PCBA both sides are patch components, the process is the main surface (TOP surface) brush paste --- patch --- reflow soldering - auxiliary surface (BOT surface) printing paste --- patch --- reflow Curing --- AOI detection --- inspection --- turn THT section. The first is the main surface cream paste patch, chip components are not subject to other collisions, the pressure may be; and then auxiliary brush paste, PCBA in the process due to the use of semi-automatic printing presses, PCB to use a number of thimble support The number of thimble used in the printing, the specific location is not standardized, thimble length of different, completely rely on the operator man-made, different batting of the thimble placement is difficult to be consistent, PCBA if the thimble position is not properly placed, just in the R57 position It will lead to R57 patch components by the strong pressure when printing, resulting in mechanical stress failure fracture. While the patch, reflow curing is to clamp the edge of the board, without causing other collisions, the pressure may be.
PCBA process is tin-sub-plate --- plug-in --- wave soldering --- maintenance --- cleaning --- dispensing --- inspection --- packaging --- storage and transportation delivery. The plug-in assembly line is the clamping plate edge, the wave soldering is used in the welding tray furnace, the maintenance line is the belt transmission, are not possible to touch the R57 chip component. Storage and use of hard plastic anti-static box, PCBA the internal through the knife to each PCBA isolation placed, it will not cause the impact of stress. Two pairs of the use of separate version of the manual release board, in the process, the board components may be due to PCB manufacturers micro-groove different depth, the intensity of the sub-plate by the different parts of the board may be subject to stress failure.
PCBA assembly in the manufacturing process to avoid errors and find problems in advance, developed and published IPC / JEDEC-9704A: 2012 "PCB Strain Test Guide" standard, which contains the PCBA assembly and testing stress test content. Standard requirements of electronic components to bear the stress standard of <800um / m, generally to control the 500 ~ 600 um / m below.
Identify the maximum stress in the PCBA manufacturing process that is potentially prone to excessive pressure to the process / station in order to determine whether the stress is within the allowable range. If the measured stress value exceeds the maximum allowable stress level of the PCBA, the fixture should be reworked or designed, or the process should be changed as required to allow the stress value during the PCBA assembly test to return within the allowable range. To ensure that the assembly process does not occur due to mechanical stress on PCBA damage or potential risks.
In the double-sided mixing process, the auxiliary parts of the welding parts are often used manual welding; especially simple PCBA assembly welding, based on the optimization of process cost considerations, often used manual welding; for the initial research and development of PCBA sample welding, PCBA many manufacturers Also use manual welding. Manual welding As one of the most basic welding methods, electronic assembly and rework is always one of the basic processes.