LED luminaire assembly process: Through hole technology has not phased out

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Many manufacturers consider through hole technology as having become obsolete. However, in reality, through hole technology co-exists with SMT technology

By Richa Chakravarty

led-luminaireTuesday, June 17, 2014: The Indian LED luminaire industry is undergoing a wave of changes, with manufacturers shifting towards automated and surface mount technology (SMT). However, the older through hole machines have still not been phased out in the production process.

For many years, through hole LEDs have dominated the high brightness LED market, particularly for outdoor video wall applications. Due to their highly reflective design with primary optics, it has been difficult to replace them with SMT LEDs.

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SMT technology surpasses through hole technology due to the number of advantages it offers, which clearly justify its use in printed circuit board (PCB) assemblies. Through hole technology, however, is expected to remain in use for testing and prototype applications that need manual adjustments and replacements. It is unlikely to completely disappear from the manufacturing scene for some time, at least.

Through hole technology refers to the mounting process used for electronic components. This process involves the use of lead on the components, which are inserted into holes drilled in PCBs and soldered to pads on the opposite side either by manual assembly (hand placement) or by the use of automated insertion mount machines.

SMT vs through hole technology

With through hole technology, only larger-sized components can be soldered onto PCBs, which leads to lower component density per unit area. The packing density that can be achieved with SMT is very high, not only because much smaller components can be soldered closer together, but also because this automated technology can be used to mount components on both sides of a PCB.

The board space for through hole components is limited to only the upper side of the PCB to avoid damage or short-circuits during wave soldering, which could further complicate manufacturing.

There is no doubt that SMT not only saves time and money but also enhances the quality of the product. However, there have to be large scale volumes to justify a shift to SMT manufacturing. This process is completely automated, resulting in fewer manufacturing errors, as pick and place robotic machines are used to place components instead of the manual assemblers in the through hole technology process. Where SMT is used, PCBs can be designed to be smaller.

Many big manufacturers consider through hole technology as one that has reached the end of its life. Opines Ravinder Gulati, deputy general manager, LED division, Continental Device India Ltd, “The though hole assembling process is now obsolete as manufacturers are moving towards SMD components.”

However, according to another school of thought, through hole technology is here to stay. “It requires an understanding of the economies of scale to figure out which technology will suit a particular manufacturer. When you have a very high volume, only then will SMT technology prove to be economically viable. Suppose a manufacturer wants to buy SMD capacitors, he will have to buy a roll of 10,000-15,000. But for the through hole process, you can buy as much or as little as you want. So unless a manufacturer has a very high demand for, say, 0.1 or 0.2 million units, it is not viable to go for SMT,” explains G Gururaja, director, operations, Avni Energy Solutions Pvt Ltd. He adds that in assembling the drivers, almost 30-40 per cent of the work is still done via through hole technology.

So, despite the cost and time advantages of SMT manufacturing, there are many LED luminaire manufacturers who are not into volume production and hence are heavily dependent on through hole technology. The trend now is to combine the benefits of through-hole and SMT technologies when manufacturing LEDs.

Through hole manufacturing process

speakersThe main components that go into an LED luminaire are the LED (chip), electronic driver, heat sink, secondary optics and mechanical fixtures.

Through hole LEDs are mounted on a PCB through auto-insertion machines or manually. After assembly, the PCB is put through a wave soldering machine, preheated and touched by a wave of hot solder to create electrical connections. This is the last step in the through hole production process for LED boards. All SMT components (such as driver ICs, resistors, microcontrollers, etc) have to be reflow-soldered before the LEDs are inserted and then sent through the wave soldering process. This significantly complicates the manufacturing process and cycle time, adding to the cost of the final product.

In the through hole process, the components have two leads (which are needle-like) that are inserted in the two holes on the PCB and on reversing the board, the leads are soldered on the PCB with the help of a soldering gun and paste. The extended or extra lead is then manually cut off with the help of a lead cutter. “The through hole soldering process can be adopted in manufacturing a driver, where 60-80 components are used.” informs G Gururaja.

Another manufacturing process uses semi-automatic assembling, in which the components are placed with the help of a reflow soldering machine. This is a commonly used method, as it speeds up the manufacturing process.

Next comes the process of bonding the LEDs with the heat sink. This is also known as housing. (Earlier, these heat sinks used to come as a separate part but currently they come along with the LED/light fixtures.) This is followed by the wiring of the LEDs with the PCB, which completes the assembly process of an LED luminaire.

Through hole components 

Through hole LEDs offer several benefits over SMT LEDs. They are brighter, can be clearer, come tinted or tint-diffused for higher contrast ratios, and have a wide range of different primary optic designs, because of which, through hole LEDs are the best choice in terms of brightness, definition and controlled viewing angles.

The disadvantage of through hole LEDs is that they have power handling limitations of 20 mA to 50 mA. Whereas medium powered SMT LEDs like KLSL2835W and KLSL5630W and high powered 350/700 mA SMT LEDs like KLSL505W , KLHP331W and KLHP3433W can withstand a thermal pad situated right underneath the internal LED chip. This allows efficient coupling of the heat transfer to the MPCB. Informs Vijay Kumar Gupta, “Through hole LEDs are being phased out, as their lead-frame structure is made of iron and does not support heat flow.” These LEDs have a low life of 5000 hours (L50).

Through hole LEDs are, however, widely used in applications like moving sign displays and traffic signals, where their narrow beam properties are handy. Here, the LEDs are not used for illumination but as indicators, and require just enough power to indicate whether the light is on or off.

Electronics Bazaar, South Asia’s No.1 Electronics B2B magazine

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