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Application of Proportional Valve in FOG Bonding Machine

Date:2021-04-01    Reading:

The function of FOG Bonding is to bond the flexible printed circuit board or ribbon cable directly on the electrode at the edge of liquid crystal glass. It refers to the whole operation process of installing flexible printed circuit board and flat cable on LCD glass. Therefore, it is easy to understand that the FOG binding process directly affects the production yield and service life of LCD screens.

As can be seen from the above figure, FOG bonding machine is composed of bracket, motor, guide rail, screw, nut, upper slider, lower slider, air cylinder, bonding head,solenoid valveElectric proportional valveAnd controller, etc.
Technical parameters of FOG bonding machine:
1. Gas source pressure: 0.5~0.7MPa
2. Binding pressure: 3~40Kgf
3. Pressure accuracy: ±0.2Kgf
4. Binding temperature: RT~499℃
5. Hot pressing time: 1~99 S
6. Hot pressing accuracy: 0.14mm
 
Workflow of FOG bonding machine:
1.ACF pre-pasting: at the pressure and temperature required by the process, paste ACF with the length required by the process at the pin where the flexible printed circuit board (FPC) and liquid crystal glass need to be bound. The location and length of ACF paste are required to be accurate, and the surface is flat and free of bubbles.
2. Pre-binding: the pins of FPC and LCD glass are aligned by CCD camera, and pre-pressed under the pressure and temperature required by the process to form a preliminary connection. In this step, the alignment of CCD camera is the key factor. As the lead pitch is getting smaller and smaller due to the improvement of production process, the pitch has reached 0.05MM, and the alignment accuracy should be within 0.005 mm.
3. Main bonding: under the pressure and temperature required by the process, the pre-bonded LCD screen is mainly bonded by using a pulse hot press. In this pressing process, the electrical connection between FPC and LCD glass is realized by the elastic deformation of ACF conductive particles and the rupture of insulating layer. Meanwhile, the glue in ACF is polymerized and hardened at high temperature to form a strong physical connection between the two different materials.
 
Detection of FOG bonding machine: the LCD screen after main binding is detected by CCD camera
Key points of process technology
1. Temperature control, heating rate and peak temperature are important factors affecting ACF curing. Heating rate determines the surface quality of ACF after curing, while peak temperature determines the adhesive strength of ACF after curing.
2. The flatness of the bonding head leads to uneven crushing of ACF conductive particles, because ACF conductive particles are very small, usually about 4um in diameter, and ACF is very sensitive to pressure. When the contact surface of the bonding head is uneven, some ACF conductive particles are completely broken, while the other ACF conductive particles are not broken normally, resulting in poor electrical conduction between liquid crystal glass and FPC.
Proportional valve control principle:

1. When the equipment is on standby, the solenoid valve controls the cylinder to rise, and the proportional valve is in exhaust state.
2. When working, the solenoid valve controls the cylinder to drop, and the proportional valve controls the pressure when the cylinder drops. The proportional valve can be adjusted in real time according to the binding process.
 
FELTON electric proportional valveAdvantages in the application of FOG bonding machine:
Pressure control, the binding pressure directly determines the crushing degree of ACF conductive particles, and thus determines the production yield of LCD screen, so it is very important to control the binding pressure precisely in the binding process. If the binding pressure is too small, the ACF conductive particles can not be broken normally, thus affecting the longitudinal electrical conduction performance. The longitudinal electricity cannot be conducted. If the binding pressure is too high, ACF conductive particles will be crushed too much, thus affecting the transverse electrical insulation effect.
 
After the FOG binding machine uses FELTON electric proportional valve, the binding pressure can be directly controlled by PLC control system, so the breaking degree of ACF conductive particles can be directly controlled by the program. Multi-stage heating pressure binding can be realized by using FELTON electric proportional valve, and the binding temperature and pressure of each stage can be set independently; The binding cylinder is driven by the FELTON proportional valve, so that the pressure can be finely adjusted, the precision is higher, and the binding pressure does not shake; To sum up these applications, felton proportional valve is also widely used in FOG bonding machine. For more information about the application of proportional valve, please contact Stalin, looking forward to contributing to your equipment.
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