Happy Mid-Autumn Festival – Wishes from Best Technology

The 15th day of August lunar (Sept 10th, 2022) is the Traditional Mid-Autumn Festival (also named as Moon cake Day) in China, families usually sit down together to have a reunion dinner and enjoy the delicious moon cake under beautiful full moon to celebrate this important day.

In order to thank all employees for their hard work and efforts, Best Technology prepared handle-made Mid-Autumn moon cakes to express our best wishes and heartfelt thanks to our staffs.

All staffs from Best Technology received the tastefully Moon cakes and everyone is permeated with warm and harmonious festive atmosphere. As a member of Best Tech, I felt full of happiness when received the cakes.

Best Tech is a big family and everyone is a member of this family that we love and help each other.

The moon cake not only represents the Mid-Autumn greetings and blessing to employees, but also shows the loving care from management for us. It not only brought laughter, also brought full of touching and motivation to everyone. I believe that in the future, we will cheer up, make persistent efforts, and create a more brilliant tomorrow for the company!

Since the establishment of company in 2006, Peter and Emily have always pay highly attention to the health care and life of our staffs, not only for Mid-Autumn Festival, but also for every traditional festival in China. Different beautiful gifts and best wishes will be always received from Best.

A bright moon and stars twinkle and shine. Here, Best Tech wish all of our customers a merry Mid-Autumn Festival, bliss and happiness, wish you a perfect life just like the round moon in Mid-Autumn Day!!

Also, Best will close for Mid-Autumn Festival from Sept 10-12th, and resume to office on Sept 13th, if you have any inquiry, please contact us.

Why is a Stiffener Used in FPC?

What is stiffener?

The biggest feature of FPC is its soft and flexible structure. But due to its soft structure, when connecting a small part such as a connector to an FPC, we need to place a reinforcing plate to intensify some certain areas of the flexible printed circuit board so that it can be easier to add or solder interconnects or components to the stiffer part. And the reinforcing plate is what we call stiffener.

Functions of a stiffener

  • To strengthen areas of the board;
  • To support some interconnects or components;
  • To keep certain areas flat and stable;
  • To constrain the flexible parts to specified areas.

3 common types of stiffeners

There are 3 main types of stiffeners – Polyamide (PI) stiffener, FR4 stiffener, and stainless steel stiffener. And we will give a brief introduction to all of them.

PI stiffener‚ÄĒWith high precision and high temperature resistance, the tolerance it can allow is +/- 0.03mm. Also, PI stiffener is generally used to increase the thickness of the ZIF connector and to give the gold finger a finer touch and full support.

PI Stiffener

FR4 stiffener‚ÄĒGenerally, there are some holes on the FR4 stiffener. And the location of the holes will fit with the holes of the FPC for a better alignment. By the way, it can also strengthen the fastness of the plug-in materials.

FR4 Stiffener

Stainless steel stiffener‚ÄĒIt is generally used for flexible circuit designs requiring anti-corrosion resistance, capability, robustness, and formability. But the process will be more complicated, and it costs more.

Stainless Steel Stiffener

To sum up, a stiffener, which is the common method of strengthening a FPC, is used to facilitate the subsequent soldering and overall assembly and to give the board enough support to stand the components during assembly. Also, there are three main types of stiffener materials, including PI, FR4 and stainless steel.

So, this is the end of the article. In case if you have any other questions about stiffener or FPC, you are welcome to contact us via email at sales@bestfpc.com. We are fully equipped to handle your FPC manufacturing requirements.

The Advantages of Rigid-flex PCB

The rigid-flex PCB refers to the circuit board with both FPC’s characteristics and PCB’s characteristics. It is formed by the combination of flexible circuit board and printed circuit board through lamination and other processes.

Because the rigid-flex PCB has both a certain flexible area and a certain rigid area, it is of great help to save the internal space of the product, reduce the volume of the finished product and improve the performance of the product.

Rigid-flex PCB

And some of the advantages that rigid-flex PCB offers are as follows

Stability

With its structure comprising of interchanging layers of the rigid-flex PCB, it offers mechanical stability.

Space saving

The designs that call for a rigid flex PCB is one where space is a luxury. They also lend themselves to easy installation in small spaces.

High durability and reliability

Rigid-flex PCB allows you to obtain equipment with greater durability and reliability.

Cost saving

Rigid-flex PCB is extremely cost-effective and ensure that your project is viable. Using rigid-flex PCB may reduce the overall cost of the product.

High-density applications

With miniaturization and high-density applications growing in popularity, the use of rigid-flex PCB is also growing.

High shock and vibration resistance

Rigid-flex PCB is resistant to shock and vibration so that it can find a place in a wide variety of applications.

To sum up, we have talked about six advantages of the rigid-flex PCB. And it is supposed that you have known about them. But in case if you have any questions, you are welcome to contact us via email at sales@bestfpc.com. We are fully equipped to handle your FPC manufacturing requirements.

Factors Affecting the FPC Connector

FPC connector is used to the connect LCD (Liquid Crystal Display) to drive circuit. It is mainly applied to various digital communication devices, portable electronics, cartronics and so on, which has become an indispensable component in digital domain. However, it is undeniable that the performance of FPC connector is often affected by various factors. And the main points are as follows.

FPC with Connectors

Quantity of Solder When Welding

In the welding of FPC connectors, it is necessary to pay attention not to adding too much solder in reflow soldering when welding the connector on the FPC, otherwise, the connector terminal cannot be welded stably and insufficient soldering phenomenon may also occur.

Number of Usage Times

When the FPC connector has been used for a long time, its lifetime will absolutely be shortened due to the wear of the needle core. So, do not insert the FPC connector when it is not needed, which helps to extend the service life of the connector.

To sum up, there are two major points that will affect the FPC connector, including the quantity of solder when welding and the number of usages times, which are necessary to be paid attention to in order to have a better performance of the FPC connector.

And Best Technology is experienced in the electronics industry so that if you have any questions about Flexible Printed Circuit, you are welcome to contact us.

What is the difference between solid copper and grid copper?

There are two different design of copper trace, namely solid copper and grid copper. Do you know what is the difference between solid copper and grid copper?

Solid copper has the dual functions of increasing current and shielding, but if solid copper is used for wave soldering, the board may lift up and even blisters. Low-frequency circuits have circuits with large currents, such as commonly used copper foil. Below is a sample picture of 2 layers FPC, the top layer is copper trace, the bottom layer is a solid copper/copper foil.

The grid copper is mainly used for shielding, and the effect of increasing the current is reduced. From the perspective of heat dissipation, the grid is good (it reduces the heating surface of the copper) and plays a certain role in electromagnetic shielding. But we need to pay attention to the spacing of the grid: if it is too small, this may cause inaccurate alignment of the top and bottom¬†copper layers¬†especially for multilayer board;¬†If it’s too big, there’s no shielding.¬†Below is a sample picture of 4 layers FPC, Layer one, layer two and layer four are grid copper layer.

Different copper trace designs also have an effect on impedance. For the same projects and materials, if the reference layer is solid copper and grid copper, the impedance they reach may differ by 20-30 ohms. It also has a certain relationship with the trace width and space of the grid copper layer. In general, the greater the impedance requirement, the grid copper should be selected, and the solid copper should be selected when the impedance is small.

If you have any question about solid copper or grid copper when you design, please feel free to contact us at sales@bestfpc.com

The different design way of pluggable connector on FPC

Flexible printed circuit board (FPC) is widely used in smart phones and LCD TVS. With the extensive use of electronic products in modern society, the demand for FPC circuit board increases greatly. More and more FPCS require connectors to be assembled at both ends, easy to connect with other devices or PCB board, and FPC can be bent in the middle, reducing the space required for assembly, see below FPC samples with different connectors.

However, FPC assembly materials are not as easy as PCB, because FPC assembly requires stiffeners or fixtures on the bottom of component areas. Especially for assembling the pluggable connectors, it needs strong support and good connectivity. Do you know the different designs of the connector area and what are the differences between them?

The first and most common design, we add a FR4 stiffener on bottom side, drill holes on FR4 stiffener in the corresponding positions of the holes, noted that there is no copper for vias of FR4 stiffener, the function of FR4 stiffener is to support the component on top side, it often used for plug-in connectors.

The second design is to make the stiffener as a single-sided FR4 PCB, there is one layer of copper, and copper plated for vias. Then laminated FPC and stiffener together, and filled with solder paste in vias when assembling connectors, the connector’s pin and stiffener can also conduct except support function. However, the FR4 stiffener and FPC copper traces are not conductive.

The third design is to make it as a rigid-flex PCB, 2 layers FPC with 1 layer FR4 PCB. Although there are only vias on FR4 PCB, but the PCB through hole can be conductive to the FPC copper traces. This design has good stability and conductivity, but it is the most expensive, the cost is 3 times higher than the first design, and 2 times higher than the second design.

Do you have any FPC project need to do assembly together? Best Technology can provide FPC, FR4 PCB, Rigid-flex PCB and SMT service, please feel free to contact us at sales@bestfpc.com

What should we pay attention to FPC with dome switch design?

Applications for flex circuits boards incorporating dome switches are extremely common now. The combination allows for reduced space requirements and design flexibility in many handheld devices. When comes to a FPC design, or some extremely complex rigid-flex circuit board designs. Any additional connectors or cabling between a rigid PCB and the dome switch area is eliminated thus saving space/weight and additional assembly costs. Then more and more applications require a dome switch mounted to a flexible circuit board.

Flex circuit board with metal domes

Gerber Layout Requirements

Creating the Gerber data set for a flex PCB applications is straightforward with only a couple of additional considerations. The footprint for the dome switch is defined by the supplier and will vary depending upon the specific switch selected.

A key element is to define the coverlay opening so that the entire footprint is exposed rather than having independent openings for the center and surrounding contacts. This prevents the taller height of the adjacent coverlay from interfering with the operation of the switch ensuring a reliable actuation. Also, having two separate openings is not manufacturable when using a polyimide coverlay or soldermask.

Top side coverlay openning

A second element is including the vent hole. This prevents air entrapment which will negatively impact the switch operation/feel and potentially cause the overlay layers to separate from the flex circuit. It is preferred to have the vent hole as a plated hole in a 2-layer flex design. For a 1-layer design, it will be non-plated.

How the flex circuit board will be mounted in the assembly and what the sealing ‚ÄúIP‚ÄĚ rating requirements are, to prevent the ingress of moisture, dirt and etc. This will define the amount of spacing required from the edge of the switch footprint to the outline of the flex circuit. 3mm spacing is a typical minimum spacing that will allow the dome switch overlay to seal to the flex circuit and may accommodate and additional sealing methods used in the final enclosure. More space may be required depending upon the application.

Flex Circuit Board Materials

The flex circuit board materials required for a specific design are usually defined by design elements other than that required to meet the dome switch specifications. In most designs, a flex tail is incorporated which then extends out to then into a connector on the control PCB. The bend requirements of this tail area, if excessively tight or complicated, we suggest to use of thinner than standard flex materials to reliably meet the minimum bend radius. There are wide variety of materials available. If the tail is to plug into a ZIF connector then an added polyimide stiffener, in the ZIF contact finger area, is required to meet the connector specifications. If the connector is an SMT or PTH male/female header type, then an FR4 stiffener will be needed to support the connector.

Stiffener & PSA Requirements

Many flex circuits with dome switches require additional stiffeners or PSAs, pressure-sensitive adhesives. An additional stiffener may be necessary to provide support for the force applied when actuating a dome switch if the enclosure is not configured to do so. These stiffeners would reside behind the switch area and be thick enough, 1mm Р1.5 mm, so as not to allow any deflection.

The ressure-sensitive adhesive resides behind the switch area and can be used in conjunction with a stiffener if a specific thickness is required to fit the enclosure. The most common PSAs used are 3M 467 and 3M 478 for flex circuits that do not have any component assembly and 3M 9077 for designs that require SMT assembly. Other adhesives are also available for unique requirements.

Flex circuit board with stiffeners.

Flex circuit board with PSA.

 

The FPC with metal dome design process is not overly complex but does have several elements that need to be evaluated and incorporated to ensure a successful design. Best Technology can support a dome switch project by providing complete or partial design services as part of our user interface product line. Please feel free to contact us at sales@bestfpc.com if you have any questions or require design support in developing a dome-switch-based flex circuit.

What you need to know about PTH and NPTH holes?

Plating copper through-holes also named vias is a requirement for double-sided and multilayer circuits. Becuase one copper layer to another copper layer stack up as below, the midlayers has a Polymide(PI) regardless of adhesive or adhesvieless stack up.

2 layers adhesiveless stack up

Copper is a conductor, Polymide(PI) is an insulator. Then we need to drill a PTH hole to make the copper layer to copper layer connect together. Below picture is a multilayers flex pcb with PTH holes.

4 layers FPC with PTH holes

NPTH (Non Plating Through Hole) refers to a hole without copper in the borehole wall. It is generally used as the positioning hole and screw hole of PCB. The hole diameter is usually larger than PTH. The easiest way to distinguish between PTH (Plating Through Hole) and NPTH (Non Plating Through Hole) in PCB is to see if there are any traces of plating on the borehole wall in the PCB. Please kindly check below picture.

Holes

The advantages of hole plating

The point of plated through holes is so you can use both sides of your printed circuit board and connect to other layers of the board. The plating on the through holes is copper, a conductor, so it allows electrical conductivity to travel through the board.

Non-plated through holes do not have conductivity, so if you use them, you can only have useful copper tracks on one side of the board. You cannot connect to the other side or other boards because there is no way for electricity to travel through. You can use non-plated through holes either to affix a PCB to its operational location or to mount components, but not to connect to other boards or the other side of the board.

The risks of hole plating

All products that contain printed circuit boards are subject to the thermal cycling effect. When we power them up, they heat up until powered down, which is when they cool. As the product is heating up, so is the printed circuit board inside it. Over time, with the board continually heating up and cooling down, the copper of the plated through hole can become fatigued and crack.

The thicker the copper plating the through hole, the longer it can go through this thermal cycling without cracking. Since this cracking will ultimately lead to failure, the life of the printed circuit board in the product is linked to the thickness of the copper plating of the through hole.

Plated through holes for IPC class 3 different types:

IPC Class 1: The least thick and the shortest-lasting, usually reserved for consumer electronics that are likely to become obsolete in a couple of years.

IPC Class 2: Longer-lasting, continuous-use holes for products like computers or copy machines that will be in frequent operation for five years or more.

IPC Class 3: The thickest and longest-lasting of plated through holes, for products that are expected to last ten years or more.

IPC Class I and II plated through holes require an average thickness of 20 microns, with spots no thinner than 18 microns, while IPC Class III holes require an average of 25 microns, with spots no thinner than 20 microns.

If you have any questions about PTH or NPTH holes, please contact us at sales@bestfpc.com

What should we pay attention to EMI shield design?

Electromagnetic interference (EMI) is associated with every electronic device we use nowadays. If you turn on your radio set and TV simultaneously, you will experience the noisy disturbance from TV interfering with the radio signal and vice-versa. We can also experience this when we board a plane and are asked to switch off the electronic devices by the crew. This is to avoid interference of mobile and electronic device signals with the plane‚Äôs navigational signals. This is the reason why EMI/EMC study and analysis is important. Does your product‚Äôs radiation disturb other devices present nearby?  

EMI Shielding Design Challenges

As we all know, the flex circuit EMI shielding added will create multiple design challenges that require careful review to ensure a successful part number. All EMI shielding will increase both the total flex circuit board thickness and cost. The thickness increased is most often the critical issue. The normal EMI shield thickness is 22um, but we also has 10um thickness EMI shield. It can easily lead to the bending effect get worse. This creates a reliability/mechanical breakage concern. The added cost is also should concern. The

Shielding is often combined with other electrical requirements; the most common is controlled impedance. This further increases the flex thickness and compounds the challenge of meeting both the electrical and mechanical design requirements.

The flexible circuit industry has multiple solutions that can be applied, which will eliminate both the absorption and or radiation of interference noise.

What should we pay attention to EMI shield design to avoid the interfering?

  1. Keep your signals separate. Keep high speed traces ( clock signals) separate from low speed signals, and analog signals separate from digital signals.
  2. Keep return paths short.
  3. Route differential traces as close as possible. This increases the coupling factor, bringing influenced noise into the common mode which is less problematic for a differential input stage.
  4. Use vias wisely. Vias are necessary because they let you take advantage of multiple layers in your boards when routing. Designers must be aware that they add their own inductance and capacitance effects to the mix, and reflections can occur from a change in characteristic impedance.
  5. Avoid using vias in differential traces. If you must, use an oval anti-pad shared by the two vias to reduce parasitic capacitance.
  6. Singled sided FPC EMI shield is not working, you need design it as a dual flex pcb at least or double sided or multilayers FPC. Below is a dual flex pcb with EMI shield stack up.
dual flex pcb with EMI shield stack up

7. Avoid sharp right-angle bends.¬†Capacitance increases in the 45¬į corner region changing the characteristic impedance and leading to reflections. This can be mitigated by rounding right angles.

8. EMI minimum solder mask opening should be more than 0.8mm, and the solder mask area need to far away from the trace more than 0.2mm. Below design solder mask opening is less than 0.8mm, it will be not able to arrange production.

EMI open solder mask design issue

If you have any EMI shield design questions, warmly welcome you to contact us. Once we received your news, we will reply to you immediately..

Which kind of FPC can be replaced by FFC?

FFC (flexible flat cables) are a type of ribbon cable, so named due to their wide flat structure. They are usually a straight connector, without any additional components. The lines are straight and the spacing is fixed.

Standard FFC BFS17386-B

FPC is made of polyimide material and etched copper conductors. FPC can accept more severe tolerance than FFC and is also available in 0.3mm thick versions. There are many different kinds of FPC, including single layer, double-sided, multilayer flex circuits.

Standard Fpc BFD21076

The cost of FFC will be much lower than FFC, and the flexibility and connectivity are almost same. Normally the FFC are used in plug connectors, there are golden fingers on both side, golden finers can be in different directions; all traces are straight and the spacing is fixed, like below picture. If your FPC project is similar to this design, no component needed, then you can design it as a FFC.

FPC with EMI shield BFD17016

The black film on above FPC, it’s EMI shield, if you want FFC to have a shielding effect as well, we can add the aluminum foil on FFC, like below picture.

FFC with aluminum foil BFS20233

If you have similar design or want to know more details about flexible flat cables, please feel free to contact us at sales@bestfpc.com