Technical Principle Of SMT Optical Alignment System

- Jul 17, 2020-

The optical alignment system is a part of SMT machine positioning, which includes X-Y/Z axis, optical alignment system and mounting head. The optical centering system of the mounter is to ensure that SMT nozzle is in the center of the element when the mounter pick the components. Dafton-SMT here to share with you the principle of optical alignment system technology.

Principle of SMT optical alignment system

After the components are picked by the mounting head, the CCD camera images the components and converts them into digital image signals. The geometric center and geometric size of the components are analyzed by computer, and compared with the data in the control program, the center of the nozzle and the center of the components are calculated at x, y, O And timely feedback to the control system for correction, to ensure that the component pin and pad overlap.

The composition of SMT optical alignment system

It consists of light source, CCD, display, digital to analog conversion and image processing system. CCD converts the light intensity distribution of the object image into analog electrical signal within a given field of vision. The analog electrical signal is converted into digital signal through a / D, and then converted into analog image after being processed by image system, and finally displayed by the display.

Resolution of SMT CCD camera

Gray resolution and scenting resolution gray value resolution is the resolution expressed by multi-level high-density image. SMT machine can distinguish the measured light intensity at a given point. The smaller the light intensity required, the higher the resolution. Generally, 256 levels of gray value are used (the gray value processed by human eyes is only about 50-60). Spatial resolution refers to the ability of CCD resolution accuracy, which is usually expressed by image elements, that is, the size of the grid covering the original image is specified. The finer the grid is, the higher the dot and image elements are, the higher the resolution accuracy is. Usually in the case of high resolution, CCD can see the field of vision is small, but in the case of large field of vision is low resolution, so in high-speed, high-precision occasions equipped with two different field of vision CCD. In order to fit the placement machine with BGA, CSP and other devices, the light source of CCD is added with BGA lighting on the basis of previous element lighting (peripheral, coaxial). BGA lighting is led more level than ever.

The function of SMT optical system

1. Confirm the position of PCB

2. Identification of positioning marks

3. The computer is fed back through BUS

4. The position error of the placement machine origin is calculated

5. Feedback to motion control system

6. Confirmation of components: the shape, center, coplanarity and deformation of component pins are also added with small-scale geometric position identification in PCB design, that is, the component image identification mark is added on the fine pitch QFP position to ensure the accurate installation of fine pitch devices.

The position of the placement machine can be corrected by the flying alignment technology

1. The CCD camera is installed on the mounting head

2. With this method, the mounting speed of QFP decreased from 0.7s to 0.3s

3. CCD camera is installed in suspension type

4. It is helpful to correct the position of SMC / SMD in motion.