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Guide to LED Application-Welding Operation
1, LED welding principle
1. 1, high-power LED welding mainly includes pin welding and copper substrate welding, and pin welding solves the problem of LED conduction.
The problem of channel, the bottom welding of copper base solves the problem of LED cooling channel.
1.2, LED is an electronic component that converts electric energy into light energy and heat energy, so it can work only when normal current and voltage are applied.
The anode and cathode of the chip are connected to the support pins through gold wires, so the pins must be properly soldered to the aluminum substrate.
1.3, high-power LED will generate a lot of heat after lighting. If the heat is not conducted to the outside in time, a PN junction will appear inside the LED.
The temperature will continue to rise, and the light output will decrease, which will lead to the LED light decay too fast and eventually die. The heat generated by the chip accounts for about 90%
They are all conducted through the copper base, so it is necessary to weld the copper base of LED.
2, LED welding method and matters needing attention
2. 1, high-power LED welding mainly includes manual soldering iron and reflow soldering (attached figure 1-2), and manual soldering iron is suitable for
For all types of LEDs, reflow soldering is only suitable for flip-chip packaged LEDs, and LEDs packaged in lenses cannot be reflowed because
The temperature resistance limit of PC lens is only about 120℃.
Figure 1 electric soldering iron Figure 2 Reflux furnace
2.2, manual soldering iron welding
2.2. 1, manual soldering iron is to melt tin with soldering iron at high temperature, and weld the lead and the aluminum substrate pad together. At the same time, on the LED,
Welding method of coating thermal conductive silicone grease between copper-based bottom and aluminum-based base.
2.2.2 For manual welding with soldering iron, it is recommended that the welding temperature should not exceed 350℃ regardless of whether there is lead-tin wire or lead-free tin wire.
The connection time is controlled in 3-5 S, otherwise the high temperature of the soldering iron will damage the PN junction of the chip.
2.2.3, soldering iron welding process, must standardize the operation, in order to avoid the welding head will die at the top of the colloid or bracket burns, affect the work.
The normal use of LED, in order to avoid live welding LED, electric soldering iron must be grounded.
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Haotian photoelectricity-value is everywhere
2.2.4. In order to obtain good heat conduction effect, customers are advised to use a thermal conductivity of not less than 2 W/m k, and
Moreover, the coating should be thin and uniform, and there should be no less heat-conducting silicone grease, but not too much.
2.2.5, after the completion of welding, must arrange personnel to conduct a comprehensive inspection of welding, inspection of virtual welding, welding leakage, welding leakage, etc.
Bad LEDs are picked out and repaired in time.
2.3, reflow soldering
2.3. 1, reflow soldering is to melt the solder paste by applying high temperature in a reflow oven, and weld the copper base of the LED and the aluminum substrate together.
, a welding method to achieve good heat conduction effect.
2.3.2. Customers are advised to use a reflow oven with stable temperature and accurate control. For high-power LED, 8 temperature zones and 5.
Reflow welding furnace can be used in any temperature range, and the temperature changes quickly in five temperature ranges.
2.3.3. It is recommended that customers use low-temperature lead-free solder paste with melting point below 180℃, and the maximum reflow temperature cannot exceed 2 10℃, because
Because the temperature is too high, it will damage the PN junction of the chip, which will lead to abnormal silicone for LED packaging.
2.3.4 Before reflow operation, set the reflow temperature curve according to the characteristics of reflow oven and the melting point of solder paste.
The general reflow soldering process is divided into four parts: heating zone, heat preservation zone, reflow zone and cooling zone (Figure 3).
Fig. 3 Flow chart of reflow soldering process
2.3.4. 1, heating zone. Its purpose is to raise the temperature of aluminum substrate from room temperature to the role of flux in solder paste.
Required activity temperature. But the heating rate should be controlled within a suitable range. If it is too fast, thermal shock will occur and lead to
May be damaged; If it is too slow, the solvent will not volatilize sufficiently, which will affect the welding quality. To prevent thermal shock from damaging the LED,
The recommended heating rate is1-3℃/s.
2.3.4.2, insulation zone. Generally around 60S, its purpose is to maintain the aluminum substrate at a certain temperature.
Range and continue for a period of time, so that the temperature of components in each area on the aluminum substrate is the same, and their relative temperature difference is reduced, and
Make the flux in the solder paste fully play its role, and remove the oxides on the surface of the element electrode and pad, thus improving the welding.
Connection quality. If the active temperature is set too high, the flux will lose its decontamination function prematurely, and if the temperature is too low, the flux will be released.
Can't get rid of dirt. If the active time is set too long, the flux in the solder paste will volatilize excessively, resulting in insufficient welding.
Less flux, easy oxidation of solder joints and poor wetting ability. If the time is too short, too much flux will be involved in welding, which may lead to
Poor welding of solder balls, beads, etc.
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2.3.4.3 recirculation zone. Generally around 30S, its purpose is to raise the temperature of aluminum substrate until the solder paste melts.
The temperature is higher than this point and the welding time is kept for a certain time, thus forming alloy and completing the welding of components and pads. In this area.
The temperature in the domain is the highest, generally exceeding the melting point of solder paste by 20-40℃. If the temperature is too low, no alloy can be formed.
Without soldering, if it is too high, it will damage the LED and aggravate the deformation of the aluminum substrate. If there is not enough time, it will be closed.
The gold layer is thin and the solder joint strength is not enough. After a long time, the alloy layer is thick and the solder joint is brittle.
2.3.4.4, cooling zone. Its purpose is to cool the aluminum substrate to obtain bright solder joints with good appearance.
The contact angle is usually set at 3-4℃ per second. If the speed is too high, the solder joint will crack, and if it is too slow, it will
Aggravate solder joint oxidation. The ideal cooling curve should be a mirror image of the reflux zone curve. The closer we get to this mirror image relationship,
The tighter the solder joint structure, the higher the solder joint quality and the better the bonding integrity.
2.4. The inverted LED colloid is not fixed and protected by PC lens, and the cured silica gel itself is soft. Once subjected to external force,
When using, the colloid is easy to move or be damaged, and it is easy to break the gold wire of LED, resulting in open circuit and dead light, so the inverted LED is used.
The principle is to avoid external force acting on silica gel colloid, as follows:
2.4. 1. If it is an automatic patch, be sure to avoid the suction nozzle touching the silica gel;
2.4.2. If it is a manual patch, when taking out the LED from the packaging box, hands or other objects should not touch the colloid, which can prevent static electricity.
Tweezers clamp the pin and take it out; In addition, it is suggested to design a fixture with hollow cross-section according to the size of colloid, so as to press down the mold.
When using LED, only the outer ring colloid of the bracket is pressed, but not the mold colloid;
2.4.3 In the process of storage and turnover, the packing box must be avoided from being squeezed, for example, handle it with care, and don't be burdened.
The object is placed on the packaging box of LED;
2.5. In order to achieve ideal welding effect, customers are advised to brush tin with steel mesh, and the thickness of solder paste is set to 0.15-0.2 mm. ..
3. Other precautions for 3.LED welding
3. 1. After welding, if there is too much flux on the surface of aluminum substrate or solder joint, the following suggestions are made when cleaning:
3. 1. 1. Wet anhydrous ethanol with a dust-free antistatic rag and carefully scrub the dirt on the aluminum substrate;
3. 1.2. Do not use strong corrosive solvents such as acetone and natural water for cleaning;
3.1.3. When the colloid of LED mold is stuck with foreign objects, you can dip it in anhydrous ethanol with a dust-free and antistatic rag, and your hands should be small.
Heart scrub; Workers should wear rubber gloves to avoid the influence of anhydrous ethanol on the skin.
3.2. Finally, due to the different characteristics of equipment and solder paste used by each company, the temperature and time during use are also different.
The settings will be different. It is especially recommended that customers know the melting point of solder paste and the temperature-resistant strip of LED when using our products.
Adjust the parameters of reflow oven properly after installation. This application guide is for customers' reference only.