LED product assembly line: SMT and through-hole turnkey solutions are available

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The future of lighting is with light emitting diodes (LEDs), despite the fact that it is currently an expensive option. If things go well and LED manufacturing gets government encouragement, in the next couple of years, India could witness a tremendous growth in this sector. Numerous enterprises are venturing into this domain—mostly manufacturing LED products and fixtures.

By Srabani Sen

Monday, September 12, 2011:  As manufacturers of LED products face the pressure to drive down costs, they are turning to higher volume automated manufacturing, accompanied by high speed inspection to increase yields and improve the quality of their products. “The main advantage of manufacturing LED based products is that it requires less power and the machines can run on solar energy as well,” says MK Krishnakumar, country manager, Essemtec India.

Presently, neither LED chips are manufactured in India, nor LED packaging is being done in volume. Hence, we will discuss the manufacturing processes of LED lights and the machines used for them.

Manufacturing process

An LED lighting product is a combination of the light fitting, LED, LED lens and LED driver. “Each of these components require a different set of machinery or equipment for manufacturing and testing,” states Kapil Sood, CEO, Fusion Power Systems.

Manufacturing LED products requires flexible and highly accurate machines and specific process knowhow. Manufacturers must have knowledge about these machines and the process knowhow. You can install a production line with the help of different machines from different manufacturers or with a full production line from one company. Many standard machines and customer specific solutions for dispensing, printing, placement, curing and soldering, are available in the market.

As per N Chandramohan, country head, Juki Corporation, depending upon the volumes and budget, an LED product manufacturing line and a complete assembly line can be automatic or manual.

The main steps of manufacturing LED products include probing, sorting of the chips, die bonding, wire bonding, phosphor coating, encapsulation, partial singulation, auto-testing, singulation, binning testing, tape-n-reel or waffle packing.

There are two types of LEDs—through-hole and SMT. LED products consisting of through-hole components can be produced with the help of through-hole machines and those consisting of SMT components require SMT machines.

In mounting and processing through-hole components, through-hole LEDs are mounted on a PCB through auto-insertion machines. After assembly, the PCB is put through a wave soldering machine, preheated and touched by a wave of hot solder to create electrical connections. Any 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.

Special requirements

Electronics for LED products are different from the standard electronics. Often, the electronic circuit for LED products is the final product, in which the substrate serves as a support for the electronic components, and the correct positioning of the LED depends on this factor. Generally, the substrate is made of composite material or is a film type of circuit, which is different from any standard PCB material. As a result, the machines used for manufacturing LED products must be very adaptable. The machines must be able to produce both prototypes and products with high quality.

Machines for LED assembly

An LED assembly line is quite simple. It consists of three steps—screen printing, SMT component mounting using pick and place machines, and reflow. As the process of LED product assembly is the same like any other PCB assembly, any standard SMT machine is suitable for LED product assembly—only the feeder and nozzle have to be changed, based on the different types of LEDs. But companies are now coming up with dedicated mounters for LED product assembly. Samsung, I-pulse, Juki, Essemtec, etc, have started making niche machines for LED lighting products.

There are over 20 major types of LED packages, and each one requires highly customised handling systems in the machines. Even when packages are similar, frequent changeovers are not recommended as the rejection rates could go up by 5 to 10 per cent leading to non-viable operations. Yet, one cannot have an automatic line for every type of LED. One has to decide and focus on a few package types, try to control cost and get into mass production to effectively compete in the market. One can go for a semi-automatic line and later scale up with auto lines.

Screen printing: Every manufacturer gets stencils designed for solder paste printing on the PCB pads. Stencil is a metal on which cutting is done as per PCB CAD data. The stencil is loaded in the manual printer; the bare PCB is then kept below the stencil, over which the stencil solder paste is applied. The operator uses a tool to paste the solder above the stencil and PCB pads get printed with the solder.

Most stencil printers align the substrate and the stencil with a vision system interposed between them. An alternative technology is the look-through method in which a camera is placed above the stencil that ‘looks through’ the substrate. This is the preferred technology used by stencil printers for small to mid-sized series production because it is simple, fast and reliable.

Component mounting: A pick and place machine mounts SMT components on the PCB. LEDs come in reel form, which are fed into the feeder—an accessory loaded on the machine. The program is set according to coordinates, that is, X-axis and Y-axis, head number, angle, etc. The machine head automatically picks LEDs from the feeder and places them on the given coordinates.

An LED pick and place machine must be able to place LEDs of different sizes, shapes, transparencies and with different connection layouts. The correct positioning and alignment of the LED in the circuit is a key quality feature for an LED product. Printing and placement are the two processes of LED positioning. SMT machines like stencil printers and pick and place machines are used for positioning.

Standard SMT mounters with longer lengths and specialised nozzles are used for mounting. “In the mounting process, handling the LED is critical. The vacuum tools must be able to hold the component firmly but must not damage lenses or surfaces. The nozzle design and its customisation is also important. Care should be taken to avoid damaging the lens during the pick and place process,” informs Chandramohan.

A teflon coating on the tool tips is suitable for handling most types of LEDs. However, for odd shaped LEDs, product specific tools often must be designed and manufactured.

Reflow soldering or curing: This is done through a reflow oven, which does the soldering. According to the solder paste melting point, the heating profile is generated in the reflow oven that melts the solder paste. The cooler then dries the solder paste and, finally, the LED legs are permanently fixed on the pad.

During reflow soldering, the temperature should be controlled carefully to ensure the safety of LED components. This process is basically limited to the assembly of the LED through printed wiring boards.

There are several techniques to connect LEDs, either using solders or conductive adhesives. The latter is mostly used on foil type substrates that cannot withstand high temperatures of soldering. An adhesive is typically chosen as per a specific application, and in some cases even developed especially for it. Some adhesives are cured by temperature, while others are cured by UV or even IR radiation.

In some applications, the LED is fixed with a non-conductive glue dot. This guarantees that LEDs do not shift when handling the substrates or during the reflow soldering process. The application of such glue dots requires precise control of the position and the amount used because the non-conductive glue must not cover any contact area, while still holding the LED firmly in place.

Research work needed

Indepth research is essential before purchasing a machine for an LED production line. Machines should be selected as per the manufacturing capacity planned for and other specific requirements. It is also important to have a good understanding of LED chip types, their brightness levels, wafer uniformities, etc. One should also have information about how a chip’s characteristics are influenced during the curing and wire binding processes, the effect of the encapsulant characteristics on the stress in the bonding wire, the encapsulant limitations for high temperature process steps, ESD characteristics, etc, before selecting a machine. A small manual line can be helpful during the R&D and learning phase.

“We have visited a number of exhibitions, undertaken several foreign trips, done a lot of online surfing and read several company brochures and other material to do a comparative study before investing in a costly production line,” adds Kapil Sood.

Cost of implementation and maintenance

A fully automatic production line is quite expensive. A manual or semi-automatic LED production line is, therefore, suggested to start off initially. “A manual or semi-automatic LED production line of 500 kpcs costs Rs 10-20 million (Rs 1 to 2 crore), while a partly automatic line costs Rs 50 million (Rs 5 crore).

The AMC for these machines can be 10-15 per cent of the machine’s cost depending on the vendor. However, self maintenance is possible if the vendor has a prompt spare shipping service. Two machines for each critical operation are recommended for manufacturers who do not wish to make their customers wait during breakdowns.

Maintenance required

Usually, these machines are made in a modular form and can easily be repaired. Periodical cleaning, oiling and greasing of the mechanical parts are essential. By replacing ageing parts as per the machine’s manual, one can enhance the machine’s life.

Companies usually conduct preventive maintenance checks three times a year, by factory trained engineers. For manual printers and reflow machines, less maintenance is required because they have no moving parts except the conveyor. But for pick and place machines, only trained engineers should do the maintenance.

For all machines—through-hole or SMT, it is recommended that the manufacturer does the maintenance, while the operator can do the basic cleaning and greasing.

After sales services

Usually, after sales service is provided by the manufacturer. Imported machinery is serviced by authorised distributors in India. Moreover, large vendors have excellent service and well developed guides. They support the customers for their production requirements, and train their inhouse operators and engineers to do the job themselves.

SMT machines for LED product assembly: what’s new in the market

Samsung: Samsung has introduced a dedicated high speed LED mounter—SLM100 series—which the company claims to be the world’s first LED mounter, capable of realising simultaneous pickup with one feeder. It is specifically designed for LED manufacturing. Its motorised feeder can pick up five parts simultaneously. The machine can be used to effectively increase speed, efficiency and throughput by featuring an adaptive head design. “This innovative feature enables it to simultaneously pick multiple LEDs from a single feeder, regardless of the size of the LEDs or tape pocket pitch. It is proficient at placing LED packages from one single feeder in excess of 43,000 CPH (optimum speed) on PCBs up to 1200 mm in length.” says Pradeep Tandon, country manager, Samsung.

The machine allows placement of two PCBs simultaneously, depending on the PCB’s size, maximising productivity. Its ‘flip over check function’ automatically checks for flip over and the incorrect insertion of LEDs through the vision system, preventing defective placement, in advance.

Juki: Juki offers pick and place machines JX-100LED, KE-2070L and FX-3. The minimum machine speed starts from 15,300 CPH and goes up to 60,000 CPH IPC 9850. The company’s 3D laser centring technology accurately measures the outline dimension of the LED and constantly detects the LEDs till placement. The pick up of LED from the feeder via HMS (height measurement system) is very accurate. These machines allow the production of long PCBs with length up to 800 mm (31.5 inch). The nozzles can be selected depending on the size of the LED. These machines are also suitable for LED strip lighting. A USP of the machines is the lighting unit for solder recognition, which is useful for BOC (PCB offset correction) recognition for the metal PCB (MC PCB) to overcome fiducial mark recognition error. Juki has also designed various customised nozzles for odd shaped LEDs.

“The LED lighting business is based on volumes, where quality, fast production, and a zero per cent production loss ratio are important for manufacturing. Juki has designed various models to meet the industry’s differing capacity and budgetary needs,” informs Chandramohan.

Essemtec: Essemtec’s Pantera-XV placement machine includes multiple alignment systems. This machine is capable of accurately placing any kind of LED. This pick and place system even features a PCB holder that is adaptable to any shape and has an exchangeable vacuum table for foils.

Essemtec’s CDS series is a specialised dispensing machine suitable for glue dot dispensing. Pantera-XV also includes a dispensing system.

A special process, known as selective radiation soldering, is under development, to solder LEDs onto PET or Mylar foils using low temperature solders. The timeframe for its availability will be published later. Essemtec is developing this process and a soldering machine in collaboration with a membrane keyboard manufacturer. The principle is that IR radiation is absorbed only by the solder joint and not by the foil. The substrate foil must be transparent for the chosen IR wavelength and does not heat up—only the solder joints do.

Essemtec has also introduced the CLM979 radial component feeder that enables the assembly of through-hole LEDs on a standard pick and place machine. The feeder releases LEDs from the tape, cuts the wire ends and prepares the component for pickup.

Leaptech: It offers specialised LED placement systems from I-PULSE Japan. It offers three different models, specifically for LED placement. These are model M10, with a speed of up to 30,000 CPH that can handle PCB sizes up to 740 x 510 mm. Its model M20 has a speed of up to 30,000 CPH and can allow production of long PCBs of up to 1240 x 510 mm. Its model M7 has a speed of up to 65,000 CPH and is suitable for PCB sizes of up to 1290 x 510 mm. “What is more important in a LED placement system is the large board handling capability and higher throughput, which is exactly what the above models offer,” says Suresh Nair, director, sales and marketing, Leaptech Corporation.

Nmtronics: The pick and place process in mounters can be customised in order to achieve the right mix of flexibility and speed. NMTronics’s Fuji NXTII is a good example of flexibility. Its placement head can be changed to suit different LED production requirements. The machine can handle LEDs of any size. “Fuji NXTII also exhibits true scalability. The machine can be reconfigured at the manufacturing site for changing requirements. For example, if we need to limit the capacity, we can add only one or two modules to suit the requirement,” explains SP Arora, senior business manager, NMTronics India Pvt Ltd. A quick changeover is also possible in Fuji NXTII. It can perform a changeover while the machine is running.

Advance Tech: Advance Tech offers Dima’s modular full vision pick and place machine, which is a modular system built for growth. It has standalone or inline 4500, 6000, 12000 CPH placement, combined with flexibility and intelligent feeder where programing is done in the feeder itself. Offline programing helps to changeover easily without engaging the machine during the programing, and optimisation helps quick change from one type to the other type of products. In the basic configuration, MP-200 has two placement heads, one component camera—high speed fiducial camera. Up to 120 feeders can be mounted (8/12 mm) for inline and 132 for offline operation. This machine can handle all SMD components, even 0201sized chips. “This machine beats all competitors on price and performance, placement accuracy +/- 50µm at 3 ∑ with 1 µm encoder. PTH LED (cut and place) can also be placed using a special feeder in the same machine. The machine can also take care of the special LEDs with silicon lens. Vision system has much higher capability to do precision job and, hence, more throughput (PPM) in production,” explains Ajay Gupta, director, Advance Tech.

Through-hole machines for LED product assembly

Ajin Systems: Through-hole machines are also widely used for LEDs used for outdoor applications. Ajin Systems Pvt Ltd offers Universal’s servo driven Radial 8 sequencer/inserter, which features positive axis control, high speed positioning, a menu driven graphical user interface, and a new VME control system. De­signed to provide the lowest cost per insertion and highest throughput per square metre, Radial 8 offers greater accuracy and more reliability than any previous radial inserter. It has insertion speed of up to 15,600 components per hour (0.23 sec/ins). It allows loading and unloading of PCBs without slowing or interrupting production.

Universal’s Radial 5 product line offers high reliability, throughput and ability to insert radially-taped odd form components. Its insertion speed is consistent, regardless of component type, size or lead span.

Machines for manufacturing LED light fittings

  • NC machines/lathe machines/traub machines: To match metal parts
  • Injection moulding machines: For moulding of plastic and metal parts
  • Drill machines: For various drilling jobs
  • Welding machines: For welding of metal parts including spot welding
  • Powder coating machines: For powder coating and the final finishing of metal parts
  • An anodising plant: For an anodised finish of the metal part

Testing equipment for LEDs

  • An LED optical spectrum analyser and sorting machine: It is the most versatile and economic equipment for testing LEDs. It can test and sort according to forward voltage, luminous flux, wavelength, X/Y coordinates, colour temperature and angle of the LED

Electronic component testing equipment

  • Digital multimeter: It is used for testing basic electronic components such as resistors, capacitors, diodes and transistors

Equipment for assembly

  • Reflow soldering machines: For soldering LED and electronic components with PCBs
  • Temperature controlled hand soldering machines: For soldering of electronic components, wires, etc

(Source: Fusion Power Systems)

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

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