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Comprehensive Guide to SMT Stencils

SMT stencil
PCBONLINE Team Sat, Sept 19, 2020

SMT(Surface Mount Technology) stencils, also called "PCB stencils" or "solder paste stencils", are very important for PCB designing and manufacturing. If you can't decide which type of SMT stencil to go for and you need a detailed guide for this topic, then you're in the right place. This article will focus on every aspect of PCB stencils and by the time you reach the end, you will develop a crystal-clear idea of using SMT stencils.

Part 1: What Are SMT and SMT Stencils?

SMT stencils of PCBONLINE

Surface Mount Technology (SMT) is a technology to assemble SMDs (surface mount devices) on printed circuit boards.

A PCB stencil is a laser-cut stainless stencil with openings to sieve solder paste on PCB pads. In this way, the PCB solder paste can be "printed" on the circuit boards. Then the board goes ahead for SMD placement, reflow soldering, AOI, then through-hole assembly, and wave soldering.

Due to the small size of SMD components, placing them on the PCB is a sensitive task that requires great accuracy and needs to be handled with a lot of care. SMT stencils are a life-saver when it comes to PCB assembly because they allow you to place tiny and delicate components on the circuit board without any hassle.

SMT stencils are designed according to the PCB layout and then a solder paste is poured on top of the circuit board while it is drying, you can place your components on the board so that they are mounted on the PCB surface correctly.

Part 2: Advantages of SMT Stencils

Using SMT stencils for PCB assembly is indeed a great choice because it solves many problems that you would otherwise face in manual PCB assembly. The advantages of SMT stencils include:

No Short Circuits

The chances of short-circuiting are high when applying the solder paste without an SMT stencil. Using one will ensure that there are no short circuits in your PCB.

No Gaps in the Soldering Process

Laser-cut stencils allow you to apply a smooth layer of solder paste which leaves no gaps in the soldering process.

Smooth Pad Walls

Using an SMT stencil ensures your PCB has smooth pad walls, which is something that every PCB designer wants.

Consistent Aperture

If the aperture of your PCB stencil is not fixed, you will get an undesirable uneven-looking PCB that won't work as expected. Using an SMT stencil will ensure that there are no defects in your PCB, by ensuring that the aperture is fixed.

Accurate Position of Pads

To achieve good pitch accuracy while printing, it is necessary to ensure that the position of the pads is accurate. Using a laser-cut SMT stencil will take care of pad positioning.

High Accuracy in Printing

SMT stencils allow you to print your PCB exactly how it looks in the software. Pitch patterns as small as 250 μm can be achieved with a high-quality laser-cut stencil.

Part 3: Where to Get SMT Stencils for PCB Assembly?

Now that you know the advantages of using an SMT stencil for PCB manufacturing, it's best to look for a trusted dealer who knows how to design a super fine PCB stencil. PCBONLINE is a one-stop shop for all your PCB-related needs. Whether you need a framed or a frameless high-quality laser-cut stencil, PCBONLINE is here to cater to all your circuit designing needs.

SMT stencil for PCB assembly

PCBONLINE specializes in manufacturing SMT stencils, printed circuit boards, and PCB assembly. They have a wholesome experience of 15 years and know exactly what it takes to manufacture the best laser-cut stencils. Here is what they offer:

    • High-precision laser cutting technique
    • Accurate cutting of stencils
    • Trapezoidal aperture design ensures that the stencil conducts as the solder paste is released
    • 0.3-0.5mil hole size error
    • Less than 0.12 mil positioning accuracy
    • SMT stencils as thin as 0.10mm-0.30mm
    • High-quality and durable stencils

Part 4: How Many Types of SMT Stencils Can You Get?

Not all SMT stencils are the same. There are four different types of stencils available at PCBONLINE which cater to different customer needs. Let's see what are the features of the types of SMT stencils:

1. Framed SMT Stencil

Framed SMT stencils are best for high-volume screen printing. These laser-cut stencils are fixed permanently in the frame. The stencil foil is tightly stretched in the frame with the aid of a mesh border, which allows high-accuracy printing. This feature makes framed stencils better than unframed ones because you don't need to stretch the stencil yourself.

2. Frameless SMT Stencil

A frameless SMT stencil is not permanently fixed to a single frame. Instead, with these kinds of laser-cut stencils, you can reuse the frame as many times as you like. You would have to fix the stencil on the frame every time you want to use one. They cost less as compared to framed stencils and also occupy less space.

3. Prototype SMT Stencil

These stencils are customized according to the prototype present in the CAD or Gerber files. Using these stencils will save you from soldering components on the circuit board and reduce the assembly time of the PCB. It is best if you want to avoid the use of machines and do not want to deal with stencil frames.

4. Electroformed SMT Stencil

These stencils are similar in construction to framed SMT stencils except that they are nickel-based and are manufactured using electroforming foil. Electroformed SMT stencils are best used in flip chips, water bumping, µBGAs, and SMT applications requiring excellent pitch.

Part 5: How to Use SMT Stencils?

SMT stencils are used to assemble PCBs by placing electronic components on a sheet of the circuit board. This can be done manually or with the help of a machine. Let's see what are the basic steps of assembling a printed circuit board using stencils.

  • Step 1: Designing the PCB stencil
  • Step 2: Printing the solder paste
  • Step 3: Placing the electronic components
  • Step 4: Reflow Soldering
  • Step 5: AOI Optical Inspection
  • Step 6: Cutting the boards
  • using SMT stencil

    Using a machine, you can place the solder paste on the circuit board according to the stencil designed, and then, as the paste is cooling down, you need to place the components on the circuit board either using a machine or manually. Using a machine will significantly reduce the chances of error while placing the solder paste and components on the circuit board.

    Next, reflow soldering is done so that the components adhere tightly to the circuit board after which the board is inspected for gaps and defects. An AOI optical inspection ensures that the quality of your circuit board is not compromised. In case of defects, you need to fix them before moving to the next step. After the defects are corrected, you need to cut the boards, and voila! Your PCB is ready for testing.

    PCBONLINE is your best bet when it comes to designing SMT stencils and manufacturing and assembling PCBs from scratch. Not only will you get a good price quote from them, but they will also ensure that you are fully satisfied with your SMT stencil.


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