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Hot Air Gun Welding Chip Tips And Methods
Mar 15, 2018

First, equipment


Hot air gun


1 anti-static electric iron


1


Phone board


1 tweezers


1


Low melting point solder wire amount of rosin flux (flux) amount


Suction tin line moderate amount of water (or wash water) amount


a) steps

1. Open the hot air gun and adjust the air volume and temperature to the proper position: feel the air volume and temperature of the air cylinder by hand; observe whether the air volume of the air duct is unstable due to temperature fluctuations.


2. Observe that the inside of the hairpin is reddish. Prevent overheating inside the fan cylinder.


3. Use paper to observe the heat distribution. Find out the temperature center.


4. The application of wind nozzles and precautions.


5. Blow a resistor at the lowest temperature and remember the position of the lowest temperature knob that can blow the resistor down.


b) Starlight Digital Heat Gun

1. Adjust the amount of air twist to let the air volume indicate the ball in the middle position.


2, adjust the temperature control, so that the temperature indicator at about 380 °C.


Note: When the hot air gun is not used for a short time, it should be put into sleep state (the switch with the sleep switch on the handle can be switched on, the switch on the handle is not working, the air nozzle is working downward, and the air nozzle is sleeping upwards). The heat gun should be turned off when not working for 5 minutes.


C) Star 936 digital thermostatic anti-static soldering iron

1, the temperature is generally set at 300 °C, if used for small components welding, the temperature can be adjusted to lower, if the welded component is larger or in a large area of metal (such as a large area of copper foil) welding, properly The temperature is increased.


2, soldering iron head must be kept white tin, if it is gray with special sponge treatment.


3, welding can not be used to force the solder joints, otherwise it will damage the PCB board and soldering iron head.


4, do not have to turn off the iron power supply for a long time, avoid empty burning.


5, electric iron is generally in the demolition of small components, processing solder joints, processing short circuit, plus welding, fly line work in the use.

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Second, the use of hot air gun desoldering flat package IC


A) Steps to Unpack Flat ICs

1, before removing the components to see the IC direction, do not reload when reloading.


2. Observe whether there are any heat-sensitive devices (such as liquid crystals, plastic components, BGAIC with sealant, etc.) next to the IC and on the back side of the IC. If you want to cover them with a shielding cover, etc.


3. Adding proper rosin on the IC pin to be removed can make the PCB board pad after removing the component smooth, otherwise it will cause burrs, which is not easy to align when re-welding.


4. Evenly preheat the adjusted hot air gun at an area of about 20 square centimeters around the component (the air nozzle is about 1cm away from the PCB board, and move at a faster speed in the preheating position. The temperature on the PCB board does not exceed 130-160°C. )


1) In addition to moisture on the PCB, avoid "bubbling" during rework.


2) Avoid stress warpage and deformation between PCB pads due to excessive temperature difference between the upper and lower sides due to the rapid heating of one side (above) of the PCB.


3) Reduce the thermal shock of the parts in the weld zone when heating above the PCB board.


4) Avoid the next IC's disorientation due to uneven heating


5) Circuit board and component heating: The distance between the air nozzle of the hot air gun and the IC1CM is the same as that of the IC, and it moves evenly along the edge of the IC. Use the tweezers to gently clamp the diagonal of the IC.


6) If the solder joint has been heated to the melting point, the hand holding the braid will feel the first time.


Wait until the solder on the IC pin has melted


Zero force is used to carefully pick up the components vertically from the board. This can avoid damage to the PCB or IC and also prevent solder shorts left by the PCB. Heating control is a key factor in rework, and the solder must be completely melted so as not to damage the pad when it is removed. At the same time, it is also necessary to prevent the board from overheating, and the board should not be distorted by heat.


(For example: 140°C-160°C can be used for preheating and heating at the lower part under conditional conditions. The entire process of removing the IC should not exceed 250 seconds.)


7) After removing the IC, check whether the solder joint on the PCB is short-circuited. If there is a short circuit, reheat it with a hot air gun. After the solder is melted at the short-circuit point, use a tweezers to gently stroke the short circuit. Solder naturally. separate. Try not to use a soldering iron as far as possible, because the soldering iron will take away the solder on the PCB board, and the solder on the PCB board will be less, which will increase the possibility of welding. The small pin pad is not easy to tin.


b) Install the flat IC step

1. Observe whether the IC pin to be mounted is flat. If there is a short circuit in the IC pin solder, use a soldering wire to handle it; if the IC pin is not flat, place it on a flat plate and press it flat with a flat tweezers; if the IC The pins are not correct. Use a scalpel to correct the defect.


2. Put a proper amount of flux on the pad. When heated too much, the IC will drift away. Protect the surrounding heat-sensitive components.


3. Place the flat IC on the pad in the original direction and align the IC pin with the PCB board pin position. When aligning, the eyes should be observed vertically downwards. All four pins must be aligned, and the four-sided pins are visually felt. The length is the same and the pins are not skewed. You can use rosin to stick to ICs due to thermal adhesion.


4. Use a hot air gun to preheat and heat the IC. Note that the entire process cannot stop the heat gun (if it stops moving, it will cause local temperature rise to be too high and damage it), observe the IC while heating, and then send the IC again. The movement phenomenon is to use a tweezers to gently adjust it without stopping the heating. If there is no displacement phenomenon, as long as the solder under the IC pin is melted, it should be found in the first time (If the solder melts, you will find that the IC sinks slightly, there is light smoke in the rosin, the solder is shiny, etc., and you can use the dice light Touch the small component next to the IC. If the small component next to it is active, it means that the solder under the IC pin is also near melting.) Immediately stop heating. Because the temperature set by the hot air gun is relatively high, the temperature on the IC and the PCB board continues to increase. If it cannot be detected early, excessive temperature rise can damage the IC or PCB board. Therefore, the heating time must not be too long.


5, after the PCB board is cooled, use the water (or wash water) to clean and blow dry the solder joints. Check for soldering and short circuit.


6, if there is a virtual welding situation, use a soldering iron a pin of the welding or the use of hot air gun to remove the IC re-welding; if there is a short circuit phenomenon, you can use a wet heat-resistant sponge to clean the iron head, Point the rosin lightly across the short-circuited pin to remove the solder from the short-circuit. Or use suction wire processing: use a tweezers to pick out the four suction tin wire and a small amount of rosin, place it in the short circuit, gently press the soldering iron with a soldering iron, and the solder in the short circuit will melt and stick on the soldering wire. Clear the short circuit.


Another: You can also use soldering iron to solder the IC. After aligning the IC with the pad, use the soldering iron to remove the rosin. Gently pass along the edge of the IC pin. If the IC pin spacing is large, you can add it. Rosin is soldered with a soldering iron ball rolling over all the pins.

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Third, the use of hot air gun desoldering heat components


A) Demolition of components

General, such as cable clips, in-line seats, sockets, SIM card seats, battery contacts, tail plugs and other plastic components easily deformed by heat, if it is indeed broken, it may be as dismantled as ordinary IC removed on the line, if you want to split It should be kept intact and it needs careful handling. There is a rotating wind heat gun with uniform air volume and heat, and generally does not blow plastic components. If you use an ordinary air gun, you can consider placing the PCB on the side of the table, and use the air gun to heat the front side of the component from the bottom upwards. Pass the PCB board to transfer the heat to the top. When the solder melts, it can be removed; The heating element is covered with an equally large waste chip, and then the edge of the chip is heated with the air gun, and the plastic element can be removed after the lower solder melts.


b) Install components

Align the pads on the PCB and put the proper amount of flux on the component pins next to the pad so that it gets a little hotter. The PCB is heated with a hot air gun. When the solder on the board is bright, it indicates that the solder has melted and the component is quickly placed on the pad. At this time, the air gun cannot stop moving and heating, and the component is adjusted in position with a tweezers in a short time. Immediately withdraw the air gun. This method is also suitable for installing power amplifiers and power ICs with large heat dissipation areas.


Some devices can be easily soldered using a soldering iron (such as a SIM card holder). Do not use a blow gun.

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Fourth, demolition resistance capacitance triodes and other small components


A) Demolition of components

1 Add appropriate amount of rosin to the component, gently clamp the component with tweezers, heat evenly the small component with a hot air gun (same as desoldering IC), take the tweezers to feel that the solder has melted, and then remove the component.


2


Use soldering iron to add some solder on the component. Solder covers the solder joints on both sides of the component. Put the soldering iron tip flat on the side of the component so that the newly added solder is in a melted state and the component can be removed. If the components are larger, add more tin to the component solder joints, clamp the components with tweezers, and heat the two solder joints rapidly with a soldering iron until the two solder joints are in a molten state.


b) Install components

1. Add appropriate amount of rosin to the component, gently clamp the component with tweezers, align the component to the solder joint, heat the small component evenly with a hot air gun, wait for the solder under the component to melt, and then release the tweezers. (It is also possible to place the component and heat it until the solder melts and then touch the component with a tweezers to align it.)


2. Use tweezers to gently hold the components. Use the soldering iron to tap on the pins of the component to solder. If there is less solder on the solder joint, place a small solder ball on the tip of the soldering iron and apply it to the pins of the component.


Fifth, the use of hot air gun demolition shield


A) Remove the shield

The PCB board is clamped with a clamp, the shield is clamped by a forceps, and the entire shield is heated with a hot air gun. After the solder melts, it is picked up vertically. Because of the high temperature required to remove the shield, other components on the PCB are also loosened. When the shield is removed, the main board cannot move, so as not to shift the components on the board. When removing the shield, it should be picked up vertically to avoid The components in the shield are bumped. You can also lift the three sides of the shield first, then cool it and fold it back and forth, and break the last edge to remove the shield.


b) Mount shield

Place the shield on the PCB and heat it with the air gun until the solder melts. You can also use soldering iron to select several spot welding PCB boards.

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Sixth, add welding element


a) welding with air gun

Add a little rosin on the PCB board where welding is needed. Heat evenly with air gun until the solder in the soldered area is melted. You can also use the tweezers to gently touch the components that are suspected to be in the soldered state. Strengthen the welding effect.


b) Welding with electric iron

For welding of a small number of components, if the IC is to be soldered, a small amount of rosin can be added to the IC pin, and the soldering iron head can be soldered to the pin one by one. Be sure to clean the tin residue on the tip, otherwise it will short-circuit the pins. If it is to add welding resistance, triodes and other small components, directly with the soldering iron tip rosin, welding the component pins can be. Sometimes in order to increase the welding strength, it is also possible to add a little solder to the component pins.


1. Correct use of hot air welding method

The nozzles of the hot air gun and the hot air soldering station can blow hot air of different temperatures to the IC etc. at a set temperature to complete the welding. The air outlet of the nozzle is designed above the nozzle, and the aperture size is adjustable, which will not cause thermal damage to the elements adjacent to the BGA device.


(1) Before the BGA device is lifted, all the solder balls should be completely melted. If some of the solder balls are not completely melted, the pads connected to the solder balls are easily damaged when the BGA device is lifted. Similarly, when the BGA device is soldered, if there is Some solder balls are not completely melted, which can also lead to poor soldering.


(2) For ease of operation, the gap between the inner edge of the nozzle and the BGA device should not be too small, at least 1 mm clearance.


(3) The hole diameter, mesh number, spacing and arrangement of the tinning mesh should be consistent with that of the BGA device. The hole diameter is generally 80% of the pad diameter, and the upper edge is small and the lower edge is large to facilitate the application of solder on the printed board.


(4) In order to prevent the printed board from being heated and deformed on one side, it can be preheated on the reverse side of the printed board firstly, and the temperature is generally controlled at 150-160°C. For a printed board with a generally small size, the preheating temperature should be controlled below 160°C. .


2. Adjustment and mastering of welding temperature

(1) The best welding parameters of the hot air soldering station are actually the best combination of the soldering surface temperature, the welding time, and the hot air volume of the hot air soldering station. When setting these three parameters, the number of layers (thickness), area, internal lead material, BGA device material (PBGA, or CBGA) and size, solder paste composition, and solder melting point should be considered. The number of components on the printed board (these components to absorb heat), the BGA device soldering the best temperature and withstand temperature, the longest welding time. In general, the larger the BGA device area (more than 350 solder balls), the harder the setting of the welding parameters.


(2) In the welding, the following four temperature zones should be mastered.


1 Preheat zone. The purpose of preheating is twofold: one is to prevent printing


One side of the board is heated and deformed, and the other is to accelerate solder melting. Preheating is more important for a larger board. Due to the limited heat resistance of the printed board itself, the higher the temperature, the shorter the heating time. Ordinary printed board at 150°C


The following is safe (not too long). Commonly used 1.5mm thick small size printed board, the temperature can be set at 150 ~ 160 °C, within 90 seconds. After the BGA device is unpacked, it should normally be used within 24 hours. If the package is opened prematurely, to prevent the device from being damaged during rework (the “popcorn” effect), it should be dried before loading. Drying preheating temperature should choose 100 ~ 110 °C, and preheating time selected longer.


2 in the temperature zone (soakzone). The preheating temperature at the bottom of the printed board can be the same as or slightly higher than the preheating temperature in the preheating zone. The nozzle temperature is higher than the preheating zone temperature and lower than the high temperature zone temperature. The time is generally about 60 seconds.


3 high temperature area (peakzone). The temperature of the nozzle peaked in this zone. The temperature should be higher than the solder melting point, but it is better not to exceed 200°C.


In addition to the correct choice of heating temperature and time in each zone, you should also pay attention to the heating rate. Generally below 100°C, the maximum heating rate does not exceed 6°C/s. The maximum heating rate above 100°C does not exceed 3°C/s. In the cooling zone, the maximum cooling rate does not exceed 6°C/s.


There are certain differences in the above parameters when CBGA (ceramic packaged BGA device) and PBGA chip (plastic packaged BGA device) are soldered: The diameter of the solder ball of the CBGA device should be about 15% larger than the solder ball diameter of the PBGA device. The composition of the solder is 90Sn/10Pb, higher melting point. After the CBGA device is de-soldered, the solder balls will not stick to the printed board.


CBGA device solder balls and printed circuit board solder paste can use the same solder PBGA device (composition is 63Sn/37Pb), so that after the BGA device is lifted, the solder ball is still attached to the device pins and will not be attached to the printed circuit board. Board





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