In PCB (printed circuit board) assembly, the welding of BGA (Ball Grid Array, ball grid array package) chips is a complex and precise process. The following are the detailed BGA chip welding steps:
1. Preparation before welding
PCB board preparation
Clean: Use alcohol or special detergent to thoroughly clean the PCB board, remove surface oil, dust and oxides, and ensure that the pad is clean and free of impurities.
Coating flux: Evenly coating an appropriate amount of flux on the solder pad of the PCB board helps to improve the flow of solder and the quality of welding.
Spot adhesive (if necessary) : Pre-spot an appropriate amount of adhesive on the solder pad of the PCB board to fix the BGA chip and prevent it from moving during welding. The adhesive shall be cured according to the specified curing temperature and time.
BGA chip ready
Check: Use a microscope and other tools to carefully check the BGA chip to ensure that there is no damage, the welding ball is complete, and the surface is clean.
Positioning: According to the mark on the PCB board and the screen frame, determine the correct placement position and direction of the BGA chip.
Solder paste preparation
Select solder paste: Select the appropriate solder paste according to the size of the solder ball of the BGA chip and the requirements of the PCB board. Solder paste usually contains metal solder (such as tin silver copper alloy) and flux.
Printing solder paste: Use solder paste printing machine to accurately print solder paste on the solder pad of the PCB board to ensure uniform distribution of solder paste without missing or accumulation.
Prepare devices and tools
Welding equipment: Prepare reflow furnace, heat gun, microscope, cleaning solution, and X-ray testing equipment.
Auxiliary tools: Prepare auxiliary tools such as tweezers, scrapers, and tin absorbers for fine operation and troubleshooting during welding.
2. Welding process
Chip placement and fixation
Place the chip: Place the BGA chip accurately on the solder pad of the PCB board using the automatic placement machine or manually, and ensure that the chip is aligned with the solder pad without deviation.
Fixed chip (if required) : If adhesive is used, cure at the specified curing temperature and time to fix the BGA chip.
preheat
Put into reflow furnace: Put the mounted PCB board into the reflow furnace.
Set the preheating curve: according to the thickness of the PCB board and the type of solder paste, set the appropriate preheating temperature and time curve. The preheating phase helps activate the flux and vaporize the solvent in the solder paste.
Reflow welding
Temperature curve setting: According to the type of solder paste and PCB material, set the appropriate reflow welding temperature curve. The temperature curve is usually divided into preheating zone, wetting zone, reflux zone and cooling zone.
Welding process: Welding according to the set temperature curve. At the reflux stage, the solder paste is completely melted and forms a good solder joint with the PCB pad.
Cooling: After welding is completed, let the PCB board cool naturally in the reflow furnace, or cool according to the specified cooling speed to avoid welding defects.
Third, welding post-processing and testing
cleanse
Remove residue: Clean the welded PCB board with cleaning solution and ultrasonic cleaning machine to remove residual impurities such as flux, welding slag and adhesive.
Quality inspection
Appearance inspection: Use a microscope and other tools to carefully check the welding quality to ensure that the welding between the welding ball and the welding pad is good, and there are no defects such as virtual welding, bridge and cold welding.
X-ray inspection: X-ray inspection equipment is used to conduct a comprehensive internal inspection of BGA solder joints to ensure that there are no holes, cracks and other defects inside the solder joints.
Electrical test
Functional test: Use a multimeter, oscilloscope and other tools to conduct electrical tests on the welded PCB board to ensure that the connection between the BGA chip and the PCB board is normal and the function meets the requirements.
Fourth, welding precautions
Temperature curve setting: Temperature curve is very important for welding quality, need to flexibly adjust the preheating temperature, maximum temperature, holding time and other parameters according to the solder paste type, PCB size and other factors.
Alignment accuracy: The use of high-precision placement machines and alignment systems to ensure that the BGA chip is precisely aligned with the solder pad of the PCB board, and the tolerance is usually within ±0.05mm.
Welding environment: The welding process needs to be carried out in a clean, dust-free and constant temperature environment to prevent pollutants such as dust from affecting the quality of welding.
Esd prevention: Take ESD preventive measures to prevent damage to BGA chips caused by static electricity.
Through the above steps and precautions, you can ensure the welding quality of BGA chips in PCB assembly, and improve the reliability and performance of electronic products.
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