Inthe SMT chip processing process, the selection and use of steel mesh aredirectly related to the effect of solder paste printing, which determines thefinal welding result. In order to avoid less tin, continuous tin and false welding,SMT engineers must strictly control the steel mesh. This process includes:selection of steel mesh, tension test of steel mesh, cleaning of steel mesh,etc.
1.Tension test standard and method of SMT steel mesh
Thesteel mesh tension standard has reference indexes in IPC electronic acceptancestandard. Generally, the steel mesh tension tester is used, which is placed15-20cm away from the edge, and 5-8 points are selected. The tension of eachsquare centimeter is greater than 35 ~ 50N. The tension must be re measuredevery time the steel mesh is used online. The test steps are as follows:
Appearanceinspection of steel mesh: whether there is scratch, burr, damage, etc
Zerothe tensiometer and tighten the zero scale screw
Thesteel mesh shall be placed horizontally on the workbench, and the steel meshshall not be pressed by hand during detection
Selectthe test point and check whether the test value meets the standard
Fillin the steel mesh tension test record form
Steelmesh cleaning
Installationand use on solder paste printer
2.Cleaning of SMT steel mesh
Afterthe steel mesh is installed in the solder paste printer, the cleaning cycleneeds to be set. Some full-automatic solder paste printing and will haveautomatic cleaning function. Manual printing equipment requires workers to wipeevery 4-10 boards after printing to avoid steel mesh blocking.