Today, Datafeng Xiaobian to introduce to you is about BGA repair table: BGA device repair process welding introduction, let's have a look ~
Selection of welding accessories: The selection of accessories for welding new BGA or BGA after ball planting is very strict. Welding auxiliary materials mainly help solder paste and solder paste two kinds. Two kinds of auxiliary materials have their own characteristics, welding paste method does not need to make steel mesh, coating is simple and fast, fast maintenance speed, but poor stability, especially for large size BGA easy to produce open circuit defects; The solder paste method needs to make steel mesh, which requires certain skills for printing, but it can effectively compensate the warping caused by PCB deformation in the heating process, effectively prevent the production of open circuit, improve the welding effect, and get better results than welding with solder paste.
For CBGA, since the tin ball is 80Pb/8Sn at high temperature and the melting point is 260℃, it does not melt in the welding process, so it must be coated with solder paste in the repair process.
Through the analysis of the actual welding process and the observation and statistics of the welding results, it is found that coating solder paste on PCB has the advantages of high stability, reducing welding defects, compensating PCB thermal deformation and other advantages that welding paste does not have. Therefore, in the actual welding process, the following suggestions are given. When the BGA size is larger than 15mm*15mm and the BGA is CBGA package condition, solder paste must be used as welding auxiliary material; When the BGA size is less than 15mm*15mm, and the PCB thickness is greater than or equal to 1.6mm, if the maintenance speed is high, you can consider using welding paste.
BGA welding process: printing solder paste (solder paste) - visual alignment - reflux
a. Printing solder paste (solder paste)
Apply welding paste: Dip the brush in a little welding paste and gently apply it back and forth on the pad. Check the application of welding paste on the pad and ask for uniform coating of welding paste. Do not contribute to the accumulation of solder paste, no fiber, hair and other residue on the pad.
Printing solder paste: There are two types of steel mesh used for printing solder paste, dustpan type and steel sheet type. The two types of applications are very common. The thickness of the mesh plate and the selection of the opening are consistent with the specifications of the SMT steel mesh production, according to the size of the tin ball diameter and spacing. The following sheet steel mesh as an example, about the process of printing solder paste.
Select the corresponding tin printing steel mesh, locate the small tin printing steel mesh and paste it on the PCB with tape (used to fix the steel mesh and prevent the tin paste from spilling); Need to make the steel mesh opening and pad completely overlap, good position. Take the appropriate amount of solder paste with a scraper and scrape it over the small steel mesh. When scraping the solder paste, try to make the solder paste can roll between the steel mesh and the scraper. Then slowly lift up the steel mesh, in the process of extraction, to reduce the shaking of the hand.
b. Visual alignment
Place the veneer coated with solder paste on the workbench smoothly, place the device on the suction nozzle of the machine nozzle, pay attention to the direction, and then carry out visual alignment, so that the image of the device and the pad overlap, run the machine, and complete the sticking action. (When tin-printing is used for repair, the BGA paste must be placed on the PCB with equipment, and manual placement is not allowed. When the brush welding paste is used for repair, you can manually place the components and use the silk screen frame for alignment. After installing the components, check whether the height of the repaired components is the same, and whether the height is uneven or the component tilt is abnormal.
After the installation check is completed, select the temperature curve program corresponding to the chip to heat the BGA. After the program is finished, the welding process of the device is completed. Remove PCB after board cooling.
Well, the above is about the BGA repair table: BGA device repair process welding introduction, hope to help you ~
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