In the SMT chip processing process, the selection and use of steel mesh are directly related to the effect of solder paste printing, which determines the final 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
The steel mesh tension standard has reference indexes in IPC electronic acceptance standard. Generally, the steel mesh tension tester is used, which is placed 15-20cm away from the edge, and 5-8 points are selected. The tension of each square centimeter is greater than 35 ~ 50N. The tension must be re measured every time the steel mesh is used online. The test steps are as follows:
Appearance inspection of steel mesh: whether there is scratch, burr, damage, etc
Zero the tensiometer and tighten the zero scale screw
The steel mesh shall be placed horizontally on the workbench, and the steel mesh shall not be pressed by hand during detection
Select the test point and check whether the test value meets the standard
Fill in the steel mesh tension test record form
Steel mesh cleaning
Installation and use on solder paste printer
2. Cleaning of SMT steel mesh
After the steel mesh is installed in the solder paste printer, the cleaning cycle needs to be set. Some full-automatic solder paste printing and will have automatic cleaning function. Manual printing equipment requires workers to wipe every 4-10 boards after printing to avoid steel mesh blocking.
