6 Flex PCB Advice To Ensure Design Success

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Oakley Mae

Home » Blog » Flexible PCB » 6 Flex PCB Advice To Ensure Design Success

We know and understand that you’re here for flex PCB advice, which is what we are prepared to offer.

Few people understand this, but flex PCB requires a different design process than the traditional rigid options.

For example, for a flex PCB, you must consider factors like stack-up, optimum material selection, cost factors, bending requirements, copper feature placements, and board outline. 

Surprisingly, a well-designed flexible circuit board is always durable, easy to install, reliable, and lightweight.

And you can use it in complex applications like satellites, wearables, medical, and IoT.

Moreover, these boards provide better endurance to high temperatures and vibrations. 

But how can you ensure a successful flex PCB design? We give you answers in the following 6 tips. 

Table of Contents

Understand Your Flex Circuit Board Bendability

(Someone holding a flexible PCB)

Flexible PCBs are highly flexible, thus enabling designers to implement them in tight spaces and compact electronics.

However, regarding bendability, you must understand to what extent your circuit board can flex and how many times it’ll flex. 

Surprisingly, how many times your circuit board can bend determines whether it’s dynamic or static.

With a static circuit board, you’re limited to about 100 bends throughout its lifetime.

Generally, these circuit boards are bent at the assembly stage. 

On the other hand, we have a dynamic circuit board that flexes regularly, and you can bend it thousands of times in your lifetime. 

Also, the bendability of a flex circuit board depends on the board thickness, which in turn depends on the following:  

  • Adhesive thickness
  • Copper layer count
  • Dielectric material selection
  • Base copper weight

You should understand the bend radius, which represents the degree to which the flexible area of the PCB can flex. Therefore, identifying the maximum angle at your circuit board can flex very early during your design process. Interestingly, this is determined by the number of circuit board layers. 

Another important aspect is the bend ratio which represents the ratio of the PCB bend radius to the thickness. A tighter band ratio translates into a high failure probability. 

Bend Area Design Tips

After understanding the PCB bendability, let’s take you through the bend area design tips below: 

  • To begin with, always employ gradual and large curved angles to eliminate damage. At no point should you use right-angle bends due to their high strain. 
  • Also, avoid placing components and plating through holes in bend areas.
  • Moreover, it would be best to have stagger conductors in multilayer PCBs to guarantee effectiveness.
  • Furthermore, if you have conductors through bend areas, ensure they’re perpendicular to the bend axis. 
  • Lastly, any conductor under 10 mils should be within the neutral bend axis. In these areas, there is the least compression and tension during flexing. 

Understand Your Flexible PCB Material

A detailed flexed PCB

(A detailed flexed PCB)

We already have the IPC 4202, 4203, and 4204 standards that define the materials and specifications.

Therefore, you need to understand the different circuit board materials and their characteristics to understand better the one that fits your design criteria. 

The material properties to consider include the following: 

  • The coefficient of thermal expansion
  • Dielectric constant
  • Glass transition temperature
  • Fire retarding
  • Moisture absorption

Surprisingly, flexible material offers better properties than rigid ones. A complete flex circuit board should have the following materials:

  • Coverlay and dielectric insulator: We use polyimide with a uniform thickness of 0.5 to 4 mills for this material.
  • Conductor: The most common conductor we use is copper, with a maximum of 2 oz. However, some designers still use expensive silver and gold. 
  • FCCL (flexible copper clad-laminate): This material gives the circuit board a tighter bend radius. 
  • Adhesives: You use adhesives between different layers to glue them together for a tighter bond. Some common adhesives you’ll find include epoxy, pressure-sensitive, and acrylic adhesives. 
  • Stiffeners: These rigid materials add rigidity, thickness, thickness, and mechanical support to mount your components. FR-4, Kapton, stainless steel, and aluminum are the most common stiffeners. 
  • Surface finish: Finally, the surface finish prevents oxidations and provides a solderable surface. The available options include a cover coat, overlay, liquid phot-imaged polymer, and photo-imaged dry film. 

Keep An Eye On Flexible PCB Layout and Routing

This is the time to focus on how you will place the different components. Also, consider whether you’ll use stiffeners or not. 

Let’s consider some of the best routing and layout practices below: 

  • Use a larger bend radius on your circuit board
  • Avoid angled traces and use curved ones
  • Employ tear guards to eliminate tears
  • Ensure you route the conductors perpendicular to the overall bend
  • Use at least two layers to stagger traces on your circuit board’s bottom and top
  • Avoid discontinuities like slits, holes, cut-outs, and vias in bend sections
  • Apply stiffeners in areas you expect excessive pressure
  • Maintain a drill-to-copper distance of more than 8 mils

Follow Design and Testing Standards

An engineer testing a PCB

(An engineer testing a PCB)

IPC standards help you design, manufacture, and test your circuit board. Let’s check out these standards below: 

  • IPC-2221: These are generic standards on PCB design. They establish the generic PCB design requirements plus other forms of interconnecting structures and component mounting. 
  • IPC-2223: We use this standard in tandem with IPC-2221. It guides you in design areas like impedance control; conductor bends consideration, material selection, and capacitance control. 
  • IPC-FC-234: With this standard, you get guidelines on using pressure-sensitive adhesives. Therefore, you’ll get information about the available adhesive types and their proper use case. 
  • IPC-6013: This standard offers flexible circuit board performance and qualification specifications. Therefore, you’ll get testing specifications, including bend, thermal, and impedance testing. 
  • IPC-600: Finally, these standards define the acceptability criteria for all PCB types through visual interpretations. 

Choose A Reliable Flex PCB Manufacturer

Female engineers working on the electronic circuits

(Female engineers working on the electronic circuits)

Many ignore this key step, but choosing a reliable manufacturer guarantees a reliable circuit board.

Therefore, you should choose a manufacturer with long-term experience delivering quality boards.

You can ask for referrals or check for online reviews. 

Also, the manufacturer you choose should guarantee a quick turn-around time. Having competent and professional technicians is enough to guarantee quality delivery.

The manufacturer should be there for you through the flexible PCB manufacturing process. 

Furthermore, they should have the relevant PCB manufacturing certifications and abide by the design standards.

And after developing the circuit board, they should test it to ensure no errors. 

Understand Factors Affecting Turn-time and Cost

The goal of any flexible circuit board designer should be to design cost-effective products without compromising performance.

Therefore, it’ll help to understand the different factors affecting cost and include the following: 

  • The number of layers you choose
  • Circuit board shape and size
  • Dimensional tolerance
  • Materials
  • Circuit board grade
  • The drill hole sizes
  • Circuit construction type
  • The copper foil thickness
  • Via features
  • Plating requirements
  • Drill to copper distance
  • The stiffener types
  • Surface finish requirements

Also, different factors delay the flexible PCB the turn-around time:

  • First, the incomplete PCB design data requirements
  • Secondly, the missing ZIF connector specs
  • Thirdly, unavailable flex-to-rigid transition zones information
  • Moreover, the inappropriate bend requirements
  • Finally, the design-related issues

FAQ

Flex PCB Advice: What’s a flexible PCB?

A flexible PCB is a circuit board that can bend into any shape you desire.

The PCB is made of a dielectric layer, a conductive layer, and adhesives between the two layers.

In some cases, there are stiffeners to give it mechanical strength. 

These circuit boards find common applications in designing compact electronics.

Therefore, they’re slowly taking over from rigid circuit boards. 

Flex PCB Advice: What are the advantages of flexible PCBs?

Flexible circuit boards have the following advantages: 

  • Firstly, they have a shorter assembly time
  • Secondly, they’re smaller, thus reducing the device volume
  • Moreover, the PCB is lightweight
  • Furthermore, it’s thinner than rigid PCBs
  • Finally, it functions well under extreme conditions

Flex PCB Advice: What are flexible PCB characteristics?

The main characteristics that define a flexible PCB are good bending properties, high wiring density, lightweight, and thin thickness.

Therefore, these properties make them perfect for designing compact electronics. 

Flex PCB Advice: Do flexible PCBs have limits?

Yes! First, they use a very complex assembly process.

Secondly, they have a high damage potential, especially when you handle them poorly.

Finally, they’re more costly than rigid circuit boards in some applications. 

Conclusion

The power to make a simple and successful flex PCB design process is within your reach.

You need to go through the above tips.

Generally, it all depends on understanding your PCB flexibility, material, and factors affecting cost. 

Also, you must choose the best flex PCB manufacturer.

Finally, focusing on the PCB layout and routing would be best.