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 We can provide you with our quality Basic Stencil and framework so you can handle assembly from the convenience of your own worktable.

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SMT STENCIL

A surface mount technology (SMT) stencil may also be called a PCB sentil, solder paste stencil, or laser stencil. An SMT Stencilmain purpose is to simply transfer the solder paste to a bare circuit board. A stainless steel foil is laser cut to create an opening for each surface mount device on the board. Once the printed circuit board (PCB) stencil is properly aligned with the top of the board, the solder paste is applied over the openings (in a single pass, with a metal squeegee). When the stainless steel foil detaches from the board,  solder paste remains, ready for the manufacture of the surface-mount device (SMD). In contrast to manual soldering procedures, this process ensures consistency and saves time.

laser stencil pcb
Laser stencil PCB

The deposited solder paste released to the board is manipulated by opening the size of the aperture, and the thickness of the SMT stencil is made out of stainless steel. Excessive paste will cause problems for connectivity and bridging, whereas less paste will compromise the strength of the soldering and joints.

 The thickness of an SMT stencil varies with the device for which it is being used. 0.020” pitch small outline integrated circuits (SOICs) can work better with a stencil giving a thin solder paste, whereas thick solder paste works best with 0.050” pitch SOICs. The thickness of the paste stencil for solder ranges from 0.001” to 0.003”. The normal thickness for most of the PCB boards is generally between 0.004” and 0.007”.

Selective Sizes with PCB Stencils Are Now Offered with Nano Coating

For nano coating, the contacting sides of the tiny components are applied with a water-resistant nano coating that opposes solder and flux as well. This phenomenon results in the better release of paste for the tiniest components. The application is made in the factory so the component is ready to use at the time of purchase. The nano coating is  recommended for fine pitches of QFN and IC, micro ball grid arrays (BGAs), and the electronic components of 0201 type.

pcb stencil maker
PCB Stencil Maker

1. PCB Prototype Stencil

 

▶ Size: 10” x 12” max

▶ Type: Squeegee

▶  Add on: Board holder

2. Prototype Oversized Stencil (SMT)

 

▶ Size: Over 10” x 12”

▶ Type: Squeegee

▶ Add on: Board holder

3. Kit-Leaded Prototype Stencil (SMT)

 

▶ Size: 10” x 12” max

▶ Type: Solder leaded paste

▶ Add on: alcohol wipes x2, gloves x1 pair, temperature marker

4. Kit-Leaded Prototype Stencil Oversized (SMT)

 

▶ Size: Over 10” x 12”

▶ Type: Solder leaded paste

▶ Add ons: alcohol wipes x2, gloves x1 pair, temperature marker

5. Prototype Kit-Lead Free Stencil (SMT)

 

▶ Size: 10” x 12” max

▶ Type: Solder lead-free paste

▶ Add ons: alcohol wipes x2, gloves x1 pair, temperature marker, grab and place tool

6. Prototype Kit-Lead Free Stencil Oversized (SMT)

 

▶ Size: Over 10” x 12”

▶ Type: Solder lead-free paste

▶ Add ons: alcohol wipes x2, gloves x1 pair, temperature marker, grab and place tool

smd stencil

Framed stencils manufactured by stencils unlimited are easy to obtain. Upload your Cream Top from the desired PCB layout software after exporting it. After automatic calculation for the best suitable thickness of your stencil, send the stencil file to sales@raypcb.com;you will get a quote immediately .

If your PCB fabrication house can make stencils, they can also make stencils for you. A Gerber file is important for panel making. Don’t forget to ask them to make the GBC file if you want to make stencil yourself!

IPC 7525 has a detailed document about calculations of stencil thicknesses. The approximate value shall be 2.64 + 0.0831 * pitch-of-component.

PCBs revolutionized the electronics industry when they replaced the earlier method of circuit design on a chassis. Before PCBs, electronic circuit design involved bulky and loose components, such as connector lugs and screw terminals, which resulted in end products with large footprints and higher costs. By replacing manual point-to-point wiring, PCBs not only automated the process of circuit design but also greatly reduced the size of electronic end products. 

Since the advent of PCBs in the beginning of the 20th century, it has gone through an evolutionary process of design improvements—such as  transitioning from single-layer designs to 20+ layer boards. Overall, the PCB design process can be broken down into the following key steps:

  • Electrical design
  • Physical design
  •  Manufacturing

The manufacturing process is followed by the placement of components on the PCB called ‘board assembly’. Traditionally, the assembly process consists of following steps:

assembly steps

Conventionally, the board assembly process was performed manually placing and soldering the electronic components by hand. However, with the increasing complexity of circuit boards and extremely small sizes of surface mount packages, board assembly is moving towards application of solder paste using PCB stencils and machine-based component placement.

During the PCB assembly process, solder paste only needs to go where a component must be in electrically conductive contact with a metal landing pad on the board itself. The hand soldering method only makes sense where the design is simple, and the number of components is minimal. Naturally, hand soldering techniques are also prone to human error, which results in inconsistent results. 

On the other hand, PCB stencils resolve these issues and are an effective and efficient method of applying solder paste. A stencil, as the name suggests, is a tool to make repetitive impressions. A PCB stencil acts as a guided template for the application of solder paste only on the desired areas of the board. The stencil is placed on the circuit board and aligned in the correct position. A runner is moved across the stencil screen which squeezes the appropriate amount of solder paste through the holes onto the circuit board.

 Every stencil is customized according to the design of the PCB so that the solder paste gets applied only on the solder pads. For surface mount technology, the stencils are called SMT stencils. An SMT stencil consists of an outer aluminum frame, polyester mesh, and stencil foil. Stencil foil is tensioned and fixed to the aluminum frame by a polyester mesh.

Stencil foil stretched and held to a frame by polyester mesh
Stencil foil stretched and held to a frame by polyester mesh.

Typically, stencils are made of stainless steel or nickel and can be categorized based on the manufacturing process (process by which aperture is formed on the stencil foil), which follows.

Electroforming: This is an additive process by which stencil foil is created by electroforming nickel.  This process is also known as E-FAB. Although this process results in a higher initial cost,price is independent from the number of apertures. Finally, higher processing time is considered a drawback of this manufacturing process.

Electroforming

Chemical Etching

This is a subtractive process by which apertures are achieved through chemical etching. This is relatively a low-cost process; however, it results in inferior results due to rough aperture sidewalls.

Chemical Etching

What is Laser stencil 

This is also a subtractive process by which removal of the stencil foil material is achieved by laser cutting. Naturally, laser cutting results in finer results and helps in achieving greater accuracy. Laser cutting also produces more consistent results than the chemical etching process. Since the process is not dependent on the chemical conditions, there is essentially no requirement for protection from moisture.

Laser Cutting
Types of stencil manufacturing technologies
Types of stencil manufacturing technologies.

Depending on the method chosen for the application of solder paste, stencils can be further divided into following types:

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These laser-cut solder paste stencils are permanently mounted on the frame where the border mesh provides the necessary tension to the stencil foil. These are designed for bulk machinery production.

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These stencils are not required to be permanently mounted on the outer frame. These low-cost stencils are recommended for prototype PCB assembly or short runs.

Prototype stencils are designed for manual printing application. It removes the element of human error from the manual printing process.

Other Important Information

How to Generate a Stencil file from a PCB File

Generate a Gerber file from the PCB, and then send the Gerber file to the stencil manufacturer to make the stencil.

Generating a PCB Gerber file:

 

➤ Open the PCB file:open all layers in setup, then click view to confirm and save.

 

➤ Create a subdirectory: click on the file, use the drop-down arrow to select create in the pop-up dialog box CAM,andtype in the folder name, then click OK.

➤ Output Gerber file: Click Addand a dialog box pops up, fill in the drawing document name in the file name, use the drop-down menu to select the drawing type in the document field, and select the corresponding defined layer name in the pop-up dialog box. Define the output layer and the content of each layer at the level, click OK, then click Run.

➤ Output D code file: open the file and select the Gerber connection diagram at the top or bottom of the dialog box. The default values of each item in the dialog box pop up, thenclick OK.

 

➤ Output list file: Put all Gerber file lists into a folder, compress them into a compressed package, and save.

circuit board stencil
Circuit Board Stencil

Whether to get perfect and reliable solder joints, printing your stencil design is the key first step. The opening size of the surrounding pad stencil is directly related to the thickness of the stencil. Generally, thicker stencils can be designed with an opening slightly smaller than the pad size, while the opening size of the thinner stencil can be designed1:1. It is recommended to use a laser to make a steel mesh with openings and electropolishing.

joker-credit

 

The thickness of the stencil determines the amount of solder paste printed on the PCB. Too much solder paste will cause bridging during reflow soldering. Therefore, it is recommended that the 0.5mm pitch QFN package use a 0.12mm thick steel mesh, and the 0.65mm pitch QFN package use a 0.15mm thick steel mesh. The size of the stencil opening can be appropriately smaller than that of the pad to reduce the occurrence of solder bridging.

Perisian-yang-dapat-berjudi-dalam-Pertandingan-Badminton-Olimpik

 

When the exposed pads on the bottom of the chip are soldered to the thermal pads on the PCB, the gas in the thermal vias and large-size pads will overflow outwards, resulting in certain air holes. Therefore, if the solder paste area is too large, it will produce various defects (such as sputtering and solder balls, etc.). However, it is almost impossible to eliminate these pores;it is possible only to minimize the pores. When designing the stencil in the thermal pad area,careful consideration is needed. 

It is recommended to create multiple small openings in this area instead of one large opening. The typical value is 50% to 80% solder paste coverage. Practice has proved that the solder joint thickness of 50μm is very helpful to improve board-level reliability. In order to achieve this thickness, it is recommended that the solder paste thickness for the underfill thermal via design beat least 50%; for the through hole, the coverage rate is at least 75% the above.

stencil solder paste
Stencil Solder Paste

SMT stencils are generally cleaned with professional cleaning equipment. Presently, the mainstream of the market is the smart stencil cleaning machine, which is aimed at the electronic industry SMT stencil, copper stencil, wire stencil, microporous stencil, and wafer trays. For the cleaning of similar stencils, the equipment uses compressed air as energy, does not require electricity, and is not a fire hazard.

 It adopts a human design and one-button operation, which helps complete cleaning and drying tasks; it utilizes high performance automatic operation of air pressure. As for cleaning equipment, the cleaning fluid is recycled, with low loss. click to know more about how to clean smt stenicl .

China and India have a strong base of SMT stencil manufacturers. Here is a list of few suppliers based in different regions around the globe:

RegionCountryCompany
APACChinaRayming PCB
APACAustraliaMasterCut
APACChinaFound Printed circuit Board Co.
APACChinaMorePCB
APACChinaPCB Sino
APACChinaJLC PCB
APACChinaPCB Way
APACChinaALL PCB
APACIndiaSatchitanand Group
APACIndiaAsahitec
APACIndiaStencil Point
APACIndiaKristeel-shinwa
EuropeGermanyLPKF
EuropeGermanyBecktronic
EuropeGermanyKoenon
EuropeItalyALBA PCB
North AmericaUSTropical Stencils
North AmericaUSStencils Unlimited
North AmericaUSEPEC Engineering
North AmericaUSOSH Stencils

 

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