An SMT stencil is a thin metallic sheet that is used for the soldering process in SMT, and it is important for the SMT soldering process. SMT helps to provide a direct connection of solder paste on SMD pads of the board, which controls errors at the time of the reflow soldering process. It provides accurate tin coverage after completion of work. In this post, we will cover details for features that help to choose an SMT stencil.
SMT Stencil Definition
- The SMT stencil is a thin metallic sheet that is made of stainless steel or copper and helps to assemble boards.
- The main use of an SMT stencil is the application of solder paste on PCB pads. This process helps to connect electronic components in a proper way and make a strong connection on the board.
Importance of Stencil in SMT Soldering Process
SMT stencil is important in the SMT soldering process, and the importance of SMT stencil for the soldering process is as follows.
Solder Paste
- • A stencil is important for PCBs, which helps to align the opening stencil through pads on the board.
Solder Paste Spread
- After that, the use of squeegee paste spread over the stencil. Paste flows through the opening in the stencil and deposits over the pads.
Stencil Removal:
- After application of the paste, the stencil is accurately removed, leaving solder paste on pads.
Component connection:
- Components are connected on PCB boards, and solder paste is used to configure them in their position.
Reflow Soldering:
- In the last step, the board is put in the reflow oven where it is heated, and the solder paste melts and makes a solid connection.
Features of SMT Stencil
Accuracy:
- • An SMT stencil helps to apply an accurate amount of solder paste on each pad, which is important for making reliable and strong connection joints.
- This accuracy helps to avoid soldering problems such as bridging and ineffective solder connections.
Consistency:
- Through use of an SMT stencil, every board comes with similar solder paste applied on an accurate point. This uniform solder paste application is important for making required board manufacturing in high volume.
Efficiency:
- The use of an SMT stencil also helps to apply solder paste easily, which is good to use for larger-scale production and also saves time with costs.
Reduced Errors:
- The use of a stencil reduces errors in the case of the application of solder paste. Reducing errors helps to avoid errors and provides high efficiency and reliability.
How to Choose an SMT Stencil
Thickness of SMT Stencil
- • The thickness of the stencil is the main factor for defining the solder paste quantity that is applied on the PCB pad. At the time of printing of the stencil, the lower stencil sheet makes a connection with the upper layers of the board.
- The thickness of the stencil defines the thickness of the solder paste that is applied on the PCB pad surface.
- SMT stencil thickness is defined based on connected components density, packages, and size with space between pins. If the spacing between components is less, it is recommended to use thin. For larger PCBs, a thick stencil is used.
- For PCBs, there are general space components over 1 mm and narrow spacing components. The thickness of the stencil is selected based on the components on the board. The main method for reducing the amount of solder paste applied on the solder pad is through setting the pad opening on the stencil. for PCB design software that is finished for solder paste layers.
- If connected components need different solder paste, find a thin stencil for components with narrow spacing. The thinning process provides the cost of manufacturing. So use the middle value of thickness for the stencil for defining the solder paste.
- The normal pitch component opening is 1:1, but for larger components that need high solder paste, openings are increased by about ten to 20 percent. For OFP and other parts, pin pitches are 0.65 mm and 0.5 mm, and the opening area decreases to 10%.
SMT Stencil material
An SMT stencil normally uses two main materials, such as stainless steel and copper.
- Stainless steel is a common material used that has high corrosion resistance and provides a durable nature. It helps to make accurate apertures for solder paste.
- Copper stencil provides high electrical conductivity and also increases manufacturing efficiency. It is less durable and is more prone to corrosion than stainless steel.
- Stainless steel is more costly than copper and heavier, and copper is less durable and has a shorter life.
- For high-volume production, stainless steel is used, and copper stencils are used for low-cost options or prototyping testing.
Size of an SMT Stencil
Outline the size of the SMT stencil selected based on the real size of the PCB board. The normally accurate size of the stencil sheet is used based on different factors like the shape and spacing of the PCB board to avoid error at the end of the manufacturing process.
The stencil needed to have a larger area of the board that gave details of the stencil than the stencil size. The valid area defines the central point where the SMT pads cut into the sheet, and the remaining space makes the stencil margin and is not cut.
JLCPCB is important and an expert in selecting the SMT stencil sizes and other parameters that help to get an accurate stencil. They are equipped with high-skilled staff and machines for finding accurate SMT thickness for certain projects.
For selecting a PCB stencil, it is good to consider the size and pitch of components and also the type of solder paste used. The thick stencil causes ineffective solder paste application deposited on pads, and the stencil that is very thin results in high solder paste deposition, resulting in bridging errors.
An expert team of JLCPCB fabrication houses helps to find accurate stencil thicknesses.
They also specialize in making other PCB-based services. They come with advanced manufacturing capabilities and a quality control process that provides stencils according to industry standards.
Here you can see the commonly used sizes and features of framed stencils at this famous manufacturer.
Factor for selecting the appropriate stencil size
- First of all, calculate the PCB board dimension accurately and choose a stencil that can apply to the complete board and also the components on the edges.
- Make sure that the stencil has a valid area with enough size that can handle the complete PCB layout.
- Set margin around valid areas so the proper stencil can be handled accurately without affecting the PCB.
conclusion
PCB stencil is important for getting accuracy at each phase of PCB production. It is helpful for avoiding extra solder paste and other errors that can affect board working. PCB designers and engineers work on different types and applications for the manufacturing of PCBs. Getting services from the right manufacturers is also important for getting the required SMT stencil features.
