Are you looking for guidance to make flexible PCB? Well, you’re certainly where you’re supposed to be, and we guarantee you’ll get exactly what you have come for.
Most designers and engineers focus more on PCB component selection, functionality, and design and consider basic design guidelines as afterthoughts.
However, ignoring the basic tips and steps to a high-quality flexible PCB makes translating your digital design to a physical reality difficult.
And that is why we’re here.
Sit back and enjoy this article to understand flex PCB, including tips for improving functionality, reliability, and manufacturability. Let’s get started!
Table of Contents
- Flexible PCBs
- Flexible PCB Based on Configuration
- Flexible PCB Based on Layers
- Steps To Getting A Flexible PCB
- Tips To Improve Functionality, Reliability, and Manufacturability
- Why Flexible PCBs?
(Electronic flex PCB with plastic membrane)
Flexible circuit boards are very popular and used in almost every electronic component you use today.
These are circuit boards that can bend and fold repeatedly without damage.
Additionally, these boards are thin and flexible enough to fit into tighter areas.
Surprisingly, the boards are also designed to withstand harsh conditions like high temperatures and vibrations.
Take, for example, the design of a wearable smartwatch.
How will you use a rigid circuit board in such a small device that is in constant motion?
Remember, rigid boards aren’t designed to work under high physical stress and won’t fit well into a small device.
We have flex PCBs to fill this void and deliver high performance.
Flexible PCB Based on Configuration
The first classification of PCBs is based on the configuration. Let’s check the PCB types under this category:
HDI Flex PCBs
The high-density circuit boards represent flex PCBs meant to handle applications that need high performance.
Surprisingly, these boards have better layouts and designs and incorporate several high-quality features like microvias.
Moreover, HDI PCBs use thinner substrates than normal flexible PCBs.
Therefore, PCB manufacturers use fewer materials to manufacture these boards, thus reducing material and manufacturing costs.
Furthermore, they experience reduced package size than other options.
As the name suggests, these circuit boards combine flexible and rigid materials to create a high-quality hybrid.
Therefore, it combines the best features of both rigid and flexible worlds.
For example, they can bend but still possess enough physical strength to support components.
Flexible PCB Based on Layers
Besides classification based on configuration, we also categorize PCBs depending on layer count.
Check out the options under this category below:
This circuit requires no explanation; you can tell what it’s all about from the name.
Generally, it’s the most basic board with one polyimide substrate layer and a single copper layer.
Surprisingly, you can only access the board’s conductive layer from the top.
However, we also have single-sided dual-access boards where you can access the conductive layer from both ends.
This circuit board has a single polyimide substrate but two conductive copper layers on both ends.
Moreover, engineers can enable electrical connections between the two layers using through-hole technology.
Finally, we have multi-layer circuit boards combining several single-sided and double-sided circuits to create one complex board.
Therefore, to join all the layers and circuits together, engineers employ the following technologies:
Steps To Getting A Flexible PCB
If you want a good flexible circuit board at home, follow these steps:
Acquire A Copper Coated Film
You should acquire polyimide materials with copper on a single side or both ends.
Generally, polyimide sheets have a high melting point, and you can identify them by their yellow color.
Sometimes, people call this material Kapton; the most common option is the DuPont material.
Surprisingly DuPont materials are available in different variations thanks to unique polyimide thickness, adhesive thickness, and copper thickness.
Remember, the copper thickness (CU) is given in mil, and we recommend a Dupont material with one mil Kapton, 0.5 oz copper, and 0.5 mil adhesive.
Use A Solid-Ink Printer
(PCB creation on laser equipment)
A solid-ink printer will help you print directly on your copper film.
Although a solid-ink printer is similar to a laser printer, it prints using melted wax, not ink.
Additionally, the wax plays an important role in forming a shielding layer for copper etching. For this exercise, we recommend the Xerox Phaser 8860.
Print The Design on The Pyralux
At this point, you can print the design. But first, you need to draw the design using reliable software like CAD.
After you finish the design, use the manual feeding tray to design on your copper sheet.
This is the time to select the different color variations, including:
Don’t use colors having light shades, as they won’t bring out your design well.
Also, ensure you use either the high-resolution or photo mode.
Although the high-resolution mode is slow, you’ll find it more efficient.
Etch The Copper Sheet
Next, put the copper sheet into ferric chloride for almost 5 minutes.
However, the exact time should depend on the temperature and copper thickness.
Since it’s difficult to determine the exact time while doing the exercise at home, keep an eye on the sheet to ensure polyimide films reach relevant areas.
Surprisingly, the process might sometimes take up to 25 minutes.
However, while applying the etchant, take safety precautions to protect your hands and skin.
Populate The PCB
(A populated PCB)
After etching the board, you can cut it into smaller pieces and solder your components.
Alternatively, you can solder your components without cutting the board into smaller pieces.
Moreover, to ease your soldering process, employ nickel plating.
Tips To Improve Functionality, Reliability, and Manufacturability
Check out the guidelines you must follow to improve your flexible PCB functionality, reliability, and manufacturability below:
- Fine-tune component placement by orienting related components in the same direction. Also, don’t place components on the PCB solder side.
- Furthermore, all surface mount components should be on the same PCB side. Likewise, all through-hole components should be on the top side.
- Route the signal, power, and ground traces for a smooth path.
- Keep things in your circuit board separate.
- Reduce heating issues as they affect performance.
- Finally, verify the circuit board layout against PCB design rules.
Why Flexible PCBs?
(A copper layer flex PCB)
You might be wondering why you should discard a rigid circuit board for a flex one. Surprisingly, flex circuits were designed to replace rigid circuits and offer better performance. Below are reasons why you should choose flexible PCBs:
- The boards are thin and lightweight and can fit multiple applications. Therefore, they have reduced package size.
- Since manufacturers design them using automated equipment, they have an accurate design.
- They have design freedom; manufacturers can create single-layer, double-layer, or multilayer PCBs.
- High-density configuration that involves combining through-hole and surface mount components.
- The circuit boards are very flexible, thus reducing space in devices.
What should you include in the flexible fab notes?
Check out the thing you should have in the fab notes:
- First, indicate the board will be fabricated as per IPC-6013
- The covercoat material will meet the IPC 4203/1
- The copper-lad material shall meet IPC-4204/11
- The maximum thickness applies after the plating and lamination process and doesn’t exceed your requirement
What are the flex drawing requirements?
You should understand the following drawing requirement to succeed in your design:
- Marking requirements
- Plating requirements
- Testing requirements
- Drill symbol chart
- Dimensional drawing and tolerances
- Flexibility (bending radius)
- Flexible material in use
- Layer order and stack-up construction
Which material is used in flexible PCB?
Whether you’re designing a single, double, or multilayer PCB, the materials are the same, and they include the following:
- A polyimide substrate as the base material
- An electrical copper conductor
- A protective finish
- A flexible copper-clad laminate
- Adhesive material
Understanding the tips and guidelines above is the first step to converting digital designs into physical circuits.
Generally, you must understand the flex PCB according to the configuration, including rigid-flex and HDI boards.
Moreover, it would be best to understand the classification based on single, double, and multilayer layers.
Your goal during the design and manufacturing process should be to improve functionality, reliability, and manufacturability.
All these are only possible if you stick by the guidelines in this article.