Printing – Stenciling – Stencils
Reexamination Certificate
2000-01-13
2001-09-18
Yan, Ren (Department: 2854)
Printing
Stenciling
Stencils
C038S102300
Reexamination Certificate
active
06289804
ABSTRACT:
FIELD OF THE INVENTION
The present invention is primarily concerned with means for applying solder paste to circuit boards and a mounting support means therefor but may be used for applying other viscous compounds such as glues or adhesives for other purposes.
The present invention provides an improved supporting and tensioning frame for a stencil having improved means for displacement of the mounting teeth and also provides separate support means for the stencil which facilitate insertion and removal of the teeth of the frame in the slots of stencil.
BACKGROUND OF THE INVENTION
In GB 2264460 of Micro Metallic Limited there is disclosed a support and tensioning frame and a rectangular stencil mountable thereon wherein at least two opposite edge regions of the stencil have apertures which receive displaceable mounting fingers or mounting teeth on opposite sides of the frame and tension the stencil by rotary or linear displacement of the teeth which abut the edges of the stencil and lie out of the main plane of the stencil in the tensioned condition.
In GB 2292115A of N. M. Baker a mounting frame is disclosed wherein springs bias stencil mounting bars inwardly into a non-tensioning position and manually operable levers are used to displace cams to move at least two adjacent mounting bars outwardly to tension the stencil. Manual operation is required and the cams may not apply the same even tension nor the same force nor is there the same ease of stencil mounting as in the present invention and the connection means of this prior application extend into the plane of the main body of the stencil.
SUMMARY
According to the present invention a support and tensioning frame for a stencil for enabling soldering paste to be applied to electric circuit boards comprises a rectangular support frame with each of at least two opposite side regions of the frame having an elongate stencil support surface against which a stencil abuts and is flexed in such region on tensioning, and a displaceable mounting bar carrying a row of projections or teeth which are insertable and engageable in apertures in opposite side regions of a stencil, characterised by the feature that the mounting bars of said at least two opposite sides of the frame are permanently biased, for example, by spring means, to move away from each other into the stencil engaging position of the teeth, and that optionally operable displacing means are provided for optionally displacing each said mounting bar against the action of its biasing means to displace the mounting bars into closer proximity and, in use, to displace the tensioning teeth out of the apertures in the opposite side regions of the stencil to permit the stencil to disengage from the teeth and frame.
For achieving most accurate stencilling results, it is desirable that a rectangular and preferably square stencil be tensioned along all four sides and thus the following description will mainly be in respect of a stencil having teeth-receiving apertures along all four sides thereof and to a supporting and tensioning frame having mounting bars and tensioning teeth along all four sides thereof.
In accordance with the inventive principle of the earlier GB Patent 2264460, it is preferred that the frame of the present invention operate such that the mounting means which will preferably be teeth, do not extend into the plane in which the main central body of the stencil lies when tensioned which means the edge regions of the stencil have to be flexed over/under surfaces of the frame to be engaged by the mounting teeth.
The optionally operable displacing means will accordingly be preferably provided along all four sides of the frame and preferably be simultaneously operable and preferably will comprise an inflatable and deflatable tubular or other flexible elongate member (normally closed at one end) which will preferably extend continuously around the four sides of the frame so as to act on the four displaceable mounting bars equally and simultaneously. Preferably a releasable valve means is provided to optionally maintain the tubular means in the inflated condition prior to tensioning of the stencil and until the valve means is released to cause deflation of the tubular means via the biassing means to enable the teeth to engage in the apertures in edges of the stencil. Preferably the displacing means will be pneumatically inflatable.
The supporting and tensioning frame will preferably be formed as a continuous channel formed of side sections preferably with corner connecting blocks and with side sections preferably of substantially U-section with preferably the outermost limb or wall being of a shorter length than the inner limb or wall to facilitate mounting of the stencil—as will be subsequently described.
Also according to the present invention a stencil support and mounting means for facilitating the engagement of teeth of at least two opposite side regions of a rectangular supporting and tensioning frame in apertures in at least two opposite edge regions of a stencil and for facilitating the deposition of said stencil, comprises a base means form which there extend at least two spaced apart projections providing support surfaces for engagement with at least two opposite edges of a rectangular or square stencil when the stencil is located extending therebetween such that the stencil is freely supportable and downwardly flexible, and guide and location means cooperable with surfaces of a rectangular or square supporting and tensioning frame for the stencil which when said stencil is supported on said projections and said frame is being guided and located seating on said support means, said projections restrain downward deflection of the edge regions of the stencil which is otherwise flexed against an elongate support surface of the frame, and the teeth in said at least two opposite side regions enter into the apertures in the at least two opposite side regions of said stencil and such that on release of optionally operable displacing means of said frame, said teeth are biased to be displaced outwardly to enter in said apertures and engage the stencil and hold the stencil in a tensioned condition.
Also according to one aspect of the invention there is provided a combination of frame, stencil and stencil support.
Preferably the base means will comprise a rectangular and preferably square sheet and the at least two projections and the location and guide means thereof are provided by at least two spaced apart stepped members extending along opposite side regions of the base sheet with the inner normally horizontal surface of the steps of at least two facing projections acting to support opposite edges of a stencil and outer substantially vertical or upper extending surfaces of the projections acting to locate and guide the supporting and tensioning frame. Preferably four location and guide means will be provided—one along each side so that a precise location of the teeth within the apertures in the stencil is achieved. Other arrangements, such as a plurality of spaced apart projections and/or corner location/guiding for the frame may be provided.
According to a preferred embodiment of the invention the stencil support and mounting means comprises a rectangular base sheet having four elongate stepped supports each extending along a side of said sheet and each having a shoulder on its inner side for supporting the edge of a stencil above the surface of the base sheet; said stepped supports being shaped and dimensioned and located so that a stencil support and tensioning frame may locate thereover and preferably around although if the projections are two-part, preferably within the outer part, so that teeth of the frame align with slots of a stencil supported on the shoulders of the support and mounting means.
REFERENCES:
patent: 2563972 (1951-08-01), Steen et al.
patent: 3303777 (1967-02-01), Feier et al.
patent: 3416445 (1968-12-01), Krueger, Jr.
patent: 3608484 (1971-09-01), Bubbley et al.
patent: 4442772 (1984-04-01), Bubbley
patent: 5111743 (1992-05-01), Umaba et al.
patent
Mintz Levin Cohn Ferris Glovsky and Popeo P.C.
Mirabito A. Jason
Sayre Robert J.
Yan Ren
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