SMT Basics knowledage Features of SMT 1. High assembly density, small size and light weight of electronic products, the volume and weight of SMD components is only about 1/10 of traditional cartridge components, generally after the use of SMT, electronic products volume reduction of 40% to 60%, weight reduction of 60% to 80%. 2. High reliability, strong resistance to vibration. Low defect rate of solder joints. 3. 3. Good high frequency characteristics. Reduced electromagnetic and radio frequency interference. Easy to automate and improve production efficiency. Reduces costs by up to 30% to 50%. Saves material, energy, equipment, manpower, time, etc. Why use surface mount technology (SMT) 1. Electronic products pursue miniaturisation, the previously used perforated insert components can no longer be reduced in size 2. electronic products more complete function, the integrated circuit (IC) used has no perforated components, especially large-scale, highly integrated IC, had to use surface mount components 3. product batching, production automation, the factory must be low cost and high yield, production of superior products to meet customer demand and strengthen market competitiveness 4. development of electronic components, integrated circuits (ICs) and diversified applications of semiconductor materials

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X-Ray Inspection AXI AXI is a new test technology that has emerged in recent years. When the assembled circuit board (PCBA) enters the inside of the machine along the rail, there is an X-Ray transmitter tube located above the board, and the X-rays emitted through the board are accepted by the detector (usually a camcorder) placed below. X-rays are absorbed in large quantities, and a good image is produced as a black spot (as shown in Figure 2), making the analysis of the solder joint quite intuitive, so a simple image analysis algorithm can automatically and reliably check for defects in the solder joint.   Advantages and disadvantages of AXI testing Advantages. (1) Up to 97% coverage of process defects. Defects that can be inspected include: dummy solder, bridging, standing stones, insufficient solder, air holes, device leakage, etc. Especially, X-RAY can also inspect solder joint hidden devices such as BGA and CSP. (2) Higher test coverage. It can check the places that cannot be checked by naked eye and in-line test. For example, if the PCBA is judged to be faulty and the PCB inner alignment is suspected to be broken, X-RAY can check it quickly. (3) The preparation time of the test is greatly reduced. (4) Defects that cannot be reliably detected by other testing means can be observed, such as: false soldering, air holes and molding, etc. (5) Only one inspection is required for double-sided and multilayer boards (with delamination function). (6) Provides relevant measurement information that can be used to evaluate the production process. Such as solder paste thickness, amount of solder under the solder joint, etc. Disadvantages: AXI technology cannot test for defects and faults in the electrical performance of the circuit. Now the application of BGA is more and more, the market requirements for the detection of BGA is also increasing, and even require 100% detection, hoping that in the automatic online detection of PCB board defects, detection speed is faster. But in the PCB assembly plant, the use of off-line X-ray inspection. Rarely used online X-ray detection. There are several reasons, * the biggest problem is the higher price of online X-ray inspection equipment; ** is the automatic online detection of defects in this machine is poor, a lot of misjudgment; third is its detection speed is relatively slow. X-ray inspection is usually used in the AOI detection of components that can not be detected, a board of many components can be detected with AOI, while the bubble can only be seen with X-ray. A large board, there are usually thousands of resistors, capacitors. bga may only be about one to three, these bga can be detected with x-ray. aoi detection speed is very fast, two-dimensional x-ray detection speed is also very fast, if you do three-dimensional processing, the speed will be a little slower. Now BGA less, so do BGA detection, you can use more AXI detection, that is, when doing the slicing process, you can do more layering process. In summary, axi and aoi combined use is the trend of industry development.

Application of AOI inspection equipment in SMT AOI inspection equipment is mainly used to detect defects in solder paste and devices: 1,Solder paste inspection is not very difficult, there are mainly two types of technology: color 3-color light source and multi-view. Solder paste detection is usually carried out after the solder paste printing, to carry out effective solder paste detection, the detection system must not only provide information on the area of the printed solder paste, but also should be able to provide volume and height information, if only consider the area information without regard to height information, the amount of solder paste on the pad is not enough will also lead to unreliable detection through. After the printed solder paste curing, the use of multi-level camera process technology, multiple lighting angles and 2-D system, it can quickly and sensitively capture the PCB, solder mask and solder paste appearance of the color change, the use of 3-D system, it can provide information about the solder paste area, as well as the height and volume of the solder paste ** information, but also according to the surface of the metal traces, PCB or solder mask, to determine the thickness of the solder paste 2,For device inspection, AOI inspection systems are usually installed before and after reflow soldering in SMT lines. The use of qualified sample-based learning and SMT-based CAD data detection, the specific technology is mainly based on the pattern recognition of pre-processed images, the former mainly uses statistical pattern recognition, through learning to establish qualified image patterns, and then through the comparison of the image of the detection object and sample image processing and arithmetic to obtain detection and identification results (1) Before reflow: The inspection is done after the components are placed inside the solder paste on the board and before the PCB is sent to the reflow oven. This is a typical location to place the inspection machine, as most defects from solder paste printing as well as machine placement can be found here. The quantitative process control information generated at this location provides information on the calibration of high speed chip machines and close pitch component placement equipment. This information can be used to modify component placement or to indicate that the placement machine needs to be calibrated. Inspection at this location satisfies the process tracking objective. (2) Post-Reflow:Inspection is performed at the *last* step of the SMT process, which is a popular choice for current AOI inspection equipment, as this location can find all assembly errors. Post reflow inspection provides a high degree of accuracy as it identifies errors caused by the solder paste printing, component placement and reflow process. Concluding remarks: A good process monitoring strategy should include a number of overlapping tools such as in-circuit testing (ICT), optical inspection, functional testing and cosmetic inspection. These processes overlap and complement each other in order to be *very* efficient.

What to learn in the SMT industry Many smt industry friends think, in SMT this industry, is to learn SMD machine, think only engage in SMD machine is considered to do SMT, in fact SMT (surface assembly technology) should also include many aspects:. Surface assembly components, surface assembly circuit board and graphic design, surface assembly special auxiliary materials - solder paste, SMD adhesive, surface mount equipment, surface assembly material soldering technology (including wave soldering, reflow soldering, etc.), surface testing technology, cleaning technology and quality management, surface assembly production management and other aspects of the content. The above content can be summarized into three aspects. 1, equipment, which means the SMT hardware aspects. 2, process, and SMT process technology, that is, the software side. 3, electronic components and packaging technology, which is the basis of SMT, but also the driving force of SMT development, which drives the SMT special equipment and process The continuous development of technology. For example, the component packaging to 0201, equipment and technology must also keep up accordingly. Surface assembly technology is a group of technology-intensive, know intensive technology group, involving components packaging, PCB technology, printing technology, automatic control technology, welding technology, physics, chemical, new materials and other professional and discipline. For example, the placement machine involves computers, image recognition systems, sensors, servo systems, etc., professional involving machine, electricity, light and other disciplines. Therefore, do not just think that only engaged in the chip machine is considered to engage in SMT, process, materials are as important, production management can also be involved in the future of the road will be wider and wider.