Dispensing technology of SMT patch processing

Requirements for SMT patch processing glue include: SMT patch processing glue shall have good thixotropic characteristics; No wire drawing; High wet strength; No bubbles; SMT patch processing glue has low curing temperature and short curing time. It must also have sufficient curing strength; Low moisture absorption; SMT patch processing glue shall also have good repair characteristics and non toxicity. The color of SMT patch processing glue needs to be easy to identify and check the quality of glue points. SMT patch processing glue shall be packaged, and the packaging type shall be convenient for equipment use.

In the dispensing process of SMT patch processing, process control plays a very important role. The following process defects are easy to appear in production: unqualified glue spot size, wire drawing, bonding pad staining, poor curing strength, easy chip falling, etc. In order to solve these problems, we should study all technical parameters and find solutions.

According to work experience, after SMT patch processing, the glue spot diameter shall be half of the pad spacing, and the glue spot diameter shall be 1.5 times of the glue spot diameter. This ensures that there is enough glue to bond the components and prevents excessive glue from penetrating the pads. The distribution depends on the rotation time of the screw pump. In practice, the rotation time of the pump should be selected according to the production conditions (room temperature, glue viscosity, etc.).

SMT patch processing dispensing pressure (back pressure). The currently used dispensing machine uses screw pump to supply dispensing needle hose, and uses pressure to ensure sufficient glue to supply screw pump. Too much back pressure can easily lead to glue overflow and too much glue. If the pressure is too low, intermittent dispensing and leakage will occur, resulting in defects. The pressure shall be selected according to the same quality of glue and working ambient temperature. High ambient temperature will reduce the viscosity and improve the fluidity of glue. In this case, the supply of glue can be ensured by reducing the back pressure, and vice versa.

In SMT patch processing, the size of dispensing needle shall be 1 / 2 of the actual working point diameter. When dispensing, the dispensing needle shall be selected according to the size of the pad on the printed circuit board. For example, if there is little difference between the sizes of 0805 and 1206 pads, the same needle can be selected, but different needles should be selected for the pads with large difference, which can not only ensure the quality of glue spots, but also improve the production efficiency.

The distance between the glue needle and the printed circuit board in the patch processing. Different dispensing machines use different needles, and some needles have a certain stopping degree (such as cam / a lot 5000). At the beginning of each work, the distance between the calibration needle and the printed circuit board, i.e. z-axis height calibration, shall be calibrated.

The temperature of SMT patch processing glue should generally be kept in the refrigerator of 0-50c, and should be taken out 1 / 2 hour in advance to make the glue fully meet the working temperature. The use temperature of glue shall be 230 ℃ - 250 ℃; Ambient temperature has a great influence on the viscosity of glue. If the temperature is too low, the glue spot will become smaller and wire drawing will occur. A 50c difference in ambient temperature will result in a 50% change in the distribution volume. Therefore, the ambient temperature should be controlled. At the same time, the ambient temperature should also be guaranteed. Glue spots with low humidity are easy to dry and affect adhesion.

The viscosity of SMT patch processing glue directly affects the dispensing quality. If the viscosity is high, the glue point will become smaller, even drawing. If the viscosity is small, the glue dot will become larger, which may lead to pad penetration. In the dispensing process, for glue with different viscosity, reasonable back pressure and dispensing speed should be selected.

The above explanation is about the dispensing process of SMT patch processing. I hope it will be helpful to you. If you want to know more about SMT patch processing, you are welcome to consult the customer service online or call the company's service hotline (the upper right corner of the website). We will wholeheartedly provide you with high-quality services!