What is the difference between FPC coverlay and EMI shield?

Covering is the film that covers and presses on the surface of the flexible circuit, usually polyimide resin, used for solder mask, etc., and has little effect on signal shielding. The Electro-Magnetic Interference (EMI) shield is generally attached to the coverlay, and the price of the EMI shield is much more expensive than the coverlay. What is the difference between FPC coverlay and EMI shield?

FPC coverlay, known as CVL in the industry, it has the same main function as the solder mask of PCB: 1) Protect the copper foil from being exposed to the air and avoid oxidation of the copper foil; 2) Cover for the areas which it do not need to do surface treatment. 3) The solder resist function in the SMT. The usual colors are yellow, black and white in Best Tech.

Coverlay
FPC with yellow coverlay

The EMI shield uses mixed composite metal as the shielding material and has excellent OSP performance and corrosion solvent resistance. It is superior to similar products in the market in shielding and winding characteristics. The EMI shield is suitable for flexible printed circuits. It has high shielding, bending and heat resistance. The usual color is black in Best Technology.

EMI material

After pressing the cpverlay, the FPC will press a layer of EMI shield as a conductive layer to shield the external electromagnetic interference. EMI shield is mainly used in 3C products such as notebook computers, GPS, ADSL and mobile phones, because they all produce noise due to high-frequency electromagnetic interference, which affects the quality of communication.

FPC with EMI shield
Rigid-flex with EMI shield

If you want to know more design guild about the EMI shield, please feel free to contact us at sales@bestfpc.com

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Did you heard of etch 6L FPC to be 2L FPC?

We received a special project, one of our customer need 2L FPC, and want the thickness between two copper layers to be 0.15mm. Because this customer is specialized in RF product, he need so thick dielectric(0.15mm) between two copper layers.

What does it means?

  1. Firstly, for adhesive material, it means “adhesive + Polyimide + adhesive” should meet 0.15mm. If Adhesive is 25um, two adhesive layer totally 50um, the minimum Polyimide thickness will be 4mil.
  2. Secondly, for 4mil Polyimide, it usually refers to adhesive-less material. So if deduct 50um adhesive, it require 6mil adhesiveless material. 6mil adhesiveless PI is very hard to purchase, need to customize, have MOQ limit, and lead time will be very long.

Is there any solution to meet customer’s need?

After discussed with our engineers and manufacture department, we put forward one suggestion. Draw an stack up with 6L FPC, it’s made up of three double-sided FPC. Etch out one copper layers in TOP and Bottom double-sided FPC. And for the middle double-sided FPC, we’ll etch out two copper layers, only leave Polyimide and adhesive. 

By doing this, it finally will only leave two copper layers, and the thickness between two copper layers is 0.15mm. (As below stack up show)

To be honest, when customer put forward to his design requirement, I was amazed, 0.15mm material is so hard to purchase. But our engineers and manufacture department find a good solution for our customer. Our customer are satisfied with our work.

If you have similar need, pls feel free to contact us. We can help you make it come ture.

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How much do you know about FPC surface finish?

How many types of FPC surface treatment have you ever seen? FPC & Rigid flex is unlike Rigid FR4 PCB, there are less types of surface treatment in flexible PCB manufacturing, and most of flex pcb defult ENIG 1u’’ for flex pcb and rigid flex pcb. Please refer to the following FPC surface finishing:

  1. Electroless nickel immersion gold (ENIG or ENi/IAu), also known as immersion gold (Au), chemical Ni/Au or soft gold, is a metal plating process used in the manufacture of flexible printed circuit boards (FPCs), to avoid oxidation and improve the solderability of copper contacts and plated through-holes. It consists of an electroless nickel plating, covered with a thin layer of gold, which protects the nickel from oxidation. The gold is typically applied by quick immersion in a solution containing gold salts.

In generally, we will default as ENIG 1u’’ for customers if there are no any special requirements from our customer. There are also some special requirements from our customer, such the whole FPC surface area need to ENIG, it is very expensive. And there are also some customers may need hard gold plating (30~50u’’)for gold finger area.  

Hard-gold-plating

The advantages of Immersion gold( ENIG) will have very smooth surface, long storage time, easy for PCB soldering; suitable for fine pitch components and thin PCB board. It is more suitable for FPC just because of the thinner thickness.

2.Organic solderable protective layer (OSP) This process refers to cover the exposed bare PCB copper surface with a specific organic material.

OSP

Advantages: Can ensure a very flat surface, in line with environmental requirements. It’s cheaper compared with other surface finish.

Disadvantages: Once removed, the bare copper is exposed and subject to oxidation. Need to use conventional wave soldering and selective wave soldering process PCBA, does not allow the use of OSP surface treatment process. And it has a very limited shelf life.

2. ENEPIG (Electroless Nickel Electroless Palladium Immersion Gold) , ENEPIG is an acronym for Electroless Nickel Electroless Palladium Immersion Gold. This type of finish offers abundant benefits that make it suitable for a variety of applications.When we consider the final finish performance in a variety of different assembly methods, it can be seen that ENEPIG is suitable for a wide range of assembly requirements. The only one disadvantage of ENIPIG is the price is the most expensive.

ENEPIG

In conlusion, we sumarized the OSP and ENIG and ENEPIG some characteristics as a form as below, please kindly check it. Sincerely hope it will be helpful for you. If you have any quetions or would like to learn more details, warmly welcome you to contact us at sales@bestfpc.com

suface-finish-form

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Why the FPC or rigid flex add the EMI shield?

Do you know what is the EMI shield? Do you know what is the EMI shield used for  and what kind of products need to add the EMI shield? Today let’s know why the FPC or rigid flex add the EMI shield together.

What’s EMI?

When your flexible PCB or rigid-flex PCB application requires limits in electromagnetic and /or electrostatic interference, EMI shielding should be applied.

Electromagnetic interference (EMI) also called radio-frequency interference (RFI), when in the radio frequency spectrum, is a disturbance generated by an external source that affects an electrical circuit by electromagnetic induction, electrostatic coupling, or conduction. The disturbance may degrade and effect the performance of the circuit or even do not get work. EMI is caused by electrical pulsing.

Whats is our EMI shield?

With EMI shielding film design, the Flexible PCB has best flexibility as well as the thinnest overall thickness. Compared to silver ink printing and copper layer design, the flex circuit cost will be lower, and the shielding capability will be in a higher degree. No need extra shielding material, like metal cover. EMI shielding film such as Tatsuta can replace the copper layer design, then to save cost without compromising on the flexibility of the board.

EMI consists of an additional layer of selectively specialized laminate on the surface of the coverlays. It has 3-layer construction consisting of an electrically conductive adhesive, a reinforced layer and an insulation layer. The insulation layer is black in color as well as friction resistant. The EMI shielding film is laminated under heat and pressure. The conductive adhesive flows into the coverlay opening which then adhere and electrically connects to the ground. Attached the EMI shield stack up for your reference, hope it will be helpful to you.

EMI shield

The normally used EMI shield is TSS200 from Toyochem. The thickness is 200um. It has the excellent flexibility, electrical conductive reliability, chemical resistance, non-Halogene and UL type. If you would like to learn more details, please contact with me.(sales@bestfpc.com), we will be very glad to share the TS 200 EMI shield specification with you. Attached some of our FPC and Rigid flex with EMI shield for your reference, hope you will be interested in.

Rigid-flex pcb with EMI shield
FPC with EMI shield

EMI Shielding application filed

Our EMI shield required customers are mainly specialize in wireless communication, 5G phone, radar, drone, camera and new energy automobile. EMI shield is becoming more and more popular in the designs of flexible printed circuit and rigid-flex printed circuit board. Many flexible PCB or Rigid-flex circuits are sensitive to either absorbing or emitting EMI. If EMI shield is out of control, it can negatively impact the performance of the design and or effect the circuit function.

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What is the FPC tooling?

Recently, many customers asking me what is the flex PCB tooling included? And why we need to opening a tooling? How many types of tooling for flexible circuit? How to choose the suitable tooling for flex pcb?

Today, let’s learn about the Flex PCB tooling together. The FPC tooling is always used for cutting the FPC outline and coverlay. So it has included the FPC outline and coverlay tooling.

For samples production, normally we will open a tooling to save the cost and time for our customers, because the tooling will be scraped if you update the new version. So we will use the laser machine to cut outline and coverlay. But the productivity of laser cutting is longer than a tooling cutting the outline, that’s why we need to opening a tooling for volume production.

In generally, there are only four types of tooling in our production process.

1.Normal tooling, it is the most common used for most the flex pcb to cutting the coverlay and outline. The FPC appearance tolerance is 0.1mm, and the gold finger size tolerance range can be controlled at 0.15mm.

  1. Mediumn silking tooling: The precision is high, and the lifespan is better. The punching times is around 200,000 times. The punching effect appearance is good and smooth. The tolerance is 0.07mm. But the cost is high, and the tooling making time is longer than normal tooling
  2. Precision tooling: The surface is very smooth, it is usually used for tolerance very strict flex pcb. The gold finger tolerance can be controlled +/-0.05mm. But the cost will be also much higher than normal tooling.

4.Knife tooling: It is usually used for cutting the simple flex pcb, more than 500 mm length flex circuit board and adhesive. The tolerance is around +/-0.2mm.

Do you still have any questions about the flexible circuit board tooling? If yes, please feel free to contact Best Technology at sales@bestfpc.com. Looking forward to receiving your feedback.

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What is the difference between assembling flex and rigid boards?

Assemble components on a flexible printed circuit board (FPC) requires that when the smart wearable industry becomes more and more popular, due to the assembly space, the surface mount of SMD on FPC has become one of the development trends of SMT technology.
But flex PCB is more difficult to assemble than rigid boards, because it is not as sturdy to assemble. Today let’s learn something about the difference between assembling flex and rigid boards.
1.Soldering process
Like the rigid PCB process, the solder paste is covered on the flexible board and the rigid-flex board through the operation of the stencil and solder paste printer. But the surface of FPC is not flat, so we need to be fixed with some fixtures or stiffeners. Normally we will stick stiffener for component area of flex PCB, you can refer to below sample picture. Stiffeners contains PI stiffener, FR4 stiffener and Sheet steel stiffener.

  1. SMT component placement

Under the current trend of miniaturization of SMT components, small components will cause some problems during the reflow soldering process. If the flexible circuit is small, extension and wrinkles will not be a significant problem, resulting in smaller SMT frame or extra mark points. If you do not want to stick stiffener on the bottom side of components, maybe you need flexibility after assembly. So SMT fixture would be a good choice, you can refer to below pictures for fixtures(fixture vs fixture with flex PCB).

  1. Reflow soldering process

Before reflow soldering, the flexible circuit must be dried. This is an important difference between the flexible circuit and the rigid PCB component placement process. In addition to the dimensional instability of flexible materials, they are also relatively hygroscopic. They absorb water like a sponge. Once the flexible circuit board has absorbed moisture, it has to stop reflow soldering. Rigid PCB also has the same problem, but it has a higher tolerance. The flexible circuit needs to be preheated and baked at ~225° to 250°F (like below pictures). This preheating and baking must be completed quickly within 1 hour. If it is not baked in time, it needs to be stored in a dry or nitrogen storage room.

If you would like to know details about the assembly of flex PCB, please feel free to contact Best Technology at sales@bestfpc.com

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What is the difference between solder mask and coverlay?

Have you ever been have trouble in selecting the solder mask and coverlay when you are design a flex pcb? Solder mask and coverlay has the same basic function of insulating, do you know the difference between solder mask and coverlay? Is it possible to make the solder mask and coverlay overlap together for insulating? Do you think the flexible solder mask is the same as rigid printed circuit solder mask?

1)Design: Actually, coverlay is widely used for flexible printed circuit board. Because of most of flex pcb will need to add the PI/FR4 stiffener and EMI shield. But if there are BGA pads and dense solder mask opening area, limits the minimum size of openings and the minimum web of material then can be retained between adjacent openings. I would like to share a coverlay and solder mask overlap together FPCB with you. The coverlay is applied first and the solder mask second with a slight overlap onto the coverlay to prevent any gaps in the combined layer. This kind of design have much higher requirements for our production to ensure your functional and reliable design. Below picture is a coverlay and solder mask overlay together FPCB, hope you will be interested in.

If the coverlay opening is square, the minimum size for coverlay is 0.6mm, and space is 0.25mm. Otherwise you need to print solder mask. If the coverlay opening is round, the mimimum size for coverlay is 0.25mm, and space is 0.15mm. Otherwise you need to print solder mask. Because too small coverlay webs will be easily damaged or broken during manufacturing process, and the limited of adhesive may not allowed for a good lamination.  Coverlay openings may also exhibit a small amount of adhesive squeeze out into the openings. Then the resulting design rules for coverlay are significantly different than those for solder mask. Attached the coverlay square and round opening picture for your reference, please kindly check it.

2)Thickness: Below is the pure green solder mask flexi pcb picture, it do not need to add the stiffener for PCBA (SMT assembly), and there are no BGA area, why it choose to use the green solder mask instead of coverlay? The normal coverlay thickness is 27.5~50um. And the solder mask thickness is 8~12um. Due to the customers need the ultra thin flex pcb. Then we suggest the customer to use the solder mask instead of the coverlay.

3)Color: The most popular coverlay color is yellow, we usually prepared the yellow, white, black coverlay in stock. Solder mask is available in a wider range of colors: green, black, white, yellow, etc. Please kindly note that the flex pcb solder mask is quite different to rigid pcb. The flex pcb solder mask cost is much higher than FR4 PCB.Because the flexible circuit board solder mask the withstand bending and high temperature is better than Rigid FR4 PCB. But the coverlay and solder mask for flex price is the same for us.

If you have any comments, warmly welcome you to contact us. Once we received your news, we will reply to you immediately. Looking forward to receiving your inquiry.

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What are the differences between the Poyester (PET) and Polymide(PI) material?

The flex pcb raw material and stack up will decide the flex circuit quality. According to the market demand, there are three types of base raw material used for Flexible circuit board. Poyester(PET), adhesive Polymide (PI) and adhesiveless Polymide (PI) . Do you know the difference between the PET and PI material? If not, let us learn about it together now.

The advantages and disadvantages of Polyester(PET) and Polymide(PI).

Attached is a form for your reference, hope it will be helpful you. And you can choose the right raw material according the below form.

 Polyester(PET)Adhesive
Polymide
Adhesiveless
 Polymide
Flexibility (2mm radius)BadGoodBest
Tear strength800g500g500g
Strip strength in the air1050N/M1750N/M1225N/M
Eatching>=20%BESTBadGood
Working temperature8085~165105~200
ChipBadGoodBest

The advantages of PET material: Production process is less, price is cheaper, lead time is shorter.

The disadvantages of PET material: Polyester material can not pass through soldering flow. Then it can not be working in high temperature environment.

The advantages of polymide (PI): It’s easy to bend. Can work in high temperature.

The disadvantages of Polymide (PI): The price of raw material is much higher than Polymide.

Below picture is the single sided FFC, ENIG 3u’’, 10pin, 0.5mm pitch, and it is made of Poyester(PET) material

BFS17386-B

Below picture is a 1layer flex pcb, 4 mil PET material, print silver ink, carbon finishing mask, insulation( protective coating), carbon resistance less than 500 ohm.

BFS18205

Below picture is 1L FPC, it is made of adhesive polymide raw material. ENIG 1u’’, 1oz Cu, 1mil PI, 1mil coveraly, and the total thickness is 0.13mm+/-0.03mm.

BFS20032

It is a single sided FPC, ENIG 1u’’, 1/2ozCu, 1mil adhesiveless PI, 1/2mil coverlay.

BFS20209

If you have any questions or would like to learn more, warmly welcome you to contact us at sales@bestfpc.com

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What’s the difference between Adhesiveless and Adhesive Polyimide (PI)?

Today I’d like to share what’s the difference between Adhesive PI and Adhesiveless PI.

Item 1: Adhesiveless PI stack up

Adhesiveless PI stack up
Adhesiveless PI stack up

As you can see in above stack up, there is no adhesive connect the Copper layer and Polyimide.

There are four advantages of adhesiveless PI:

  1. Thinner Thickness

As you know, the thickness of adhesive is around 12.5um, 15um, 20um. If you have strict requirement for the whole board thickness, it will be a good choice to use adhesiveless PI.

2.Better Bending

Adhesiveless substrate is thinner than adhesive substrate, so it’s bending is better.

3.  Heat resistance

Due to the adhesive have poor performance in heat resistance, so without the adhesive, the adhesiveless base material have better heat resistance.

Under the same temperature, such as 200℃,the tearing strength of adhesiveless PI change a little. But the tearing strength of adhesive PI material rapidly decrease.

4.  Dimensional stability

The dimension of adhesiveless board change very small when the temperature increase. Even under the temperature of 300℃, it’s dimensional changing rate is no more than 0.1%.

Good dimensional stability will be great help for fine wiring process.

5.  Chemical Resistance

The adhesiveless substrate have good performance of chemical Resistance, it’s tearing strength have no obvious change with time increased.

The adhesive base material has poor chemical resistance, so it’s tear strength decreases greatly with the increase of time.

The only disadvantage for adhesiveless PI is it’s a little expensive than adhesive PI.

Item 2: Adhesive PI stack up

Adhesive PI stack up
Adhesive PI stack up

As you can see, the thickness of  2 layer adhesiveless FPC is 0.19+/-0.03mm.

The thickness of  2 layer adhesive FPC is 0.23+/-0.03mm.

If you need thicker thickness, the adhesive PI might can meet your requirement, the cost will be much lower than increase copper thickness or PI thickness.

There are two mainly advantages for adhesive PI:

  1. Thicker thickness.
  2. Cheaper price.

Anyway, if your project need thinner thickness or smaller line width and space (0.05mm), adhesiveless PI will be the best choice. Welcome to contact us at sales@bestfpc.com if you need to know more details.

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What is the Dual access flexible circuit?

Have you ever been heard about the dual access flexible circuit? Why it named dual access flexible circuit? After you read my e-mail, you will find the answer.

Dual access flexible circuit board is similar to double side FPC, but it has different stack up to double side FPC. Why it named dual access FPC? Dual access can access to both side by copper, so it named the dual access flexible circuit. Dual access flex PCB only have 1 layer copper, and coverlayer on both side. They can connect both side by layout through coverlayer opening, and do not need to drill the holes like 2 layers flex PCB to connect both side.

Dual access flexible circuit samples picture:

Dual access flexible circuit sample
Dual access flexible circuit sample
Dual access flexible circuit sample
Dual access flexible circuit sample

Working principle: The coverlayer play the role as an insulator, the copper is a very good kind of conductor. One side is anode, and the other side is cathode. If they the current flow, they form a closed loop circuit.

Stack up of dual access flex circuit:

Stack up of dual access flex circuit
Stack up of dual access flex circuit

Dual access circuit advantages:

  1. It can be connected to both side through copper, and do not need to make a through hole. If it is 2 layers FPC. You have to make a through hole to connect both side.

2. The appearance will be more beautiful than 2 layers flex PCB. Because we can conduct by trace, it will be more beautiful than through holes to conduct.

Dual access circuit disadvantages:

  1. Complex production process: The production process is similar to 2 layers flex circuit, but it will be more difficult and complicate compared with 2 layers flex PCB. It is easy to scrap. And many factories can not make dual access circuit board due to production technique.
  2. Easy to wrinkle. Because the dual access is very thin. Only one copper and two coverlayers, it will be easy to tear up. When it comes to laminate process, is also very easy to laminate wrinkles and blister.

If you have any questions or would like to learn more details, please feel free to contact us.

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