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- January 12, 2023
- PCB knowledge
- (0)
- 05 mins
PCB stencil – a complete guide on its making, printing, types and cost
What is a PCB stencil?
PCB stencil is a sheet that helps set solder paste around surface mount devices on a circuit board. Its other name is steel mesh because of consisting of stainless steel. The stainless steel used here consists of laser-cut openings.
Stencils on a bare PCB board effectively ensure flawless and well-aligned component placement. Usually, manufacturers face severe problems managing electrical and mechanical stresses while handling surface mount devices.
Stencils help determine the amount of solder paste required to make the solder joints functional and robust enough to cope with extreme stresses.
Moreover, the perfect implementation of stencils on a PCB circuit helps gear up the PCB assembly process, significantly impacting the manufacturing cost. That’s why PCB stencils play a crucial role in PCB manufacturing.
What is a PCB stencil made of?
- Mesh
Stainless steel and Polyester meshes are used to set the frame and sheet. - Stencil frame
Movable and fixed frames are used in applications based on cost constraints and required durability. - Sheet
Stainless steel, Nickel, Copper, polyester, etc. - Glue
This material helps maintain adhesion, along with pasting the sheet and frame.
What is PCB stencil thickness?
Improper PCB stencil thickness causes solder bridging that is not good for electronic devices. That’s why you must calculate the stencil thickness correctly.
You can use the following formula to find out the best thickness concerning the aspect ratio and pad area-
Types of PCB stencils
PCB stencils comes with versatility in their mounting process, functionality, and types of aperture. Let’s check the most notable types of stencils used on advanced printed circuit boards-
- Laser-cut stencils
If you want premium precision in PCB soldering or component placement, laser-cut stencils are the best option. Here, the openings are formed through laser beams on stainless steel, which improves the design precision to a large extent.
- Prototype stencils
If you intend to use stencils for exercise purposes and with manual printing, prototype stencils are helpful. Prototypes are usually based on customized designs, designed through the Gerber File or CAD files.
- Framework stencils
In this case, a robust frame with a mesh border is placed around the stencils. This framework ensures accuracy to a certain degree by keeping the stencil sheets close to each other.
Most noteworthy, framework stencils offer consistency and excellent print quality, making them compatible with high-volume PCB productions.
- Frameless stencils
In contrast to framed stencils, frameless PCB stencils are portable and more cost-effective. As these stencils don’t come with any permanent frame, they are reusable, and you can set them at any edge per your requirements.
Besides, you don’t need to rely on automated soldering in this case. That’s why you need to trade off between accuracy and cost.
- Chemical etch stencils
Here, the apertures are etched on the circuit board by using harsh chemicals like Acids. These types of stencils are adequate for low manufacturing costs at high speed. But chemical-etch PCB stencils are not durable enough to protect the components from intense chemical attacks.
- Hybrid PCB stencils
Hybrid stencils, a well-made combination of laser-cut and chemical-etched stencils, are worthwhile for modern high-frequency and high-speed PCB applications.
- Electroformed stencils
To ensure long shelf life, electroformed stencils are more impactful than stainless steel-based stencils. These stencils are mainly made of Nickel, which metal helps release the solder paste quickly.
Along with hardness, Nickel offers a lower frictional coefficient than stainless steel. That’s why stencils become functional for a more extended period against a harsh environment.
In the case of Fine Pitch PCB manufacturing, Electroformed PCB stencils are a good choice for the manufacturers.
What is PCB stencil printer?
PCB stencil printers come with a repeatable printing capacity in both low- and high-volume PCB manufacturing. SMT stencil printers are available in automated and semi-automated formats.
Along with printing stencil sheets, these printers are supportive of maintaining underside stencils, print speed, squeeze pressure, etc.
How do you make a PCB stencil?
You can make PCB stencils in 3 viable ways. These are-
- Laser-cutting
- Chemical etching
- Electroforming
Among these three, laser cutting is the most popular way of making stencils on a PCB. Let’s have a look at the basic procedures of making laser-cut stencils.
Stackup of mylar sheets
- Stack two sheets together
- Create a separation between the stack and the opening sheet by heating the mylar sheet
- Pull off the first sheet.
Design file exportation
Now, export the design file using software like EagleCAD, Altium Designer, etc.
Resize the pads
As the melting of stencil pads increases the pad size, you need to cut down the pad size via Viewmate. To import your design file to view mate, click on “File>Import>Gerber>Setup>D Codes>Operation>Swell.”
Before clicking on Operation, you must select all columns. Then, adjust the pad size concerning the laser specifications.
Cutting of stencils
When the very opening sheet gets soften through the laser heat, the next sheet will soak up the melted pad so that you can easily pull off the sheet.
How much does a PCB stencil cost?
A PCB stencil cost varies depending on its size, mounting, types, delivery time, etc. Usually, its price covers a vast range between $10 to$1000 concerning your applications.
How to use a PCB stencil?
You must follow some basic and crucial guidelines while using PCB stencils. Such as
- Clean the stencils with Isopropyl Alcohol or distilled water to keep them clean after transportation.
- Steer the solder paste evenly on the bare circuit board. It reduces the probability of the blockage of openings.
- Control the pressure during printing concerning the placement of solder paste.
- Try to apply pasteboard printing to get the best outcome.
- Never heats the stencils with robust components.
- Demoulding speed should be under control.
- After the usage, store the stencils in a safe place and handle them carefully.
PCB stencil is a sheet that helps set solder paste around surface mount devices on a circuit board. Its other name is steel mesh because of consisting of stainless steel. The stainless steel used here consists of laser-cut openings.
- Mesh
- Stencil Frame
- Sheet
- Glue
- Laser-Cut Stencils
- Prototype Stencils
- Framework Stencils
- Frameless Stencils
- Chemical Etch Stencils
- Hybrid PCB Stencils
- Electroformed Stencils
Conclusion
Here, we have explained all the necessary details about PCB stencils you need to know. IBE, a dependable PCBA manufacturer in China, offers different stencils at affordable costs. Get in touch with us to experience the premium stencils for your projects.
