Stencils for surface mount assembling of PCBs
The advantages of laser cut stencils:
- Smooth walls and tapered aperture profile. It's increase possibility of solder paste to pass through stencil apertures during print cycle.
Figure 1 Cross-sectional profile of an aperture formed by laser cutting
- High geometrical accuracy of apertures allows precise and repeatable deposition of solder paste volumes to the PCB lands time after time.
- High accuracy of land profile replication in the stencil allows easy and reliable position stencil on PCB.
- Stencil manufacturing is performed directly from CAD/CAM data eliminating problems with phototool imaging and fabrication quality, as well as quality of surface preparation and photoresist application to the foil as it is the case with chemical etching method of stencil manufacturing.
- Stainless steel serving as base material for these stencils has high tension rate. Therefore, the stencil doesn’t change in sizes, and the aperture pattern is not distorted even after 10,000 printing cycles that making the stainless steel stencil very reliable in usage.
Due to so high performance of these stencils they are recommended for assembling of any PCBs and especially for assembling PCBs containing fine-pitch components.
Laser cut stencils are the choice of those who know the value of their time and costs and care about their products quality!
Cost:
The base price of a stencil includes the following options:
- Order preparation by our engineer according to customer's requirements
- Laser engraving (up to 25 characters)
- Final electropolishing
- Stencil verification with a specialized stencil Automated Optical Inspection system, the final report will be attached to the order
- Contrast marking including all information about the order (file name, order number, material thickness, board side, manufacture date) made on the stencil side faced to the operator during operation
- Packaging with a hard support and a carrying handle suitable for transportation and further stencil storage
The price depends from apertures quantity and stencil size, and calculated for each order individually.
We provide special discounts depending from total orders quantity history and time of cooperation with our company in the stencil production.
Then more orders we make for you, then less the price for stencil manufacturing!
Production time:
The standard production time is 1 working day excluding the day of ordering and the day of dispatching for delivery.
It is possible to make production time not more then 6 working hours at double cost rate basis. In this case production time is counted from the moment of confirmation order by our department.
Options:
Electropolishing is the process of final stencil treatment wherein a thin metal surface layer is removed from the stencil by electrical current impact. As result of this process is a formation of thin smooth metal film on the surface layer of metal including inside walls of the apertures.
Figure 2 View of an aperture edge before and after electropolishing
The result - formation of almost ideally smooth surface with characteristics close to surface of electroformed stencils.
A slight chamfer is formed on the apertures edge. This improves solder paste pass through the stencil apertures practically not leaving residues of paste inside.
Figure 3 Chamfer formation on aperture edges
Recommendations for application
Electropolishing is recommended for stencils with high density of components or with apertures of:
- Finepitch or ultrafinepitch components
- BGA
- microBGA
- QFN
- 0402 or 0201 chip components
Advantages of using electropolishing
- The solder paste pass-through function of the stencil is improved.
- Achieve better paste prints definition. As a result, the printing cycle time is decreased, and stencil operation time between cleaning cycles is increased.
- Stencil's surface quality and resistance against solvents used for stencil cleaning are improved. Due to smooth surface, the stencil cleaning is easier and faster.
- The risk of bridging associated with stencil separation is decreased.
- Light burrs produced by laser cutting is removed from the stencil surface and inside walls of apertures.
Figure 4 Example of enforcing of stencil edge
Enforcing of stencil edge done by contact welding of additional strips of material 0.2 mm in the perforation area. Drawing of perforation of strip repeats the pattern of perforation of basic stencil.
Enforced edge lets:
- Reduce possibility of breakthrough for perforation of stencils made of thin materials (0.1 mm or less), and also their crushing during stretching of stencil
- Increase hardness of stencil on the cross-twisting during stretching of stencil
- Secure the edge of the stencil for personnel working with stencils, by thickening and blunting the edge of stencil