Printing – Stenciling – Stencils
Patent
1995-07-03
1997-03-04
Burr, Edgar S.
Printing
Stenciling
Stencils
1011271, B41N 124
Patent
active
056069111
DESCRIPTION:
BRIEF SUMMARY
This invention relates to screen printing and is particularly concerned with screen stencils used in such a process.
Screen printing is well-known whereby ink, paint or other media is passed through apertures formed in a stencil onto the surface of a substrate.
The same process is used in the preparation of printed circuit boards where an amount of solder paste is deposited on the stencil and is then squeegeed through the apertures to the surface of a printed circuit board positioned therebelow. The stencil is usually made of thin stainless steel or other suitable metal foil.
Because of the demands for extreme accuracy in solder printing of circuit boards, the stencil is precisely positioned within a frame under tension and the frame is mounted in position on parts of the printing machine. Various methods of applying tension to the stencil are known.
In one current practice a pre-tensioned mesh is first bonded to a rigid framework, the perimeter of the stencil foil is bonded to the mesh and then the mesh is removed from the printing area. Thus the tension present in the mesh is transmitted to the stencil foil. This system is complicated, time consuming and therefore costly. Furthermore the stencil foil and the frame become a semi-permanent assembly which demands substantial storage space, each stencil requiring a separate frame.
In an attempt to overcome that problem an arrangement has been devised and is shown in PCT patent specification 92/08616 whereby edgemost portions of the stencil foil are formed with slots which are located over studs on the frame. The frame is then placed in tension pneumatically to rigidify the foil to some degree. However, it is found that in this arrangement the tension is unevenly distributed across the foil giving rise to so-called "strain lines" with consequent distortion of the apertures and inaccurate deposition of solder paste onto the printed circuit boards.
In a further method, described herein and in our co-pending PCT patent application number PCT/GB93/02040 published as WO 94/07696, a self-tensioning mount or frame for a stencil foil engages the foil at opposite ends of the frame, and the foil is tensioned by cam or the like means acting uniformly across the width of the stencil, so as to raise or lower same with respect to the frame, while the ends of the stencil remain clamped in the frame.
There is disclosed in Patent Abstracts of Japan publication number JP2295793 a screen plate for printing in which the screen plate is fixed at opposite ends to a frame. On one side only of the printing pattern in the plate there is formed an elastic part of the plate positioned in-line with the printing pattern and being somewhat wider than it, this elastic part being provided to avoid deformation of the printing pattern by the squeegee when the latter advances from the elastic part over the pattern to the corresponding non-elastic part. The pre-characterising portion of claim 1 hereof is based upon the disclosure in this prior publication.
An object of the present invention is to provide a stencil in the form of a metallic foil adapted to be mounted directly on a self-tensioning mount or frame by means of a row of apertures formed in the stencil foil to co-operate with corresponding pins or the like, wherein the technical effect of strain or tension lines which tend to be produced in the stencil upon tensioning is mitigated or overcome.
In an embodiment there is provided a stencil foil for mounting in tension on a mount therefor, the foil being formed with one or more regions of weakness located in the region of at least one edge of the foil.
The region of weakness is spaced inwardly from an edge of the foil and extends generally parallel to said edge of the foil. The region of weakness is formed by an array of perforations. Alternatively, the region of weakness may be provided by removing some of the material of the foil from a surface thereof, in order to reduce the cross-sectional thickness of the foil in the weakened region. Such thinning of the foil may be provided instead
REFERENCES:
patent: 2925774 (1960-02-01), Scheeler
Burr Edgar S.
Colilla Daniel J.
LandOfFree
Screen printing stencil does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Screen printing stencil, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Screen printing stencil will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2138992