PCBA Tech - SMT modern electronic assembly inspection technology

At present, the miniaturization of electronic products will inevitably make the components continue to develop in the direction of miniaturization, all of which puts forward very high requirements on the quality inspection technology of products produced by SMT. The following is an introduction to the detection methods of several major SMT products, the working principles and detection techniques of related detection equipment, and the corresponding improvement methods after lead-free. SMT technology is used in modern electronic assembly technology, and the inspection techniques used mainly include manual visual inspection (MVl), automatic visual inspection (AVl), automatic optical inspection (A01), online circuit inspection (ICT), and automatic X-ray inspection (AXl) ), function test (FT), needle test (FP) and other methods.

SAKI AOI appearance, compared with other testing technologies, AOI can be used in multiple locations on the production line. At present, AOI is mainly used in 3 testing processes:

1) SMT solder paste is inspected after printing, and defects in the printing process are found in time to minimize soldering defects caused by poor solder paste printing. 100% 2D and 3D inspection methods are often used to detect the location and location of solder paste deposits. thickness.

2) Inspection after placement to check for defects generated during solder paste printing and placement.

3) Inspection after SMT reflow welding, mainly to check the defects after welding.

There are many forms of applying AOI technology in SMT, but the basic principle is the same, that is, the image of the measured object is obtained by optical means. Generally, the illumination image of the detected object is obtained through a sensor (camera) and digitally processed, and then a certain This method of comparison, analysis, inspection and judgment is equivalent to automatic and intelligent manual visual inspection.

The AOI system is a precision equipment involving multiple disciplines. According to technology, AOI system can be divided into four parts: precision machinery, electrical control, image processing (CCD camera or vision system) system, and software system. The main modules can also be divided into functions according to needs.

1. Control system AOI's control system mainly completes: x, y precision workbench for m-level precision motion control, z-axis direction (CCD camera system) motion control, image acquisition, automatic positioning of the PCB board, automatic control of vacuum solenoid valves, etc. Function. AOI's control system is composed of main control computer, motion control card, image card, I/O interface board, etc., realizes three-coordinate and peripheral I/O interface control, ensures the accuracy and rapid response of motion, and cooperates with mechanical and vision modules Realize the functions of the whole machine. The main control computer is the core of the entire control system, which realizes the functions of data collection and transmission, analysis and processing of the whole machine, and issues instructions to each part to complete the functions of mechanical transmission, image processing and detection. The motion control card mainly realizes the collection of three-coordinate motion control signals, transmission of various processing data, and action execution command functions. The image card is mainly to complete the image acquisition and conversion of the PCB board.

2. CCD camera system module The CCD camera system is mainly composed of a camera, an image card, and an LED program-controlled light source. LED is a solid-state semiconductor device called a light-emitting diode, which can directly convert electricity into light. The video image signal acquired by the camera is transmitted to the image capture card, and the image capture card is controlled to complete the image capture. After the main control computer processes the captured video image, the result is returned to the main control program, and the image can be real-time through the display Observe and complete other corresponding control processes. In AOI's CCD camera system, the optical illumination is completed by the LED light source, and its main function is to control the switch, brightness and direction of the light source. The CCD camera system can perform functions such as real-time image acquisition, closing the acquisition, reading in images, and displaying images through the man-machine interface control system. When the man-machine interface system sends a job command, the CCD camera system realizes automatic scanning. The camera system can effectively identify PCB boards in various states.

3. Precision mechanical system module When each PCB board is inspected, the workbench of the AOI system must automatically move to the camera position for image capture. Even if the program has set the data related to these actions, if the parameters of the machine are changed due to changes in the accuracy of the mechanical motion, etc., the correct detection process will not be completed. In order to realize the accurate operation of the precision workbench, the precision ball screw driven by the AC servo motor and the rolling linear guide rail are used to realize the closed loop control of the position.