What’s the difference between rigid-flex PCB and flex PCB with FR4 stiffener?

In the production of FPC, normally we need to add different stiffener to meet the total thickness or hardness, such as PI stiffener, FR4 stiffener and stainless steel stiffener. But the FR4 stiffener after laminated is very similar to the rigid-flex PCB, especially there are also have drilling holes in FR4 stiffener.

Do you know how to identify FR4 stiffener and rigid-flex PCB? Please refer to the below picture. On flex PCB, you can see there are many PTH holes, maybe these boards are need to insert connectors and connect it to other products. So they need the hardness in this area.

From the left sample, we added the FR4 materials on bottom side, there are also have vias on stiffener, but no copper in vias, so this is FR4 stiffener. It can only increase the hardness of flex. From the right sample, the green part are still FR4 materials, but we plated copper for all vias, so it’s a rigid-flex PCB.

FR4 stiffener VS Rigid-flex PCB

Rigid-flex board has many production processes, high production difficulty, low yield rate, so its price is relatively expensive and the production cycle is relatively long than flex PCB. If the FPC with FR4 stiffener can meet your requirements, then it would be a better choice for you.

If you have any other question about stiffener or rigid-flex PCB, please feel free to contact us at sales@bestfpc.com

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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.  

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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.

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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:µm); c=Copper Thickness(unit: µm); D=Thickness of Coverlay(unit:µm); 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.

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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.

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3 Notices for Layout Double-Side BGA for FPC

Layout double-side BGA for FPC is used in some products, but since the complexity of manufacturing process and maintainability need to be taken into consideration, the designers need to pay attention in followings:

1. Do not overlap when layout double-side BGA and a certain of distance is required left. The reason why to do that as it is difficult to repair if there is poor BGA on one of sides.

2. In order to prevent the BGA on the bottom from melting during the second time reflowing, it is required to decrease the bottom temperature in the second time reflowing. It is better to decrease the bottom temperature lower than to the melting temperature of solder joints to ensure that the solder joints do not melt again. What’s more, you can fix the bottom BGA with jig.

4 ways to increase deformation resistance for flex circuits:

1. The stress resistance of BGA can be strengthened by a supporting iron frame around it.

2. The stress resistance of BGA can be strengthened by gluing around it or on the corresponding back of flexible PCB.

3. If you aim at protecting the BGA, then you are able to add screw to fix the other parts around BGA. In this way, the other parts around BGA won’t deform easily.

4. Strengthening the outer shell of flex circuits to avoid its deformation affecting the inner circuit.

As the premier expert in flexible circuit fabrication, Best Technology has a team which always striding for high quality flex circuits and services. If you would like to know more about Best Technology, please give us a call at 0755-29091601 or view our website: https://www.bestfpc.com/

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The Keys in the Mobile Phone

With the development of smart phone, the mechanical key has been already eliminated from the stage. There is only the HOME key left on the front side of the phone. Even sometimes the HOME key is also out and there are only two keys left–volume key and power key. These two are usually used a FPC to save cost as well as space. The structure showing as below:

power key & FPC

power key & FPC

For the design of volume key and power key, there are two things required to considerate. On one hand, the position of the flex circuit. Since the flexible circuit is glued on the supported wall, three directions need to be limited if you would like to fix the FPC. As well, the designers still need to consider the installation position of the keys itself, which determines the basic structure of the keys.

On the other hand, the volume key and power key are moving parts. Therefore, taking the stroke of metal domes into account is necessary and as general rule the stroke is 0.3. In addition to hard contact mode, there is also a soft contact mode (P+R), which is to use rubber or TPU (Thermoplastic polyurethanes) for the part where the key is contact with the dome, so that the sound is softer.

key structure

key structure

Best Technology is the premier expert in the manufacture of electronic components, brings a unique combination of technology and quality that offers a competitive supply of flex circuits and rigid-flex circuits and other flexible circuit products. To find out more, contact Best Technology at 0755-29091601 or check the website: https://www.bestfpc.com/

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New Technology for Flex Printed Circuit – Components under Coverlay

With the development of modern industry, there are more and more projects need to use flexible circuit, and the requirements of assembly are getting higher and higher.

In the Flex Printed Circuit (FPC) typical production process, normally we will finish the entire flexible PCB production process, and then arrange to solder components. But such a finished product, components exposed, it can not pass the waterproof test. Our traditional waterproof process is to cover Silicon or conformal coating.

But how can you make the components waterproof more fastness after flex circuit assembly?

Our engineers decided to change the production process after discussion. For new technology,

  • The first step is trace Etching;
  • Second step is surface treatment (normally is ENIG (Electroless Nickel/Immersion Gold);
  • Third step is component assembling;

flex circuit with component stackup

flex circuit with component stackup

 

 

 

 

  • The Forth step and the most important step is making the pure adhesive between base material and coverlay, we need to laser cutting or punching the cutout above the area of component, so that there’s no extra adhesive in that area and then the total thickness of that area will no be too high.

flex circuit with component stackup2

flex circuit with component stackup2

 

 

 

 

 

And you can see the full picture showing step 3 to step 4 of flex circuit components making.

flex circuit with component stackup

flex circuit with component stackup

 

 

 

 

 

 

 

After that, we put the Polyimide on pure adhesive and then go the next step of lamination process. (To laminate the coverlay on the surface of component.).

You can see below pictures.

flex circuit with components

flex circuit with components

 

 

 

 

 

 

flex circuit with components details

flex circuit with components details

 

 

 

 

 

 

 

 

You can visit our website or send us your email if you would like to know more about flex printed circuit.

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NB board and FPC: the only hope in 2009 PCB industry

Look into the prospect of 2009 PCB industry, due to the fact that the Notebook (NB) and intelligent mobile phone still have the potentiality to grow, therefore, people in the industry generally believe that there are still hope for the growth of NB board and FPC.

Because the prices of NB fall year after year, and people’s demand for PC mobility increases constantly, the tendency that NB will replace the desktop computer becomes more and more obvious. Some brokers in Taiwan expect that the worldwide turnout of NB in 2009 will be 131 million sets, increasing by 3.7% than that in 2008. Considering the additional demand for low cost NB, they estimate that the turnout of whole NB will reach 155 million sets. Annual growth rate will reach 12.58%. This growth prediction is rarely seen recently. Therefore it’s unnecessary for the NB board manufacturers to worry about. The NB turnout of Hann Star board and Gold Circuit Electronics in 2008 will increase 7% and word wide market share will rise from 63% (in 2007) to 70% which will make NB market a duopoly and there is nearly impossible for a new company entering into.

Besides, the market generally believes that the overall mobile phone demand in 2009 will decline. For intelligent mobile phones which use lot of FPC, however, the turnout in 2009 is estimated to be 186 million sets. The annual growth rate is still as high as 18.1%, which becomes the largest growth power for Taiwan FPC industry. As for the aspect of supply, because of the fierce competition, many second-tier FPC factories became bankrupt, which will be helpful to keep the  stability of FPC industry.

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FPC for LCD Module

FPC for LCD module also named  LCD Module FPC. This kind of FPC is flex printed circuit used in connected with LCD, in most case. So its someone named it as “LCD module FPC” or “FPC for LCD Module”.

One end of FPC will be inserted into the connection area of LCD and the others will be connected with other input or output machines. The major function is to transfer data smoothly and safetly.

LCD Mould FPC bottom view

LCD Mould FPC bottom view

As quantiyt of LCD is related big, so the quantyt for this kind of FPC will also have a certain quantity. So people should be very careful in designing and manufacturing, because normally the L/S and L/W is small, about 3~4 mil. Without suitable manufacturing artwork and technology, the yield will be very low.

We have much experience on making LCD flex circuits, knowing what’s the keystone, what kind of problems maybe happened owing to its own charactericstic, how to avoid it and how to make FPC in great condition.

Please contact Best Technology now for more informaiton about  FPC for LCD moduleLCD Module FPC.

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