What is PCB Stencil and How to Align It With PCB Accurately

What is PCB stencil?

Laser cut the stainless steel foil to create an opening for each surface-mounted device on the board. After the template is properly aligned on the circuit board, apply solder paste to the opening (single pass with a metal wiper). When the stainless steel foil is separated from the board, the solder paste will remain and the SMD is ready to be placed. In contrast to manual welding methods, this process ensures consistency and saves time. You can add the PCB stencil to any PCB manufacturing order. Go to Nextpcb Quote to order and choose from a variety of template types and sizes to meet every requirement of your template.

The type of PCB stencil

Framed SMT Stencil

The framed SMT template or "glued" template is a laser cut solder paste template, which is permanently fixed in the template frame with mesh frame to tightly stretch the taut template foil in the frame. The framed template is designed for mass screen printing on printed circuit boards. The SMT template with frame has smooth hole wall, which can be used for below 16 mils and micro BGA. It has the following functions:

• The unique process can achieve smooth hole wall
• Very clean laser cutting aperture
• Excellent printing performance
• It is very suitable for a large number of stencil printing on printed circuit board
• Unique craftsmanship creates a permanent, immovable and indelible benchmark
• All SMT molds with frames are double bonded to ensure extreme wear
• 24-hour turnover standard

Frameless SMT Stencil

The frameless SMT template, also known as foil, is a laser cut solder paste template designed to work with a template tensioning system known as a reusable template frame. There is no need to permanently glue the formwork to the frame. The price of frameless template is much lower than that of framed template, which can save cost and provide excellent quality and performance. It has the following features and functions:

• Reduce storage space requirements
• It is much cheaper than frame formwork
• Very suitable for prototype PCB assembly or short-term production
• Smooth hole wall, can be used for micro BGA and below 16 mil
• 24-hour turnover standard

PCB Stencil Quote

Electroformed SMT Stencil

The electroformed SMT template is nickel based electroformed foil. The mesh frame is used to permanently tighten the tightened template foil in the template, and the nickel foil is permanently fixed in the template frame. Electroforming templates provide the best slurry release characteristics and are typically used in small pitch (20 to 12 mils) SMT applications on printed circuit boards. They are also used for the fabrication of μ BGA, flip chip and wafer bumps (1200 mil to 6 mil). It has the following features:

• The smooth trapezoidal side wall of the electroforming mold can release the solder paste better
• The friction coefficient of nickel is lower than that of stainless steel
• The electroformed foil is harder than all hard stainless steel of the same thickness, which can provide longer service life of the template
• 24-hour turnover standard

Prototype SMT Stencils

The prototype SMT template is a laser cutting template customized according to Gerber or CAD files to match the prototype PCB. These frameless solder paste molds are specially designed for manual printing. It has the following features and functions:

• It eliminates the tedious and error prone process of manual welding prototype circuit board
• Reduce pcb prototype assembly time
• Improve the quality of prototype PCB
• The cost is lower than the production mold
• Contains a complete "how to use" description
• 24-hour turnover standard

how to align it with PCB accurately

Use stencil printer

It is necessary to print solder paste on the pad of PCB before mounting surface mount components on the board. The stencil made of thin stainless steel is used as a screen for printing solder paste. If there is no template printer, align the pads on the circuit board with the holes on the template, and check the circuit board and template carefully to make sure they are aligned correctly. Then, fix the mold with adhesive tape.

For IC with 1.27mm spacing or 0.8mm spacing, this method can be used for alignment, but for narrow spacing pads (such as 0.5mm spacing or 0.4mm spacing), this alignment will become very difficult.

Use Pins Alignment

Diameter measurement, which is a simple way to align them using pins. Measure the diameter of the pin.
Creating a library
Create a library of holes for pins in kicad's footprint editor. Place a pad. Double click to open its properties.

• Hole size X: pin diameter + 0.1mm
• Dimension X: pin diameter + 0.1mm
• Check F. paste

Click the [local gap and settings] tab, solder mask gap: 1 mm

• Click [OK]
• Save space

The library has been completed with a hole with a diameter of 1 mm and a solder mask hole with a diameter of 1 mm above it. Put the footprints just made on the four corners of the separated slide rail.

• Find a PCB Manufacturer to order the stencil.
• When you receive the board and stencil, make sure that the holes are drilled in the four corners of the board. 
• Print solder paste.
• Mount the components.
• reflow it