Printing – Stenciling – Stencils
Patent
1997-08-26
1999-11-09
Funk, Stephen R.
Printing
Stenciling
Stencils
1011271, 1011281, B41N 124, B41F 1536
Patent
active
059793120
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an improved stencil or mask for use in applying solder paste on to circuit boards and to a support frame therefor.
2. Description of Related Art
It is known to produce electric circuit boards with solder connections for components, such as integrated circuit chips, by applying a solder paste to the circuit board by means very similar to screen printing. In one such known printing arrangement, a solder stencil or mask comprises a thin but still relatively stiff sheet of stainless steel or brass in which fine lines or apertures for the passage of solder paste have been formed, for example, by etching or laser cutting. The metal sheet is bonded to and supported by a thin peripherally surrounding flexible perforate sheet, of polypropylene or like, which in turn is bonded at its edges to a rectangular rigid metal frame. Such known arrangement is expensive and time-consuming to produce--particularly in view of the curing time necessary for the bonding of the adhesive. Additionally, the mesh and mask are not removably replaceable on the rectangular support frame without destruction of the mesh.
More recently it has been proposed to provide a rigid rectangular support frame wherein on two opposite sides and extending along a substantial part of the length thereof there are mechanical coupling means for interconnection with opposite sides of a metal printing stencil or mask with one mechanical coupling means being mounted on displaceable support means which are displaceable to tension the sheet when connected between the coupling means by suitable hydraulic, pneumatic or spring or mechanical tension devices as will be apparent to persons skilled in the art and well known. The mechanical coupling means includes two metal strips which underlie the normally lowermost surface of the mask sheet when in the operative position of the printing frame and mask and are coupled to the mask sheet along two opposite edges by means of a plurality of apertures in each strip at relatively large spacing and secured by screws, rivets or the like. While such arrangement is suitable for relatively small circuit boards, it does have the disadvantage of not permitting circuit boards of large area to be printed because of the projection of the opposite side strips of the mechanical coupling means beneath the lowermost surface of the mask. Additionally, the arrangement produces a very rigid mask when tensioned which may not allow for slight irregularities in the circuit boards which were tolerated by the first abovementioned arrangement.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an improved solder stencil or mask which may be readily mechanically connected with a supporting and printing frame such that the mechanical coupling means do not project below the lowermost surface of the mask in its operative position and, preferably, a mask which is readily detachably connectable to the support frame.
It is also an object of the present invention to provide a solder stencil or mask which has opposite sides modified so as to be more flexible than the main body of the sheets from which the mask is formed so as to be deflectable without kinking or other deformation or possibly consequential permanent deformation in the mechanical coupling with the support frame.
According to the present invention there is provided a solder stencil or mask having opposite side regions adapted or modified by being apertured or of reduced thickness so as to be more flexible than the main body of the sheet from which the mask is formed so as to enable the opposite side regions to be bent without kinking or other deformation in the mechanical coupling with a support frame and subsequent tensioning.
Still further according to the present invention there is provided an improved stencil or mask comprising a sheet of material more flexible than known mask sheets or having at least two opposite edges adapted to be more flexible than the main body of t
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IBM Disclosure Bulletin, vol. 16 No. 7, Dec. 1973, "Uniform Tensioning of Screen Mesh to Frame", Crimi et al., p. 2114, cl. 101 sub 127.1.
Alpha Fry Ltd.
Funk Stephen R.
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