What is the difference between solder mask and coverlay?

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

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

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

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

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

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

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

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

Item 1: Adhesiveless PI stack up

Adhesiveless PI stack up
Adhesiveless PI stack up

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

There are four advantages of adhesiveless PI:

  1. Thinner Thickness

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

2.Better Bending

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

3.  Heat resistance

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

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

4.  Dimensional stability

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

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

5.  Chemical Resistance

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

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

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

Item 2: Adhesive PI stack up

Adhesive PI stack up
Adhesive PI stack up

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

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

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

There are two mainly advantages for adhesive PI:

  1. Thicker thickness.
  2. Cheaper price.

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

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What is the Dual access flexible circuit?

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

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

Dual access flexible circuit samples picture:

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

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

Stack up of dual access flex circuit:

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

Dual access circuit advantages:

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

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

Dual access circuit disadvantages:

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

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

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14-Year Anniversary Celebration of Best Technology-Thank you!

Recently, Best Technology has completed 14 years of its glorious journey. Every small step is worth celebrating. On June 26, 2020, our founder, Peter, Emily, group leaders and all the employees spent this unforgettable festival in union.  

Best Technology Team
Best Technology Team

On Best Technology successful journey, Peter stressed- “These past 14 years have been a period of growth and a learning experience for us as we went through several trials and errors till we deliver successful business. Today we are proud of the fact that our employees can make great progress day by day after training with us and feel confident taking on tough project-related challenges,thanks for all the endeavour from employees and thanks for the great support from our suppliers and customers. Best Technology’s continuous development can not do without them.”

We have come a long way from 2006 when we started off with just 1 people(Peter). Today we are proud to announce that we have nearly 100 employees and many sister companies spread all over China mainland and also have customers in over 150 countries around the world.

number of employees
number of employees

From above, it is evident that there has been a staggering growth in the number of employees in the span of 14 years. This enhanced employee strength has built the roadmap to Best Technology’s success.

annual sales volume
annual sales volume

The above graph presents our company’s growth against the years 2006 to 2020. It can be seen that the growth rate is very high from 2006($8000) to 2019($6560,000). At this year 2020, Best Technology still keeps growing with increasing sales volume in spite of COVID-19 outbreak.

Best Technology’s unique journey has been a brick-by-brick progress and has entailed years of  efforts. Our company’s commitment in becoming world class distinctive solution of printed circuit board and metal domes in 2025 has paved the way to the series of milestones achieved. These are equally appreciated by the correct leadership of our chairman, Peter.

The primary aim of our company has been to equip the professionals with all possible accoutrements to tackle on-job challenges. Today’s ever changing face of businesses demands deeper knowledge, quality, and on-time delivery. Customers are always looking out for continuous and improved delivery. The best means to achieve the same is to keep improving.

14-year anniversary
14-year anniversary

We will continue our journey towards innovating the new ways of learning, delivering excellence to the customers and lending a hand to achieve professional goals.

What’s more, Best Technology’s 14th-year anniversary celebration is a solemn procession of efforts and dedication of the trainers and staffs who have spent their quality time to provide the best services and meet more expectations of the ever evolving PCB world.

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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!

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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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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 ½ 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 μm=.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.

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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.

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