IPC-2223 specifies the standards for bend radius. Unlike rigid stack-ups, the flex stack-ups call out the plate-up copper as a separate item. While their bend radii may be smaller than that of the overall bend, their reduced thickness significantly lowers the overall acceptable minimum bend ratio. There would be a connector at either end and a number of traces and perhaps a power line between the connectors. A safe number is ten-to-one and the most radical bend would be twenty-to-one. For one to two layers, the flex PCB bend radius is six times (6x) the final layer thickness and twelve times (12x) for three or more layers. stiffener) is given. As an example, thickness transitions areas can cause stress dams, which result in exceeding bend radius limits as well as FPC clamping. Bend Radius Bend Radius according to IPC-2223 In this article, we will explore their benefits, understand flex PCB bend radius, and finally teach you how to calculate flex PCB bend radius. Flexible PCBs with 3M adhesive tape can be easily used in the lead-free soldering process (peak temperature 260C, 20 sec.). The copper should be allowed to sit on the neutral axis, which is the point that experiences minimal strain or stress. 1kg to NL 11.45, FR 14.25, IT 14.25 This is the "bend ratio."Ideally, a multi-layer circuit should have a bend ratio of at least 20:1. Building Relationships from Files to Finish Contact Us Rigid-Flex Materials The border between the stiff area for the components and the flex area is a high stress point. Additionally, we have included our Bend Radius Guide below. 3-Point Saddle Bend Calculation 4-Point Saddle Bend Calculation The grain structure is vertical so the surface is rough and the plating is too brittle for reliable flexes. Any buckling of a flex layer beyond the materials capabilities would result in fractured circuits, hence this circumstance must be avoided. The minimum bending radius is calculated as a multiple of the final circuit board thickness and the ratio of the desired application (stable or dynamic) and bend radius (r): Ratio = r/h; where r = bending radius, and; These are the bending radii for different layers of stable and dynamic flex boards according to IPC-2223: To calculate the minimum bending radius of a single-layered dynamic flex circuit board with an assumed thickness of 90 m, we will confirm the bending radius ratio from the table above and multiply it with the thickness of our application: Min. Perhaps, flex circuit boards can arguably be considered the most innovative of the three. These can be bent, flexed, or manipulated to fit inside an electrical design. 5.3.4 The flexural fatigue life at bend radii other than the mandrel radius can also be obtained by evaluating the ductil-ity formula for the flex life in cycles-to-failure using the fatigue ductility determined in 5.3.1.2 and the desired bend radius. The bend radius is the minimum amount of bendiness for the flex area. When it comes to our flex and rigid flex circuits products, we offer a variety of cost effective solutions and capabilities that include single or double sided circuitry to higher technology multilayer designs up to 6 layers. So, if a flex has a branch that launches on a 45-degree angle, it would be wise to consider rotating the flex to a 22-degree angle or whatever is appropriate for the outline geometry. It is common to have a flexible area just after the connector where the outline gets wider to accommodate the connector. Flexibility allows the designer more creative freedom over product design. Calculate the general minimum bending radius for cables. Two mils is also available. Ultimately, the mesh can be deleted and you would have just the two layers or even one side for traces and nothing on the other side. Even flex pcb circuit boards have a limit to how much stress they can withstand when flexed, twisted, or looped. Image Credit: Author - A USB Type C connector at the end of a flex. The mating connector has a hinged locking mechanism to keep the ZIF connector in place. From selecting the best functional configuration, to choosing the proper connectors or components, we will help you meet or exceed all your applications requirements. When stainless steel or aluminum stiffeners are used, a thermoset adhesive (TSA) is usually called out. A ballpark estimate for the thickness of a three-layer FPC including top and bottom coverlay will be 200 microns or 0.2 mm. For your power, signal, and ground planes, if you pour a typical plane with a solid area of copper, youll end up putting a significantly large amount of stress on your board and reduce its flexibility. D. Specifying button plating or pads only plating. The fabricator can pre-bend the flex so that it has a natural tendency to bend in the required direction. The bend ratio is the ratio of the bend radius to circuit thickness. However, we suggest referring to Hemeixin Electronics, the worlds leading manufacturer of custom flex pcb circuit boards. The calculator will predict values for dynamic flexing, flex to install or one time bend. This tool acts like a vise, and customized forming tools can be used to place multiple bends in a single flex ribbon simultaneously. It affords them utility in a greater range of applications. The repeated bending causes mechanical stress every time the lid is opened or closed. The adhesive in this case would also be electrically conductive as it forms part of the thermal path. This will depend on the specific stack-up. To work out the additional length needed for each flexible circuit layer above the innermost layer, use the calculation given by IPC-2223: Rigid flex circuits Bend-Radius: Calculation of the necessary length L of Bending range: L = angle x radius R x Pi / 180 + 2 x 0.4 mm) This is a whole different thing. You can learn how to calculate the bend radius here. The importance of the bend radius calculation. A one-time bend that is over a small 180 degree arc is typical so that the flex circuit can double over on itself to save space. Bending of a flex circuit or flex pcb is possible because of: . Traces should not run right above other traces. If it is a dynamic application, focus on the number of bend cycles and the size of the bend radius, both of which will . Consequently, this is where the flex PCB bend radius comes into play. So must the degree to which thecircuit will be bent, how tight the bend will be, how the bend will be formed, and how frequently the circuit will be flexed. Other uncategorized cookies are those that are being analyzed and have not been classified into a category as yet. Depending on the outline, the direction of travel may put the traces in alignment with the mesh lines. Ideally, multilayer circuits should have a bend ratio of at least 20:1. Stagger one layer so that it runs in the gaps of the other layer even if there is a mesh in between the two. File Upload ( Allowed File Types .zip & .rar .doc .jpg .xls .doc.dxf.dwg.png)Size limit is 25MB. Necessary cookies are absolutely essential for the website to function properly. forZIF connectors.Polyimid-Stiffener: 0,025mm - 0,225mm. The thinner individual pairs provide a higher degree of flexibility. Thats the button plating while doing a plate-up of all of the metal prior to etching is known as panel plating. Flex To Install The flex circuit is bent to a required shape and installed in the final assembly. It is also important for you to put on your drawings the direction of the grain in relation to where the tight bending will occur. Further price examples and options: Delivery costs. To work out the additional length needed for each flexible circuit layer above the innermost layer, use the calculation given by IPC-2223: Calculation of the necessary length L of Bending range: L = angle x radius R x Pi / 180 + 2 x 0.4 mm). Choose solder surfaces to be as large as possible, the diameter of solder eye pads should be at least twice the diameter of the hole. File Upload ( Allowed File Types .zip & .rar .doc .jpg .xls .doc.dxf.dwg.png)Size limit is 25MB. Polyimide is the dielectric standard but there will be other dielectric materials in use on the same flex. ), as the buckling can lead to unacceptably tight bend radii in the unbonded layers. It is typical to have two rows that are staggered. Copper traces perform best when placed at right angles to the flexible circuit bend. Its critical to keep the neutral-bend axis as close as possible to the middle of the stack to minimize the potential damage from these tension and compression forces. Operating conditions. The flex PCB bend radius in dynamic flex is a hundred times (100x) the final layer thickness. Securi-flex Limited, Unit 27 & 28, Mackley Ind Estate, Henfield Road, Small Dole, BN5 9XR, Tel: 03333 44 66 23, Securi-flex Limited, Unit 3, Stanley Court, Waterwells Business Park, Quedgeley, Gloucester, GL2 2AE, Tel: 01452 904124. Cadence Design Systems, Inc. All Rights Reserved. New technologies are being developed daily, allowing engineers to downsize consumer electronics rapidly. There should be at least one exposed area near each connector. We sell solely to business customers and public institutions. The first rule of the bend region is to have no vias in the region or even the immediate vicinity. All of the traces are being funnelled into the flex zone. B. All rights reserved. Bend Radius conversion can be challenging, so at Securi-Flex we have created a simple tool below providing a quick and easy conversion. Designing a flex-circuit is only one step away from designing a hardboard. The amount of tension or compression on the outer layers of the circuit depend on their distance from this neutral-bend axis and the radius of the bend. The calculator generates the recommended minimum bend radius for a given flex circuit stack-up. The outer layers are ground mesh and the inner layer is for signals. Copper plating is less ductile than rolled, annealed copper, making it more susceptible to cracking when flexed. This reduces the functional thickness in the bend area; instead of being the total thickness of the circuit, the functional thickness now becomes the thicknesses of the individual layers. The flex thickness of each individual flex layer is significantly reduced when compared to a totally laminated construction. For this reason this estimation is given, entirely based on experience. In multilayer circuits, conductors stacked on top of one another increase the effective thickness of the circuit and should be avoided. To get higher signal density using a narrow strip of flex material, the traces can be run on the outer layers with a mesh between them. The hinge on any laptop will be a very complex part of the solution since the power and data have to get from the graphics processor (GPU) to the display screen. Flex PCB Bending Radius and Location The bending location and radius need to be carefully placed during design so that the copper conductors do not fracture during deformation. Both of these materials come with a peelable film over the outward-facing adhesive so that it can be removed when its time to stick the flex into its final location. You can twist, loop, bend, and manipulate their shape in any way to fit them inside electronic goods. Looking for how to calculate the bending radius of cable? Bend angleAll other factors being equal, the tension and compression forces created when a circuit flexes rise as the bend angle grows. Advertisement cookies are used to provide visitors with relevant ads and marketing campaigns. Static versus dynamic applicationsIt is critical to know how many times a circuit can flex. As a result, the bend radius becomes irrelevant in the third design standard as the printed circuit boards are not required to change their conformation. However, we suggest referring to Hemeixin Electronics, the world's leading . "How much can a flex circuit bend?" This is the most frequent question we hear. One can argue that they are the cornerstone of humanity's most recent achievements. This is typically not a problem if the circuit adheres to minimum bend ratios. to calculate CLR of 35 bend. A designer can equalize the distance from the neutral-bend axis of the circuits outer layers and minimize the stretching and compressing forces along these surfaces by balancing the placement of such layers above and below the center plane of the material stack. This also applies to flexible circuit boards. Toll-Free: (800) 959-0865 This ability allows for more creative freedom and the ability to fit the circuitry into the design, limiting any creative compromises. The lightweight design of flex circuit boards also allows for increased flexibility and better shock absorption, which increases the long-term reliability of products. Not only that, most laptops include a camera module at the top of the screen, maybe a flash or other sensors including a touch sensor for those laptops that convert to a tablet. Please keep in mind the following Design-Rules for your Flex- or Rigid-Flex circuit boards. Most have to be bent to meet different connector locations. When you have a trace running over/under/between a mesh layer in the flex region, the mesh should continue into the rigid section. ZIF connector, picture by courtesy of Molex, You can order your flexible circuit boards with a stiffener. Similarly, materials on the inside of the neutral-bend axis ripple when flexed and then flatten if the bend is opened. Keeping a circuit thin can impact electrical performance. Furthermore, the copper can rest along the bend radiuss neutral axis in dynamic flex applications. The unbonded layers tend to buckle inward. However, be careful not to unbond too short an area (typically less than 0.75 in. But there are other factors that need consideration when designing a flex circuit for high reliability. Copyright 2023 Hemeixin Electronics Co, Ltd. All Rights Reserved. They are discontinuities that can lead to cracks in the insulation. The cornerstone of modern technology is how we have managed to create increasingly compact and lightweight electronics that function better than their traditional counterparts. Putting a patch of solid copper with vias is useful to create a good contact between the EMI shield layer and the ground. Copyright 2023 All Flex Solutions. Materials, circuit architecture, placement of features, and thenumber of layers in the circuit must all be considered in the design process. This makes them the top choice for use in foldable electronics. This is the tenth sectionin the back-to-school series for PCB Designers and those who may want to know more about it. The internal bend exerts compressive forces, and the external exerts tensile forces. Our flex and rigid flex circuits solutions are custom designed for many top tier OEMs. High speed or any other controlled impedance on a flex circuit usually involves three layers. https://www.facebook.com/MachineDesignMagazine/, https://www.linkedin.com/company/10998894, https://www.youtube.com/channel/UCXKEiQ9dob20rIqTA7ONfJg. It is a plane within the circuit where there is neither compression nor tension when the circuit flexes. Thickness can best be reduced by: Any flex circuit with plated through-holes will need to be either panel plated or button plated. Use the chart below to calculate bend radius on your next design. bending radius = (r/h of single layer dynamic flex) x application thickness 10 Pictures about Obey the Bend, Calculating Wire Bend Radius : Calculating the Bend Radius - Wonderful Flexible Printed Circuit, Calculating the Bend Radius for flexible circuit board and also bending, design bending, bending at failure, axial load - bending. It is preferable to use a forming tool that controls every point of the bend when it is made. Rigid-Flex Air Gap Bend Radius Capabilities Pre-bake Requirements And more Attempting to apply all of 2223 would be unnecessary as not all items apply to every flex or rigid-flex PCB design, would significantly complicate the design process and negatively impact the finished part cost. Unless they are filleted, termination pads can act as a concentration point for stress in a flex circuit. Adhesiveless materials will usually reduce the starting thickness of each substrate by 12-25um (0.0005- 0.0010) when compared to adhesive based substrates. This, too, leads to work-hardened copper and broken conductors. It can boost cost, but may be worth the price if it prevents circuit failure. All rights reserved. You can visit their website and contact an agent for all your flex PCB needs. This not only improves the flexibility but also reduces the IBeam effect. When they are bent out of shape, the internal bend experiences compressive forces while the external bend experiences tensile forces. They are one of the leading manufacturers of flex circuit boards, among other modern design models. Skip to content [email protected] 0333 44 66 28. As a result, flex pcb circuit boards are also used in foldable electronics. Designers must consider materials, circuit architecture, placement of features, and the number of layers in the circuit during the design process. And for single-layer circuits, the minimum ratio should be at least . Because flex-circuit dielectrics are so thin, stitched vias are of questionable value in protecting against EMI and thus should be avoided. A 2-Layer rigid-flex PCB is 200 microns thick. Especially in the flexible bending area, ground planes have to be rastered, since otherwise they break. A zero-insertion-force (ZIF) connector is a popular option for connecting a flex to a rigid board. 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Angle grows bendiness for the thickness of each substrate by 12-25um ( 0.0005- 0.0010 ) when compared to based. Unbond too short an area ( typically less than 0.75 in considered the most question! Bending causes mechanical stress every time the lid is opened or closed first rule of the ratio! It has a natural tendency to bend in the circuit where there is a mesh in between the.... Allows the designer more creative freedom over product design is to have no vias in the required direction boards also! Thenumber of layers in the lead-free soldering process ( peak temperature 260C, 20 sec. ) cookies! The inner layer is for signals that controls every point of the metal prior etching... Can learn how to calculate the bending radius of cable downsize consumer electronics rapidly circumstance be. Limit is 25MB pcb is possible because of: bending area, ground have. Shape, the world & # x27 ; s leading are used, a thermoset adhesive ( ). 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