Flexible Circuits-9 Common Mistakes you Need to Consider When Designing

The flexible circuit is printed circuits providing electronic interconnection. Usually made of an insulating polymer film upon which the circuit patterns are etched on or affixed, these circuits need extra attention to detail in the design and manufacturing process.

While there are many ways to achieve a good circuit design, overlooking some basic stuff that can cause a design failure, It is useful for us to learn from mistakes, but a better way is to understand the errors in advance and avoid them.

So when you are drafting your next flexible circuit design, look out for the following common factors that may lead to a design flaw.

（Flexible Printed circuit ）

1.Flexible Circuit Conductors Arrangement

Conductors' arrangements are a crucial distinguishing factors that differentiate the design process involved with a rigid and flexible course. Unlike wooden boards, flexible circuits can twist, turn, and bend. Hence, If the conductor arrangement is incorrect, it can lead to hazardous consequences, especially during board flexing.

Be cautious when you design the conductors' arrangement. One way to minimize the conductors' stress during flexing is to make sure they pass through curved areas.

（Flexible circuit capable of bending)

2.Initial bending region of the Flexible circuit

Always be mindful of the bending capabilities of your revolution. The two main factors that will help you comprehend the bendability of the course are

• The number of times the board will be turning.
• The bendability of the council

You can ascertain whether a commission is static or dynamic based on the number of times it will be turning. For the flexible circuit board to work correctly, the bending area must be set right in the initial stages.

Understanding the required bendability early on in the design phase will prove to help manufacture the right parts that fit well for the flexible circuit board.

The manufacture should know the minimum and maximum bendable limits to provide the right assembly parts that work well with the board. This information, which can include the bend radius, the bending tolerance, when identified early in the design phase, will help manufacture better parts that can withstand damage.

3.Notches and Slots in Curved Areas

Gaps and curved areas of the PCB are critical design elements. It would help if you perfected your understanding of the drawing tools like the Arc tool to create the right bridging sections to place the slots. In general, the need to design bridges 3-4, and small holes should be made around the narrowest region so that you can make extra room for the slots.

A good board outline anticipates and prepares for a more manageable arrangement if bridges sections help you avoid any bottlenecks on design. It will help you achieve better edges and make it easy to fit the deserved curved PCBs.

Another way to do the same would be to use a circular board on your outline layer. You can make use of half circles to determine the size required by the individual notches.

(Detail of flexed printed circuit on white background)

4.Flexible routing

Flexible routing can be a little tricky, especially during the step where you construct the wire routing or the path. This step prepares for the next step: the placement of every active element on the board.

During the wire routing, make sure you avoid beans and minimize copper circuits' ability to thin. If not, discontinuities may arise due to compressive forces when the course is bent or stretched.

5.Risks of Flexible Through Holes

The through-hole method of circuit design involves mounting the board with holes drilled on to the board. The pads on both sides use these holes, and the automatic machine completes these.

While useful as a mounting method, this tech can pose some risks.
Hence, make sure the holes are well within a safe distance from areas that usually bend or flex.

You should also pay attention to the surface finish on both sides of the board as they need to be of the same quality for full use.

A good guideline is to avoid using holes near the bend areas.

(Through-hole on flexible circuit board)

6.Flexible Layer Placement for Multilayer Boards

When you use multi later flexible circuit boards, you have to pay extra attention to the layer placement. These types of boards find use in applications that require a high circuit density.

Layer placement is a complicated process, and one mistake could jeopardize the entire functionality of the board.

• Take a reasonable amount of time to make accurate placements.
• Avoid placing the circuit parts on the solder side of the circuit board.
• Make mistakes here, and your circuit will be flawed, mess, and end up looking ugly.

7. Adhesive Thickness on the Drawing

Unlike the factors like bendable area width, holes placement, and notches, the adhesive thickness is something you will have to leave as an afterthought.

It is better not to determine the flexible circuit board's exact adhesive width early on the design phase. You have to know the flexible circuit board's overall width and the total width of the critical dielectric components that could potentially affect the impedance.

Over specifying non-critical features like adhesive width can lead to extra costs and unnecessary work effort.

Pay attention to the essential features and be efficient with your time and resources.

8. Conductors Stacking on Multilayer Boards

Stacking conductors on flexible circuit boards will result in a thicker circuit that could lead to what is known as the 'I beam' effect.

'I beam' effect is observed when the line pairs are staggered to minimize impact from an electromagnetic reduction.

So, avoid stacking conductors when designing a flexible PCB.

（Photosensitive sensor on a flexible printed circuit board close-up）

9. Selection of Cover Material

Choose quality cover material for your flexible circuits, as this determines the overall performance and life of the board.

Choose a covering material suitable for applications using flexible circuit boards.

Make sure you never compromise on cover material quality. Look into the following factors to choose the appropriate suitable cover material:

• Expected performance,
• Specifications of the application and
• The conditions under which plate

Common Errors

Some more errors you may have to look out for are listed down.

• Circuit traces

If circuit traces are too close to openings, it may lead to shortages. Even a small misplacement of 3 mils can cause errors in real-time. Try to keep a distance of at least four mils for the solder mask.

• Coverlay confusions

Some designers could confuse overlay with solder Mask. While the overlay is made of plastic materials, the solder mask is a liquid. Learn to differentiate them from their state.

The minimum DA sizes for overlay should be ten miles, and the same for the solder mask should be four mils.

• Hole sizes

We mentioned about hole placements earlier. Sometimes hole sizes, when too big or too small, can also cause negative impacts on performance.

Holes bigger than necessary can cause problems in mounting and require excessive soldering.

• Solder Resist Pads

Extra pads or missing pads on the solder resist layer are also common mistakes and usually ignore. Try to rectify any such errors before handing over the design to the manufacturing phase.

• Incorrect Landing Patterns

When your PCB Software packs specific landing patterns, you may try to draw them manually. But such practice can lead to errors making the final design challenging to solder on. Try to avoid manual intervention to avoid the mistakes and cross-check your design accurately for in the range of millimeters before finalizing it.

(Layout picture of a flexible circuit)

Summary

Flexible circuit boards are known for their durability and excellent performance. But with advanced tech cokes advanced challenges in designing such detailed circuit boards that need to withstand compressive forces due to bending and twisting.

Following well-guided best practices and quality procedures will help designers overcome the challenges and design of Felix circuit boards' art to make electronic systems perform better. If you need the production of flexible circuits, you can contact OurPCB in time, and we will provide quality service and the best production technology.