Printing Stencils & Foils
Precision Micro has made many significant contributions to stencil printing that have benefited the electronics industry.
Demountable foil frame systems
The Company was responsible for both concept and design of the Vector and Tetra demountable stencil foil systems and produces stencil blanks for subsequent laser cutting by licensees.
For ultra fine pitch printing and wafer bumping, Precision Micro produces electroformed stencils. These highly precise, tight tolerance stencils are manufactured from a special grade of nickel and offer exceptional durability, low wear characteristics and long life. Electroforming is an additive process in which the stencil is ‘grown’ on a mandrel. The process produces a particularly smooth underside for excellent gasketing to minimise under-stencil paste bleed and trapezoidal apertures with exceptionally smooth sidewalls for optimum paste release. The introduction of LEEF technology has taken the production of ultra-fine stencils to new levels of precision.
The problems of using polyester and stainless steel wirecloth emulsion screens for industrial screen-printing have been highlighted for many years and are well documented. In many applications metal stencils have replaced polyester mesh screens with great success but using a metal stencil has its limitations, especially where continuous or large area deposits are required. Typical applications are for encapsulation and encapsulation dams, bonding pads and tracks, screening can attachment, printable gaskets, etc.
MicroMesh provides a viable solution for such applications, combining the benefits of both screens and stencils, while overcoming their limitations.
The 'squeegee side' of the MicroMesh stencil emulates a woven screen by having perforations that form a mesh. This mesh prevents any squeegee scavenging of the material, even on large area deposits. The mesh size depends on the deposit required and the material in question and is calculated precisely. Several different mesh sizes can be incorporated into the same stencil to give different deposit characteristics within one squeegee pass.
The underside of a MicroMesh stencil is essentially a cavity that matches precisely the required print area. Continuous deposits are possible, as there is no interference from mesh weave over the printed area. For large print areas, the cavity is prevented from collapsing by the inclusion of minute columns on the underside to support the mesh. This maintains the cavity volume during the print cycle for optimum results.
MicroMesh technology can be used in all stencil-printing machines from hand frames to fully automated, in-line robotic systems.
Screens wear in use and are susceptible to mechanical failure. Cleaning solvents can cause delamination of emulsions. MicroMesh metal stencils, when used along with a mechanical foil tensioning system, overcome these problems.
High print definition
The nature of woven screens means that deposit edges tend to be ragged and imprecise, especially when used to print with "snap off". MicroMesh stencils permit positive contact printing where the stencil itself forms a gasket with the substrate, producing higher definition deposits.
Deposit thickness control
Deposit thickness is a function of the mesh parameters in a conventional screen. It can be varied within limits by changing the mesh but you can only have one mesh size on one screen so deposit thickness is fixed. MicroMesh can incorporate any number of mesh parameters in one stencil allowing multiple deposit heights from a single squeegee pass.
Large area suitability
Physical limitations of conventional stencils make them unsuitable for printing large contiguous areas or continuous tracks. MicroMesh is ideal for this purpose and is far quicker than the continuous dispense option.