(1) Disassembly of BGA chip
① Do a good job of component protection, when removing the BGA IC, pay attention to whether it affects the peripheral components, some mobile phone font, temporary storage, CPU is very close. During de-soldering, a water-soaked cotton ball can be placed on the adjacent IC. Many plastic amplifiers and soft packages have poor high temperature resistance, and the temperature is not easy to be too high during blow welding, otherwise, it is easy to blow them out.
② Put an appropriate amount of flux on the IC to be removed, and blow it into the bottom of the IC as far as possible, so as to help the solder joint under the chip to melt evenly.
③ Adjust the temperature and wind of the heat gun, the general temperature is 3-4, the wind is 2-3, the air nozzle is moved about 3cm above the chip and heated until the tin bead under the chip is completely melted, and the whole chip is picked up with tweezers. Note: When heating the IC, blow the IC around, do not blow the middle of the IC, otherwise it is easy to blow the IC bulge, the heating time is not too long, otherwise the circuit board blowing bubbles.
④ After the BGA chip is removed, the chip has more tin on the pad and the machine board, at this time, add enough solder paste on the circuit board, remove the excess solder on the board with an electric soldering iron, and can be properly tinted to make each solder foot of the circuit board smooth and smooth, and then use the water to wash the flux on the chip and the machine board, and be especially careful when removing solder. Otherwise, the green paint on the pad will be scraped or the pad will fall off.
(2) Planting tin
① Do your homework. The solder on the surface of the IC can be cleaned with an appropriate amount of solder paste on the surface of the BGA IC, remove too much solder on the IC with a soldering iron, and then wash the IC in the water, and check whether the IC solder joint is bright after washing, such as some oxygen, you need to use a soldering iron with flux and solder to make it bright, so as to plant tin.
There are a variety of fixing methods of BGA IC, the following two practical and convenient methods: Label paper fixing method: The IC is aligned with the hole of the planting tin plate, and the label sticker is attached to the IC and the planting tin plate, after the IC is aligned, the planting tin plate is firmly held by hand or tweezers, and then the other hand scrapes the tin.
Under the IC napkin fixing method: under the IC pad several layers of paper towels, and then put the tin plate hole and the IC foot on, with the hand or tweezers firmly planted tin plate, and then scrape the tin paste.
③ On the tin paste. If the tin slurry is too thin, it is easy to boil when blowing welding, resulting in ball difficulties, so the more dry the tin slurry, the better, as long as it is not dry into a hard block, if too thin, you can press a napkin to absorb a little. Usually can pick some tin paste on the tin paste cover, let it dry naturally. Use a flat knife to pick an appropriate amount of tin paste onto the tin planter plate, scrape down vigorously, and press while scraping, so that the tin paste evenly fills the small hole of the tin planter plate.
④ The wind power of the hot air gun is reduced to 2, and the air nozzle is sloshing slowly and evenly heating the tin plate to melt the tin slurry slowly. When you see tin balls forming in individual holes of the tin plate, it means that the temperature is in place, and the heat gun should be raised to avoid further temperature rise. Too high temperature will make the tin slurry boiling violently, resulting in tin planting failure. Serious IC overheating damage. If the blow welding is successful, it is found that some tin balls have uneven water, or even some have not been tinned, you can first use a scraper to trim the exposed part of the large tin ball along the surface of the tin plate, and then use a scraper to fill the hole where the tin ball is too small and the foot is missing with tin paste, and then blow it again with a heat gun. If the tin ball flood is not uniform, repeat the above operation until the ideal state. The amount of replanting must be cleaned and wiped dry. When taking the tin plate, press down with the tip of the tweezers at the four corners of the IC while it is hot, so that it is easy to remove more.
(3) Installation of BGA chip
① Apply appropriate amount of solder paste to the side of the BGA IC with welding feet, and set the heat gun temperature to 2 to gently blow, so that the solder paste is evenly distributed on the surface of the IC. Thus, the IC tin bead is positioned in preparation for welding. Then set the heat gun temperature to 3, heat the plate first, and blow the flux. Then put the BGA IC planted with tin beads on the circuit board according to the position before disassembly. At the same time, move the IC back and forth with hands or tweezers and gently press, then you can feel the contact of the welding feet on both sides. After alignment, because a little solder paste is applied to the IC foot in advance, there is a certain viscosity, the IC will not move. If it's out of position, reposition it.
② After the BGA IC is positioned, it can be welded. As when planting the tin ball, adjust the heat gun to the appropriate air volume and temperature, so that the center of the air nozzle is aligned with the central position of the IC, slowly heating. When you see the IC sinking down around the solder paste overflow, it means that the tin ball has fused with the solder joint on the circuit board. At this time, you can gently shake the heat gun to heat evenly and fully, due to the effect of surface tension. The solder joint between BGA IC and circuit board will be automatically aligned, pay attention to the heating process do not force the BGA, otherwise it will make the solder overflow, easy to cause foot and short circuit. After the welding is finished, clean the board with heavenly water.
(4) Disassembly method of BGA chip with glue
At present, many brands of mobile phone BGA IC are filled with sealant, disassembly is more difficult, for the removal of this type of IC to remove glue skills. The following is a detailed introduction.
For MOTOROLA mobile phone sealant, there are many brands of sol water on the market can be easily removed glue, after many experiments found that V998 CPU with banana water soaked, the effect of removing glue is better, generally soaked 3-4 hours, the sealant is easy to remove. It should be noted that the font library must be removed before the V998 phone immersion, otherwise the font library will be damaged. Because the 998 font bank is a soft package of BGA, it can not be soaked in banana water, tena water or sol water. These solvents have strong corrosion to the glue in the soft package of BGA font bank, which will make the glue expand and lead to the scrap of the font bank. Of course, if you do not have sol water, can also be directly disassembled, MOTOROLA sealant low temperature resistance, easy to soften, and the CPU is more resistant to high temperature, as long as you pay attention to the method, can also be successfully disassembled.
① First adjust the wind speed and temperature of the heat gun to the appropriate position (general air volume 3, heat 4, can be adjusted according to different brands of heat guns)
② Move the hot air 5cm above the CPU and blow it. After about half a minute, use a small blade to start from the direction with more ground feet of the CPU. Generally, pry from the first foot, that is, above the register.
③ The CPU is removed, and then the glue is removed, blow with a hot air gun, and carefully scrape with a knife slowly and little by little until the pad is clean.
The base glue of Nokia mobile phone is initially special injection molding, and there is no better method of falling glue at present. Pay attention to the operation skills when disassembling:
① Fix the plate, adjust the heat gun temperature between 270℃-300℃, increase the air volume, do not blow the resistance and capacitance components prevail, preheat the removed IC sealant for about 20 seconds, and then move the air gun, and then preheat the plate after cooling, the preheat 3 times, each preheat to add oily heavy flux, so that the oil flows into the welding disc to play a protective role.
② Set the heat gun temperature to between 350 ° C and 400 ° C, continue to heat the IC, while heating the IC with tweezers, when you see the tin beads extruder from the sealant, you can pick a few holes on the side of the sealing glue with the tip of the tweezers from the side with fewer components, so that the tin beads flow out, remember that you still have to keep putting the oil flux.
③ Remove the IC, when you see that there is no longer a tin bead below the IC, use a fine-pointed tweezer with a curved hook to put it under the IC at the tin, and gently pick it off.
④ Clean the sealing glue, after most of the IC is removed, the sealing glue is left on the main board, first put the flux on the tin point on the main board, and absorb the tin beads on the sealing glue with a soldering iron, more than a few times, you can clearly see the bottom bright pad so far, the main function is to completely separate the solder joint and sealing glue. Adjust the temperature of the gun between 270℃-300℃, heating the sealing glue of the motherboard, at this time the sealing glue is basically out of the pad, and the safe place between the solder joint and the solder joint is picked with tweezers, the strength of the pick should be controlled well, if the plot is just right, a pick can take off a large piece. For the slow removal of the sealant on the IC, first clean the IC, and then glue the double-sided adhesive on the back of the IC, and fix it on the welding table, the temperature of the wind gun is still adjusted to 270℃-300℃, put the flux, heat the sealant, and remove it with tweezers.