Flex LED PCB Assembly: A Look Into the Process

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Oakley Mae

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Although LED strips are usually PCB-based, there’s the option of flex LED PCB assembly, with which you can custom design your flexible PCB with LED lighting.

And because of the advantages of such boards and the numerous applications, there’s been a rise in the demand, which has led to an increase in its components and manufacturing.

This article outlines the assembly process of flex LED PCBs, factors to consider when assembling, and some modern-day applications.

Table of Contents

What Is Flex LED PCB?

A flex LED PCB is a flexible PCB with a LED light strip mounted onto its surface.

Designers employ surface mount technology (SMT) to mount the LED strip.

Then upon completing the mounting, they place the diodes ad power the LED.  

Image of LED strips

(Caption: Image of LED strips)

Flex LED PCB Assembly Process

There’s a lot that goes into assembling flex LED PCB, including:

Concept and Design

In this step, a designer lays the groundwork for producing a product that works effectively and meets expectations.

To do so, you must understand what the board must achieve regarding needs, functionality, size, shape, and signal requirements.

Also, ensure the board concept and design supports expansion and contraction and has wider tacts to support increased routing complexity. 

Material Prepping

First, clean and apply a photoresist.

Then, select the most suitable material, typically FR4, depending on the requirements you must meet about solder masking, production speeds, and component placement.

Lastly, you’ll conduct the buildup process of depositing copper on the substrate.

Etching

To etch, you’ll use an etchant, typically sulphuric acid-based, and carry out the process in a plating tank.

Etching removes unwanted material to expose the board’s internal components, such as pads, on the back side of the board for drill holes.  

Coverlay Application

You’ll apply a polyamide coverlay on the board panels before laminating them.

That way, the board components remain safe from damage during drilling and soldering.

Drilling

After etching, you’ll drill to create through-holes to insert components and solder.

Remember, after drilling the holes through the coverlay, you should apply glue to enclose the various parts of the board, preventing damage. 

Copper Plating

Next is copper plating, a process that involves using a chemical to fill in the pads and traces on the board. It removes unwanted material, exposing a flat surface.

Applying Stiffener

Once you’re finished with copper plating, the next step is to apply a stiffener, a thin layer of fiberglass-based copper material.

For optimum results, wait until you’ve cured the coverlays before applying the stiffener on the flexible PCB. Still, right before the final lamination, you can be sure that the board won’t wrap when you bend, solder, or employ high-speed inserts. 

Electrical Testing

First, this test plays a vital role in detecting any short or open circuits on the board. Such issues can occur during the manufacturing process and can cause errors.

This test verifies that the board’s internal parts, circuits, and connections function properly, guaranteeing its quality and reliability.

Remember that you’ll need to conduct several electrical tests to ensure the board works well.

Fabrication

This final fabrication step involves a quality inspection for irregularities like missing components or solder splashes.

Additionally, you want to test to ensure the board meets all the client’s requirements.

LED Flex PCB Assembly Considerations

Types of Layers

Usually, to make board layers, manufacturers use an aluminum alloy metal substrate. As a result, it’s easy to employ through-hole technology, a technique that enables proper heat dissipation and transfer.

When you use such a board, you’ll notice that it can withstand high temperatures and has better machine performance due to its ability to protect against mechanical stress.

Board Type

Interestingly, some board types have no definite shape, and because of this, users often employ LED PCB panels as this help cut down on factors like time spent testing, labor, and effort.

  • Single-piece board: These boards have one or two layers. To make this board, manufacturers use basic FR4. And concerning thickness, the board can measure anywhere between 0.4 mm to 1.0 mm.
  • Panel (or in-panel) board: LED PCB panels generate plenty of heat and can’t cool off using conventional methods. For this reason, many people prefer to use aluminum as the primary metal.      

Number of Layers

More often than not, a flex PCB will have one or two sides or layers. However, flex circuits also have more than two layers (multi-layer FCBs), even up to 16 layers.

And although having many layers negatively impacts a board’s ability to bend, multi-layer boards are the most appropriate if you’re designing for a device that must function at high speeds.

Board Size

While suppliers offer both maximum and minimum board sizes, here are some factors you should keep in mind when choosing board dimensions for your design:  

  • Base material: First, you should know the nature of the circuit you’re working with because only then can you select PCB coating material and size that suits your requirements.  
  • Spacing: When it comes to spacing, it’s best to ensure that the space between LED PCB components equals their height. For example, a component of about 0.04 inches should be approximately 0.04 inches close to the other component. With this kind of spacing, the inspection phase of PCB components and solder joints goes more smoothly.

Hole Size

This is one of the most critical aspects to consider before assembling a PCB.

And the reason for this is that the ratio of the thickness of the board to the diameter of the drilled hole is of utmost importance. And this ratio is the PCB aspect ratio

Solder Mask

Now the solder mask, or stop coating, forms the thin layer covering the copper. What it does is help make the PCB dependable.

Also, it allows the PCB to perform at higher levels, plus the resin used to make the solder mask resists temperature, humidity, and insulation. Further, it has some aesthetic features. 

Silkscreen

This refers to the artwork done using formulated meant for identification purposes.

Some of the information you’ll find on a silkscreen is the logo of the device’s manufacturing firm and the settings of the switches.

Also, there are identifiers for the different components used in the board, version numbers, and test points. 

Gold Fingers

These are the connectors found at the edge of the PCB that resemble fingers.

Its surface finish offers a planar layer necessary for resisting wear and tear due to repeated insertion.

Further, you can use a gold finger with other surface treatments. 

Stiffeners

In some cases, a flex PCB may require some rigidity, and that’s where stiffeners come into play.

And these comprise FR4 material with a thickness ranging between 0.008 and 0.59 inches.

Generally, the thicker the stiffener, the better it provides the support needed for PCB components. 

Surface Finish

Because a surface finish can protect the copper from corrosion, choosing an ideal one is essential.

In addition, a surface finish makes it possible to solder components directly onto the board.     

Flex LED PCB Applications

There are several fields where LED PCB assembling methodologies are applied, including: 

Telecommunications Equipment

Most of the telecommunication equipment available employ LED PCB assembling methodologies.

That’s large because the process involves using aluminum, which aids heat transfer and dissipation, a basic requirement for such equipment. 

Consumer Electronics

Flex PCB on inside keyboard membranes

(Caption: Flex PCB on inside keyboard membranes)

Over recent years, LED PCB assembly has become a significant aspect of the production of consumer electronics.

That’s because such devices require a material capable of efficiently transferring and dissipating high temperatures. 

Automotive Industries

The automotive industry has largely adopted LEd flex PCB methodologies to make vehicles of a lightweight design and enhanced visibility. 

Medical Equipment

Flexible LED strips have grown popular in their application in medical equipment ranging from surgical lighting to patient monitoring systems. 

Industrial Applications

Flexible PCBs are used in industrial applications, such as controlling machines and monitoring temperatures. 

FAQs

How Do You Fix a Broken LED on a PCB?

First, you will need to identify the LED light that’s not working and remove it. Then, replace it, connect the replacement lamps, and complete the fix.

How are LEDs Mounted on a PCB?

Primarily, it’s done using two processes – surface mount and through-hole technologies. 

How is Flex PCB Manufactured?

It’s done using a process that involves embedding a flexible circuit into a rigid board and then proceeding to layer it up.

Why Are Flex PCBs So Expensive?

Generally, the raw materials used to manufacture flex PCBs tend to cost way more than those in conventional PCBs. 

Conclusion

LED PCB assembly is a critical element of today’s industrial development.

That’s why most of the electrical devices in the market are being built to accommodate such processes, especially considering their heat transfer and dissipation capability.