LED production & assembly lines: Start with semi-automatic & scale up to auto lines

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The future of lighting rests on light emitting diodes (LEDs), says the industry, despite the fact that presently it is an expensive option. If things go right and LED manufacturing gets government encouragement, in the next couple of years, India can witness a tremendous growth in this segment. Numerous enterprises are venturing into this domain—mostly manufacturing LED products and fixtures. India is slowly moving into the production stage, aiming at lower cost and maximised yields.

By Srabani Sen and Sandhya Malhotra

Wednesday, March 24, 2010: 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. “As the market for LED is huge and their application being so many, this sector has a strong future in the coming years. The main advantage of manufacturing LED based products is that it requires less power consumption and the products can run on solar energy as well,” says M K Krishnakumar, country manager, Essemtec India. Essemtec’s production systems are used for manufacturing and assembly of LEDs.

According to N Chandramohan, country head, Juki Corporation, depending upon the volumes and budget, an LED production line and a complete assembly line can be made 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,” says K Vijay Kumar Gupta, managing director, Kwality Photonics Pvt Ltd, the manufacturer of power LEDs ‘PolyWa’ for lighting applications, etc. It is also in the LEDs packaging business. “This is a backend process as compared to semiconductor wafer processing/epilayer growing and chip fabrication,” adds Gupta.

There are two types of LED based products being manufactured—through hole and SMT. Through hole LED based products are produced by a slow manual process, whereas SMT LED based products are produced through automatic production line.

“In mounting processes, handling LED is critical. The nozzle design and its customisation is also important. Care should be taken to avoid the damage of the lens during the pick and place process,” informs Chandramohan. During reflow soldering, temperature should be controlled carefully to ensure the safety of LED components. This process is basically limited to the assembly of LED through printed wiring boards (PWB). Machines available for mounting are standard SMT mounters with longer lengths and specialised nozzles.

An LED based lighting product is the combination of light fitting, LED, LED lens and LED driver. “Each of these components require a different set of machinery or equipment for manufacturing and testing,” says Kapil Sood, managing director, Amptek. Amptek is setting up an LED based product facility in Uttarakhand to manufacture LED based light fittings, etc. “These facilities use a combination of imported and Indian machines. We did an extensive research before purchasing them,” says Sood. The company manufactures general LED based lighting, ceiling lighting, display lighting, accent lighting, garden lighting, under cabinet lighting, spot lighting, fountain lighting, swimming pool lighting, etc.

Research work needed

According to Gupta, in-depth research is essential before purchasing a machine for LED production line. “It’s very important to have a good understanding of LED chip types, their brightness levels, wafer uniformities, etc. One should also have knowledge about how a chip’s characteristics are influenced during curing and wire binding processes, the effect of 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 R&D and learning phase,” he says. “We have visited a number of exhibitions, undertook several foreign trips, did massive online surfing and read several company brochures and other materials to do a comparative study before investing in the costly production line,” adds Sood.

There are over 20 major types of LED packages, and each one requires highly customised handling system in the machines. Even if 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 few package types and try to control cost and do mass production to withstand the competition from global players. One can go for semi-automatic horizontal and vertical leadframe bonders with flexible encap dispenser and curing systems and later scale up with auto lines,” suggests Gupta.

Cost of implementation and maintenance

Fully-automatic production line of LED is quite expensive. A manual or semi-automatic LED production line is therefore suggested for manufacturing initially. “A manual or semi-automatic LED production line of 500 kpcs costs Rs 1 to 2 crore, while a partly automatic line costs Rs 5 crore. Fully-automatic line is not available for many new packages,” says Gupta.

After sales maintenance contract (AMC) of these machines can be 10-15 per cent of the machine 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 is recommended for manufacturers who don’t wish to make their customers wait due to breakdowns,” says Gupta. “By investing Rs 10 to 50 crore, one can have a wide range of LED based products in the product portfolio,” he adds.

Chandramohan is of the opinion that investment is based solely on quantities which need to be produced and the automation level desired.

Maintenance required

Usually, these machines are made in modular form and can easily be repaired. Single sub-assembly, especially in circuit boards, can work at multiple places with small changes in jumper settings. Periodical cleaning, oiling and greasing of the mechanical parts are essential. By replacing ageing parts as per the machinery manual, one can enhance the machine’s life.

Juki provides preventive maintenance three times a year for its pick and place machines by factory trained engineers, who change air filters and do greasing, etc. For manual printer and reflow machines, less maintenance is required because they have no moving parts except the conveyor. “For pick and place machine, only trained engineer is allowed to do the maintenance. The company can only do routine maintenance in-house before starting production. For reflow machine also, only the manufacturer is authorised to do the maintenance, but the operator can do basic maintenance,” points out Chandramohan.

After sales services

Usually, after sales service is provided by the manufacturer. Imported machinery is serviced by the authorised distributors in India. Moreover, big vendors have excellent service and well developed guidelines. However, says Gupta, “It is generally observed that local support engineers are not always helpful as they are familiar with only few types of machinery and sometimes cannot even handle the changed version of the same machine.”

“We directly support our customers for their production requirement and train their in-house operators and engineers to do the job themselves,” says Krishnakumar.

“We are one of the leading manufacturers of SMT machines. As we operate directly in India, the major advantages for our customers are the best price and services we offer, which is very important in any capital equipment,” he adds.

Tips for setting up production line

There is always a learning curve in every business before one hits a viable production system. “India needs many more LED packaging companies. Kwality would like to support a local bonder manufacturer who could help SSI units to produce low cost LEDs profitably and create large scale employment,” says Gupta.

“My advice for those who are planning an SMT line for LED based PCB cards is to go for manual screen printer as there is no accuracy required. Go for reliable and high throughput pick and placer, conveyorised with Surface Mount Equipment Manufacturer Association (SEMA) compatibility, which can work for 24 hours a day to produce big volumes. Depending upon volumes, one can choose either 3 zone table top reflow machine, 5 zone reflow or 7 zone, either locally manufactured or from imported brands. One should note that LED based PCB cards’ changeover time is zero. I would also like to point out that some manufacturers use glue dispensing machine after solder paste printing to glue loctite in between two solder pads. However, use of glue is not compulsory, but it depends upon the application. Users must be sure that the equipment must fulfill the process requirements. Verifying a machine’s performance beforehand is the key,” concludes Chandramohan.

Basic theory of LED operation

LED manufacturing process is divided into three stages—epitaxy or epiwafer (upstream/frontend process), chip producing (midstream/chip fabrication process) and packaging downstream/backend. The frontend is preceded by inputs from the substrate manufacturer producing sapphire and silicon carbide substrates.

LED chip manufacturing process: In the frontend stage, producers use single chips as substrates for epitaxy and then employ different epitaxies (such as LPE, MOCVD and MBE) to foster multi-layer and polynary thin film materials with different thicknesses. In chip fabrication, according to the demand of LED structural components, producers first perform evaporation and then make metal electrodes on both the terminals of LED through photolithographic and heat treatment on EPI wafers and then cut them into LED dices after wearing down substrates and polishing them.

LED package manufacturing process: In packaging, producers impart user friendly leadframe, protective and optical encapsulation to LED chips to produce LEDs in the form familiar to users. The high power LEDs have a third connection (metal slug under the LED chip) to evacuate heat.

Source: Kwality Photonics

Machines for LED manufacturing

Die Bonders: Die attach machines or die bonders are used to mount or attach the die to the die pad or die cavity of the support structure of the package. A typical die attach machine consists of a system for holding and indexing the lead frames or packages on which the dice will be mounted, a system for dispensing the die attach material on the die pad or die cavity, and a pick and place system for ejecting a die from the wafer, picking it and positioning it on the dispensed die attach material. Examples of manufacturers of die bonders: Alphasem, ESEC and K&S.

For the laser diode attachment on the sub mount of various active photonic packages, high precision die bonders with a placement accuracy of 5 microns or better are suitable. “To keep pace with the high growth photonic market, we have fully automated flip chip bonders (ESEC micron 2) with high throughput, high accuracy and high flexibility to suit high volume production demand,” says Vijay Kumar Gupta, managing director, Kwality Photonics.

Dispensing: The dispensing machine delivers controlled quantities of epoxy or phosphor or conductive paste in repeatable and accurate manner. They are also associated with robot arm or XYZ gantry.

Encapsulation: Molding is the process of encapsulating the device in plastic material. Transfer molding is one of the most widely used molding processes in the semiconductor industry because of its capability to mold small parts with complex features. In this process, the molding compound is first preheated prior to its loading into the molding chamber. After pre-heating, the molding compound is forced by a hydraulic plunger into the pot where it reaches melting temperature and becomes fluid. The plunger then continues to force the fluid molding compound into the runners of the mold chase. These runners serve as canals where the fluid molding compound travels until it reaches the cavities, which contain the lead frames for encapsulation.

Leadframe Cutting: The leadframes are horizontally stacked holders/ headers for the LED chips, so that 20 to 100 devices are handled at a time in each machine, instead of them being fed in individually. For testing, few shorts/legs are opened in a press punch, to enable tests to be performed on all devices in one shot.

Singulation Machine: The final operation in making the LED is to put the partially separated strips of LEDs into a high speed automated tester. Singulation machine separates individual LEDs fully using tool dies. Up to nine different bins, combinations of colour and intensity can be used. All LEDs are sorted by intensity, and yellow (and sometimes green) LEDs by emitted colour or hue.

Wire Bonding: Wire bond machines or wire bonders are used to connect electrically the die of the device to the leads of the package using very fine wires. A typical wire bonder consists of a system for holding and indexing the lead frames or packages for wire bonding, a system for ensuring that the units are at the right temperature during wire bonding, and a system for connecting the wires from the die to the bonding fingers of the lead frame or bonding posts of the package. Examples of manufacturers of wire bonders: ESEC, ASM, Kaijo and K&S.

Machines for LED assembly

LED assembly line is quite simple. It consists of three steps—screen printing, SMT component mounting using pick and place and reflow.

Manual screen printer: Every manufacturer gets stencil designed for solder paste printing on the PCB pads. This is loaded in manual printer, bare board PCB is then kept below the stencil and above the stencil solder paste is applied. The operator uses a tool to paste solder above the stencil and PCB pads get printed with solder.

Pick and place machine: This mounts LED on PCB. LED comes in reel form, which is feeded in the feeder. Feeder is an accessory of pick and place. The feeder is then loaded on the machine. Program is set according to coordinates, that is, X-axis, Y-axis, head No., angle, etc. Machine head will automatically pick LED from the feeder and place on the given coordinates.

Reflow oven: This machines does the soldering. According to solder paste melting point, heating profile is generated in the reflow oven and melts the solder paste. The cooler then dries the solder paste and finally LED legs will permanently get fixed on the pad.

“Juki has modified its existing machines—JX 100, KE 2070 and FX 2—to suit LED manufacturing. The selection depends on the speed of production required,” informs N Chandramohan, country head, JUKI Corporation.

LED assembly process

  • Dispensing of conductive glue
  • Dispensing of adhesives
  • Placement of LED (SMD or through hole) onto PCB, foils and other materials
  • Soldering or curing of LED connections
  • Manufacturing of complete keyboards with LED and keys (metal domes)
  • Machines for manufacturing LED light fittings
  • NC machine/ lathe machine/traub machine: For matching of metal parts
  • Injection moulding machine: For moulding of plastic and metal parts

Drill machine: For various drilling jobs

  • Welding machine: For welding of metal parts including spot welding
  • Powder coating machine: For powder coating and final finish of metal parts
  • Anodising plant: For anodised finish of the metal part

Testing equipment for LED

LED optical spectrum analyser and sorting machine: It is the most versatile and economic equipment for testing LED. It can test and sort out 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 machine: For soldering LED and electronic components with PCB
  • Temperature controlled hand soldering machine: For soldering of electronic components, wires, etc

Source: Amptek

Machines for manufacturing LED chip

  • Crystal growth
  • Wafer preparation and shaping
  • Chemical cleaning
  • Thermal oxidation
  • Photolithography
  • Chemical etching (wet and dry)
  • Chemical vapour deposition tech niques
  • Thermal diffusion
  • Ion implantation
  • Metalisation
  • Chemical mechanical polishing
  • Rapid thermal processing

Source: Kwality Photonics

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