Flex Circuit Specific Terms and Definitions

Recently, I was having a few discussions with someone very new to flex design. I was trying to be helpful and going through several things that are specific to flex and rigid flex design which should be considered as you start your first design. So, this blog is written for those of you who are new to flex and rigid flex, and may be unfamiliar with some of the terms that get volleyed around in conversation.

Flexible Circuit(flex pcb, pcb flex, flexible pcb, flex circuits):  

A pattern of conductive traces bonded on a flexible substrate. There are several different substrates available, the most common being polyimide. Different than rigid materials, these laminates will have rolled annealed (RA) copper for improved flexibility.

flex pcb
flex pcb

Rigid-Flex PCB(rigid flexible pcb):  

This is a hybrid construction, using flex materials in areas that need to bend or flex and rigid materials in areas with dense component areas, surface mount components on both sides of the PCB, and applications with higher layer count, dense routing areas.  Most common rigid materials can be incorporated into a rigid flex construction.

rigid flex pcb
rigid flex pcb

Flex Tails:  

Typically refers to the areas of flex extended out past the rigid portions of the rigid flex. This may be one flex region, or several bands of flex areas that extend in various directions. Rigid flex is often used to solve packaging issues and connect on multiple planes. Flex tails enable this.

Banding:  

Often used to accommodate a shorter flexible area if there is no room for a service loop. Instead of using the full width of the flex region between areas for each inner layer, the area can be divided into smaller bands of equal width for each inner layer, eliminating buckling and stress in that area.                                                                   

Pouch:  

This is a protective barrier material often used in rigid-flex fabrication. Often, this is a coverlay material used to protect exposed flexible materials during processing and is removed from the flexible portion of the board before shipment.

Coverlay:  

A layer of insulating material applied to the flexible circuit to insulate the conductor pattern. Coverlay is typically a layer of polyimide with acrylic adhesive. Film based coverlay is much more flexible than cover-coat materials and highly recommended for dynamically flexing applications or flex that will have a tight bend radius. It is important to be sure to spec enough adhesive to fully encapsulate the copper conductors.

Bend Radius:  

This is the ratio of the bending radius measured to the inside of the bend to the overall thickness in that area.  Typically, recommendations for non-dynamically flexing designs is 10:1 for single and double-sided construction, and 20:1 for multilayer construction. These can be exceeded but should be evaluated carefully. Dynamically flexing applications should be discussed with your fabricator for a recommended stack up.

I always wrote a blog about how to calculate the bending radius of fpc.

Button Plate:  

Fabrication process to selectively electroplate copper to vias and onto the pads capturing the vias. The remaining copper traces do not have electrodeposited copper, increasing the flexibility of the circuit.

I-Beam Effect:  

Stacking conductors on adjacent layers directly on top of one another, increasing the stiffness of the circuit in the bend or fold areas. Staggered conductors are recommended if possible, to retain the maximum flexibility of the circuit.

I hope this helps explain some of the common terminology with flex and rigid-flex materials and design. Please reach out to me with any questions for further information!

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

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.

Copper Thickness Requirements for Flex Circuits

If an end user will specify the copper thickness of a printed circuit, there must be many reasons. For example, current carrying capacity, but copper thickness also directly impacts thermal performance and impedance. All these are vital properties, which have a great influence on the functionality and reliability of a flexible circuit.

flexible circuits
flexible circuits

At the point, it is important to understand the functional needs driving a copper thickness requirement.

Some of the common functional requirements could be:

1.Minimum thickness in a connector area to assure robust contact.

2.Adequate current carrying capacity directly related to the cross sectional area of the trace.

3.Proper conductivity, a function of cross sectional area and metal type of the trace.

4.Proper impedance in high speed circuits driven by the cross sectional area of the copper, the surrounding dielectric constant, and distance from signal trace to ground plane.

5.Thermal properties directly related to metal type and trace profile.

Copper weight is used in the industry as a “thickness” measurement. Circuit manufacturers commonly purchase copper foil with descriptions of Âœ ounce, 1 ounce, 2 ounce and so on. The number is the weight of copper in a square foot of foil. Also, +/- 10% is the industry accepted tolerance for copper foil thickness from the material supplier.

flexible pcb
flexible pcb

Drawing specifications will frequently define a flexible PCB copper thickness using weight. For example “circuit to be 1 ounce copper”. This can lead to some ambiguity, as copper plating on double sided circuits can easily add an ounce of copper to the surface of a trace. So by specifying thickness in this fashion, it is not clear if this is intended as a finished thickness or an original thickness. Additionally, controlled impedance designs work best when copper plating is restricted to the vias with no copper plated on the surface of the traces. This will minimize trace thickness variability and suggests a specific product category requiring a process known as “Pads Only Plating” or “Button Plating”. For controlled impedance designs, one of these terms should be called out in the drawing notes.

What affects final copper thickness is the variety of manufacturing processes that add or subtract copper thickness. Micro-etching is a common “cleaning” process used to prepare a surface for plating or coating. This process removes a small amount of copper. Likewise copper plating will add thickness. The circuit fabricator will directly measure added (or subtracted) thickness in mils (1 mil =.001”) or microns (25 ÎŒm=.001”).

The most accurate method for determining thickness is to do a micro section. This is a destructive test, so it is common to use coupons located in unused areas of the processing panel. These coupons are located and sized to be “representative” of the circuitry copper thickness. Copper thicknesses will vary slightly across a panel depending on current density from electroplating. Current density can be a function of the copper trace pattern so differences among various part numbers will occur. As a general rule, copper plating thickness will tend to be thinner on the outer edges of the panel and thicker toward the center.

In summary, when defining the specific copper thickness for an application it is highly recommended to start with a discussion of the myriad functional requirements. Also, the manufacturer can help recommend copper thicknesses and tolerances as well as the best methods for measurement.

Best Technology is the professional vendor of flex circuits, from 1 layer to 10 layers, 2 layers rigid-flex circuits to 16 layers rigid-flex circuits, and one-stop service including components purchasing, assembly, IC programming, testing. Choose us, you can always enjoy our best service at a good price.

Good news: We can support your masks demand now!!!

Global demand for supplies used by our customers to treat and help protect people, such as respirators, is currently exceeding supply. Best Technology expects demand for respirators to outpace supply for the foreseeable future.

disposable face mask
disposable face mask

Throughout all the recent developments, Best Technology is working hard to uphold the commitments we made to supporting your business. We are very focused on protecting the health and safety of our workforce while maintaining the ability to keep serving you.

With more than 10 years of domain expertise in the industries we serve, we are here to help you adjust to whatever may happen next.  

The COVID-19 pandemic continues to affect all of us, and all Best Technology colleagues are working around-the-clock to help provide critical tools for the fight. Our current focus: supporting health care and front-line workers as well as our regular and new customers around the world by providing products they need to help protect their lives.

We are seriously in choosing partners who can provide various kinds of respirators as well as medical products:

The partners who can double their global output rate to nearly 100 million respirators per month are in our priority;

Also, we anticipate doubling global capacity of our partners to almost 2 billion respirators in the next 12 months.  

We have not increased the prices we charge for our respirators in this crisis.

KN95 mask
KN95 mask

Our efforts are guided by our value of Caring – for our people and their families, our consumers, and importantly, for those most in need right now. We want to share a few of the ways that we are responding to this global health crisis.

If it’s difficult for you to find protection devices, such as face mask(disposable face masks and KN95 face masks),non-surgical isolation gown, medical gowns (protective coveralls), surgical cap, surgical dress, medical gloves, safety goggles, medical helmet, infrared thermometers, contact us, we are glad to support you.

(for more information, you can refer to: www.besttechmedical.com).

Moreover, after our efforts, all of our face masks, KN95 masks and all of other medical products have passed GB2626-2006 and CE standard. You can also find out the certificates from the above website.

Anything I can do for you? If there is a need, contact us anytime. Our sales team will be here to reply you instantly. Please keep safe and take good care of yourself and your families. Come on, our friends, wish the pandemic will end asap and everything can return to normal soon.

Measures China took to fight against the COVID-19

China’s fight against COVID-19 epidemic has achieved victory at this stage. Infected patients were found in 337 cities in China but now only 28 cities remaining patients in cure. So far till March 31st, there were 82545 confirmed cases in China, while 76225 cured and only 3006 remaining now. Most importantly, many of the areas finds only one figure number increase and others stop increasing for quite some days. If the first half of COVID-19 fighting is inside China national territory, the second half will be on the international stages while noticeable growth on COVID-19 infected cases are spreading all over the world now.

corona virus updates
corona virus updates

Best Technology has been collecting the measures in China on epidemic controls so in order to provide a more objective and useful reference for overseas professionals which we hope they could refer to and protect better themselves from the COVID-19.

Governmental Measures

During the height of the outbreak, trains didn’t stop at the disease’s epicenter, Wuhan

Wuhan trains
Wuhan trains

Trains, as well as other tightly packed forms of transportation, can serve as vectors of illness. The more people, the more closely packed, and the more poorly ventilated the space, you can imagine that’s a bad situation because there are a ton of people, they’re in very close quarters, and they’re a totally captive audience. Cutting off transportation was considered on the top three measures to contain the spread of the virus.

China built new hospitals in a rush, with workers toiling night and day to get them done.

China Newly-built Hospitals
China Newly-built Hospitals

China built two new 1,000-1,300-bed hospitals to fight the corona virus, one created in six days, and the second in 15 days, using prefabricated modules.

Corona virus testing was easily accessible and free

Corona virus testing
Corona virus testing

In China, patients who were confirmed to have the corona virus were either sent to an isolation center or hospital. The government also made clear that testing for the new virus was free, and COVID-19-related charges that weren’t covered by a person’s insurance would be paid for by the government.

The country implemented large-scale contact tracing in the early 2000s

Contact tracing
Contact tracing

During the SARS outbreak in 2002-2003, China set up large-scale surveillance systems that included contact tracing, a front-line public-health strategy that involves identifying and following up with people who may have come into contact with an infected person.

The country postponed non-urgent medical care and moved many doctor’s visits online. Not all patients were given the critical care they needed during the outbreak, though

Doctor's online visit
Doctor’s online visit

In China, elective surgeries and other non-critical doctors’ visits were delayed, and many medical services were moved online. Someone in one place said 50% of their consultations are now done online; they just moved a whole bunch of what was normally done physically online to be able to keep the regular health services going.

Centers for Disease Control exploring a way of therapeutic plan combing Traditional Chinese medicines and Western medicines.

 Traditional Chinese medicines treatment
Traditional Chinese medicines treatment

The combination of Traditional Chinese medicines and Western medicines had been proven effective on the SARS fights. Doctors of traditional Chinese medicines had volunteered for consulting and participating into the virus fights.

China used technology that aims to trace every single COVID-19 case

Civilian Measures

Traditional epidemic prevention manufacturers speed up and similar production lines integrating to make more necessary products

mask production line
mask production line

Many medicinal and pharmaceutical substances manufacturers launched automation assemble lines and increase manpower to speed up the mass production of necessary drugs, masks, ventilators to meet the huge consumption during virus fighting. Many of these companies arranged 24-hour shifts for maximizing the production.

Meanwhile other manufactures such as automotive OEM had change their assemble line into masks productions machines.

At the blast of COVID-19, returning Chinese carrying back epidemic products from overseas as much as they can

 epidemic products brought by overseas Chinese
epidemic products brought by overseas Chinese

Returning travelers carried extra masks on their flights back to China and donated them to the hospital and governments in need. Some overseas Chinese unions also had helped ordering these products and sending to China.

Chinese citizens did their part to curb the disease’s trajectory on an individual level, too, though we may never know the true scale of their complaints or sacrifices in this outbreak.

China's road
China’s road

In contrast to reports in the US of people clamoring over the last hand-sanitizer, the attitude of people in China was that they were all in this together. People stay at home for self-quarantine, lockdown and response to the postpone returning to work and school.

People who thought they might have the corona virus could go to one of the nation’s many fever clinics

fever clinics
fever clinics

People who thought they had the novel corona virus in China would often be sent to a special fever clinic, which have been widespread since the country dealt with an aggressive SARS outbreak in 2002. Their temperature would be taken, and they’d discuss their symptoms, medical history, travel history, and any prior contact with anyone infected with a doctor.

If necessary, patients might receive a CT scan, which is one way to do an initial screening for COVID-19. Each machine did maybe 200 a day. 5-10 minutes/scan. A typical hospital in the West does one or two an hour.

People quickly shifted jobs in order to assist during the outbreak

volunteers
volunteers

When it came to the non-medical response, there was a nationwide sense of solidarity with Hubei. Other provinces sent 40,000 medical workers to the center of the outbreak, many of whom were volunteers.

Workers in transportation, agriculture, and clerical positions were encouraged to new positions such as delivery, courier and epidemic prevention manufacturing, too.

While staying home, it’s been relatively easy for Chinese people to get extra food and supplies

Enough food
Enough food

China essentially mandated a country-wide shut down, demanding that every Chinese resident stay home until the curve was flattened. But in West, unlike China, a country-wide shutdown would be difficult to enforce.

Fifteen million people had to order food online. It was delivered. Yes, there were some screw-ups. But few said: every now and again there’s something missing from a package, but food supply is pretty much normal via ordering online.

We know it’s difficult for most of people around the word to find protection devices, such as face mask, Non-surgical isolation gown , Medical gowns, protective coveralls, Surgical Cap, Surgical Dress , Medical gloves, Safety Goggles, Surgical Helmet, infrared thermometers, please contact our sales, we will be glad to support you.

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.