RST Gauge LLC has developed an economical system to measure the tension on a mounted SMT stencil foil. For many years quality assurance managers have been asking for tension gauges that will give them accurate results on SMT stencils. Since stainless steel foil has a much higher modulus of elasticity than polyester screen fabrics, conventional mesh tension meters do not give accurate readings. The proximity of the mounted foils to the edge of the polyester screens prohibits accurate readings of the mesh tension as well.

Using the SMT Foil Tension Analyzer will allow quality control personnel to take readings on incoming stencils, and to check them after cleanings to assure that they are maintaining consistent tension. Readings should be taken in the middle of the foil. Readings taken in corners will show higher and should not be considered.

Measurements with this device are in one one-thousandth of an inch (0.001”). Tolerance is +/- .001” A conversion chart is provided to allow deflection readings in .001” to be converted to N/cm. Please note these readings are considered to be a relative measurement on a given stencil. Foils of different thickness on the same size frame will show different deflections. For example a 6 mil foil will deflect less than a 4 mil foil, thus resultant tension will be considered higher.

Each stencil should be checked for tension upon receipt. Readings can then be taken periodically after cleanings. If a dramatic change in tension is noticed, then the stencil should be examined for damage. Possible causes are foil wear (from squeegee pressure), torn mesh, and failed bonds.