What Are Laser Cut Stencils？ A Guide for PCB Assembly

Traditional PCB assembly processes require the manual placement of electronic components before soldering. However, the increasing complexity of electronic printed circuit boards, combined with the need for miniaturisation, necessitates mechanical assembly and solder paste application using SMT stencils. Placing and soldering many small components on a small circuit board is no longer practical.Stencils replace the hand soldering of surface mount components and the inconsistencies caused by hand soldering. As the unique tool for surface mount devices (SMD), a laser stencil helps to apply the solder paste to exact positions.

PCB stencils are broadly manufactured by incorporating stainless steel foil-based sheet metal plates with cutouts for surface mount components. A laser machine cut the stencil into a circuit pattern that matches the locations where the components are installed.

JLCPCB provides high-quality laser-cut stencils with precise apertures, ensuring accurate solder paste application and reliable assembly.The stencil is placed on the circuit board and perfectly aligned using registration points called fiducial marks. After alignment, the solder-paste is applied using a metal squeegee. Using the right PCB stencil when applying solder paste can speed up the PCB assembly process. It will also be easier and more accurate. The current and most widely used technology for soldering components onto a PCB is SMT.

1.    What is a Laser Stencil?

Laser stencil is a type of stencil used for assembling components in PCB manufacturing. There are three stencil types according to different processes: laser cutting, chemical etching, and electroforming. Laser Stencil is usually a thin sheet made of stainless steel, and it is more precise than the other two stencil types. Standard laser cutting often results in finer output, which helps achieve greater precision. It also provides a more consistent output or results compared to chemical etching processes. Note, however, that no moisture barrier is required as the process does not depend on the chemical environment.

You can choose a framework or non-framework stencils when placing an order. Framework stencils are used for automated and semi-automated stencil machines, and there are several standard sizes to be chosen. Non-framework stencils are typically used for hand soldering, and you can customize the stencil sizes according to your requirements. Let’s see all of these terms one by one and draw a final conclusion on SMD stencils.  

2.    What is a PCB Stencil made of?

Screen frames are majorly categorised into movable frames and fixed frames. The movable ones attach the steel plate directly to the frame, and the template frame can be used repeatedly. The fixed frame attaches the wire mesh to the formwork with an adhesive. A strong frame is easily achieved with a uniform steel tension, typically between 35 and 48 N/cm2. Here are the key differences between Framed and Non framed stencils.

3.    Cutting Vs Etching Speed

For less demanding applications with larger features (>300 μm) and lower cost sensitivity, etched stencils can be an acceptable alternative at a lower price point. But laser cut stencils outperform etching for fine pitch work. Laser systems offer much faster stencil fabrication time compared to chemical etching.

   ⦁    Laser cutting speed up to 100 mm/s

   ⦁    Typical stencil cutting time < 1 hour

   ⦁    Etching rates 10-25 μm/min vertically

   ⦁    Foil etching time 1.5 to 4 hours

   ⦁    Laser ~4-10x faster than etching

The slower etching process limits throughput. Lasers provide rapid turnaround which is advantageous for prototyping and short run stencil needs. Precision laser cutting can reliably achieve ~25 μm accuracy and ±10 μm tolerance on stencil aperture dimensions down to at least 150 μm. Lasers can cut apertures smaller than 100 μm.

4.    Using a SMT Stencil:

All circuit-board stencils are made by forming openings or holes within a steel sheet or a foil. The process is assisted by lasers and the positioning indicates where the SMT components would be inserted. The stencil is placed on the surface of the PCB and perfectly aligned with the registration marks. The general process of stencil manufacturing consists of the following steps:

Step 1: PCB Stencils process starts by cutting all the apertures in a stainless steel foil-base sheet using lasers precisely at the specified locations where Surface-Mount parts are required to be inserted.

Step 2: The stencil is positioned on top of the PCB and carefully positioned in perfect alignment using fiducial markings.

Step 3: A metal squeegee blade is used to apply the solder paste over the board after being aligned.

Step 4: Solder paste is applied to the PCB board where surface-mount components have to be installed.

Step 5: All components can be placed on the board once the stencil is removed.

Conclusion:

PCB stencils are essential tools for ensuring accuracy at every stage of PCB manufacturing. They are very helpful in keeping excess solder paste and other imperfections from building up that can prevent the circuit board from functioning properly. Laser cut stencils offer superior accuracy and lifetime for fine pitch SMT printing. However, etched stencils can provide a lower cost option when resolution requirements are more relaxed.

Characteristics of the target PCB, components, and solder paste should be evaluated to determine which fabrication method best suits the application needs. Both technologies continue improving, but laser cut stencils are expected to maintain advantages as electronics assemblies become progressively more miniaturized. In addition, finding the right partner for your PCB assembly needs will help you get her PCB solder paste stencils suitable for your PCB assembly needs.

JLCPCB offers professional SMT stencil manufacturing with fast turnaround times and excellent dimensional accuracy. Whether you're prototyping or preparing for volume production, JLCPCB’s one-stop PCB fabrication and assembly service ensures consistent, reliable results.