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How to Select the Suitable Laminate for Your Flex PCB

Introduction

Every so often, consumers get confused when trying to find the right PCB laminate to fit their specific application and design. As expected, the main thing that most clients seem to be so curious about the price. However, if you take your time and get past the customer’s office and take time with an engineer, you’ll learn that there are other critical factors to consider when selecting the right laminate for your flexible circuit board.

Every printed-circuit-board manufacturer today has a different dielectric formulation to ensure their printed circuit boards, meet the consumers’ expectations. In an ideal world, one PCB material would be used in all application. However, because the requirements of one application may differ from the other, a single flex PCB laminate can hardly serve both purposes optimally.

Understanding a PCB-Laminate Designation

During the manufacturing process, laminates are created through curing under controlled temperatures and pressure, layers of paper featuring thermoset resin. The weave pattern, thickness and percentages of resin on the pressure paper usually determiner the thickness and dielectric characteristics of the laminate.

The thermoset-resin system, something that most manufacturing companies are secretive about, and the fabric of material used determine the designation type: FR-4, PTFE, CEM etc.

Different laminates have different characteristics based on the aforementioned factors, and they are the ones that should guide us when choosing the right one. Some of the critical aspect to focus on include, the level to which the flex PCB laminate is fire retardant, thermal conductivity, dielectric constant, thermal expansion coefficient (CTE) and how it determines the z-axis expansion. To the uninitiated, that means how PCB thickness changes with a corresponding change in temperature.

Laminate Application

One thing that most consumers should consider when they in the quest for the right laminate is the application. Most high -frequency-laminate manufacturers are paying much focus on application and the specific requirement in each application. That has compelled them to develop different formulations to suit specific purposes such as high-power and high-frequency amplification. Understanding the application is what can help an engineer to select the best flexible circuit board laminate. Additionally, you need to know the performance measures as a critical basis upon which you choose the right material.

Type of Laminate

Recently, consumers have continuously preferred acquiring the multilayer hybrid flex PCB because of its ability to accommodate most of the required features. Typically, you want a flexible circuit board with common layers of the PCB material. Some manufacturers choose to combine both high-frequency and multi-layer FR-4 laminates to create high-end, high-performance products.

Even so, that hardly compromises the manufacturing process; not unless you are dealing with a PTFE laminates. That requires special manufacturing procedure that involves sodium etching. In that case, when PCB companies design hybrid-stackups, they are mostly concerned about regulating the mixture of the laminate and the coefficient of thermal expansion. If there’s any mishap in the processing, the PCB laminate can warp.

On the other hand, PTFE substrates offer great electric conductivity. Nonetheless, because of the high thermal expansion coefficient values, using a multi-layer hybrid version of this may not offer desirable reliability benefits. Notable, good electrical and thermal conductivity enhances smooth electromagnetism thus increasing the versatility of PTFE substrates.

The post How to Select the Suitable Laminate for Your Flex PCB appeared first on PCB Labs.

source https://www.pcblabs.com/how-to-select-the-suitable-laminate-for-your-flex-pcb/

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Simple Flex Circuit Quality Control

 DRC Check

The Design Rules Check (DRC) is one of the most important steps in flex circuit quality control. Upon receiving an order, use this automated tool to verify if the layout does not have any addressable layout errors, such as specific placement or routing. The DRC check verifies the layout and netlist against the flexible PCB design rules and constraints.

The DRC examines the component placement of the board and traces the routing integrity for components that overlap, pins that are untraced, and incorrect layer placement among other constraints.

Our system also does the manufacturing rule check in order to ensure that the flex circuit design can be manufactured.

Automated Optical Inspection (AOI)

Automated optical inspection is more repeatable and reliable than the manual visual inspection. Use automated optical inspection to test the inner layers of flexible PCBs that are multi-layered. In this method, the surface of the flexible PCB is visually scanned by several light sources that light the board. A number of high definition (HD) cameras or a scanner observes the surface. As a result, all areas of the flex circuit’s board can be monitored.

The automated optical inspection for a bare flexible PCB board detects the following features:

Spacing violations

Hole breakage

Cut traces or pads

Missing pads

Line width violations

Excess copper

Shorts circuits

Restriction of Hazardous Substances Directive (RoHS)

The RoHS has restrictions for the use of six hazardous materials in the production and manufacturing of various electrical and electronic equipment. The flexible PCBs should be free from hexavalent chromium, flame-retardants polybromide biphenyl, polybromide diphenyl ether, lead, cadmium, or mercury. All your products should comply with the RoHS requirements.

Electrical Testing

Prototype Orders

For small volume and prototype orders of flex circuits, you can use Flying-Probe E-Test. Your clients’ flexible PCB board should be analyzed through a Flying-Probe E-Tester. This tester checks for open circuits, short circuits, and ensure that the nets that we make are the same as the ones for your design. The process is efficient, and it ensures that the fail rate of your PCB boards will be not more than 1%.

Production Orders

Production orders are tested using testing fixtures. For instance, the traditional electronic test fixtures such as a bed of nails tester have many pins that are placed in holes in an epoxy phenolic glass cloth laminated sheet, which is aligned by tooling pins in order to make contact test points that are on the PCB.

The traditional electronic test fixtures comprise an array of spring-loaded pogo pins that make contact with a node in the circuitry of the device on test (DUT). Reliable contact is quickly made with thousands of individual test points that are within the DUT circuitry.

This tester also checks for open circuits, short circuits, and ensure that the nets that we make are the same as the ones for your design. The process is efficient, and it ensures that the fail rate of your PCB boards will be not more than 0.1%.

UL Certification

All your products should comply with the UL safety certification 94V-0. Your flexible PCBs should satisfy all the UL requirements and meet the flame rating 94V-0. The typical rating of flexible PCB material should be at least 94V-1. Note that the higher the number, the lower the rating, for instance, 94V-0 has a higher rating than 94V-1. Our manufacturing process and materials are subjected to UL inspections.

The post Simple Flex Circuit Quality Control appeared first on PCB Labs.

source https://www.pcblabs.com/simple-flex-circuit-quality-control/

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Flexible Circuit Board Handling and Storage Guidelines

Flexible circuit boards are manufactured using very sensitive components. Therefore, if you handle the flex PCBs carelessly, the board will be damaged. Exerting pressure on any of the small components of the flex PCB causes serious damage, and a minor static electricity may destroy the board completely. To prevent such damages, you need to maintain the static electricity generation at its minimal level, discharge static electricity that has been build up, and handle the flex printed circuit board with care.

Below are some of the critical precautions you need to take when handling and storing flexible circuit boards:

Be Properly Grounded

Before you handle a flexible circuit board, you are advised to put on rubber soled shoes to help you ground yourself. This will help prevent static electricity build up, which can severely damage the circuit board.

You should also wear a wrist strap that is connected to earth ground whenever you are handling a circuit board assembly.

Touch a Piece of Metal

You are advised to touch a metal piece for at least two seconds to help you discharge any residual electricity that may have been stored in your body.

Maintaining High Humidity

You should create and maintain high humidity in your work station. This will limit the build-up of static electricity, which is prevalent in dry atmosphere.

Keep Static Generating Materials Away

Unless it is absolutely necessary (highly likely that it will never be), you should remove any static generating material from the immediate vicinity of the flex PCB. Materials such as plastics, fabrics, vinyl, and Styrofoam have a tendency of building up static charges.

Put on Gloves

During unpackaging, you should putt on gloves when handling flexible circuit boards. While you remove the circuit board from an anti-static bag, you need to keep at least one of its edges touching the anti-static bag. You should lay the flex circuit board directly on the bag and leave it on that spot until when you will be ready to install the circuit board.

Proper Installation

You need to install the flex circuit board into the correct module of the product or equipment using the required pressure (never exert excess pressure) to snap it into its right place. Never ever force the component into place.

Check for Protection

Designated workstations and storage areas of flexible circuit boards should be periodically checked to make sure that they are safe for flex PCB continued protection. The main areas of concern are static dissipation of work surfaces, proper grounding methods, the operation of ion blowers and ion air guns, as well as static dissipation of floor surfaces.

Use Shielded Bags or Boxes

Since flexible circuit boards are sensitive, you should enclose them in shielded bags or boxes when not being worked on. Here are three types of electrostatic discharge (ESD) protective enclosure materials. They include:

Antistatic: this material offers antistatic cushioning for the electronic assemblies.

Static Shielding: this material prevents static electricity from penetrating the package.

Static Dissipative: this material has adequate conductivity that helps dissipate static build up.

Use Dedicated Lotions

Do not use lotions and hand creams that contain silicone since they are likely to cause epoxy adhesion and solderability problems. Ensure that you use lotions that are specially formulated to prevent contaminating flex PCBs.

The post Flexible Circuit Board Handling and Storage Guidelines appeared first on PCB Labs.

source https://www.pcblabs.com/flexible-circuit-board-handling-and-storage-guidelines/

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How to Prevent Dent and Fracture for Your Flexible PCB

A flexible PCB is both mechanical equipment as well as an electrical gadget. The neutral bend axis of a flex circuit board may not be in the exact middle of the circuit stack. Proper handling of a flex circuit board may help in preventing dent and fracture for your flexible PCB.

A flexible PCB is as much as mechanical equipment as it is electrical equipment. Conductors are laid out in a way the entire circuit functions reliably and adequately. Unlike the traditional rigid printed circuit board (Rigid PCB), a flexible PCB can bend, flex, and contort to fit the final assembly. This bending, when stretched beyond waa certain point, can severely strain the circuit leading to fracture and dent in your flexible PCB.

The flexibility in the flex circuits gives designers an array of options that lacks in rigid PCB. Even though flex circuits are ideal for usage, that needs curving and twisting, it does not mean that, the flexible copper trace can never crack. As in all materials, there are limits to the types and amount of stress that copper can withstand.

There exist a wide variety of flexing challenges. When dynamic bending is required (continuous flexing while the product is in use), or in applications that require circuits to be folded into tiny spaces within a multilane enclosure, precision, and extra caution is necessary to avoid fractures

Factors to Consider To Optimize Flexing and Bending of a Flexible Circuit.

Understand the stress point and bend radius

You need to know the design issues for bending, folding, and flexing— understand the physics of bending. For a single-sided flexible circuit bend, if the extension or the compression goes past the bend radius or stress point, the copper layer will eventually fracture. Always ensure you are operating within these parameters.

Neutral Axis

For dynamic flex applications, it is advisable to use single sided— one layer of copper circuits. This gives room for the copper to shift in the center of construction with an equivalent thickness. With this kind of structure, the copper layer is neither in compression nor in tension during dynamic bending or flexing.

Thinner Is Better

The thinner the layers, the smaller the inner bending radius hence less stress on the outer layer. For applications that require frequent bending, it is best to use thinner copper and thinner dielectric layers.

I-Beam Design

I-beam construction is when the opposite side of copper or dielectric lays directly over each other. This type of construction becomes more rigid on a folded area. The extension forces of the outward side significantly increase because of the compressed layer of the inside layer. To get rid of this problem, traces of the opposite sides should be staggered.

Sharp Bending or Folding

Many flexible circuit boards are folded as part of the design package. A well-constructed circuit can easily withstand the first fold, twist, or crease. However, creased circuits should not undergo frequent folding, as the copper will eventually crack. This is not recommended under any circumstance. To avoid this problem, some design considerations are provided. For instance, flex circuits boards with radiused traces are designed for this purpose.

Other considerations to keep in mind to avoid trace fracturing on flexible circuits include:

Using solder or solder coated path traces

Using RA (Rolled Annealed) Copper or electrodeposited copper (ED), and grain direction

Covering the areas that get bent or flexed with the polyimide film,

Using stiffeners on the bottom and coverlay on top.

The post How to Prevent Dent and Fracture for Your Flexible PCB appeared first on PCB Labs.

source https://www.pcblabs.com/how-to-prevent-dent-and-fracture-for-your-flexible-pcb/

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Game Changing Technologies Affecting the Rigid Flex Industry

In this internet-driven world we live, it is imperative that you integrate technological tools in your business so you can remain viable. Today, it is not enough to just have desktops a computer. There is a vast latitude of technologies to keep tabs on and profit from.

Even as the world of the Internet of Things keeps on evolving, there has been an increased demand in rigid-flex circuit boards and for all great reasons. First, the number of rigid flex manufacturers has increased providing a wide variety of products to consumers. In addition, markets have shifted from the Far East, and today, anyone can purchase flex machines from China when you have a reputable manufacturer.

New Advanced Circuits

The demand for rigid-flex circuit boards has increased as advanced technological tools are created. The industry is highly competitive, compelling rigid flex companies to introduce new and better products to meet consumers’ needs. Rigid-flex circuit boards are becoming popular as they meet form-factor thresholds, enhance performance, and reduce the use of connectors.

Optimized Use of Technology

Another beneficial aspect of rigid-flex circuit boards is that their assembly requires a short time. Consumers have continuously demanded a reduction in price and assembly time. Since flex-rigid requires no connectors to function, consumers can enjoy reduced time and increased reliability level. Other game-changing technologies include:

Data

With data, you should think of the tech tools and techniques employed in collecting and using the ever-increasing stream of data with an objective of expanding its visibility to improve the business environment and offer information to help in rational decision-making.

Cloud-based technological systems will see an increase in utility as a complementary service to other data management systems and programs to control the expanding data space. The situation is difficult to control as it is a hard trend that can hardly be overlooked.

On-Demand Technological Services

Technological services will continue to be in demand as long as businesses seek new ways to dispense their services. Rigid-flex companies join the big pull of Software as a Service companies to offer individuals and other companies better IT management services. Both sectors will experience tremendous growth as they offer business alternative means of cutting expenses such as having a large team of IT personnel. As such, it relieves the IT department of other responsibilities and thus, they can focus on contributing to business development processes to enable organizations to reach their goals and objectives.

Mobile Banking

The need to provide consumers with convenient payment systems has resulted in the rapid growth of mobile banking. Currently, there is a widespread use of smart devices as a form of eWallet; thanks to the increased accessibility of Near Field Communication tools. More important rigid flex companies and other financial institutions have already adopted m-banking systems.

3D Printing

Also known as Additive Manufacturing, 3D printing involves the use of 3D printers to design, build and manufacture products by depositing a plastic or metal in layers until the desired final product is achieved. Initially designed to work in the creation of prototypes, 3D printers are increasingly being used in the jewelry, car dashboard, phone casings, and jet-engine industries.

The technological world is ever changing. Individuals and business organizations must keep up with the trending technologies so they remain competitive in their various industrial sectors.

The post Game Changing Technologies Affecting the Rigid Flex Industry appeared first on PCB Labs.

source https://www.pcblabs.com/game-changing-technologies-affecting-the-rigid-flex-industry/

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Rigid Flex Fabrication Process

As the name implies, rigid-flex PCBs undergoes a fabrication process with the combination of both rigid and flexible circuit boards. These two boards are then permanently interconnected to form PCBs of various types. During the fabrication process of rigid-flexible circuit boards, certain considerations and precisions must be taken into account in order to produce a perfect final product.

Some of the more significant considerations are;

Laser profile cutting

Selective Pad Plating

Material dimension tolerances

Thin material handling capabilities and procedures, and

Plasma desmear and etch back

The flexible substrate materials used in fabricating rigid-flex PCBs have more benefits than the traditional rigid PCBs. They are:

Lighter in weight,

Accessible for interconnection assembly,

Lower in thickness,

Are dynamically bendable,

Are more space saving,

Have excellent electrical and thermal performance,

Have higher freedom of electronic design and mechanical design, to mention a few.

Steps involved in Rigid Flex Design and Fabrication Process

1.  Preparation of the Base Material:

The first and foremost step in the rigid-flex fabrication process is preparing/cleaning the laminate. The laminates contain copper layer (with adhesive coating) and must be thoroughly cleaned before moving to the next step. Basically, pre-cleaning is done to remove the anti-tarnish layer that vendors use to coat copper coils that prevent oxidation. To remove the coating, fabricators performs the following steps:

First, the copper coil is dipped in a concentrated acid solution.

Sodium persulphate treatment is used to micro-etch the copper coil.

The copper coil is comprehensively coated using suitable oxidation agents to provide adhesion and oxidation protection

2. Circuit Pattern Generation

After base material preparation, the next step is generating the circuit pattern. This is done using two main techniques:

Screen Printing: This is the most popular technique. It creates the required pattern directly on the surface of the laminate. And the total thickness is at maximum of 4-50 microns.

Photo Imaging: This technique is the oldest and is popularly used to depict the circuit traces on the laminate. Dry photoresist film and UV light are utilized to transfer the pattern from the photo mask to the laminate.

3. Etch the Circuit Pattern

After generating the desired pattern, next is carefully etching the copper laminate. This process is either done by dipping the laminate in an etch bath, or it is exposed to an etchant spray. To achieve a perfect result, both sides of the lamination are etched simultaneously.

4. Drilling Process

High-speed tool tools with 100% precision are used to make a number of holes, pads, and vias. Laser drilling tech is used for ultra-small holes.

5. Through-hole Plating

This process is done with extreme precision and care. The drilled holes are precisely deposited with copper and chemically platted to create a layer of electrical interconnection.

6. Apply Cover Layer or Cover coat.

A cover layer is applied to protect the top and bottom side of the rigid-flex circuit boards. Its primary goal is to provide comprehensive protection to the circuit board from harsh physical and chemical conditions. A polyimide film is usually used and imprinted onto the surface using screen printing techniques.

7. Cutting out The Flex

Cutting and blanking individual flex board is executed with caution. For mass production, hydraulic punching is used, while as a specialized knife is used in small production.

8. Electrical testing and Verification.

Testing and verification is the final and last step. It is imperative to assess the integrity of the rigid-flex circuit boards as even the slightest flaw will drastically affect the functionality, performance, and durability of the final rigid flex.

The post Rigid Flex Fabrication Process appeared first on PCB Labs.

source https://www.pcblabs.com/rigid-flex-fabrication-process/

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Handling and Storage Methods for Rigid Flex Circuit Boards

Majority of people tend to disregard careful consideration into handling and storing of PCBs among other electronic devices. In reality, there are numerous ways such electronic devices can be completely written off through nothing else rather than improper handling and storage. The components of rigid-flex PCBs are susceptible to a variety of physical, environmental, and chemical conditions. Any of which can independently lead to rendering the unit inoperable.

Cold temperatures can ultimately harm electronics over time

If you put your PCBs to extremely low temperatures, they can experience condensation. When you put them back into operation, once the power starts to heat the device, the moisture from the temperature difference will accumulate around the PCB’s components. This exponentially increases the chance of having an internal short-circuiting. This problem is challenging to troubleshoot. And it is common with laptops and cell phones that have been left out in a cold vehicle for a night or two.

Never Store Your PCBs in Storage Facility with High Levels of Humidity

Humidity and cold weather have the same damaging effects to PCBs. Once the humidity reaches a certain level, the formed moisture could be catastrophic to electronics. Even the PCBs that are well packaged in boxes, the humidity will eventually compromise the seals and the cartons and subject them to molds. The exposed parts of the PCBs will drastically be destroyed by the moisture.

Avoid Storing your PCBs in Places with Excessive Heat or Direct in the Sunlight

Excessive heat and direct sunlight could be devastating to PCBs. Ensure that your storage facility is well ventilated during the hot months of summer. Avoid putting your gadget in an oven like places as the heat could easily lender your PCBs inert.

Avoid Improper Stacking of Boxes

Failure to properly arrange your devices well, but instead stack them improperly can as well put your PCBs at risk. When a heavier unit sits on a lighter circuit board, it will be crushed. Similarly, the force of gravity can pull down the heavy objects that are not adequately supported thereby destroying any other gadget that is beneath it.

Store Your Devices in a Dry Box or Cabinets

Due to the recent sporadic fluctuations in the levels of humidity in the atmosphere, majority of manufacturers are designing and producing dry boxes and cabinets that keep humidity at bay. These units intelligently use temperature and humidity sensing components and fans to keep locked items free from moisture and secured from any harsh external environmental impacts. These boxes and cabinets come in an array of designs, sizes, shapes, and capabilities depending on the intended purpose.

You can never be over cautious when it comes to safe handling and storing of your electronic devices, especially those with sensitive components such as rigid flex circuits. The importance of going an extra mile to ensuring that your PCBs are handled and stored with care cannot be stressed enough. Once a rigid flex PCB is damaged from whatever reason, it is usually complicated and time-consuming to repair, and acquiring a new is very costly.

Always keep your PCBs in a dry, cool place, and away from direct sunlight, excessive heat, frigid temperatures, high humidity, and an improperly arranged stack of boxes. Most importantly, seek help or consultation from PCB professionals to help you determine the best solution that fits your needs.

The post Handling and Storage Methods for Rigid Flex Circuit Boards appeared first on PCB Labs.

source https://www.pcblabs.com/handling-and-storage-methods-for-rigid-flex-circuit-boards/

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Rigid Flex Circuits Design Guide

Flexible foils of polyimide with a thin thickness covered with copper are the primary materials for pure flex circuit boards. The usage is due to their affinity to withstand high temperatures.

Rigid flex circuits combine the best of both rigid boards and flexible circuits integrated into one channel.

Rigid-flex offers the designers with a variety of opportunities that helps in conforming with mechanical restrictions of the existing systems. Rigid-flex aids in solving some parts of factors, form, and fitness thus allows the designers to meet the variables of the entire design. The main advantage of rigid-flex is that it will enable the use of many variables and achieves the requirements for signal processing and other predictable values.

Guide to designing rigid-flex circuits

To develop a rigid flex, follow the considerations below to ensure the best results.

Considerations during designing rigid-flex circuit

To produce a rigid-flex PCB with unmatched quality and functionality, you have to follow the correct manufacturing practices. Here are set guidelines and standards that the manufacturer must consider during designing and manufacturing of flex circuit boards.

Decide on the manufacturing process and material to use in advance

Depending on how much flex you require, you need a prior decision on the stuff to use and the means to follow. Example; when the boards you are designing need folding only during the manufacturing process and be in a fixed position afterward without a bend, then you can decide on the following

Copper type and grade

Method of manufacturing

The number of layers to use.

On the other hand, if the board is for those applications with frequent moves, vibrations, and shocks, you must be specific when choosing the following:

Copper coils

Adhesives and

Number of layers

Position copper traces on right angles of the rigid-flex

Copperworks perfectly when placed on the right edge of the board. Avoid bending copper traces at the corners as it strains and might not produce the best flex. With the PCB flex that requires turning at the angles, use sharp radius bends to avoid staining copper traces.

Provide exposed copper with enough pad support

Repeated stress caused by frequent bending can cause copper on circuitry can detach from polyimide substrate. Support exposed copper with pads to prevent detach.

Use hatched polygons

Hatched polygons instead of solidified copper pour helps to retain the flexibility of the flex PCB.

Leave at least 1/2mm clearance between the copper annulus and Adjacent Vias

The 1/2mm helps aids in avoiding fatigue due to frequent bending. Placement of Vias in stationary areas of the board helps avoid frequent movements and bends thus producing the best rigid-flex.

Contact your raw material supplier

In case you have planned to use adhesive fewer laminates and non-standard base dielectric materials you should contact your materials supplier during the design stage. Contacting supplier is necessary since elements come in standard sizes through special ordering and may take time before delivery in case there is no prior communication.

The Takeaway

While there are numerous design options when combining rigid boards with flexible circuits, this article gives you the best guideline on designing rigid flex circuits.

The post Rigid Flex Circuits Design Guide appeared first on PCB Labs.

source https://www.pcblabs.com/rigid-flex-circuits-design-guide/