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Today we will learn about LED PCB Assembly.

Our guide covers every aspect in the LED PCB assembly &#; from specification, BOM, assembly techniques, and many more.

What&#;s more?

You&#;re going to learn about the challenges, possible solutions and packaging processes.

By the end of this guide, you&#;ll be an expert in LED PCB assembly process.

What is LED PCB Assembly?

This is the processes of mounting electrical components on a PCB.

Depending on the nature of the task, you can use a number of methods and technique. You will see that later in this guide.

Remember, LED printed circuit boards are made from aluminum material.

Aluminum base provides a link between the heat sink and the IC. It has the ability to resist heat.

By the end of the LED PCB assembly process, you&#;ll have something like this:

LED PCB Assembly

Types of aluminum used in the LED PCB Assembly

There are three different types of aluminum used in manufacturing a LED PCB.

a)Flexible aluminum

This is made up of ceramic fillers and polyimide resins which gives better insulation and flexibility.

b)Hybrid aluminum

FR4, a non-thermal material is merged with aluminum metal. This helps in making the LED PCB rigid.

It also preserves its thermal characteristic. Hybrid aluminum has some benefit which includes:

• Cheaper construction cost as compared to the use of all thermal conductive materials.
• Has better heat dissipation compared to FR-4products?
• Does not have any cost for heat sinks since it does not have it.

c)Multi-layer aluminum

High heat transfer and effective thermal conductivity are highly needed in very complex LED PCBs. Because of this, multi-layer aluminum is very relevant for such.

They are applicable here because LED lights PCBs consume less power.

Also, they have no mercury, work efficiently and lasts longer as compared to other lights PCBs.

Application of LED PCB Assembly

The LED PCB Assembly technique has been applied in telecommunications, Automotive, Computer, and medical equipment assembly.

So in this chapter, let us look at these applications in a more detailed manner.

·Companies manufacturing Telecommunications equipment

Many telecommunication equipment are made using LED PCB Assembly technique.

This is because the LED PCB Assembly is mounted using Aluminum.

Telecommunication circuit boards

Aluminum aids in heat transfer and dissipation, which is a basic requirement for these equipments.

·Automotive Industries

Cars use aluminum LED PCB in the manufacturing of brake lights, headlights, and indicators.

LED PCB is relevant in automobile industries because the aluminum component makes these parts durable.

·Computer manufacturing Companies

LED PCB Assembly has recently become of more interest to computer companies. Computers are very sensitive to heat, particularly the power unit and CPU.

Computer motherboard

These parts require a material that can easily transfer and dissipate heat efficiently, making LED PCB the best option.

·Medical equipment

Surgical and medical examination equipment are made up of high powered LED lights.

They, therefore, require the ability to transfer and dissipate this high heat, making LED PCB assembly the best option.

CT Scan equipment

This also makes the equipment efficient and long-lasting.

BOM for LED PCB Assembly

First of all, let us talk about BOM.

What is BOM?

Bill of Materials (BOM) is essential data that is used throughout the process of assembling an electronic device.

 BOM &#; Photo courtesy: RayMing

It means a list of all materials required to build up a particular printed circuit board.

BOM of PCB is generated from PCB software.

This software is engrained in its CAD system where all parts are designed, installed and kept in the CAD library.

Once it&#;s installed, it can be pulled and used for different parts of the bill of Materials.

So, what does a BOM do in LED PCB Assembly?

A well-developed BOM clearly illustrates the time for production, the cost, and the materials required to process the product.

In addition to these, it shows the process of manufacturing it and its quality once it is produced.

It is imperative to choose the materials for your components before you can go ahead and develop a BOM list.

Factors to Consider when Developing a BOM.

1&#;Select locally available materials or materials that can easily be found without having to wait for it for a long time.

When materials are far-fetched, consumers may lose confidence in getting your products.

2&#;Use components that are durable. This will reduce the burden of revising the design now and then.

It will also help in the selection of the appropriate BOM for LED PCBs.

3&#;Place all components to be mounted on the same layer at the surface. This reduces the cost of manufacturing by

around 25%.

4&#;A good PCB BOM must have comments, description of each part, a designator of each part and footprint. Let us look

at what these are.

Comment: Every PCB part has peculiar identifications which distinguish it from others.

For example, parts can be numbered using vendor number like &#;27--03&#;. This helps to distinguish these parts from others even if they may appear to be alike.

Description: Unique identifier is described.

For example, it could be described as &#;CAP 10Uf 20% 6.3V&#;. This description helps to eliminate confusion when mounting because each part will stand out different from others.

Designator: Each part has its purpose for which it is being mounted on the PCB. The difference is made through their designators.

For example, for the case of a 12uF capacitor is designated for &#;C27.&#;

Footprint: The name of a footprint being used from a CAD. For instance, C27 could use a CAD footprint of &#;CAP-.&#;

LED PCB Assembly Component Mounting Technique

There are three main LED PCB component mounting techniques, namely:

1. Through &#;Hole
2. Surface Mount
3. COB (Chip-On-Board)

LED PCB Assembly

I will take you through these briefly. (Get more on these techniques from our other guides)

Through-hole LED PCB Assembly

Through-hole LED PCB is dated back in the s. It was widely used to manufacture optoelectronics and other electronics for over twenty years.

Many people thought it will be outdated, but even up to date, through-hole PCB assembly technique still stands due to some benefits that other technologies cannot offer.

Advantages of through-hole assembling technique

Through the hole, the LED PCB Assembly has some benefits, and that is why some device manufacturing companies prefer it.

So let us go through these benefits. They include:

• Its components can easily be interchanged. That is, they are easier to prototype.
• They can endure a lot of heat and therefore are durable even when the product is in extreme acceleration and collisions.
• Its devices use power efficiently and economically because there is a good bond between the circuit board and the components.
• Due to its ability to withstand stress, it is used to assemble PCB boards for electrical devices like transformers.

Semiconductors, Connectors, and electrolytic capacitors are also assembled through this technique.

Through-hole technology is currently evident in LED lights on billboards and some stadiums. Also, many machines used in both industries and at home are made using through-hole PCB Assembly.

THT is relevant here because these machines are exposed to harsh physical environmental conditions. Other PCB Assembling techniques cannot endure these conditions.

Setbacks for through-hole assembling technique

Just like any other technology, through-hole PCB Assembling technology has some disadvantages. Here are some of them.

• It&#;s relatively expensive since it requires hole-drilling.
• It takes considerably longer time to solder lead through the drilled holes.
• The technique makes weak solder point which results in unreliability as compared to Surface mount assembling technique.

Surface Mount Assembling Technique

Another technology used in the LED PCB assembly is Surface Mount Technology. This technology was invented around the year s.

It began to replace the through-hole technique in the year s.

Surface mount technology &#; Photo courtesy: Wikimedia

Currently, most manufacturing companies use surface mount LED PCB Assembly.

The components required in surface mount Assembling techniques are different types of resistors and capacitors.

Some of the Surface mount devices are too small in size. Therefore, they are assembled using a microscope and component lifting machines.

Advantages

• Devices smaller in size can be assembled using the technique.
• Automated assemblies are possible.
• It uses both sides of the board.
• Cost effective option
• It has good thermal property.
• Can be assembled faster than through-hole PCB Assembly.

Disadvantages

It proves to be unreliable when attachment for board components go through mechanical and environmental stress like high heat.

Also, the components cannot be assembled manually; thus it is sometimes costly.

LED PCB Assembly Specifications

There are various specifications that must be adhered to when using LED PCB assembly. Let us look at some of them.

LED PCB Assembly specification

i.Number of layers

These layers are made up of aluminum and magnesium.

Aluminum PCBs stand out among other PCBs because it has a good insulation characteristic and has a better machinery performance.

ii.Types of layers

Normally, the base layer is made using aluminum alloy metal.

This aluminum alloy substrate used in making the base makes it ideal for through-hole technology which transfers and dissipates heat.

A thermal insulation layer is made using some ceramic polymer which has good viscoelasticity characteristics.

It is highly heat resistant and protects the PCB against heat and mechanical stress.

The circuit layer, which is covered by a copper foil which can range from one to ten ounces.

iii.Board type- single or in panel

Some boards are shapeless. For this reason, LED PCB panels are used. This reduces time, labor production and testing time.

Some LED PCB Assembly is done on a single board while others are done on panel boards.

·Single piece board

This has one or two layers. It is made from normal FR-4 board. Its thickness can, for example, be 0.4mm, 0.6mm, and 1.0 mm and so on.

·Panel-board

LED PCB panel produces much heat and cannot cool off traditionally. Because of this, aluminum is used as core metal material for manufacturing the pane board.

iv.The number of flexible PCBs

Flex PCBs has either one or two sides. It can either be single or multiple layers PCB. Devices desired to perform with high speed are ideal for multi-layer flex PCBs.

Unfortunately, these devices lose their flexibility.

v.Dimensions

Manufacturing companies like twisted trace provide both minimum and maximum board size. For example, look at the dimensions illustrated in the table below.

The dimension of a PCB is critical. This is because manufacturing cost depends on the size and layout of the board.

Considerations for Choosing Board Size

• The available area should be smaller than the board size
• A tolerance value must be maintained during the manufacturing process of a PCB.
• Type of closure is also very important.

 vi.Base material

An engineer can specify circuit nature. He can also specify PCB coating material, PCB size and a variety of other specifications which may also be included.

PCB base is made of different materials.  Therefore, let us see these materials that are used to make a base of the LED PCB board.

Materials commonly used are:

• FR-4 and epoxy- FR-4 is a very poor heat conductor and therefore does not last long even though they are cost-effective.
• The Metal-core- Is also a material used at the base of LED PCB.

It is not like epoxies material because it&#;s PCBs are very efficient just like its applications. Also, it is more useful in devices which are used for heat transfers.

A metal-core base is made up of aluminum metal which is covered with a copper layer.

These two metals (aluminum and copper) enables the circuit board to resist and conduct heat.

Choice of a base material selected depends on whether the manufacturing company needs a device with thermal qualities or not.

Fr-4 is for low thermal devices while Metal-core is meant for devices with high thermal qualities.

vii. Minimum spacing

The space between LED PCB components should be equal to its height.

For example, a component that is 0.04 inches, should be 0.04 inches closer to the next component.

This spacing aids in an inspection of solder points and other PCB components.

Surface mount Technology uses the minimum space width of 0.006 inches.

It is because some of the devices of SMT are smaller in size.

viii.Hole-size

Hole-diameter is one of the aspects that should be considered when you want to manufacture a printed circuit board.

The ratio of a thickness of the board to the diameter of the drilled hole is very paramount. This ratio is called a PCB aspect ratio.

In an aspect ratio of 3:1, the thickness of a PCB is 24mils, and the diameter of the drilled hole becomes 8 mils. Board sizes of between 8mils to 10 mils can have a minimum hole-diameter size of 6mils.

ix.Solder mask

It is also known as solder stop coating. It forms a thin layer that covers copper. It is used to make the PCB reliable and to make a PCB have high performance.

The material used to make the solder mask is resin. It is resistant to humidity, temperature, insulation, and solder. It is also aesthetic.

The known color of PCBs is usually green. This green oil color of a solder-stop coat is applied on the board on top of the Copper layer.

However, solder masks can be of different colors: black, white and red, blue, yellow among other colors as shown below.

Solder mask on PCB

The difference in color of a solder mask is determined by different demands including:

Some manufacturing companies usually produce PCBs which have red solder masks for their new products.

Main reason here is to easily distinguish these new products from the mass-produced ones.

Black solder mask is preferred when the manufacturer wants the end product to look like the solder mask.

This is particularly very important when the end product circuit board is supposed to be displayed partially or fully.

When you want to apply a solder mask, you must make sure the circuit board is clean and free from oxidation.

Cleaning of the circuit board is done using aluminum oxide. Dry it before applying solder mask.

Shenzhen Thriver Digital Tech Co., Ltd. supply professional and honest service.

Let us go through some functions of the solder mask on the circuit board.

Solder mask prevents soldering bridges from reaching the covered areas on a printed circuit board.

It prevents copper traces from connecting with solder paste. When copper and solder come into contact, there are usually shorts cuts which develop.

This compromises the reliability and performance of a device.

It can prevent copper traces from being oxidised, corroded and being dirty.

x.Silkscreen

It is an artwork done using a formulated ink that serves the purpose of identification.

Information that is entailed on silkscreen includes settings of the switches and a logo of the device manufacturing company.

It also shows the identifiers of the components used on the board, test points and numbers for different versions.

In the early days of innovation, silkscreen was done using a stencil.

But as technology advances, there have been new developments in terms of silkscreen applied on a circuit board.

The formulated color that some companies use in silkscreen can either be white or black.

Ink-jets are directly used to create the image from the digital data that is contained on the circuit board.

Small ink droplets are then sprayed onto the panel of the image.

You can have another information image on the opposite side of the board. In this case, the ink tank must be dried and spraying repeated.

This process ideally takes less than ten minutes.

Methods of silkscreen

• Manual screen-printing is possible when lines width is more than 7mils, and it must have a registered tolerance of 5mils. When the image line width is bigger than 4mm, Liquid Photo Image is relevant.
• Sometimes, direct legend printing becomes useful particularly when we want to work on complex printed circuit boards.

Silkscreen is not only used during fabrication but also as one of the important steps in the PCB assembling process.

Silk screening is used to accurately place the following components on to the circuit board:

• Reference indicators which are meant to identify components from Bill of materials.
• A pin1 indicator which illustrates how all pins are supposed to connect to footprint pad.
• Polarity indicator providing information on components that have been polarized.
• Component outline which serves the purpose of pointing out the location of component placement.

A component outline can be lacking especially if the pads are smaller in size. But there has to be a systematic way showing how these components have to be placed.

Wrong placement of components affects the function of a device.

Now let us look at the reasons why silkscreen is such an important issue in a LED PCB.

• It directs a technician on where the measurements should be taken during the testing process.
• Furthermore, it is used to verify how the device functions and find out if the device has some faults.

Factors to consider when designing silkscreen.

• Contract manufacturers have technical know-how on fonts that are visible when printed on a circuit board. It is advisable for the company technicians to use recommended standards.
• Strictly follow the clearance and dimension guidelines which have been given by contractor manufacturer.

This is good because it will prevent silk screen materials from being covered by other board components.

When they are not covered, they become more visible to the technicians.

xi.Gold fingers

Gold fingers are the connectors at the edge of a PCB. It looks like a finger, thus the name.

It is a type of surface finish that provides a planar surface.

Gold finger PCB

A planar surface is very useful as it provides the ability to resist any tear or wear as a result of a repeat of insertions.

A gold finger can be used together with other surface treatments.

It is normally applied to PCB areas that are more susceptible to tear and wear. For example, the edge connector and the keypads.

Which are the specifications for a gold finger?

• The distance between the gold finger and the outline must be 1.0 mm
• PCB should be 1.0 mm or above in thickness
• There has to be a distance of not less than 30mm between gold fingers

xii.Stiffeners

Flex PCB sometimes requires some rigidity in some of the board parts.

This is where stiffeners will come in handy to support some components on the printed circuit board.

Some stiffeners are made up of FR4 material. Stiffener thickness usually ranges from 0.008&#;&#; to 0.59&#;&#;. The thicker the stiffener, the more support it provides to the PCB components.

When are stiffeners relevant to PCB assembly?

• Board components are close to each other, in a dynamic or a flex area.
• Size of the board components is likely to cause stress onto the flex.
• Larger number of surface mount pads make planarity critical.
• When they are intended to reduce board component stress.

xiii.Surface finish

This must also be designed on a PCB. Choosing a good surface finish is very crucial since it&#;s the surface finish that protects the copper from corroding.

The surface finish gives the PCB the ability to solder its components right on the board.

Now, I want us to outline factors that influence the choice of a surface finish for PCB.

• Cost of environmental impact the surface finish material will have
• Duration you want the device to last
• Volume you are expected to produce
• Components you intend to mount on the PCB

LED PCB Assembly surface finish

Surface finish exists in numerous types. In our next learning process, I want us to go through the different types of surface finish.

Types of surface finish

·Hot solder air leveling

This is the cheapest PCB surface finish. The PCB is dipped into molten solder and then leveled using a hot air knife.

It works well in through-hole PCB or in larger surface mount technology components.

Hot air soldering leveling is not ideal for small components because the surface is not completely leveled.

Some of the Advantages of hot air leveling are:

• Provides good solderability
• Less expensive
• Ideal for large processing of PCBs

Disadvantages

• A difference in level between small and large pads exist
• It cannot be used in the processing of small components Bridging must be done on fine pitches
• It&#;s not good for HDI products.

·Immersion in tin surface finish

Here, a flat metal is immersed into copper traces. It can be used when processing small components on a PCB.

Tin is used because it is cheap even though a PCB immersed in tin tarnishes. When it has tarnished, it cannot produce good solder points.

For this reason, a PCB immersed in surface finish must be used with thirty days.

The advantages include:

• Produce a good flat surface of the same level
• Ideal for small pitch or small PCB components
• Relatively cheap
• Provides a good soldering surface even after it has undergone a lot of heat excursions.

Disadvantages of immersed surface Finish

• Handling it requires hand gloves
• It is not friendly to solder mask
• Solder mask that peels off easily cannot be used.

·Lead-free hot air solder levelling

Instead of using Tin-lead, it uses Tin &#;copper or tin-nickel. For this reason, it is cost effective.

Some of the advantages of the above type of Surface finish.

• Cheap to produce
• Produces perfect solder points
• Allow large pad processing
• Has the ability to handle many heat excursions.

Let us see some of the Disadvantages of Lead-free hot air solder levelling:

• There is a difference in thickness at the surface of the board between the small and larger pads. This disqualifies it from being used to process small components.
• It has a high processing temperature
• Bridging must be done on fine pitches

Immersion silver surface finish

Silver produces good surface finish because when a PCB is immersed into it, it does not react like tin. But if exposed to air, it also tarnishes.

Therefore, it should be stored in an anti-tarnish package. When it is stored as recommended, it can be used for soldering within twelve months.

Immersion silver surface finish has some benefits as follows

• Produces a completely flat surface which is ideal for mounting small PCB components.
• Relatively cheaper
• Can be reworked

Disadvantages of Immersion silver surface finish

• It is very sensitive to handling. The special packaging which prevents it from tarnishing increases its cost of production.
• Mask that peels off cannot be used when you choose to use an Immersed silver surface finish.

·Electro-less nickel immersion gold surface finish

For this type of surface finish, the surface is made up of nickel which is covered by a thin layer of gold.

This surface is hard and lasts longer as compared to other types of surface finishes.

Because of this, it is the most expensive type of surface finish.

Advantages of Electro-less nickel immersion gold surface finish

• Surface finish is flat, and this makes it relevant for mounting small components on PCB.
• It is bonded with wires, and this makes it strong and durable.

Disadvantages

• An expensive surface finish type
• Not friendly to solder mask

LED PCB Assembly Process

For us to have a successful LED PCB Assembly process, its functions must be defined. Compliance requirement is defined to reduce the effect when components are selected.

The Bill of Materials is then generated from the information installed on the PCB.

Width and routing are then defined while considering voltage, grounding, and noise among other components.

LED PCB Assembly process

All this information is used to assemble components which are identified from MOB to the PCB.

After that, the routing of traces is determined to each component, based on the size, shape of the circuit board and location of connectors.

Methods of LED PCB Assembly

We have two methods, namely hand and automated LED PCB Assembly

Hand assembly of LED PCB

The technician carefully places LED Components on to the circuit board. In this case, he uses a specialized tool to do the assembly.

PCB Assembly

The disadvantage of this assembly process is that it is long and tiresome. Therefore, it slows the production process.

Automated Assembly of LED PCB

Mostly used in surface mount technology.

Vacuum pressure and a precise nozzle are used to quickly and efficiently pick and place numerous LED components on the board.

Automated PCB assembly

Stages of the pick-and-place process used in an automated assembly of LED PCB

We have different stages involved in a pick-and-place process.

These are the processes.

• Picking-Vacuum nozzle withdraws components from a tray.
• Holding- the machine detects the proper alignment of the components and hold them in readiness to move them to the circuit board.
• Transport-This process involves moving components from their location to the circuit board for assembly.
• Placement-This is the process of lowering components onto their respective locations on the circuit board.
• Release- Nozzle releases the components in their designated locations on the board. It releases them and begins a new process of pick-and-place.

Note that the inability of a nozzle to pick-and-place results in assembly default. This can increase the cost of production.

An automated Concept of Surface mount LED PCB Assembly process

Once it has been set up is it very simple. It has five processes which include:

• Producing a PCB with solder points on both sides of the circuit boards.
• Screen printing machine will then depositing solders on the pads that join the components to the board.
• Picking of components and placing them on solder points by a pick-and-place machine.
• Reflow oven then breaks the PCB at a temperature to harden the solder to its final state without having to damage the components.
• Inspection of PCB is then carried out using an automated optical inspection machine.
• Faulty components are removed repaired.

Fabrication of LED PCB

LED PCB is fabricated using aluminum as the core metal. This aluminum has a thin layer of copper which conducts heat.

Fabrication involves soldering of components onto a LED PCB.

During the fabrication process, these components are electrically connected and mechanically tightened on to the circuit board.

 LED PCB design and layout

Initially, fabrication was done manually but this slowed down the production output.

Currently, automated CAD software is used to manufacture LED PCBs.

This software does the layout which is used repeatedly to produce LED PCBs in large numbers within a very short time.

The devices made from automated LED PCB are cheap and efficient.

Testing of LED PCB

Testing of LED PCB can be done using an automated optical machine. However, there are other machines which we are going to look at later on in this guide.

Testing PCB

This machine checks if there are some mistakes that have been made when assembling LED PCB. It specifically inspects solder joint quality and other board components.

In most cases, movement occurs during the reflow process. This results in short cuts, poor connection quality or even completely, lack of connection.

When a component is misplaced, they may connect with the circuit board they are not meant to connect to. To identify these mistakes inspection has to be done.

There are three main ways of carrying out a test on LED PCB as listed below

• Manual check
• Automated optical inspection
• Automated X-ray inspection.

Challenges of LED PCB Assembly Process

LED PCB has the following challenges:

LED PCB Assembly

Replacing vulnerable components.

When electronic devices are used, some parts wear and tear. These parts that wear or tear require some repair or replacement.

Soldering of components must be done even though it consumes time.

Solution

It is recommended that bases should be added to the vulnerable components.

Another solution is that connections can be done using plugs or insertion rows.

Improvement of pad off and solder layer off

When PCB is being maintained, disassembling or soldering cannot be avoided.

Old PCBs always develop pad off or solder layer off on plate-hole wall when components are disassembled from PCB.

Solution

A nearby pad on the same route can be connected via a short line. This depends on the distance and the amount of current it can hold.

For Short distances, we can use trimmed pins for soldering.

Soldering layer off comes together with disassembly of PCBs. It is suggested that pad holes would be between 0.3 to 0.5 mm larger than pins during the design process.

Pins of new components are installed before in coating with soldering tin layer a little bit thicker.

Then solder tin layers on the pins are soldered back to the pads on PCB.

Withstanding Voltage protection of multi-channel power Rectification LED.

Short-cut blasts usually take place due to the withstanding voltage problem of LED PCBs. This can result in the destruction of the whole device.

Solution

Anti-interference capabilities of CPU must be increased and installed.

Interference source should also be reduced.

For example, an anti-interference capability with relay driven amplifies can be installed.

Packaging LED PCB after Assembly

Packaging enables outer leads to be linked to electrolyte LED chips. This helps in protecting the chips and improving the luminescence of LED lights.

Packaging PCB

The packaging of the LED PCB promotes the normal operation of diode chips. It also makes sure visibility light is exported out perfect.

Machine for packaging LED PCB

Cristal precision solid machine is used for packaging surface mount PCBs devices.

For luminescence not to be compromised, LED chips must be placed well into the package.

Failure to place them well leads to LED light not reflecting fully from a reflective cup. This interferes with LED&#;s brightness.

Types of LED packaging

• Lamp-LED
• Surface Mount Device-LED
• Side-LED
• Top-LED
• High power-LED
• Flip chip-LED

Conclusions

LED PCB Assembly is very crucial in the current industrial development. Many electrical devises are being innovated and the old once being improved.

LED PCBs are useful due to the fact that they are made using materials that can transfer and dissipate heat. This characteristic increases device durability.

Recent technology also allows for mass production.

Since consumers prefer durable, light and efficient devices, LED PCB assembling technique is very much relevant in the current world.

Are you interested in learning more about Led Lighting PCB Assembly? Contact us today to secure an expert consultation!