You must have surely used letter stencils back in grade school. Then the stencils were primarily used to color or paint perfect letters but today commercial and hobbyist sign makers take help from with creating basic signs and lettering. So, what is the relation between these basic stencils and PCBs? In the world of printed circuit board assembly, the application of laser cut SMT stencils isn’t all that different.
What is a Laser Cut SMT Stencil?
Used in electronics manufacturing but more specifically in the assembly of printed circuit boards, laser cut stencils help with the easy application of solder paste to all surface mount component pads. The stencil is an important component when it comes to accurate surface mount assembly. Repeatable and accurate solder paste disposition is also realized with the help of the stencil.
Why Is It Needed In PCBs?
A stencil is used for the following reasons (in electronics manufacturing);
- Use of SMT, i.e. Surface Mount Technology when designing printed circuit boards.
- Use of automated component placement equipment (unless the equipment is hand loaded prototype)
This negates the requirement for hand soldering each component, as the automated SMT replaces the manual process. Once components are placed on the PCB (solder paste applied), the board is baked (heated) which helps the components to attach (soldered) to the PCB.
SMT stencils are usually used in conjunction with a stencil printer. The aim is, of course, to assemble PCBs as accurately as the quality and standard requirements set forth by the IPC demands.
The Different Kinds of Stencils Used In PCB Assembly
There’re mainly 4 kinds of stencils used by PCB manufacturers;
The Desktop Stencil
This stencil is used when hand assembly of prototypes is required. As compared to other the other stencils, desktop stencil is incredibly simple in its working but makes it undeniably easier to apply solder paste by hand on the PCB.
The Framed Stencil
Framed stencils are in turn categorized in two main types: fixed and universal frame. Fixed framed stencils are found in sizes from 15” x 15” up to 23” x 23”. These use either a solid frame to hold the stencil or one made from hollow aluminum. The stencil itself is attached (or fixed) to the frame permanently.
In universal framed stencils however, the fabricator can make changes to the stencil as is necessary. This helps to manage overall costs incurred, as instead of the complete stencil (with frame) only a frameless one is needed.
The Frameless Stencils
These stencils are more commonly ordered and then attached to the frame, by hand or manually. This is usually done by the manufacturer or fabricator itself.
The Rework Stencils
This type of stencil is small in size and frameless. Rework stencils are usually used for just one component and it’s so small that the manufacturer can easily reload one problem component by hand on a PCB already loaded with components.
Some Key Measurements of Stencils in Use
- The most common material used in construction of stencils is stainless steel and Mylar due to the durability factor.
- Thickness of the stencil is usually about 0.005” to 0.007”.
- The most common size of framed stencils is 20” x 20”.
The IPC provides a standard requirement when it comes to stencil design, which can be found here. As a manufacturer and fabricator of quality PCBs, Super PCB strictly upholds to these standard requirements and uses only the best stencils available in market. Get an instant online quote today.