BGA repair mainly involves the following steps: preparation, disassembly, ball planting, welding and testing. Da Tai Feng Xiaobian today to talk about the preparation
Drying: This is the most overlooked procedure, but it is also a very important and critical procedure. The main purpose of circuit board and chip drying is to remove moisture. Otherwise, due to the rapid temperature rise during welding, the moisture in the chip and circuit board will be vaporized immediately, resulting in chip damage. After drying, the board should be disassembled and welded within 24 hours. At the same time, the chip before the planting ball should also be ensured to be dried and the planting ball should be completed within 24 hours. Before baking, remove temperature-sensitive components, such as optical fibers, batteries, and plastic handles, and bake them. Otherwise, it is easy to cause heat damage to the device.
Product protection: This is another overlooked but important part. There are optical fibers on the front and back of the repair board, and batteries in the accessory areas need to be removed before repair. If the back of the repair board is 10mm away from the repair chip and there are radiators, insert crystal oscillator, electrolytic capacitor, plastic light guide column, non-high temperature bar code, BGA, BGA socket, etc., 5-6 layers of high temperature adhesive paper must be affixed to the surface for protection.
Preparation of nozzles and supports: for boards with widths greater than 100mm, the heating table of the workstation should be supported. The position of the support rod is preferably located in the middle of the PCB board, so that the PCB remains flat and cannot be supported on the device. Nozzles with actual size 2 ~ 5mm larger than BGA are selected.
Disassembly/welding curve: Since the actual temperature of the BGA tin ball during heating is closely related to the size of the BGA, the packaging material, the heating system efficiency of the equipment, the size and thickness of the PCB, and the location of the PCB in the workstation, if the repair curve program is stored in the computer, it should be measured before each disassembly/welding. If there is no program, the temperature curve needs to be made. The production rule of temperature curve board is similar to that of SMT's reflow temperature curve board. A test board is used, which is the same as the repaired PCB. For BGA components, holes should be drilled at the bottom, and the thermocouple should be inserted into the BGA tin ball, and then fixed with high temperature tin or epoxy resin.
There are two common types of temperature curves used in SMT reflow soldering process. They are usually called insulated (platform) and tent (triangle) temperature curves. In the insulated curve, the assembly experiences the same temperature over a period of time. The tent temperature curve is a continuous rise in temperature from the time the assembly enters the furnace until the assembly reaches the desired peak temperature. Unlike reflux furnace, repair workstation has limited temperature zone, so it is difficult to make platform curve, so triangle curve is generally adopted. Pay attention to control the temperature rise slope below 3 degrees/second; It is also necessary to pay attention to the cooling slope. If the tin point is cooled quickly, the strength of the tin point will be slightly larger, but it should not be too fast to cause the temperature stress inside the element. Generally, the cooling slope is not more than 5 degrees/second. The key to making curves is to adequately preheat the bottom of the PCB to prevent warping; Reflux time and maximum temperature can refer to the recommended parameters.
So the above is about the BGA repair platform: BGA device repair process, I hope to help you ~ pay attention to me
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