The transparent flex PCB market is rapidly expanding as appliance manufacturers look for new ways to win over customers.
Some sections of the electronics market are eager to have lightweight and transparent devices.
And to achieve this, electronics manufacturers are turning toward transparent printed circuit boards.
Moreover, transparent circuit boards are finding greater use in 5G systems and other newer technologies.
You are in the right place if you’re interested in making one such board.
Today’s article briefly introduces the world of transparent flex PCBs and what the future holds.
Table of Contents
- What is Transparent Flexible PCB?
- Advantages of Transparent Flex PCB
- Applications of Transparent Flex PCB
- Transparent Flex PCB Design
- Transparent Flex PCB Base Materials
- How Do You Make a PCB Transparent
- Transparent Flex PCB Design Rules
What is Transparent Flexible PCB?
To understand a transparent flexible PCB, we must examine its two attributes.
A transparent PCB is one whose substrate material is transparent.
On the other hand, a flexible PCB is a printed circuit board that can twist, bend, or move in any direction with the application of a force.
Combining the two definitions, we can say a transparent flexible PCB is a circuit board that’s both transparent and flexible.
Advantages of Transparent Flex PCB
(Circuit layout on a transparent circuit board)
Some advantages of transparent flex PCBs include the following:
- They have many excellent optical features
- They support miniaturization, reducing the form factor, and weight of electrical products
- They easily bend, twist, fold, and move in any direction within a 3-D space.
- Reduces the weight of a printed circuit board by almost 90 percent compared to a similar-size rigid PCB. Such weight reduction is important for low-weight portable devices.
- Transparent flex PCBs have stable dimensions and can achieve micro/nano level PCB manufacturing accuracy.
Applications of Transparent Flex PCB
(A smart contact lens with digital implants)
Advancement in technology is pushing forward the need for lighter printed circuit boards.
Consequently, transparent flexible PCBs are used more in instrument panels, medical devices, and ABS systems.
Additionally, here are other areas that use transparent flex PCBs.
- Mobile phones
- Smart contact lenses
- Electronic skins
- Automatic control systems
- And, cameras
Moreover, there’s been a trend among appliance manufacturers to make completely transparent devices.
We have prototype transparent mobile phones that appear to be glass blocks only to light up at pressing a power button.
The future is bright with transparent flex PCBs.
Transparent Flex PCB Design
Preparing Transparent Flex PCB Circuit Design
First, use CAD software to design your PCB’s schematic diagram and autoroute tool for the circuit traces.
Next, isolate the oaths layer in your PCB pallet and export a PNG file image.
Also, use a negative photoresist as you’ll need to expose the board to sunlight.
Transparent PCB Printing
At this stage, align several layers (at least three) of OHP prints to prevent unwanted UV light from reaching the circuit board.
Failure to do so means the light leaks through and negatively affects your prints.
Use Glue to Attach Your Copper Foil to the Glass
Attach the copper foil to both sides of the glass and etch out all excess copper to leave the circuit traces in place.
To do this, use a ferric chloride solution that leaves a 0.05mm thick copper foil.
Transparent Flex PCB Base Materials
(A transparent flex PCB on a plastic membrane)
The base material determines whether the printed circuit board shall be rigid or flexible.
For instance, flexible transparent PCBs have polyimide and polyester as the base materials.
The two are quite clear, with a transparency of 95 percent.
Additionally, the fact that these boards are transparent doesn’t mean they are weak.
Polyimide transparent PCBs are quite strong, and you can’t tear them by pulling them apart with your hands.
On the other hand, transparent rigid PCBs have ceramic and aluminum substrates.
Usually, they are less clearer than polyimide and guarantee almost 80 percent transparency.
How Do You Make a PCB Transparent
Manufacturers follow steps that differ from those of standard PCBs when making transparent PCBs. Here’s what you should do:
First, organize all materials you’ll need to manufacture your printed circuit board, such as polyester and ferric chloride.
Second, create the circuit design layout before printing it.
Afterward, make the PCB’s substrate using transparent materials and add copper foil on both sides of the PCB.
Copper foil is the material that forms the circuit traces and connections throughout the board.
Next, place your transparent flexible printed circuit board under sunlight or expose it to an artificial light source.
At this stage, your next step is adding the photoresist before etching the PCB using a ferric chloride solution.
The solution eliminates all unwanted copper from the circuit board, leaving only the circuit traces in position.
Finally, test your transparent PCB to ensure it works before installing it.
Transparent Flex PCB Design Rules
(Engineers designing a PCB design)
Like any product design, transparent flex PCB has its own design rules that all manufacturers must adhere to.
First, transparent flex PCBs with more than 50 panels must have a panel dimension exceeding 100mm.
Moreover, keep the circuit board’s thickness to 0.38mm and do metallization with a silver-palladium alloy.
When dealing with the vias, maintain a 5 to 12 mils diameter while keeping a 3 to 12 mils spacing. I
n line spacing, keep a constant minimum distance of 0.8 mils between the lines and less than 4mm dimensional tolerance.
Keep the trace lengths as short and direct as possible to avoid errors that may arise during manufacturing.
Also, add a power plane for efficient grounding and power distribution throughout the circuit board.
And employ decoupling capacitors to lower signal interference in high-speed signal transmission systems.
Lastly, always check for updates since these design rules keep changing according to industry standards and regulations.
What are the types of transparent PCBs?
We have three transparent PCBs: glass, ceramic, and Flex.
First, glass PCBs have the highest optical transmissivity among the three, close to 99 percent.
Additionally, glass is an eco-friendly material that’s readily available globally.
On the downside, it is weak and will break upon falling on when under sufficient stress.
Therefore manufacturers of transparent glass PCBs prefer using tempered glass to maximize durability.
Higher-end products mostly go with an even sturdier material known as sapphire.
Second, ceramic, transparent boards have materials like magnesium oxide, alumina, and glass-based solder mask.
Consequently, they have less transparency than glass (75 to 80 percent).
Thirdly, flex PCBs contain thin polyester films that are less transparent than glass ones.
What are the disadvantages of flex PCBs?
The first disadvantage of flex PCBs is their high initial cost during manufacture.
Generally, the materials to manufacture these PCBs are costlier than those of rigid and rigid-flex PCBs.
Second, repairing the circuit boards is tough since you’ll incorporate most connectors within the flex PCB structure.
You’ll have to strip the protective layer before working on the board.
Afterward, you must restore the protective film before your board can be operational.
Thirdly, flex PCBs are somewhat new to the industry, and not all manufacturers have the right equipment to make and repair these boards.
Many projects that need the circuitry to be invisible or blend in with the background use transparent printed circuit boards.
Opaque substrate materials don’t add aesthetic value to your PCB.
Manufacturers use them solely because they are cheaper to procure and mold into a desirable product.
But if you have the skill and technology, why not use transparent flex PCBs?
They are unobtrusive, making them suitable for DIY projects requiring transparent circuitry to view the background.