Layout tips and tricks
Assemblies with combinations of small and very large components make it difficult to transfer the right amount of solder paste to the PCB with only one stencil thickness. The same applies when using THR components. Therefore step stencils are used here. They make special demands on the layout: The squeegee of the paste printer is very flexible, but height differences between steps require a certain space/distance to the next opening. If this is not available, the paste is not completely removed. More paste is applied to the pad than intended. This often leads to soldering defects (short circuits, solder beads). We would be pleased to design these stencils for you.
Typical step stencils have a thickness of 100/150 µm or 120/200 µm. Usually the height of steps is 50 to 80 µm.
According to the rule of thumb of IPC 7525B the distance a
For a step with 50 µm: a = 0.05 mm/0.025 mm x 0.9 mm a= 1.8 mm
For a step with 80 µm: a = 0.08 mm/0.025 mm x 0.9 mm a= 2.9 mm