In surface mount technology (SMT), stencil alignment and stability are key to consistent, high-quality solder paste printing. One often-overlooked detail that plays a big role in this is border holes – also called location holes, tooling holes, or alignment holes. These are not just for fixturing; they directly affect how stable the stencil is during print and, by extension, the repeatability and quality of your solder deposition
How Can You Ensure the Accuracy of the Stencil for Printing Purposes?
Stencil accuracy depends on a few critical factors:
- Proper alignment between stencil and PCB
Border holes help align the stencil with the board, especially when used with locating pins or tooling plates. The better the fit, the lower the chance of lateral movement during printing. - Consistent stencil tension
A well-tensioned stencil maintains a flat, stable print surface. Combined with secure alignment through border holes, this ensures reliable paste release and crisp apertures. - Minimizing movement during print cycles
Every pass of the squeegee applies force that could shift the stencil if it’s not locked in place. Properly located border holes anchor the stencil and keep it stable throughout multiple prints. - Repeatability across prints and runs
Whether it’s the first print of the day or the hundredth, border holes allow the stencil to consistently locate in the exact same position, reducing variability.
Low Surface Tension
Stencil tension describes how taut the stencil foil is when mounted in a frame. It plays a major role in print performance. Low tension can lead to:
- Inconsistent paste deposits
- Stencil bowing or sagging
- Poor gasket seal between the stencil and PCB
High and uniform tension across the stencil helps maintain a clean wipe, improves paste release, and keeps the foil flat over the apertures during the squeegee stroke.
Low Surface Tension
Tension should be measured using a tension meter, often in Newtons per centimetre (N/cm). The reading is taken by placing the meter on the stencil foil and recording resistance to deflection.
Key points:
- Target tension: Typically around 35–50 N/cm, depending on stencil size and frame type.
- Check tension at multiple locations, especially corners and the centre.
- Check before use and after cleaning cycles, as tension can degrade over time.
- For frameless stencils, ensure the frame system applies consistent and even tension every time.
Maintaining proper tension ensures the stencil performs the same way from print to print.
Border Holes for Solder Stencil
Some SMT printers use frameless stencil foils, which rely on the machine’s own tensioning system rather than a fixed frame. To allow these foils to be properly tensioned, a border hole pattern must be laser-cut around the perimeter of the stencil. These holes engage with the printer’s mechanical tensioning arms to stretch the foil evenly before each print cycle.
At Datum, we supply thousands of foils each year with pre-cut border hole patterns, ready to drop into a wide range of machine systems. This saves our customers the step of cutting these holes themselves and ensures the foils are immediately compatible with their chosen frame or tensioning setup.
Border holes are used to:
- Align the stencil to the PCB or printer tooling plate
- Prevent movement during squeegee passes
- Ensure repeatability in high-volume production
Best practices for location holes:
- Use at least two holes for alignment (three for large or complex stencils).
- Place them as far apart as possible for better accuracy and to minimize angular misalignment.
- Keep them clear of any aperture areas to avoid weakening the stencil.
- Match the printer or fixture pin locations – this is often standardized within a line or company.
Custom Border Hole Patterns for Your Tensioning System
Stability during solder paste printing isn’t just about materials or printer settings-it starts with smart stencil design. Border holes are a small feature with a big impact: they reduce stencil shift, support proper alignment, and improve print quality across batches.
When combined with good tension control and thoughtful placement, these holes help keep your SMT process stable and repeatable.
By purchasing foils with pre-cut border holes, customers save valuable processing time, increase manufacturing capacity, and improve overall efficiency-making stencil preparation faster, easier, and more consistent.
A wide range of SMT screen printing platforms are available on the market, each employing distinct stencil tensioning systems. Datum’s precision-manufactured stainless steel SMT stencil foils are fully compatible with these systems and are specified by contract manufacturers across the electronics assembly industry.
To discuss your requirements or request a quote for pre-cut border holes, get in touch with the Datum team-we’re ready to help you find the right solution for your equipment and process.