The Dispensing Control System And The Research Of Its Performance Control For IC Packaging

The process of time-pressure dispensing system has been widely used in the semi-conductor packaging industry. It is employed as advanced integrated circuit encapsulation and surface mount technology. What's more, it can prevent the corrosion of the connection and relieve the stress resulting from the thermal-expansion coefficient differences between the chip and the substrate. It uses pressurized air to drive the fluid and delivers the fluid to boards or substrates. And it has the advantage of flexibility to different application situations, simple operation and easy maintenance. Because of the effect on the air pressure during its delivering, nonlinear rheological behaviour and others, it is hard for the time-pressure dispensing to keep a good consistence. One fundamental requirement in dispensing is that the flow rate of encapsulant must be controlled to be consistent over the dispensing process, so that an uniform profile of the dam dispensed can be formed and the amount of encapsulant dispensed can be accurately manipulated on the substrate. However, complexity of the process includes the air-fluid coupling and their nonlinear uncertainties, so it is vital to have a further understanding of the whole process for better controlling. The time-pressure dispensing method is widely used, but its controlling is proved to be a challenge task. For the purpose of analysis and control, we build a dispensing equipment based on PC to run it and a computer vision system to check. The dispensor is a complex system and is needed to control the flow rate and the position to be dispensed at. Inconsistent quality is caused by internal and external variations, particularly when high speed is required. The paper uses the theory of integrated design and control, considers the design synthetically from the aspect such as hardware, software and controlling scheme. According to the hardware setting, the applied software is programmed and the issue about sampling of pressure and timer controlling of the system. The encapsulant for electronics packaging usually exhibits rheological behaviour and its viscosity is dependent on the shear rate, temperature, and even on the shear time, so the fluid flow rate in dispensing is largely affected by it. This paper presents the epoxy rheological behaviour and gives some experimental modal for the character. In order to understand the dynamics of the system, the pneumatic system is divided to a few parts, each of which is derived with a physically accurate and mathematically simple approximate process model. At the same time,some details is presented to tell the forming process of the fluid dot and the tailing. The time-pressure dispensing deals with the delivering of air and complex non-Newtonian fluid. And with the running of dispensing, the condition is changing, such as the declination of the left fluid height in syringe. All these affect the dispensing quality. It can not be solved only by hardware, so the system should be controlled. Traditionally the dispensing system is not controlled and only relies on the operator to adjust based on his experience. The paper emphasizes on the affection on pressure by the fluid height in order to compensate its influence by adding dispensing time. This paper analyses the dynamic of pressure according to the height, and then get a method to evaluate the height during the process using the sampling pressure. Some modeling and control literature relating to the dispensing process are also overviewed. Grounding on the condition of force acting on the fluid in the syringe needle, a simple evaluation model is attained for the flow rate and the dot volume. Using this model, based on the theory of statistic process control and PI control algorithm, an approximate control method is build. The simulation and experiment verifies its effectiveness.