Decoupling Nonrecurring Engineering Expenses from Unit Component Pricing in Turnkey Hardware
Uncoupling engineering charges from unit component costs prevents perpetual margin penalties and secures design ownership for secondary factory transfers.
SMT Stencil Fabrication
Meaning
Manufacturing process of creating a thin metal sheet with laser-cut apertures used to deposit solder paste onto a printed circuit board. For high-density board assemblies, SMT stencil fabrication is a critical step that determines the volume and shape of the solder joints on the surface mount technology line. This fabrication is bounded by the layout of the product’s PCB and does not apply to through-hole component assembly.
Solder Accuracy
Incorrect solder paste volume is the leading cause of defects such as solder bridges or open circuits. High-quality SMT stencil fabrication uses electro-polishing to smooth the walls of the apertures, which ensures that the paste releases cleanly onto the board. This precision prevents defects and reduces the need for manual rework after the reflow oven.
Material Selection
Stainless steel is the most common material used for these stencils because of its durability and resistance to wear. During SMT stencil fabrication, the thickness of the metal sheet is chosen based on the pitch of the components being assembled. For boards with a mix of large and very small parts, step-up or step-down stencils are used to vary the paste thickness across different areas of the board.
This variation is critical for ensuring that both tiny resistors and large connectors receive the correct amount of solder.
Production Throughput
Solder paste printing is the first step in the assembly line. When an run begins, the stencil must be cleaned regularly to prevent paste build-up. This cleaning is performed automatically by the printer or manually by operators.