5 Major LED Packages-Amazing Introduction

We will introduce LED package types, DIP package, flat package, SMD LED package, piranha packaging technology, and high-power LED packaging.

Share This Post

How are LED lights packaged?

This article will introduce the functions of LED packages and the commonly used LED package types, such as DIP package, flat package, and will also introduce surface mount diode – SMD LED package and piranha packaging technology, and finally, will focus on high-power LED packaging. 

why is packaging so important?

4 major functions of LED packaging

The LED chip is a tiny solid whose two electrodes can only be seen under a microscope. And it only emits light when an electric current is applied. In the manufacturing process, in addition to welding the two electrodes of the LED chip to lead out the positive and negative electrodes, it is also necessary to protect the LED chip and the two electrodes. Therefore, the LED chip needs to be packaged.

LED packaging technology is developed and evolved based on semiconductor discrete device packaging technology. The die of ordinary diodes is sealed in the package, and the function is to protect the die and complete the electrical interconnection. 

The packaging of the LED is to realize the functions of inputting electrical signals, protecting the normal operation of the chip, and outputting visible light, including design and technical requirements for both electrical parameters and optical parameters.

The core light-emitting part of the LED is a PN junction chip composed of P-type and N-type semiconductors. When the electrons and holes injected into the PN junction recombine, visible light, ultraviolet light, and near-infrared light are emitted. However, the photons emitted by the PN junction region are non-directional. That is, the probability of being emitted in all directions is the same, so not all the light generated by the chip can be emitted.

The core light-emitting part of the LED

How much light can be emitted depends on the quality of the semiconductor material, chip structure, geometry, packaging internal materials, and packaging materials. Therefore, for LED packaging, the appropriate method should be selected according to the size and power of the LED chip.

Why is LED packaging so important?

Packaging is necessary and crucial for chips. (Click to Tweet this)

Packaging can also be said to refer to the housing used to install semiconductor integrated circuit chips.

It not only plays an important role in protecting the chip and enhancing thermal conductivity but also serves as a bridge between the internal world of the chip and the external circuit and the general function of specifications.

1. Physical protection

Because the chip must be isolated from the outside world to prevent the corrosion of the chip circuit caused by the impurities in the air and cause the electrical performance to decline, protect the chip surface and connect the leads, etc. So the chip is protected from electrical or thermal physical damage from external forces.

Based on the requirements of heat dissipation, the thinner the package, the better.

When the power consumption of the chip is greater than 2W, a heat sink needs to be added to the package to enhance its heat dissipation and cooling function. Forced cooling must be taken when the temperature is 5 to 1OW.

On the other hand, the packaged chips are also easier to install and transport.

2. Electrical connection

The size adjustment (pitch conversion) function of the package can be adjusted from the ultra-fine lead pitch of the chip to the size pitch of the mounting substrate, thereby facilitating the mounting operation.

For example, from chips with sub-micron (currently below 0.13μm) as feature size, to chip solder joints in units of 10μm, to external pins in units of 100μm, and finally printing in millimeters Circuit boards are all realized by packaging meters.

The package plays a role in changing from small to large, from difficult to easy, and from complex to simple, so that operating costs and material costs can be reduced, and work efficiency and reliability can be improved.

In particular, by realizing the wiring length and impedance ratio, the connection resistance, parasitic capacitance, and inductance are minimized to ensure the correct signal waveform and transmission speed.

3. Standardization

The general function of specifications means that the size, shape, number of pins, spacing, and length of the package have standard specifications, which are not only easy to process but also easy to match with the printed circuit board. The related production lines and production equipment are universal.

This is very convenient for packaging users, circuit board manufacturers, and semiconductor manufacturers, and it is convenient for standardization. In contrast, bare chip implementation and flip-chip do not currently have this advantage.

Since the quality of assembly technology also directly affects the performance of the chip itself and the design and manufacture of the printed circuit board (PCB) connected to it, assembly technology is a very critical part of many integrated circuit products.

4 major functions of LED package

LED packaging
  1. Mechanical protection to improve reliability.
  2. Strengthen heat dissipation to reduce chip junction temperature and improve LED performance.
  3. Optical control, improve light output efficiency and optimize beam distribution.
  4. Power supply management, including AC/DC conversion, and power control.

Five major LED packaging

1. DIP Package

The LED lead-type encapsulation powder uses lead frames as the pins of various package shapes, and the common one is a cylindrical (5mm for short) package with a diameter of 5 mm. 

This technology is to bond the LED chip on a lead frame (usually called a bracket), the positive electrode of the chip is bonded to another lead frame with gold wire, and the negative electrode is bonded to the bracket reflector cup with silver paste or with gold wire and the pins of the reflector cup are connected, and then the top is encapsulated with epoxy resin to make a circular shape with a diameter of 5mm.

The function of this packaging technology is to protect the chip and the gold wire of the bonding wire from external erosion. The cured epoxy resin can form different shapes to play the role of a lens, thereby controlling the emission angle of light.

The refractive index of the chip is very different from the refractive index of the air so that the critical angle of total reflection inside the chip is very small, so only a small part of the light generated by the light-emitting layer of the chip is taken out, and most of the light is absorbed by multiple reflections inside the chip.

Selecting the epoxy resin with the corresponding refractive index as the transition can enhance the light extraction efficiency of the chip. The package made of epoxy resin has good moisture resistance, insulation, and high mechanical strength, has a high refractive index and transmittance to the light emitted by the chip, and packaging materials with different refractive indices can also be selected.

The influence of the geometry of the chip shape on the light extraction efficiency is different. The distribution of the light intensity is related to the structure of the chip, the light output method, and the material and shape of the packaging lens.

2. Flat Package

A planar light-emitting device is a structural device composed of a plurality of light-emitting diode chips. Through proper connection (including series and parallel) of light-emitting diode chips and appropriate optical structure, the light-emitting segments and light-emitting points of the light-emitting display can be formed, and then various light-emitting displays, such as surface-emitting displays, digital tube, symbol tube, “meter” tube, matrix tube, a beam of light, etc.

A. digital tube

digital tube

B. Light tube

Light tube

Compared with other display devices (such as general fluorescent displays, electroluminescent displays, plasma displays, vacuum filament displays, etc.), flat-panel displays made of light-emitting diodes have the advantages of low operating voltage, power saving, multi-color, bright colors, and long life, vibration resistance, and other characteristics.

Various types of planar light-emitting devices

3. SMD LED Package

Surface Mount Diode (SMD) is a new type of surface mount semiconductor light-emitting device, which has the advantages of small size, large scattering angle, good uniformity of light emission, and high reliability.

SMD package

There are various luminous colors, which can meet the needs of various electronic products with surface mount structures, especially the needs of mobile phones, notebook computers, etc.

3.1 Process of SMD Package

SMD packages generally have two structures: one is a metal bracket chip LED, and the other is a PCB chip LED.

The process of SMD package:

Chip Mounting ⇒ Silver Paste Curing ⇒ Gold Wire Bonding ⇒ Packaging ⇒ Drying and Curing ⇒ Dicing ⇒ Test Sorting ⇒ Taping ⇒ Shipping Inspection

At present, many manufacturers use automatic machines for solid products and wire bonding, and the products produced are of good quality and consistency.Ideal for mass production.

It should be noted that when making SMD white LEDs, the point phosphor is a challenge due to the small size of the device.

Some manufacturers first mix the phosphor and epoxy resin to make a mold, and then make the epoxy resin with the phosphor powder into a glue cake, stick the glue cake on the chip, and fill the surrounding with epoxy resin, to make a white LED in an SMD package.

4.Piranha LED Package

eagle-eye led

The Piranha LED is an encapsulated, square, transparent resin package with four leads and a missing lead at the negative side.

 

It is said that this kind of LED immediately attracted everyone’s attention when it was first born, and its development trend is as fierce as a piranha, hence the name. Another theory is that it is shaped like a piranha in the Amazon.

The eagle-eye led belongs to the astigmatism type LED, the luminous angle is greater than 120 degrees, the luminous intensity is very high, and it can withstand greater power. There are many brake lights and turn signals used in cars.

4.1 Advantages and Disadvantages of Piranha Superflux LED Packages

The advantage of Piranha Superflux LED Packages:

The Piranha LED has 4 feet, which is two more feet than the general 5mm LED, and there is a certain distance between the light-emitting part of the 4-foot handle and the welding place of the circuit board. The design of the 4 feet and the space left make the heat dissipation of the Piranha LED much better than that of the general LED, and the working current through it is also larger, and the maximum can be 40-50MA. The general LED is 20MA, so the brightness is higher than the general LED.

The disadvantage of Piranha Superflux LED Packages:

The volume is a bit larger than the ordinary 5mmLED, and the angle is around 3045, 60, 90, 120, 140, 160, and there is no other angle. The effect of full-color RGB mixed light is not good, which is better than the LED of a 5mm straw hat.

 

Among the low-power LEDs, the piranha LED is the brightest, but it is nothing compared to the high-power 1W and 3W.5W. The most used piranha LED is the light-emitting module in the advertising words.

However, each type of LED has its own use. It cannot be compared with the brightness alone. The outsider just compares the brightness. The insider looks at the ratio of parameters, consistency, and chips used.

It is better to use 10MM LEDs or high-power 1W LEDs when used in the car’s mid-grid lights and eyebrow lights, both with small angles, and piranhas do not have too small angles.

4.2 Application of Piranha LED

Piranha superflux LED is getting more and more attention, because it has better heat dissipation than 05mm LED, larger viewing angle, less light decay, and longer life. Piranha LED is very suitable for making line lights, backlight light boxes, and light sources in large font slots.

Because line lights are generally used as outline lights for high buildings in cities, and the lightbox advertising screens of the backlight and the lights with large fonts are placed at high places, if the LED lights are not bright or dimmed, maintenance is very difficult. Due to the good heat dissipation of the piranha LED, compared with the ordinary LED of 5mm, its light decay is small and the life is long, so the use time is also longer, which can save a considerable amount of maintenance costs.

Piranha LEDs can also be used as brake lights, turn signals, and reversing lights in cars. Because the piranha LED has advantages in heat dissipation, it can withstand a current of 70~80 mA. For example, in a running car, the voltage of the battery often fluctuates greatly, especially when the brake light is used, the current will suddenly increase. But this situation doesn’t have much effect on piranha LEDs, so they are widely used in automotive lighting.

5.Packaging of high-power LEDs

At present, LEDs are developing in the direction of high power and high luminous efficiency, which is the development trend of the LED industry. In the future, many manufacturers can produce more than 1W LED chips which can be packaged in a variety of ways.

What kind of package can make high-power (W-level power) LED achieve high luminous efficiency and long life? This is the goal pursued by those in the packaging industry.

The packaging of high-power LEDs cannot simply apply the materials used in the packaging of traditional low-power LED devices. High-power LEDs have large dissipation power, large heat generation, high light output efficiency, and long life. Therefore, in the design of packaging structure, The selection of materials and equipment must be reconsidered.

the structure of high power LED

To improve the light-emitting efficiency of high-power LEDs, many people hope to increase the brightness by increasing the size of the LED chip, which is also the method adopted by some chip manufacturers.

Increasing the effective light-emitting area and size of a single LED can indeed improve the light-emitting efficiency, but it is not that the larger the chip area, the stronger the light-emitting and the higher the light-emitting efficiency.

If the chip area is too large to a certain extent, it is impossible to continue to improve the brightness, and it is even more impossible to improve the light extraction efficiency. For packaging manufacturers, to maximize the light output under the same chip area and work stably and reliably, it is necessary to study the packaging method.

Several high-power LED packaging methods will be discussed below.

5.1 V-electrode high-power LED chip package

Let’s discuss the 1 W high-power chip “V-shaped electrode” of GREE Company in the United States, which has an electrode on the upper and lower sides.

The bottom layer of the silicon carbide (Sic) substrate is first plated with a layer of metal, such as gold-tin alloy, and then in the heat sink. It is also covered with a layer of gold-tin alloy. The metal on the base of the LED chip and the metal on the heat sink are fused together, called eutectic bonding.

Eutectic Welding

Eutectic Welding

For this packaging method, it must be noted that when the LED chip and the heat sink are heated together, the contact between the two is better. It is best to add a certain pressure between the two, and the contact surface must be evenly stressed and balanced on both sides. Control the ratio of gold and tin, so that the welding effect will be good.

The LED made by this method has smaller thermal resistance, better heat dissipation, and higher luminous efficiency. 

This type of sealing package is the upper and lower sides of the input current, if a pole connected to the heat sink is directly conducive to the heat sink, the heat sink also becomes an electrode.

The heat sink is glued to the radiator with a thermally conductive adhesive. Use this LED to test whether the heat sink and its contact with a pole is zero resistance. If the resistance is zero, then it is connected, so the heat sink is connected to the installation of the radiator to pay attention to the heat sink insulation.

The heating temperature is also called the eutectic point. The temperature depends on the ratio of gold and tin:

Ratio

Eutectic Point

Time

AuSn (Au 80%, Sn 20%)

282°C

within a few seconds

AuSn (Au 10%, Sn 90%)

217°C

within a few seconds

AgSn (Ag 3.5%, Sn 96.5%)

232°C

within a few seconds

5.2 L-shaped electrode high-power LED chip package

For the L-type electrode LED chip, as shown in Figure 5-2, the P and N junctions of the two electrodes are on the same side.

The bottom of this kind of LED chip is usually an insulator (such as A130g, sapphire), and the bottom shell of the insulator is generally coated with a light reflection layer, which can reflect the light hitting the substrate back. So that the light can be emitted from the front, to improve light efficiency.

This package should use a thermally conductive (insulating) glue on the lower surface of the insulator to bond the LED chip to the heat sink, and the two electrodes are soldered out with gold wires.

Special attention should be paid to the large current passed by high-power LEDs. The current of 1WLED is generally 350mA, so we use thick gold wire.

However, sometimes thick gold wires are not suitable for wire bonding machines, and two gold wires can be welded in parallel, which reduces the current passing through each gold wire.

The baking temperature of this chip is 100~150°C, and the time is generally 60~90 min.

Packaging of L-shaped Electrode LED Chips

Packaging of L-shaped Electrode LED Chips

When encapsulating high-power LEDs, due to the relatively large amount of heat generated when lit, a layer of silicone gel can be covered on the LED chip instead of epoxy resin.

In this way, on the one hand, it can prevent the gold wire from being pulled apart due to the inconsistency between the thermal shrinkage and the epoxy resin.

On the other hand, it can prevent the epoxy resin from turning yellow and contaminated due to high temperature, resulting in poor light transmission performance. So when making white LEDs, we need to use silicone gel and phosphors.

If the bottom layer of the LED chip has been filled with gold-tin alloy, it can also be done with a eutectic point of 217°C~282°C (depending on the ratio of gold and tin).

5.3 Flip-chip packaging of L-type electrode LED chips

5.3.1. Traditional formal LED

Pictures down there shows the location of the blue chip electrodes at the bottom of the sapphire village on the light-emitting surface of the chip. Due to the difficulty of doping P-type GaN, a method of preparing metal transparent electrodes on P-type GaN is currently commonly used, to diffuse current and achieve the purpose of uniform light emission.

However, the metal transparent electrode absorbs 30% to 40% of the light, so the thickness of the current diffusion layer should be reduced to several hundred nanometers.

The thickness reduction in turn limits the current spreading layer to achieve uniform and reliable current spreading on the P-type GaN layer. Therefore, the P-type contact structure restricts the operating current of the LED chip.

At the same time, the heat of the PN junction of this structure is dissipated through the sapphire substrate, and the thermal conductivity of sapphire is 35 W (m K), which is worse than that of the metal layer. Therefore, the heat conduction path is relatively long, the thermal resistance of this LED chip is relatively large, and the electrodes and leads of this structure will also block part of the light.

Schematic diagram of GaN chip structure on traditional sapphire substrate

the structure of GaNg chip on traditional sapphire substrate

5.3.2 Flip chip

Traditional formal LBD chips are not optimal for the light extraction efficiency and thermal performance of the entire device. In order to overcome the shortage of formal installation, American Lumileds Lighting invented Flipchip technology.

flip chip structure

In this packaging method, large-sized LED chips suitable for eutectic soldering are first prepared, and at the same time, silicon substrates of corresponding sizes are prepared. And the gold conductive layer and the lead-out conductive layer (ultrasonic gold wire ball welding point) of the eutectic welding electrode are made on it. Then use eutectic bonding equipment to bond the large-size LED chips to the silicon substrate.

At present, most of the products on the market are produced by chip manufacturers that have been flip-chip welded and equipped with anti-static protection diodes. The packaging manufacturer glues the silicon base plate and the heat sink together with thermally conductive adhesive, and the two electrodes use a ∅3 mil gold wire or two ∅1 mil gold wires respectively.

To sum up, based on doing a good job of flip-chip, the following three issues should be considered when packaging:

  • Since the LED is a W-class chip, what size of gold wire should be used?
  • How to fix the flipped chip on the heat sink, whether to use thermal paste or eutectic soldering?
  • Consider making a concentrator cup on the heat sink to focus the light energy from the chip into a beam.

According to the different heat sink bottom plates, there are two common flip-chip methods of heat sink bottom plates on the market:

One is to use the eutectic welding equipment described above to weld the large-size W-class LED chip and the silicon base plate together, which is called the silicon base plate flip-chip method.

Another one is the flip-chip method of the ceramic base plate. First, an LED chip with a suitable eutectic welding electrode structure and a large light-emitting area is prepared, and the eutectic welding conductive layer and the lead-out conductive layer are made on the ceramic base plate. Then use eutectic bonding equipment to bond the large-size LED chips to the ceramic base plate.

Conclusion

This chapter addresses process and technical issues related to LED packaging, with a focus on packaging technology for high-power LEDs.

The packaging technology of high-power LEDs has developed rapidly, and the process has become more mature. For various packaging methods, various manufacturers have accumulated a lot of experience, and in the aspects of automated manufacturing equipment and testing equipment, new packaging materials and new process technologies are constantly emerging.

Therefore, it is just around the corner to produce LED devices with high power, high reliability, and high luminous efficiency.

Subscribe To Our Newsletter

Get updates and learn from the best

More To Explore

full spectrum lights for home
Uncategorized

Full Spectrum LED-11 Things You NEED To Know

Today we mainly introduce several hot issues of full-spectrum LEDs: the characteristics and influence of full-spectrum LEDs, full-spectrum lights for birds, and how to choose full-spectrum lamps.

LED packaging
Uncategorized

5 Major LED Packages-Amazing Introduction

We will introduce LED package types, DIP package, flat package, SMD LED package, piranha packaging technology, and high-power LED packaging.