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

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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 “IP” 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 – 1.5 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.

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How to choose the FPC stiffener?

 Flexible PCB -Flexible Printed Circuits are made of thin dielectric substrate & high ductility metal foil, flexible pcb can be bent or folded and used in static and dynamic applications. 

Do you know why the fpc need to add the stiffener?

Flexible-only PCBs can withstand fewer components than rigid-flex. The rigid part of rigid-flex can also be as complex as a traditional rigid Circuit Board. Stiffeners are occasionally laminated the same time as the coverlay.

When we need to add the Stiffeners ?

Components are near or in an active, or dynamic, flex zone
Component size and weight will import stress onto the flex
A large number of SMT pads make planarity critical
Connectors that require repeated insertions or assemblies require a stiffener, or something to help alleviate the stress of pads.

When we don’t suggest to to add the Stiffeners ?

 Small “static” components do not exert a large amount of strain on the flexible of the PCB.There are no components in the flex region.
 

How to choose the FPC stiffener?
 As we all know, the Stiffeners are typically made of FR4, PI(Kapton), stainless and alumimum stiffener.Then how we we too choose the right stiffener?

PI is often used when the end of the flex must be thickened and inserted into a ZIF connector. However, the use of Kapton(PI) requires a separate lamination cycle. For golden area, we will be need to add the PI stiffener to meet the total thickness 0.2mm, 0.3mm or 0.5mm.   

PI stiffener

FR4 stiffener can be done within the same lamination cycle. FR4 stiffener usually added for the USB connector area.

FR4 stiffener1

Stainless stiffener is not easy to transformation. And it has the good hardness. And it can play a conductive and inductive role.

Stainless stiffener

Aluminum stiffener has the best heat disspation effect, because it usually need to openning a tooling to cut the alumunum stiffener outline, then the cost is the highest.

Alumininum stiffener

Are you got it? If you have any comments, please kindly feel free to let me know. Please contact Best Technology at sales@bestfpc.com.

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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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Do you know the difference between ENIG and plating gold?

Before we point to the topic, I’d like to share one story with you first.

Recently, one of our customers, whose projects need ENIG(1u”) on whole surface, and we didn’t know these projects was strict with the gold surface on some special area. 

There are two pre-treatment for ENIG, one is gridding plating, another is sand blasting. At first, what we used is gridding plate, so when customer watched the gold surface can saw some cracks.

Gridding plate

To solve this issue, we suggested to try sand blasting ENIG pre-treatment. Compared with gridding plating, it only need slightly brush the plate. But it’s still cannot meet customer’s need.

Sand blasting

For normal design, change the surface treatment from ENIG(1u”) to gold plating can completely solve this issue. But in this design, the PADs on boards are separate, and there are in different gridding with outside. So gold plating is infeasible for this design.

Only when the inner PADs lie in same gridding with big copper plate, the gold plating is feasible.

So, let going to today’s the topic. What’s the difference between ENIG and plating gold?

  1. The difference in process.
  2. ENIG is called immersion gold, achieved by chemical deposit. Through an oxidation-reduction chemical reaction, it formed a layer of coating. It’s one of chemical nickel-gold depositing methods, can reach thicker gold layer.

It need pre-treatment gridding plating and sand blasting before immersion gold, need brush the board to enhance the adhesion between the board and the gold surface.

2)Gold plating use the principle of electrolysis, also known as electroplating. Needn’t pre-treatment before plating gold.

  • The difference in color.

ENIG is golden.

Plating gold will be slightly whiter (nickel color).

  • The difference in performance.

The crystal structure between ENIG and gold plating is different. Compared with plating gold, ENIG is easier to weld and will not cause bad welding.

The stress of ENIG is more easily controlled, for the products with bond, more conducive to the processing of the bond.

.

Last but not least, as we mentioned at the beginning, if your project need plating gold, pls make sure these area need gold plating can connect with outside gridding.

Hope above information is helpful for you to know more about ENIG and plating gold.

If any further question, pls let us know.

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What should be paid attention to in the bending process of FPC?

Flexibility is the most obvious advantage for flex PCB, but we should maintain a degree during use, not just bend casually, so what should we pay attention to when bending?

BESTFPC1
bestfpc2
  1. Although the FPC can be bent, if it is bent at 180°, this may cause damage to the copper traces, and it lead to open or short circuits.
  • Most of the ink-type protective layer is not resistant to bend, such as text/silk screen, marking, solder mask, etc. It is strictly prohibited to have more than 90° bending action in the assembly process.
  • The corners of the FPC outline, which are prone to tearing during the assembly process, reminding users to pay attention to it.
  • The exposed part of the FPC is subjected to surface plating treatment, such as gold/gold plating, etc., the focus is on preventing oxidation. This area is not suitable for bending.
  • Although there is a stiffener design in the golden finger plug-in area, it is still not suitable for bending in this area. Special attention should be paid to the assembly process.
  • Do not bend directly on the via area of FPC.

If you have any design question about bending area, please feel free to contact us at sales@bestfpc.com. We will share more details about increasing the bending times soon.

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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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What do you know about the connection ways of PCB panel?

As we all known, some customer need to do following assembly in their side when received the bare boards. In order to facilitate customers for subsequent assembly, we’ll ship out boards in panels. So, what’s the difference between FPC and PCB paneling connection mode?

  1. For FPC , we often use connecting tabs to connect the boards. 
FPC connecting tabs
  • For Rigid PCB, we often use V-cut and connecting tabs(with stamp holes) to connect the boards.
PCB V-cut
  • For Rigid-flex PCB, we’ll use connecting tabs(without stamp holes) in flex part, and use connecting tabs(with stamp holes) in Rigid part.
connecting tabs(with and without stamp holes)

Take the Rigid-flex PCB for example, if the boards are easy to fallen from panels when do assemble, how to improve the design?

There are two direction we can go, one solution is add more connecting tabs in paneling, another solution is broaden the width of connecting tabs.

Hope our suggestion are helpful for you. If any further question want to discuss with us, pls feel free to contact us at sales@bestfpc.com.

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We will be exhibiting at electronica Munich 2020

Best Technology, a China- based assembly manufacturer will be exhibiting at electronica Munich 2020 in Bavaria, Germany at booth No. 623(Hall B1) from November 10, 2020 to November 13, 2020(Western Time). Actually, we have participated in this exhibition for continuous 2 years. Here are some pictures for your reference.

pcb exhibition
pcb exhibition
pcb exhibition
pcb exhibition
pcb exhibition
pcb exhibition
pcb exhibition
pcb exhibition

At our exhibition booth, attendees will be able to learn more about our company for PCB manufacturing and PCB assembly technology.

For interested professionals, Best Technology had on hand experts to offer detailed insights and experience on PCB assembly, covering PCB prototype and low/high-volume production. For more information on PCB assembly and fabrication, welcome to visit our booth.

You will see 10mm to 1,500 mm flexible circuit board, from 2 layer rigid-flex circuit to 50 layers, 1/2 OZ copper to 3 OZ, 0.15mm extra thin FR4 PCB to 30 OZ heavy copper, turn-key service from components sourcing,board fabrication(FPC, PCB, MCPCB, Ceramic PCB) and final assembly with programming and testing and metal dome that is used in conjunction with a printed circuit board, flex circuit, or membrane, become normally-open tactile switches. we have four types of metal domes: four legs with size from 5mm-20mm; triangle with size 4mm-12mm; round dome with size 4-16mm, oblong dome with size 3.7mm-58.1mm, and we also make dome with adhesive, named dome array.

You are warmly welcome to see how we can manage the components wastage and efficiency to help save your time, money and energy.

About electronica Munich:

Electronica is the international trade show for electronic components, systems and applications and shows the full range in all its diversity in width and depth as the world’s leading trade fair. It reflects the high degree of innovation throughout the industry. Exhibitors and users in the areas of systems, applications and technologies of electronics can receive the information of the latest innovations and developments in the fields of system peripherals, power engineering to printed circuit boards or EMS.

Welcome to visit us at Booth 623 from November 10, 2020 to November 13, 2020(Western Time).

electronica 2020
electronica 2020

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HS Code and Import Tariff Rates of Face Mask in Some Major Countries

Regarding HS code and duty rate of face masks in some major countries, we collected some information in main trade partners (US, Japan, EU, Korea, Taiwan, Australia, New Zealand) of China. This is aimed at the face masks such as personal protective masks without special function components, including medical face masks and disposable face masks. All of below information were published by the custom officially.

US:

According to Harmonized Tariff Schedule of the United States, HTSUS, the HS code of face masks in the US is 6307909889. And the duty rate imported from China is 7%. Regarding tariff imposed, according to announcement from the United States Trade Representative on March 12, 2020, the tariff is excluded for the face masks belonging to this HS code since September 1, 2019. Since then, all the face masks imported from China has been exempted from tariff. You can refer to the below chart for more information.

face mask tariff
face mask tariff

Japan:

The HS code of face masks in Japan is 630790029. The duty rate imported from China is 4.7%. To learn more, see below:

face mask tariff
face mask tariff

EU:

The duty paragraph for face masks imported from China in EU is 6307909899 and the duty rate is 6.3%. You can see below for more information:

face mask tariff
face mask tariff

Korea:

The duty paragraph for face masks imported from China in Korea is 6307909000, and normally, the tariff is 10%. However, from March 18, 2020 to June 30, 2020, Korea has been suspending imposing tariff for face masks from China(0 tariff currently), see below for more information:

face mask tariff
face mask tariff

Taiwan, China:

The HS code(also referred to as duty paragraph) of face masks imported from China mainland in Taiwan is 63079050.

And, the duty rate for face masks imported from China mainland is 7.5%. However, from February 27, 2020 to May 26, 2020, provisional tax rates (also referred to as“flexible tax rate”in Taiwan area) for face masks was carried out in Taiwan area, i.e. the tariff is zero. You can see below for more information:

face mask tariff
face mask tariff

Australia:

The HS code of face masks imported from China in Australia is 63079099 and the duty rate is 5%. See below for more information:

face mask tariff
face mask tariff

New Zealand:

The HS code of face masks imported from China in New Zealand is 63079028. Zero tariff is applied to the face masks imported from China according to “New free trade agreement”. See below for more information:

face mask tariff
face mask tariff

To learn more, see below document:

face-mask-hs-code-and-tariff-in-some-countries

Hope the above information is useful to you. And if you have any queries, comments or suggestions, contact us anytime. We will be glad to help you.

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