The process flow for using printed solder paste in pcb manufacturers is: preparation before printing → adjustment of printing machine operating parameters → printing solder paste → printing quality inspection → cleaning and finishing.
The steps and introductions of the FASTPCBA electronic technicians to summarize the process are as follows:
(1) Preparation before printing. First, check the printing work voltage and air pressure; familiarize yourself with the process requirements of the product; read the PCB product certificate, if the PCB manufacturing date is greater than 6 months, the PCB should be dried, and the drying temperature is 125 °C / 4h, usually in The previous day; check whether the solder paste manufacturing date is within 6 months, and whether the brand specifications meet the current production requirements, the stencil printing paste viscosity is 900-1400Pa feels, the best is 900Pa feels, from the refrigerator After removal, it should be restored under heat for at least 2h, and fully stirred and ready for use. The newly activated solder paste should record the opening date and user name on the can lid; check whether the template is consistent with the current PCB and whether the window is blocked. Is the appearance good?
(2) Adjust the working parameters of the printing press. After the power supply and air source are turned on, the printing machine enters the on state (initialization). For the newly produced PCB, first input the length, width, thickness of the PCB and the relevant parameters of the positioning identification mark (Mark). Mark can correct the PCB processing error. When making the Mark image, the image is clear, the edge is smooth, the contrast is strong, and the working parameters of the printing machine should be input, including the printing stroke, the blade pressure, the blade running speed, the PCB height, the template separation speed, and the template. The number of related parameters such as the number of cleanings and methods.
Once the relevant parameters are set, you can place them in the template. Transfer the PCB to the printing machine working platform, so that the position of the template window and the position of the PCB pad pattern are kept within a certain range (the machine can automatically recognize). When the thickness of the PCB is less than 0.5mm, the side fixing method will cause the deformation of the PCB. In this case, the vacuum can be used to position the reverse side of the PCB, and the corresponding work surface of the printing press should be provided with a positioning support plate for adsorbing the PCB.
Install the scraper and perform the test run. The PCB and the template should normally be kept at “zero distance”. Perform trial printing on the first PCB, check the printing effect, further adjust the positional relationship between the PCB and the template in X, F, Z and θ, realize the precise alignment of the template window and the PCB land pattern, and adjust the equipment again. Related parameters, in order to achieve the best printing effect after the overall adjustment, save the relevant parameters and PCB code. Once completed, a sufficient amount of solder paste can be placed for official printing.
The above-mentioned sequence of operations varies from machine to machine, and machines with a high degree of automation are easy to operate and can be successful at one time.
(3) Printing solder paste. When printing solder paste officially, pay attention to the following items: The initial use of solder paste should not be too much, generally estimated by PCB size. The reference amounts are as follows: A5 is about 200g; B5 is about 300g; A4 is about 350g. During the use, you should pay attention to the new solder paste to ensure that the solder paste can roll forward during printing. Pay attention to the environmental quality when printing solder paste: no wind, clean, temperature (23 ± 3) ° C, relative humidity <70%.
(4) Printing quality inspection. For the detection of stencil printing quality, the methods currently used mainly include visual inspection, two-dimensional detection/three-dimensional detection. When testing the quality of solder paste printing, different inspection tools and methods should be used according to the component type. The visual method (with magnifying glass) should be adopted. It is suitable for the case of non-fine pitch QFP components or small batch production, and its operation cost is low. However, the data returned from feedback is low in reliability and easy to miss. When printing complex PCBs, such as computer motherboards, it is best to use visual inspection, and preferably online testing, with 100% reliability, which not only monitors, but also collects the real data needed for process control.
The principle of inspection standard: when there is fine pitch QFP (0.5mm), it should be fully inspected; when there is no fine pitch QFP, it can be sampled.
Inspection standard: According to the enterprise standard established by the enterprise or ST10670199 and IPC standards.
Disposal of nonconforming product: When there is any problem with printing quality, stop the inspection, analyze the cause, and take measures to improve it. If the QFP pad is not qualified, clean it with anhydrous alcohol and reprint it.
(5) Clean up and end. When a product is finished or the day is over, the template and scraper must be cleaned. If the window is clogged, do not use hard metal needles or shackles to avoid damaging the window shape. Place the solder paste in another container and decide whether to reuse it depending on the situation. After the template is cleaned, use compressed air to blow it clean and keep it on the tool holder. The scraper should also be placed in the specified place and the scraper head should not be damaged. At the same time, let the machine return to the shutdown state, and turn off the power and air supply, fill in the work log table, and carry out machine maintenance work.
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