Stencils are thin sheets made of brass or stainless steel. It has a circuit pattern cut into it that matches the pattern of the surface mount devices required (SMD) on the PCB. They simplify the application of solder paste to surface mount components in a PCB assembly. In this post, we will discuss the role of stencils in PCB assembly.
How to Use Solder Paste Stencils?
The stencils aid in the precise and repeatable solder paste deposition in PCBs. With the use of solder paste stencils, a PCB fabricator can apply solder paste only where he needs it.
Position the stencils with the desired circuit pattern cut into it on to the board accurately, and then apply solder paste evenly.
Remove the stencil after passing the assembly through the reflow oven.
The board has now solder paste deposition only where needs it.
Common Types of Stencils
The following are the common types of stencils that are widely chosen for the electronics assembly process.
Desktop Stencils: These are the basic stencils preferred when assembling circuit boards by hand. Desktop stencils allow easier and accurate application of solder paste on to the board.
Framed Stencils: These "glue-in" stencils are permanently mounted in a stencil frame. They feature a solid or hollow aluminum frame to hold the stencil and are designed for high volume screen printing on printed circuit boards. Framed stencils feature clean laser-cut apertures and provide excellent print performance, which makes them popular.
Frameless Stencils: Generally used for prototype printed circuit board assembly or short runs, these stencils do not need to be permanently glued in a frame. They are less expensive than framed stencils and require minimal space for storage.
Prototype Stencils: These frameless SMT stencils are specifically designed to avoid the likelihood of common errors while hand soldering. You can rely on these types of stencils when you demand fast assembly with minimal cost. They are affordable, compact, easy to handle, and easily disposable/recyclable.
Rework Stencils: These solder paste stencils are laser cut from the finest grade, anti-static polymer film for printing precise deposits of solder paste when components need to be reworked or replaced.
So far we have disused the role of stencils in PCB assembly, how are they used, and common types of stencils. In the next post, we will discuss the benefits of using stencils, and more!