LED forms of packaging structureon January 10th, 2012 at 2:34 AM
The current global LED capacity breakthroughs happen quite obvious, including Taiwan, Japan, South Korea and China have a certain degree of production capacity and technology promotion. Take China for example, planning industry goal is an annual output of 30000000000 LED, at the same time, hope to have super high brightness AiGslnP LED wafer, LED grain, except for the lower order of red LED, also plans to GaN material consisting mainly of blue light, white light LED products production. While the Japanese high brightness white, three-color LED, RGB backlight LED have better ink, the city occupying rate is also high.
If we observe the LED industry supply chain, the upstream LED substrate chip and substrate production, the middle is the LED grain design and production, the downstream LED packaging and testing, but with industry booming development, middle and lower reaches of the integrated approach is obvious, such as Japan and Asia, middle and lower reaches is included, and the Taiwan manufacturer is a divided into upstream and downstream portion of the upstream, middle to absorb.
In general, discrete components of the grain are sealed in a package body, encapsulation protects grain and completes the electrical interconnect. While the LED package is complete the output signal, protect the grain work, output: visible light function, both the electrical parameters, the light design parameters and technical requirements, not simply be discrete device packaging for LED. The core of LED light emitting portion is composed of a p type and N type semiconductor constituting the PN crystalline grain, when injected into the PN nodes of the minority and majority carrier compound, emit visible light, ultraviolet light or near infrared light. But the PN junction region emitted photons is non-directional, i.e. each direction emission have the same probability, therefore, not grain to produce all light can be released, it mainly depends on the quality of the semiconductor material, grain structure and shape, internal structure and encapsulation encapsulation materials, application requirements and improve LED inside, external quantum efficiency. Conventional than 5mm type LED package is the side length 0.25mm square grain bonding or sintered in the lead frame, the grain anode by spherical point of contact with the wire, bonding to inner lead and a pin connected, through a reflective cup and cathode lead frame pins connected to another, then the top with epoxy resin coating letter.
The reflective cup used to collect the grain side, the interface of light, to the expectation direction angle of emission. Top encapsulation epoxy resin into a certain shape, there are several functions: protection of grain is not affected by external erosion; using different shapes and material properties ( with or without adding bulk toner ), since the lens or a diffusing lens function, control the angle of divergence of the light; crystal refractive index and refractive index of air is too big, the grain total internal reflection critical angle is small, the active layer to produce light a small portion removed, most easily in grains by multiple reflection and absorption, easy to produce total reflection lead to excessive loss of light, the choice of the corresponding index of epoxy resin for the transition, improve the grain of the light emitting efficiency. Used as a form of shell and tube epoxy resin having moisture resistance, insulation, mechanical strength, on grain light refractive index and high transmittance. Select a different index of refraction package materials, package geometry on the photon release efficiency effect is different, the angle distribution of luminous intensity and grain structure, light output, package lens materials used and the shape. If using a resin lens, the light is focused onto the LED axis direction, the corresponding angle is smaller; if the top of the resin lens is round or flat type, the corresponding angle will increase. In general, the LED light emitting wavelength with temperature change for the 0.2-0.3nm / C, spectral width increases, affect the color brightness.
In addition, when the current flows through the PN node, the node area heating loss temperature rise, at near room temperature, temperature rise of 1 C, LED luminous intensity will be reduced about 1%, package heat sink; maintain the color purity and luminous intensity is very important, this paper reduces the drive current approaches, reduce junction temperature, the majority of LED drive current limit is about 20mA. However, LED light output varies with the current increasing, at present, a lot of power LED driving current can reach 70mA, 100mA or even 1A level, need to improve the packaging structure, the new LED package design and low thermal resistance encapsulation structure and technology, improved thermal characteristics. For example, a large area grain flip structure, selection of good thermal conductivity of silver colloid, increase the metal stent surface area, solder bumps in the silicon carrier mounted directly on the heat sink for method. In addition, in the application design, PCB board, thermal design, thermal conductivity is also very important. Enter after twenty-first Century, LED high efficiency, high brightness, full color change ceaseless development innovation, red, orange LED tube light effect has reached 100Im / W to 501m / W, green LED, single LED flux can reach tens of Im.
LED grain and package no longer along the Gong Chuantong design concept and mode of production, an increase in grain light output, R & D is not limited to change material within the amount of impurities, lattice defects and dislocation to improve internal efficiency, at the same time, how to improve the grain and package internal structure, enhanced LED internally generated photons from a chance, improve photosynthetic efficiency, to solve the heat, and light and heat sink optimization design, improved optical performance, accelerate the surface adhesion of SMD process is the industry mainstream direction.
Product packaging structure types since the ninety’s of last century, LED grain and materials technology R & D made a number of breakthroughs, transparent substrate trapezoidal structure, texture surface structure, grain flip structure, commercial super high brightness (above 1CD ) red, orange, yellow, green, blue LED products have asked the city,, 2000 beginning in the lower, the light flux of special lighting applications. LED, industry of the middle reaches on by hitherto unknown value, further downstream of the packaging technology and industrial development, with different packaging structure forms and sizes, different light emitting colors and color, grain or trichromatic combination, can produce a variety of series, varieties, specifications of the products.
LED product packaging structure types, but also in accordance with the luminous color, grain material, luminance, size, feature classification. Single grain generally consists of point light source, a plurality of grain assembly generally be a surface light source and a linear light source, as indicative of the state information, and display, light emitting display is also used more grain by grain, the appropriate connections ( both series and parallel) with suitable optical structure which is formed by the combination of forming a light emitting display, luminous segment and a luminous point. Surface mount LED may gradually replace the pin type LED, application design more flexible, have shown in the LED market occupies a certain share, have accelerated development trend.
Solid light source are part of the product will be listed, in LED, long-term development direction. Pin type package LED foot type packages using the lead frame for a variety of packaging appearance of the pin, was the first to successfully launch package structure, breed is numerous, technical maturity is high, inside the package structure and the reflecting layer is still in continuous improvement. Standard LED was most customers think is currently displaying industry in the most convenient, the most economic solution, typical of traditional LED placement in withstanding 0.1W input power envelope, the 90% heat is produced by the negative pin rack emit to the PCB board, and then released into the air, how to reduce the work PN junction temperature rise is encapsulated and application must be considered. Encapsulation material used in high temperature curing epoxy resin, its optical performance, good technological adaptability, reliability is high, can be made of colored transparent or colorless and transparent colored or colorless scattering scattering lens package, different lens shapes to form various shapes and dimensions, for example, according to the diameter of circular divided than 2mm, diameter 3mm, DIA 4.4mm, a 5mm, a 7mm and several kinds of epoxy resin, the different components can produce different luminous effect.
Color point light source has a variety of different packaging structures: the ceramic base epoxy resin has good temperature performance, the pin can be bent into a desired shape, small size; metal base plastic reflecting cover package is a kind of energy-saving lamp, suitable for power indication; flashing CMOS oscillation circuit and LED grain grain composite package, can generate strong visual impact of flashing light; two-color type by two different light emitting colors consists of grains, are encapsulated in the same epoxy resin lenses, except for two color can also obtain third mixed color, in the large screen display system is widely used, and can be composed of two color packaging display device; voltage will be constant current source grain and LED grain combination package, can be directly replaced the 5 – 24V all kinds of voltage indicator lamp. Surface light source is a LED grain bonding in miniature PCB board on the defined position, using reflective plastic box cover and potting epoxy resin to form, PCB plates of different design to determine the outer leads are arranged and connected, a dip with single inline structure. Point, surface light source has developed hundreds of kinds of package shape and size, suitable for the market and customer.
LED light emitting display by the digital tube or pipe, tube, the word symbol matrix tube composed of a variety of many products, from the actual needs of the design into a variety of shapes and structures. Digital tube as an example, a reflection type, integrated type, a seven section three kinds of packaging structure, connections are common anode and cathode two, a bit is usually said that digital tube, two or more generally referred to as display. Reflection type with large fonts, material saving, flexible assembly of hybrid packaging features, usually with white plastic made with reflective cavity seven shaped shell, a single LED grain bonding with reflective cover seven reflection cavity and mutually aligned PCB panels, each reflecting cavity at the central position of the bottom is the grain formation of luminescent District, in bonding method of bonding wire, the reflecting hood drop in epoxy resin, and stick good grain PCB board aligning bonding, and then curing the is.
Reflection type is divided into air sealing and closure in two, the former uses scattering agent and dye epoxy resin, used for the unit, a device; the latter cover color and uniform optical film, and in the grain and the bottom plate coated with transparent plastic insulation, improve the output efficiency of light, generally used for more than four digital display. Monolithic integrated in the luminescent material is produced on the chip to a seven digital display graph grain, and then dicing is segmented into single graph grain, bonding, bonding, packaging with lens ( commonly known as the fisheye lens ) shell. A seven section will have good production of large area LED grain, cut into contain a or a plurality of grain luminous strip, so the same seven bond in the digital orthographic Kovar frame, by pressure welding, epoxy resin package. Monolithic, one type is characterized by miniaturization, can adopt a dual-in-line package, mostly is the special product.
LED bargraph displays in the 106mm length of the circuit board, the placement of 101 grain (up to 201 grains ), belongs to the high density packaging, using the optical refraction principle, make the point light source through the transparent shell 13-15 raster imaging, complete each grain from a point to a line of the display, packaging technology complex. Semiconductor pn junction electroluminescent mechanism of LED can not produce a continuous spectrum of white light, at the same time, a single LED is not likely to have more than two kinds of high intensity monochromatic light, one can in a package with a fluorescent material, blue or ultraviolet LED grains coated with fluorescent powder, indirect broadband spectral synthesis, or white; the use of several ( two or three, multiple ) with different colour grain is encapsulated in a module casing, through light consists of a mix of white light LED. The two methods have practical, Japan in 2000 the production of white LED amounts to 100000000, developed into a kind of stable white light products, and a plurality of white LED design assembly paired luminous flux requirements is not high, mainly to local decorative effect, the pursuit of trendy electric light source.
Surface mount package in 2002, surface mount package LED ( SMD LED ) have been gradually accepted by the market, and a certain market share, from the pin type package to SMD the entire electronics industry development trend, many manufacturers to introduce such products. Early SMD LED mostly with transparent plastic body SOT-23 improved, dimensions 3.04 x 1.11mm, reel-to-reel tape packaging container. Based on SOT-23, developed with lens of high brightness SMD SLM-125 series, SLM-245 series LED, the former is a monochromatic light emitting, the latter for the double color or rgb. In recent years, SMD LED become a hot topic for the development, very good solution to the brightness, perspective, smoothness, reliability, consistency, using lighter PCB plate and a reflection layer material in the reflective layer, display needs filled epoxy resin is less, and the removal of the heavier carbon steel pin, by reducing the size, reduce weight, be easily product weight reduced by half, finally make the application more perfect, especially suitable for indoor, outdoor full-color display application. Table 3 shows the common SMD LED several dimensions, and according to the size ( with the necessary clearance ) calculated from the optimal viewing distance. The pad is the important channels for dissipation, manufacturers to provide SMD LED data are based on a 4 x 4.0mm pads as the foundation, use the reflow soldering can be designed into the pads and pins.
Ultra high brightness LED products can be used PLCC ( plastic leaded chip carrier package ) – 2, dimensions of 3 x 2.8mm, through a unique method of assembling high brightness grain, the thermal resistance of 400K / W, press CECC welding, the intensity in the 50mA drive current to 1250mcd. Seven section type A, two, three and four digital SMD LED display character height is 5.08-12.7mm, display size wide selection scope. The PLCC package avoids pin seven digital display required manual insertion and alignment pin process, in accordance with the automatic pickup – mount equipment production requirements, design flexible, bright display clear. Multicolor PLCC package with an external reflector, simple and luminous tube or optical combination, with reflective alternative current transmission type optical design, for a wide range of areas to provide uniform illumination, development in 3.5V, 1A driving work under the conditions of the power type SMD LED package. Power type LED packaging grain and package to high-power direction, under large current generated than a 5mmLED 10-20 times the luminous flux, must adopt the effective heat dissipation and without deterioration in the encapsulation material attenuation problem solve, therefore, the tube shell and packaging is one of the key technology, can bear a number W power LED package has appear to. 5W series of white, green, blue and green, blue power type LED from the beginning of 2003 supply, white LED light output of 1871m, 44.31m / W green light efficiency decline, developed under 10W LED power, large area tube; the time dimension of 2.5 x 2.5mm, in 5A current work, light the output of the 2001m, as a solid light source have great development space.
Luxeon series power LED is A1GalnN power type flip flip chip bonding in grain with solder bump on the silicon carrier, and the complete flip chip bonding silicon carrier mounted heat sink and the tube shell, the bonding wire package. This package for light extraction efficiency, heat transfer performance, increase working current density design is best. Its main features: low thermal resistance, generally only 14 C / W, a conventional LED 1 / 10; high reliability, internal packaging filling stable flexible gel, in 40-120 DEG C, not due to temperature change stress produced, the wire and lead frame is disconnected, and prevent the epoxy resin lens yellowing, the lead frame also won’t because