SMT stencils are used for transferring the right amount of solder paste to the correct positions in a bare circuit board ready for assembly, which means that stencils can fast and efficiently ensure the most accurate solder paste amount and optimal electrical connection. Solder stencils work so easily with metal squeegee blades, applying solder paste over openings in a PCB and following the surface of an advanced circuit board rather well.

Using SMT stencil manufacturing technologies, we can offer two kinds of stencils: laser-cut stencils and chemical-etch stencils. Apart from all kinds of PCBs, it is in the PCBX line to fabricate solder paste stencils to meet the SMT requirement.

Laser-cut Stencil

The apertures are laser-cut on pure stainless steel. In general, this type of stencil can be fabricated with great quality and high precision in a short time.

Advantages

high accuracy

Less affected by objective factors

Trapezoid opening helps de-molding

Suitable for cutting precise apertures

Reasonable price

Disadvantages

Relatively lower production rate

Chemical Etch Stencil

The openings are etched into the metal using acid. Typically, this stencil provides better protection against material temper and hardness.

Advantages

One-time formation

Relatively high manufacturing speed

Low cost

Disadvantages

Tend to form sand clock shapes or large openings

Multiple manufacturing stages and accumulating errors

Not suitable for fine pitch stencils

Bad for environmental protection.

How to Determine the Size of the Stencil?

The size of the PCB stencil consists of two parts: internal size and overall size. The internal size is compatible with the PCB ready to be assembled, while the overall size is compatible with the printer parameter limit. As long as both sizes are accurately designed, it will make full play of its functions.

The internal size of the stencil can be worked out according to the following:

• Width of Framed Stencil = width of PCB + 100mm while its Length = length of PCB + 100mm

• Width of Frameless stencil = width of PCB + 200mm while its Length = length of PCB + 200mm

For example, if one circuit board size is 50*50 mm in dimension, its framed stencil size should be about 150*150 mm and its frameless-stencil size should be about 250*250 mm.

It is easy to remember and operate. Thus, it can work for manual solder paste printing in SMT before an automatic printer is created. Different internal size of stencils can be obtained from different PCB sizes, so different versions can be derived.

Now, let's discuss the automatic solder paste printer which is quite good. In any case, the overall dimensions of the stencil must be limited by the parameter limit of the equipment, that is the printer, because the stencil must work inside the printer's range with a frame. The specifications for different printers vary. As far as PCBX is concerned, 650 mm*650 mm or 736 mm*736 mm may work perfectly as the stencil size to match up with our printer.

A PCB designer must consider the stencil's interior size. Its overall size does not need to be considered because it is often decided by the printer parameters utilized in your contract assembler workshop.