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PCBA Tech
​Knowledge points of various processing of circuit boards
PCBA Tech
​Knowledge points of various processing of circuit boards

​Knowledge points of various processing of circuit boards

2021-11-05
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Author:Downs

The following introduces the knowledge points of patch processing, PCBA processing, and SMT labor and material processing:

1. What is the personality of solder paste? Viscosity, vibration, thixotropy, the melting point is usually lead 183 lead-free 217 and so on. 2. What is the soldering process of solder paste components? It can be divided into 4 stages: heating, constant temperature, reflow, and cooling. Heating: the printed and patched PCB is added to the reflow soldering, and the temperature is gradually increased from room temperature, and the heating rate is controlled at 1-3°C/S. Constant temperature: After protecting the quiet temperature, the flux in the solder paste is efficient and evaporates in a proper amount. Reflow: At this time, the temperature rises to the highest, the solder paste is liquefied, and alloy is formed between the PCB pad and the solder end of the part, and the soldering is completed. The time is arranged in 60S, which is determined by the solder paste. Cooling: Close to the cooling of the welded board, the cooling speed can be controlled well to get a beautiful solder joint, such as ROHS 6-7°C/S. 3. How to optimize process parameters like this? Such as the optimization of the profile curve? Generally, three methods of presetting, measuring and arranging are required to obtain the best parameters. Take the furnace temperature curve as an example. First, preset the reflow soldering speed and the temperature of each temperature zone according to the type of solder paste, PCB thickness, etc., and then use the furnace temperature tester to measure the intrinsic temperature curve of the PCB board. Refer to the usual experience and the conventional process of solder paste soldering to beg for understanding, repeat arrangements and repeated examinations based on the preset temperature and speed, so as to obtain the most consistent curve file.

pcb board

4. The efficiency of solder paste, process parameters, and rigid equipment are related to printing solder paste? How to innovate? At the beginning, the solder paste was probably due to its identity ratio, particle size, and the use of atypical characteristics such as moldability, thixotropy, vibration, etc., which resulted in the display of collapse, short circuit, and less tin during printing. Process parameters such as printing pressure, squeegee speed, squeegee angle, etc. will result in insufficient tin, sharpening, irregular molding, or even tin paste after the solder paste. The hardware is important in the formation of poor printing such as squeegee hardness, stencil relaxation force, opening size, tooth shape, surface roughness, stencil thickness, and the support and fixation of the printing machine on the PCB. In short, the essential factors of solder paste printing are determined. many. In the essence of consumption, based on this questioning question, we can comprehend the undesirable reasons that have formed so as to reconcile them to the best. 5. The creation of Profile DOE? The creation of CPK for placement machine? DOE: Trial arrangements. A statistical method for placing tests and comprehending test data. The creation of Profile DOE can be completed in the following steps: 1. According to the company's "Reflow Soldering Homework Guide Book", select the target to be tried: such as the set speed, the set temperature of each temperature zone, and so on. 2. Refer to the Comprehension Test Center and determine the most suitable test position on the board as the test position. 3. Expected (with the experience of body odor as a reference) the expiration of the test status (such as bridging, virtual welding, etc.) will be listed and waiting for statistics. 4. After the preparation is completed, several sets of experiments are repeated, the statistics are cut off, the comprehension is cut off, and the best parameters are judged. 5. Test and subscribe the result Profile, do a good job of summarizing and reporting, and complete. The CPK of the placement machine is equal to the goal of the placement machine's precision process capability. There are formulas to estimate, but for the time being, there are softwares for automatic estimation (such as Minitab). Equipment CPK creates a dry test arrangement: In terms of equipment dry accuracy correction, use standard jigs to carry out repeated placement attempts with different heads, different positions, and different angles, and then measure the position tendency, and close the winning sets of data Input the offset of Yubi into the CPK estimation software to obtain the CPK value. The general standard CPK is greater than 1 period and the manufacturing process is normal. 6. How does SPI prove that the system is Ok, and is the data accurate? I don't understand the question a bit. Three understandings of SPI: There is an SPI system (software process correction), an American company that completely handles preparations for sale, and an SPI device. The two in the front are not very clear, only that the SPI device is a device for trying solder paste printing. After three-color illumination, coordinated red laser scanning, gather samples to obtain the surface shape of the object. Then automatically identify and understand the solder paste area, and estimate the height, area, volume, etc. Er most likes its ability to automatically learn the board, and automatically export the EXCEL file of the natural coordinates. Ha, maybe the SPI of the problem is not understood at all. . 7. In case of bad incoming materials, the plating layer of the component pins? How many bad samples will be taken? Incoming materials need to have IQC based on related standard documents, such as project approval samples, IPC general standards, and meeting standards, etc., and conduct random inspections; the number can be determined according to GB/T2828, and the number of samples can be determined according to the AQL acceptance standard. Or not. The plating layer of the component pins is generally pure tin, tin-bismuth or tin-copper alloy, only a few microns thick. The end structure of the chip element is: the inner palladium silver electrode, the central nickel barrier layer, and the outer lead-tin layer. 8. How does IMC produce? What is the efficiency of the thickness of IMC in terms of welding? How thick is the IMC layer and what is its scope? IMC (Intermetallic compound) Intermetallic compound is formed by the explosive migration, infiltration, separation, and common methods of the metal body during welding. It is a thin layer of alloy, which can write molecular formula, such as between copper and tin: benign Cu6Sn5, malignant Cu3Sn, etc. The IMC layer will be displayed when there is usual welding, and the IMC layer will age and thicken, and it will stop until it encounters the stop layer. On its own, it will form welding hardening, and then the difficulty of tinning. The general thickness is 2-5μm. 9. What is the important basis for engraving the stencil? What are the area ratio and simplicity ratio? The opening of the steel mesh is mainly based on the Gerber file of the PCB or the actual PCB. The simplicity and area of the open steel mesh have been fixed after long-term testing and exhaustion. When the pads are extremely large, the central frame grid should be used to protect the relaxation force. The center of the second question is not clear. On the surface, the component can be placed. As long as the function is considered reasonable, if it is a component on the top of the channel function, then the left channel runs to the power zone. It's always bad to pull a line. Others, note that if the component is a plug-in component, it is necessary to plan the rationality of the production process (refer to the following questions) and so on. 12. What are the factors of DFM in veneer technology? The production process should be emphasized when DFM is arranged: 1. Although the method of reflow soldering is adopted, it is cheap because of its small hot punching, few soldering defects, and high soldering stability. 2. If there must be plug-in components, although the arrangement and placement of the components are common, if permitted, the chip components should be reflowed first, and then the wave soldering process will be less difficult. 3. When there are many PCB components and must be double-sided, if there are not a few interposer components, double-sided reflow can be used, and then the interposer can be soldered. 4. When the PCB double-sided board has a flood of plug-in parts, although the second side patch parts can be reduced; after the first part is reflowed, the other part of the red glue solidified patch parts is then plugged into the crest.