SMT Stencils for PCB Assembly Framed, Frameless, and Step-Up

What is an SMT Stencil

An SMT stencil, also known as a PCB stencil or solder paste stencil, is a nickel or steel stencil made according to the top paste layer and bottom paste layer in your PCB design file Gerber.

A PCB stencil is manufactured when PCB fabrication happens. The quantity of SMT stencils depends on how many SMT lines you want the PCBA manufacturer PCBONLINE to turn on for your project.

How is an SMT stencil used in SMT PCB assembly? It is used for silkscreen printing solder paste on the PCB pads.

Before PCBA manufacturing, the SMT stencil is put in an automatic solder paste printing machine for preparation. When a PCB goes into the machien and is at the bottom of stencil, a scraper presses the solder paste to pass through the holes of teh SMT stencil.

In this way, the solder paste leaks through the holes on the SMT stencil and is printed on the designated PCB pads. The solder paste thickness falls in the range of ±0.03mm of the stencil thickness.

In regards to the SMT stencil types, there are framed stencils and frameless stencils.

Besides, the advanced PCB manufacturer and PCB stencil maker PCBONLINE can create step-up and step-down stencils for complex PCB assembly, including QFP/SOP with the pitch at 0.635mm and below, power modules, transformers, common mode inductors, and connectors.

How Does PCBONLINE Create Holes on SMT Stencils

At the PCB stencil maker PCBONLINE, holes on SMT stencils are designed in a way that the aperture on the top side is 1mil to 5mil larger than the aperture on the bottom side.

The hole's vertical section is trapezoid-shaped. We design SMT stencil holes in this way for a better release of the solder paste for silkscreen printing.

We follow the IPC-7525 standards to design and make SMT stencils for our clients.

Most openings of the stencil are in the 1:1 ratio as the pads, but for special SMT component pads, we need to avoid stress concentration.

One principle of our design is that we make sure the opening width can support at least the 4 largest tin balls to pass at the same time.

for narrow-width IC/QFP, we design the openings with two rounded ends;for BGA, 0402, 0201, and 01005 packages, we design the openings to be square-shaped;for USB/mini USB and CF/SD cards, we design the opening width in the 1:1.2 ratio as the padsfor ICs with right-angle pads, we design the openings with a larger width than the pads.

The professionals at the SMT stencil maker and PCB manufacturer PCBONLINE have more than 20 years of experience in PCB assembly and electronics manufacturing.

With precision SMT stencils, successful SMT and PTH assembly can happen smoothly. You can have one-stop PCB assembly at PCBONLINE or assemble the PCBs on your own with our best-quality PCBs and SMT stencils.

Advantages of SMT Stencils

SMT stencils are a necessary tool to surface mount components on PCBs. The advantages of SMT stencils include:

SMT stencils allow solder paste to be accurately printed on PCB pads in an automatic or half-automatic way.For the same PCB design, SMT stencils are reusable and can be used again and again for prototype assembly and bulky PCBA production.SMT stencils make fine-pitch assembly, flip-chip, and BGA assembly available and highly efficient.

The SMT stencils are fabricated while PCB fabrication and delivered with the bare PCBs. If you need SMT stencils, contact PCBONLINE at info@pcbonline.com.