PCBA Tech - ​What should be the technological process of COB bonding?

PCB circuit board bonding is a wire bonding method in the chip production process. It is generally used to connect the internal circuit of the chip with gold or aluminum wires to the package pins or the gold-plated copper foil of the circuit board before packaging. It comes from ultrasonic generation. The ultrasonic wave (generally 40-140KHz) of the transducer generates high-frequency vibration through the transducer, and is transmitted to the wedge through the horn. When the wedge is in contact with the lead wire and the welded part, it will wait under the action of pressure and vibration. The surface of the weld metal rubs against each other, the oxide film is destroyed, and plastic deformation occurs, causing the two pure metal surfaces to come into close contact, reaching a combination of atomic distance, and finally forming a strong mechanical connection. Generally, after bonding (that is, after the circuit and the pins are connected), the chip is packaged with black glue.

PCB circuit board bonding is a wire bonding method in the chip production process. It is generally used to connect the internal circuit of the chip with gold or aluminum wires to the package pins or the gold-plated copper foil of the circuit board before packaging. It comes from ultrasonic generation. The ultrasonic wave (generally 40-140KHz) of the transducer generates high-frequency vibration through the transducer, and is transmitted to the wedge through the horn.

When the wedge is in contact with the lead wire and the welded part, it will wait under the action of pressure and vibration. The surface of the weld metal rubs against each other, the oxide film is destroyed, and plastic deformation occurs, causing the two pure metal surfaces to come into close contact, reaching a combination of atomic distance, and finally forming a strong mechanical connection. Generally, after bonding (that is, after the circuit and the pins are connected), the chip is packaged with black glue.

COB bonding process process:

Clean PCB-Die Adhesive Adhesive-Chip Paste-Bond Wire-Seal Adhesive-Test; When cleaning the PCB circuit board, wipe the oil, dust, and oxide layer on the position with the skin, and then wipe the test position with a brush Brush clean, or blow clean with air.

When the adhesive is applied, the amount of adhesive drop is moderate, and the glue dots are evenly distributed at the four corners. The adhesive is strictly prohibited from contaminating the pad. When chip sticking (solid crystal), vacuum suction pen is used, and the suction nozzle must be flat to avoid scratching the surface of the chip. Check the direction of the chip. When sticking to the PCB, it must be "smoothly and positively". The chip and PCB must be parallel and close to each other. The chip and PCB are not easy to fall off during the entire process. The chip and PCB reserved positions are fixed upright and cannot be deflected. The direction of the chip must not be reversed.

When bonding wire, the PCB of bonding has passed the bonding tensile test, 1.0 wire is greater than or equal to 3.5G, and 1.25 wire is greater than or equal to 4.5G. When bonding the standard aluminum wire with the melting point, the wire tail is greater than or equal to 0.3 times the wire diameter and less than or equal to 1.5 times the wire diameter, and the shape of the aluminum wire solder joint is oval. The length of the solder joint is greater than or equal to 1.5 times the wire diameter and less than or equal to 5.0 times the wire diameter. The width of the solder joint is greater than or equal to 1.2 times the wire diameter and less than or equal to 3.0 times the wire diameter. The bonding process should be handled with care, and the points must be accurate. The operator should observe the bonding process with a microscope to see if there are any defects such as broken bonding, winding, deviation, cold and hot welding, aluminum lifting, etc., if there is any To notify the relevant technical personnel to solve the problem in time. Before the formal production, there must be a first-hand inspection to check whether there are any errors, few or missing states, etc.

In the production process, there must be a dedicated person to check its correctness at regular intervals (at most 2 hours). Before installing the plastic ring on the chip, check the regularity of the plastic ring to ensure that its center is square without obvious distortion. When installing, ensure that the bottom of the plastic ring is closely attached to the surface of the chip, and the photosensitive area in the center of the chip is not blocked. . When dispensing, the black glue should completely cover the PCB sun ring and the aluminum wire of the bonding chip, and no wire can be exposed. The black glue can not seal the PCB sun ring. The leaked glue should be erased in time. The black glue cannot penetrate the chip through the plastic ring. superior. During the dispensing process, the needle tip or the wool swab must not touch the surface of the chip in the plastic ring or the bonding wire.

The drying temperature is strictly controlled: the preheating temperature is 120±5 degrees Celsius, and the time is 1.5-3.0 minutes;

The drying temperature is 140 ± 5 degrees Celsius, and the time is 40-60 minutes. The surface of the dried vinyl shall not have pores or uncured appearance, and the height of the vinyl shall not be higher than the plastic ring.

PCB testing generally uses a combination of multiple testing methods, such as manual visual inspection, automatic wire bonding quality inspection by bonding machines, and automatic optical image analysis (AOI) X-ray analysis to check the quality of inner solder joints.