fpc. Excessive stress will lead to delamination of fpc, fracture of copper foil and so on.Therefore, the laminated structure of fpc should be arranged reasonably in the design, so that the lamination at both ends of the center line of the curved surface should be symmetrical as far as possible. At the same time, the minimum bending radius of fpc should be calculated according to different applications.

Situation: the minimum bending radius for single-sided fpc:

 Bending Radius for Single-sided fpc
Bending Radius for Single-sided fpc

  The calculation methodR=c/2[100-Eb/Eb]-D
WhereinR=Minimum Bending Radius(unit:”m); c=Copper Thickness(unit: ”m); D=Thickness of Coverlay(unit:”m); EB=Copper Elongation Desired(Measured as a Percentage)
Copper elongation desired also differs among various types of copper.

A.The maximum copper elongation desired for RA Copper ≀16

B.The maximum copper elongation desired for ED Copper ≀11

Moreover, value for copper elongation desired for the same material will be different in different applications. For one-time bending, the limit of the critical state of fracture is used (for RA Copper, the value is 16%). For bending installation design, use the minimum deformation value specified by IPC-MF-150 (10% for RA Copper).For dynamic flexible applications, copper elongation desired is 0.3%. For magnetic head applications, copper elongation desired is 0.1%. By setting the copper elongation desired, the minimum bending radius of fpc can be calculated.

Dynamic flexibility: In these applications, copper functions through deformation. For example, the phosphorus and copper metal dome in the IC card seat, i.e. the part where the IC card contacts with the chip after being inserted, and the metal dome is constantly deformed in the process of inserting. This kind of application is flexible and dynamic.
If you have any queries or comments on bending radius of fpc, contact us anytime.

Do You Know the Standard Flex Stackup for 1 Layer, 2 Layers, or Multilayers?

Standard flex stack up for 1 layer flex pcb:

1 layer flex pcb stackup
1 layer flex pcb stackup

This is the simplest flex pcb. Generally, base material and adhesive and copper foil are used as raw materials, or protective film and adhesive are used. Firstly, copper foil needs to be etched to get traces required. Protective film needs to be drilled to expose pad. Both are combined by using rolling process after cleaning, then the exposed pad should be electroplated with gold or tin for protection. In this way, the flex PCB is finished and can be punched into small flex pcb.

Standard flex stack up for 2 layers flex pcb:

2 layers flex pcb stackup
2 layers flex pcb stackup

When the traces of flex pcb are too complicated, the 1 layer flex pcb can not meet the needs of wiring, or needs copper foil for grounded shield, 2 layers flex pcb or multilayers flex pcb can be used.

Standard flex stack up for multilayers flex pcb:

The via holes are added to make multilayers flex pcb different from 1 layer flex pcb, so that copper foil in each layer can be connected. Generally, for base materials and adhesive and copper foil, the first processing technique is to make via holes. The base materials and copper foil should be drilled firstly and then electroplated with copper of certain thickness after cleaning. Thus the via holes are finished. The subsequent manufacturing techniques of multilayers flex pcb are almost the same with 1 layer flex pcb.

For example, here is the standard flex stack up for 4-layer flex pcb

4 layers flex pcb stackup
4 layers flex pcb stackup

There may be some differences among the stackup for 1 layer flex pcb, 2 layers flex pcb and multilayer flex pcb, but similarities also exist among many manufacturing techniques of flex pcb. Different techniques are just added in some basic places, so as to be applied in different fields.

If you have any queries or comments about flex pcb, welcome to contact us anytime.

How to Improve Reliability & Flexibility in an 8 Layer Stackup Flex PCB?

When designing a flex PCB stackup, you may face some restrictions in enhancing the reliability of the board. Today, we will discuss the ways to improve the reliability of a board by increasing the flexibility and improving design considerations of a multilayer PCB stackup. These steps can be implemented for PCB stackup designs as seen in 8 layer flex PCBs.

flexible circuits

flexible circuits

Improve Flexibility by Reducing Overall Thickness

All or some of the below mentioned steps can be executed to lower the overall thickness of the PCB. A thinner PCB stackup will allow it to be more flexible.

1.Reduce the base copper weight.

2.Reduce the adhesive thickness.

3.Reduce the dielectric material thickness.

4.Using adhesiveless base materials can reduce the thickness of the substrate by 1-2 mils, which is almost 25-50Όm.

5.Make use of selective plating to avoid copper plating the conductors.

Improve Reliability by Reinforcing the PCB

Here, the boards, components, and the layout should be designed to deliver a robust structure that can withstand flexing.

1.The weight on both sides of the PCB should be equal. This includes the weight of the conductors and the material.

2.The conductors on different layers of a PCB should not be placed on top of each other. Instead, they should be placed in a staggered pattern.

3.Conductor thickness should always be constant in and near the bend areas.

4.There should be no plated-through holes in the bend areas.

5.There should be no discontinuities near the bend.

6.Traditional copper can be proved to reduce the flexibility of a PCB. Opt for screened-on coatings like silver epoxy.

7.For slits in the circuit, reliefs or tear stops need to be built into the PCB.

flexible pcb

flexible pcb

Tight tolerances will have to be put in place to ensure that your stacked up PCB can provide flexibility as well as reliability. Several of the above-mentioned steps can easily be incorporated in the designing process itself. Your PCB manufacturer should be able to help you with the most appropriate improvements for your application.

Do You Know the Materials Used for Constructing 6 Layer Rigid-Flex PCB?

A six layer Rigid-Flex PCBs, as the name implies, is manufactured using six conductive copper layers. However, do you know the materials used for constructing 6 layer rigid-flex PCB? Now let me lift the veil for you.

6 layers rigid flex pcb

6 layers rigid flex pcb

Base Materials – The most commonly used base materials for manufacturing 6 layer rigid-flex PCB is woven fiberglass impregnated with epoxy resin. The use of cured epoxy makes the board more rigid. Manufacturers also prefer Polyimide rather than normal epoxy resin to ensure extreme reliability in complicated applications. Polyimide is chosen due to their extreme flexibility, toughness, and heat resistance properties. Polyester (PET) is also another material of choice for the PCB fabrication. Manufacturers often choose the most suitable materials according to the specific application requirements of customers.

Films – Manufacturers prefer PET films for producing 6 layers rigid-flex PCB due to their corrosion and heat resistance properties. The thickness of PET films used for the PCB manufacturing vary from 1/3 mil to 3 mils.

Conductors – Copper is the most preferred conductor of choice for making 6 layer rigid-flex PCB and various types of copper are used according to the specific application requirements. Annealed copper is used when repeated creasing or movement of the flex circuit is demanded.

6 layers rigid flex PCB

6 layers rigid flex PCB

Adhesives – The use of high quality adhesive is crucial to make a fine bonding between the conductor and films. Acrylic or epoxy based adhesives are the most commonly used adhesives to achieve a firm bonding, while silicones, hot-melt glues, and epoxy resins can also be used for bonding.

Manufacturers who are very familiar with the properties of the aforementioned materials can conduct their mechanical design, evaluation and testing of the PCBs better. Therefore, a manufacturer who fabricates 6 layers rigid-flex PCB for the automobile industry must quite know the moisture, chemical, shock & vibration resistance properties of the materials used in the construction. This contributes to enhancing the durability of PCBs in the case of industrial specific applications.

Rigid vs Flexible PCBs: Which One is the Best for Your Next Project?

Speaking of “PCB”, many people will think of a rigid PCB. However, the term “PCB” can refer to either a rigid PCB or a flexible PCB. Flexible PCBs are more commonly known as flex circuits(flex boards, flexible circuit boards, flexible printed circuit boards and flexible electronics). Recently, Flex circuits are highly welcome in the market since they can be bent or twisted. However, in the most basic sense, rigid PCBs and flexible PCBs have the same ultimate function of connecting various electrical and mechanical components together.

When to Use Rigid and When to Use Flexible

Rigid PCBs typically cost less than flex circuits as flex circuits may eliminate the need for components such as connectors, wire harnesses, and other circuit boards. By removing these components from a design, material cost, labor and assembly cost are all reduced.

flexible pcb

flexible pcb

Many electronic devices (laptop and desktop computers, audio keyboards, solid-state drives, flat-screen TVs and monitors, children’s toys, and various electronic gadgets) employ rigid PCBs instead of flexible PCBs. However, flex circuits may be found in ultra-compact and/or high-performance devices, including GPS units, tablet PCs, smart phones, cameras, and wearables. Flex circuit makes installation get much easier.

Finally, a flex circuit and a rigid circuit can be used together—as a rigid flex PCB(Rigid flex circuit)—if necessary. The proper application of rigid flex circuit offers optimum solutions for difficult, limited space conditions.

Rigid flex pcb

Rigid flex pcb

Should you have any other queries about flexible pcb, rigid pcb, rigid flex pcb, feel free to contact us. Our sales representative will reply you at our earliest convenience.

What Materials Are at the Forefront of Wearable Technology?

If you were to go to your doctor’s office today for a routine physical, the first five minutes would involve getting your blood pressure taken, taking your pulse, and getting your temperature. In the future, wearable technology may allow you to upload all of this crucial data to your doctor instantly from the devices and sensors already woven into your clothing or even tattooed on your body.

Wearable technology is evolving at a breakneck speed, with the help of advances in flexible printed circuit boards. One of the biggest challenges researchers and manufacturers face when devising wearable technology is creating materials that can flex and stretch while also maintaining conductivity and connections with the different circuits.

FPC in the wearable

FPC in the wearable

Developing just the right materials is a crucial piece in the future of wearable technology.

What Materials Work Best with Wearable Technology?

Wearable technology is a big category and includes everything from patches that can be layered onto skin to coats, shirts, and even sports bras. Each iteration of wearable technology offers unique challenges when finding the right materials.

Graphene

Graphene is a popular material choice, because it is an excellent conductor of electricity and also very flexible. Graphene offers an important alternative to wearables that rely on rigid components that can’t flex well. Researchers are actively experimenting with ways to blend graphene-based inks into cotton cloth.

Thermoplastics

Another option is the thermoplastic polyurethane, a highly adaptable plastic material. Already, a German company is using polyurethane to develop wearable skin patches that are breathable and hypoallergenic. Another thermoplastic polymere called polyethylene terephthalate (PET) offers excellent transparency, good flexibility, and is easy to fabricate.

Soft Silicones

The latest material innovations has been the development of soft silicone elastomers. Not only do these materials offer great flexibility, but they are prized for their ability to conform to a wide variety of shapes and textures. This puts them at the forefront of stretchable, wearable sensors. Some of the top soft silicone elastomers are: EcoFlexÂź, DragonSkinÂź, and SilbioneÂź.

The field of wearable technology materials is advancing at breakneck speed. Here at Best Technology, we are keeping on top of these trends so that we can continue providing the most advanced flexible printed circuit boards to our customers.

flexible circuits

flexible circuits

Space Is Money – How Flex PCB Can Help You Save Big

In the electronics industry, the name of the game is lighter and smaller. Consumers want sleek, beautifully designed computers and gadgets that still pack a big computing wallop. That is to say, for designers, at least, space is money.

If you can make your product smaller and less bulky than the competition, you will gain the market advantage. Flex printed circuits boards (aka flexible circuits or flexible pcb) are designed to give you all the space you need to create innovative new product designs.

Now let me talk about the trouble with Rigid Printed Circuit Boards

If you’ve ever had to work with rigid printed circuit boards before, you know how much of a nightmare they can be. You have to find space for them and work the rest of the components around them. Flex printed circuit boards give you back control over your design. Because they can flex, you can fit them into smaller spaces, which frees up space for more components, that can make your product more powerful, more efficient, or both. They fold, twist, and roll, making it easy to find a spot for them. This also gives you the opportunity to place other parts in a better order for the most efficient sub-assembly possible. Better part placement refers to less energy waste, a longer battery life, a more solid overall configuration, and a better operating product. It also means you have control over how you map out the inner workings of your product for optimum setup.

In the fierce electronics industry, even a slightly better assembly can put you ahead of your competition and turn your product into a bestseller, while they get left in the dust.

Flex PCBs also weigh less. Even shaving off a few ounces on your product could make a noticeable difference that will make it easier for your customers to use it, wear it, and carry it. The more they want to interact with your device, the more hooked they’ll become.

Want to learn more about flex PCBs? Just contact Best Technology. Do not hesitate any more. We can explain how they work and help you determine if adding them to your next product will save you space and money.

Introduction to A Flexible Circuit Coverlay

During the flexible printed circuit board manufacturing process, a flex circuit coverlay (aka coverfilm) is used to encapsulate and protect the external circuitry of a flexible circuit board.
A flexible circuit coverlay serves the exact same function as solder mask that is used on a rigid printed circuit board. The difference with a flex coverlay is the needed element of flexibility and durability it provides to the flex PCB design.
The coverlay consists of a solid sheet of polyimide with a layer of flexible adhesive that is then laminated under heat and pressurized to the circuit surfaces. The required component feature openings are mechanically created using drilling, routing, or laser cutting.
Typical coverlay thickness is 0.001″ polyimide with 0.001″ of adhesive. Thicknesses of 0.0005″ & 0.002″ are available, but only used as needed to meet specific design requirements.
For more information visit our website to learn more about our flex & rigid-flex PCB manufacturing process!