To use the bag chip mounter, different machines use different methods, and the attached instructions are described in detail.
Replacement of socket (seat):
The size of socket (seat) is large, and it is usually welded by wave soldering in the production line. The wave soldering machine can melt the solder into solder paste and make the solder paste form waves. The peak of the waves contacts with the lower surface of the pcb board, so that the socket (seat) and the pad are welded together. For small batch production or maintenance, the socket (seat) is often replaced by a tin furnace.
Dismantling and welding skills of SMD components
A 2 ~ 28℃ temperature-regulating tip soldering iron should be selected for disassembling and welding SMD components. Substrates of SMD resistors and capacitors are mostly made of ceramic materials, which are easy to be broken by collision. Therefore, skills such as temperature control, preheating and light touch should be mastered during disassembly and welding. Temperature control means that the welding temperature should be controlled at about 2 ~ 25℃. Preheating refers to preheating the components to be welded in an environment of about 1℃ for 1 ~ 2 minutes to prevent the components from being damaged by sudden thermal expansion. Touching means that welding head should first heat the solder joint or conductive tape of the printed board when operating, and try not to touch the components. In addition, it is necessary to control the welding time to be about 3 seconds each time, and let the circuit board cool naturally at room temperature after welding. The above methods and skills are also applicable to the welding of SMD crystal diode and triode.
SMD integrated circuits have a large number of pins, narrow spacing and low hardness. If the soldering temperature is not appropriate, it is easy to cause faults such as solder short circuit, virtual soldering or separation of printed circuit copper foil from printed board. When the SMD IC is disassembled, the temperature of the temperature-regulating soldering iron can be adjusted to about 26℃. After all the soldering tin of the IC pins is sucked by the welding head and the solder suction device, the pincers with pointed mouths are gently inserted into the bottom of the IC. While heating with the soldering iron, the pincers are used to gently lift the IC pins one by one, so that the IC pins are gradually separated from the printed board. When lifting the integrated circuit with tweezers, it must be synchronized with the heated part of the soldering iron to prevent the circuit board from being damaged by rushing.
before switching into a new integrated circuit, all the solder left by the original integrated circuit should be removed to ensure that the pads are flat and clean. Then clean the pins of the integrated circuit to be soldered with fine sandpaper, evenly tin-lining, align the pins of the integrated circuit to be soldered with the corresponding solder points of the printed board, lightly press the pins on the surface of the integrated circuit during soldering to prevent the integrated circuit from moving, operate the soldering iron with the other hand, dip a proper amount of solder in the soldering iron to solder and fix the pins at the four corners of the integrated circuit with the circuit board, then check and confirm the model and direction of the integrated circuit again, and formally solder when it is correct, and adjust the temperature of the soldering iron to about 25℃. One hand holds the soldering iron to heat the pins of the integrated circuit, and the other hand sends the solder wire to the heating pins for welding until all the pins are heated and welded. Finally, carefully check and eliminate the pin short circuit and virtual welding. After the solder joints are naturally cooled, use a brush dipped in anhydrous alcohol to clean the circuit board and solder joints again to prevent welding slag.
before overhauling the circuit board of the module, it is advisable to clean the printed board with a brush dipped in anhydrous alcohol to remove dust, welding slag and other impurities on the board, and observe whether there is any phenomenon such as virtual welding or short circuit of welding slag on the original circuit board, so as to find the fault point early and save the overhaul time.
bga solder ball replacement process
★ Understanding
1. Introduction
bga, as a large-capacity smd, promotes the development of smt. Manufacturers and manufacturers realize that bga has great vitality and competitiveness in large-capacity lead package. However, a single bga device is expensive, and there are often many tests for pre-research products. It is often necessary to remove bga from the substrate and hope to reuse the device. Because the solder balls of bga are destroyed after it is taken down, it can't be soldered on the substrate directly, and the balls must be replaced. The technical problem of how to regenerate the solder balls is in front of our technicians. Bga special solder balls can be purchased in indium company, but it is obviously not advisable to repair each solder ball of bga one by one. This paper introduces a process technology of solderquick to regenerate bga solder balls.
2. Equipment, tools and materials
Pre-formed defects \ fixture \ flux \ deionized water \ cleaning plate \ cleaning brush \ 6-inch flat tweezers \ acid-proof brush \ reflow oven and hot air system \ microscope \ finger sleeve (some tools can be selected according to specific conditions)
3. Technological process and matters needing attention
Heat the reflow oven to the required temperature of the temperature curve.
3.2 process steps and matters needing attention
3.2.1 put the preformed part into the fixture
put the preformed part into the fixture, with the side marked with solderquik facing downwards. Ensure that the preform is loose fit with the fixture. If the preform needs to be bent before it can be loaded into the fixture, it cannot enter the operation of the next process. The failure to put the preform into the fixture is mainly caused by dirt on the fixture or improper adjustment of the flexible fixture.
3.2.2 Apply a proper amount of flux to the repaired bga
Apply a little flux to the soldered surface of bga with an injection syringe filled with flux. Note: Make sure that the solder surface of bga is clean before applying flux.
3.2.3 spread the flux evenly, and brush the flux evenly on the whole solder surface of bga package with an acid-resistant brush to ensure that each pad is covered with a thin layer of flux. Make sure that each pad has flux. The welding effect of thin flux is better than that of thick flux.
3.2.4 put the bga to be repaired into the fixture, and put the bga to be repaired into the fixture, with the side coated with flux facing the preformed defect.
3.2.5 put the bag flat, and gently press the bga, so that the preform and bga can be positioned in the fixture, and make sure that the bga is placed flat on the preform.
3.2.6 reflow soldering
put the fixture into a hot air convection furnace or hot air reflow station and start the reflow heating process. All the reflow station curves used must be set as the curves dedicated to the bga solder ball regeneration process that has been developed.
3.2.7 cooling
take the fixture out of the furnace or reflow station with tweezers, put it on the heat conducting plate, and cool it for 2 minutes.
3.2.8 take out
when the bga is cooled, take it out of the fixture and put its solder ball face up in the cleaning tray.
3.2.9 soaking
soak bga in deionized water for 3 seconds, and then proceed to the next operation until the paper carrier is soaked.
3.2.1 peeling off the solder ball carrier
use special tweezers to remove the solder ball from the bga. The stripping method is best to start stripping from an angle. The stripped paper should be intact. If the paper is torn during peeling, stop immediately, add some deionized water, and wait for 15 to 3 seconds before continuing.
3.2.11 remove the scraps of paper on bga. After peeling off the carrier, occasionally a small amount of scraps of paper will be left, and the scraps of paper will be pinched away with tweezers. When holding scraps of paper with tweezers, the tweezers should move gently between solder balls. Be careful: the head of tweezers is sharp, and if you are not careful, you will scratch the fragile solder mask.
3.2.12 cleaning
put bga in deionized water immediately after removing the paper carrier. Rinse with plenty of deionized water and brush bga hard.
be careful: support bga when brushing with a brush to avoid mechanical stress.
note: to get the best cleaning effect, brush in one direction, then turn 9 degrees, brush in another direction, then turn 9 degrees, and brush in the same direction until it turns 36 degrees.
3.2.13 rinse
rinse bga in deionized water, which will remove a small amount of residual flux and paper scraps left in the previous cleaning step. Then air-dry, not dry it with a dry paper towel.
3.2.14 check the package
use a microscope to check whether the package is contaminated, the solder ball is not placed and the flux remains. If cleaning is needed, repeat 3.2.11-3.2.13.
note: since the flux used in this process is not clean-free, it is necessary to carefully clean it to prevent corrosion and long-term failure.
the best way to determine whether the package is clean or not is to test the ion contamination with an ionization chart or an efficiency device. The test results of all processes should meet the standard that the pollution is less than .75mg naaci/cm2. In addition, the cleaning step of 3.2.9-3.2.13 can be replaced by sink cleaning or spray cleaning process.
4. Conclusion
Because the devices on bga are very expensive, it is necessary to repair bga, and the key solder ball regeneration is a technical difficulty. This process is practical and feasible, and bga can be welded and regenerated only by purchasing preformed defects and fixtures. This process solves the key technical problems in bga repair.
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