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Explore the process of SMT bonding in PCB circuit boards
Explore the process of SMT bonding in PCB circuit boards

Explore the process of SMT bonding in PCB circuit boards


Bonding process:

Clean PCB-Drip Adhesive-Chip Paste-Test-Heat Sealing Adhesive-Test-Warehouse

1. Clean PCB: The clean policy is to clean the dust and oil on the PCB board bonding pads to improve the bonding quality. After washing, the PCB board still has oil stains or oxide layers and other dirty parts. Use a skin wipe to test the positioning or test the needle position to wipe the PCB board with a brush or blow it with an air gun before flowing into the next process. Ion blower must be used to deal with products with strict anti-static properties.

2. Adhesive glue: The policy of adhesive glue is to prevent PCB products from falling apart during the process of communication and bonding. In the COB process, however, the needle transfer and pressure injection method are rejected:

1) Needle transfer method: Use a needle sinker to take a small drop of adhesive and apply it on the PCB. This is a very fast dispensing method.

2) Pressure injection method: Put the glue into the injection device, apply certain air pressure to squeeze the glue in. The size of the glue point is determined by the size of the injection device nozzle and the pressure and pressure. It has nothing to do with viscosity. This process is also widely used in the passive configuration of dripping machine or DIE BOND.

pcb board

3. Chip paste. Chip pasting is also called DIE BOND (solid crystal), DIE Bang DIE Bang IC and other companies have different names. In chip sticking, the material hardness of the vacuum suction pen (suction nozzle) is required to be small (some companies also reject cotton swab sticking). The diameter of the suction nozzle depends on the size of the chip, and the tip of the nozzle must be flat to avoid scratching the appearance of the DIE. The DIE and PCB model must be searched when pasting. Whether the index of the pasting target is accurate, the DIE towel must be "stable and upright" to the PCB. "Positive" means that the DIE and the PCB reserved position are stuck in the right direction, and there is no deviation in the whole process. It must be detailed chip (DIE) target indicators must not have signs of reverse.

4. Bond wire (wire bonding). Bond wire (wire bonding) Wire Bond Bonding The connection name is different. Here, bonding is taken as an example. Bonding connects the two solder joints of each state line according to the position determined by the BONDING chart, so that it is adjacent to the electrical and machine. Bonding PCB requires its tensile strength to meet the company's standard (refer to 1.0 line greater than or 3.5G, 1.25 line greater than or 4.5G) aluminum wire solder joint shape is oval, The shape of the gold wire solder joint is spherical.

5. Plastic closures. The most important thing for sealing is to apply black glue to the PCB board that is tested OK. When dispensing, the vinyl should completely block the PCB sun circle and the aluminum wire of the bonding chip. There is no sign of ruth, and the vinyl cannot be sealed outside the sun circle and there is vinyl in the center. If there is any leakage, use a cloth strip Wipe off immediately. In the entire glue dispensing process, neither the needle nor the wool swab will meet the DIE and bonded lines. The appearance of the dried vinyl shall be free of pores and signs of uncured vinyl. The height of the black glue should not exceed 1.8mm, and the rated requirement should be less than 1.5mm. The temperature of the preheating plate and the drying temperature during dispensing should be strictly controlled. (Zhenqi BE-08 vinyl FR4PCB board as an example: the preheating temperature is 120±15 degrees and the time is 1.5-3.0 minutes, and the drying temperature is 140±15 degrees and the time is 40-60 minutes). Method and pressure injection method. Some companies also use glue dispensers, but their costs are higher and their lives are lower. In all cases, cotton swabs and syringes are rejected, but the dominating staff must have proficient dominating skills and strict technical requirements. It will be very difficult to repair the chip if it breaks. Therefore, this process management staff and engineering staff must be strictly controlled.

6. test. In the bonding process, there will be some bad signs such as broken wires, coiled wires, false soldering and other undesirable signs that cause chip obstruction, so the chip-scale package must be tested for function. According to the detection method, it can be divided into non-interference detection (search) and non-intervention detection (test). The non-intervention detection has grown from manual visual inspection to passive optical image analysis (AOI) X-ray analysis, from the detailed circuit diagram The search grows to the quality search of the inner solder joints, and from the independent search to the target indicators that are linked to quality monitoring and defect repair. Of course, the bonding machine is equipped with passive welding wire quality inspection results (BQM) because the passive welding wire quality inspection of the bonding machine is important to reject the two methods of end-party inspection (DRC) and pattern recognition. DRC searches the quality of PCB bonding wires based on some given ends, such as geometry whose melting point is less than the wire diameter or some set standards greater than that of the geometry. The pattern recognition method compares the stored digital images with theoretical items. But this is all affected by PCB process control, process regulations, parameter transformation and so on. Which method should be rejected in detail should be based on the detailed premise of each unit's consumption line and the product. But no matter what the prerequisites are, visual inspection is the basic inspection method and one of the contents that COB process staff and inspection staff must master. The two should be complementary, and they should not be changed over and over.