Stencils, also known as Surface Mount Technology (SMT) Stencil, are a kind of SMT special tooling. Professionals use it to assist in the deposition of solder paste; the purpose is to transfer the exact amount of solder paste or red glue to the precise location on the empty PCB. Professionals commonly divide the SMT placement processing in the stencil production process into Etching and Laser processes.
General Production Technical Requirements
Frame size depends on the requirements of the printing machine, Such as DEK265 and MPM UP 3000 models, the frame size of 29’*29′, using aluminum, frame profile specifications for 1.5’*1.5′.
Technicians use the Mesh frame to support the stencil (SMT formwork), usually made of metal, wood, or other materials. There are two types: fixed and adjustable. The most commonly used is the pneumatic mesh frame made of aluminum profile.
The characteristics of the frame: A variety of mesh frames has its features, in the selection, according to the different circumstances and the choice of other materials for mesh frames. The steel mesh frame made of the hollow aluminum profile is lightweight, regular size, beautiful, and easy to operate.
When using a hollow profile to make a mesh frame, a reasonable section shape can reduce the deformation of the mesh frame. Because the point of inertia of sections with the equal sectional area but different forms is not similar.
Net frame material:
The material used to make the net frame should meet the needs of the tension of the taut net, strong, durable, lightweight, and inexpensive. In the case of significant changes in temperature and humidity, its performance should remain stable. It should have a certain degree of water resistance, solvent resistance, chemical resistance, acid resistance, alkali resistance, and other properties.
The screen frame selection: Screen frame is one of the essential materials for producing the stencil printing plate. The appropriate choice of framing or not on the quality of the plate and the printing quality has a direct impact.
Technicians must evenly scrape the red glue + aluminum tape in the aluminum frame and adhesive joints on a layer of protective paint. In the meantime, to ensure the mesh has sufficient tension and good flatness, it is recommended that the stainless steel mesh be kept 25mm-50mm from the inside of the mesh frame.
The reference point: according to the size and shape of the PCB information provided by the 1:1 way to open, and the reverse side of the printing engraved semi-transparent. The whole PCB has at least two datum points at the corresponding coordinates.
Position and size to ensure high accuracy of the opening, strictly following the opening way and open provisions.
The Independent opening size cannot be too large. The width cannot be greater than 2mm, pad size bigger than 2mm, the need to frame a 0.4mm bridge to avoid affecting the stencil’s strength. The opening area must be centered.
For the convenience of production, professionals recommended that manufacturers engrave the lower left or lower right corner of the stencil with the following characters: Model; T; Date; the name of the production company.
To ensure the amount of solder paste printing and welding quality, smooth and uniform stencil surface, and uniform thickness. Stencil thickness refers to the above table. Stencil thickness should meet the fine pitch QFP BGA as a prerequisite.
If there are 0.5mm QFP and CHIP 0402 components on the PCB, the thickness of the stencil is 0.12mm. If PCB has 0.5mm QFP and CHIP 0603 or more parts, stencil thickness is 0.15mm. What is the difference between the Etching process and Laser cutting process?
magnifying glass, corrosion out of the hole wall is cabochon, feel smooth. The surface is jagged, rough like teeth gnawed. The general difference is this, the laser stencil is naturally suitable, but there are flaws. For example, what is the step stencil or double-side stencil? It is necessary to use the etching process to produce.
When opening a hole into a straight shape, there will be a lot of iron miscellaneous around, feeling little sticky hands and not too smooth, plus electropolishing after 100 times magnification to see the square hole is almost straight. The microscope can be seen under the soft wave type. In SMT SMD production, using a laser stencil can ensure the amount of solder paste in the PCB pads under the tin to avoid components welding, false welding, false welding, and other phenomena.
What Is The Standard SMT Stencil Thickness Requirement?
According to the product chip minimum PITCH and minimum CHIP to determine the PITCH < 0.4MM, there is a 0402 chip. The thickness of the steel plate is generally 0.1mm, 0.12mm, 0.13mm, and different according to the process, and there is IC PITCH> 0.4MMM. 0603chip is generally 0.15mm0.14mm, 0.13 mm. In addition, the actual thickness of a 0.13mm steel plate is only 0.127mm.
After the general use of SMT electronic products, volume reduced by 40% to 60%, weight reduced by 60% to 80% because of the high density of assembly, electronic products small size, lightweight, SMD components of the volume and weight of only about 1/10 of the standard cartridge components. It has high reliability, high shock resistance, and a low defect rate of solder joints.
What Is The Size Of The SMT Stencil We Can Support?
Small stencils are: 30*40, 37*47, 42*52, 45*55, 52*52. Large stencils are 58*58 (23 inches), 55*65, 60*60, 65*65, 60*65, 73.6*73.6 (29 inches), etc. We can make SMT stencils of different sizes according to the customer’s printing machine and the size of the PCB.
LED stencil generally use longer size stencil, such as: 50*80., 50*90, 50*100, 50*120, 50*150, 50*180, etc. Technicians can determine the specific size according to the actual size of the PCB.
Precautions When Using Stencil
Step1: Hold and place lightly.
Step2: Wash (wipe) the stencil before use to remove the dirt carried by the transportation process.
Step3: Stir the solder paste or red glue to avoid blocking the open hole mining.
Step4: Printing pressure to the best: scraper can scrape all the stencil solder paste (red glue) when the pressure is best.
Step5: Solder paste (adhesive) is relatively easy to cure. It would be best to clean the stencil promptly after removing it from the machine or after it has been left on the press for 1 hour without printed solder paste. If not cleaned in time, it will block the opening of the stencil, and the next printing will be challenging.
Step6: Stencil should be stored in a specific place, not at random, to avoid accidental damage to the stencil. At the same time, after use, you should get it back to the packaging box and place it on a unique storage rack. The stencil should not be stacked together, which is not good to take and may bend the frame.
How To Clean The Stencil?
At present, there are three ways to clean the SMT stencil:
Manual cleaning plus solvent (the most primitive cleaning method, the disadvantage is damage to the stencil and cleaning is not clean).
Ultrasonic cleaning stencil: Compared to the manual, ultrasonic cleaning has more advantages. The disadvantage is that cleaning is not easy.
The complete pneumatic stencil cleaning machine (is the more mainstream cleaning method at this stage, Germany has an intelligent stencil cleaning machine, all pneumatic without electricity, clean. The disadvantage is that the price is high compared to the previous two kinds)
So, according to the customer’s solution (price and demand), choose the right way for them.
Why Should You Partner With Us?
We offer the following:
- Optimal configuration for your stencil SMT.
- Providing a wide range of storage systems and solutions.
- The use of standard and more sophisticated SMT stencil technology.
- Individualized SMT stencil solutions.
- Affordable step stencil design.
Venture electronics in the electronics processing industry has more than 15 years of experience in selecting stencils. It also has its own set of methods. PCB board pads have BGA, QFN, QFP, and other precision components, spacing in 0.2MM-0.4MM like this board we will recommend to customers on behalf of the laser stencil and minor. CHIP pieces will only need customers on behalf of the open. Etching stencils can save time, trouble, and money!