Due to Flexible boards are suitable for more and more fields with their unique advantages of lightness, thinness and compactness. There are also many boards that need to be assembled components or various signal transmission, so the requirements for impedance are increasing.
Normally there are four factors will affect impedance. 1), DK Value. 2), copper thickness. 3), copper trace and space. 4), dielectric layer thickness (PI&coverlay). You can know more details from below picture.
Er1: DK value for base material, the DK value of different brands’ materials and thickness are not the same, the normal range is 3.15 to 4.2
T1: copper thickness, this is the finished copper thickness, it’s marked 30um in below table, that’s means the base copper thickness will be around 18um.
W1: copper trace width, and S1 is copper trace space. Trace width and space are important for impedance.
H1: dielectric layer thickness, that is the PI thickness of the base material, PI thickness with adhesive thickness for adhesive materials.
W1&S1: copper width and space.
C1/C2/C3: coverlay thickness. 1/2mil coverlay is 28um, 1mil coverlay is 50um.
CEr: DK value for coverlay, 1/2mil coverlay is 2.45, 1mil coverlay is 3.4
Normally customers has required impedance value and total board thickness (stack up). So what can we do to meet the customer’s required impedance?
The first step, adjust copper trace and space to meet impedance, the smaller the trace width, the greater the impedance. Our minimum copper trace and space is 2mil, if we still can not meet impedance when copper trace adjusted to 2mil, then we have to move to second step.
The second step, normally the reference layer of impedance is copper foil, we can change the copper foil to grid copper, because the greater the grid spacing, the greater the impedance value.
The third step, if the above two steps still cannot meet the impedance requirement after adjustment, we need to communicate with the customer to adjust the stack up which included copper thickness, dielectric layer thickness and coverlay thickness.
Finally, we can calculate impedance and adjust copper traces for you if you need our service. If you would like to know more details, please contact us email@example.com
Today I’d like to share what’s the difference between Adhesive PI and Adhesiveless PI.
Item 1: 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:
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.
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
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:
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 firstname.lastname@example.org if you need to know more details.
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.
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.
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:
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.
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.
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.
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.
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.
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.
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.
Normally the rigid-flex PCB need to use in a small space area, and the flex area needs to be bent repeatedly or better bend radius. So many customers are concerned about the bending effect of the flex area, do you know how to improve the bend effect when you design? Here are a few suggestions for your reference.
The first one, the thickness of flex PCB board. The thinner the board, the better the flexibility. Such as below 6 layers stack up with 2 layers flex, we can used 1/3 oz copper instead of 1/2oz or 1oz, and 1/2mil PI instead of 1mil PI, then total thickness will be around 0.1mm.
The second one, adhesiveless material instead of adhesive material. The adhesive in base material will also affect the flexibility. Such as below stack up of flex part, there is no adhesive between Copper and Polyimide, but the coverlay must be glued and then laminated.
The third one, design a loose leaf (air gap) for flex area. Loose leaf can reduce the total thickness of flex part, especially for multilayer flex circuits in rigid-flex PCB design. Such as below sample pictures, no matter 2 layers or 4 layers in flex part, many customers will add one air gap. If you think the flexibility is not very good when we add one air gap, it’s okay to add two or more air gaps for multilayer flex PCB.
If you would like to know more details, please send your questions to our email email@example.com
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.
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.
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.
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.
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.
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.
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.
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.
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.
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!
Best Technology, a China- based assembly manufacturer will be exhibiting at electronica Munich2020 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.
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 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).
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.
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.
The HS code of face masks in Japan is 630790029. The duty rate imported from China is 4.7%. To learn more, see below:
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:
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:
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:
The HS code of face masks imported from China in Australia is 63079099 and the duty rate is 5%. See below for more information:
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:
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.
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.
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.