Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41C—PROCESSES FOR THE MANUFACTURE OR REPRODUCTION OF PRINTING SURFACES
  • B41C1/00—Forme preparation
  • B41C1/14—Forme preparation for stencil-printing or silk-screen printing
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41M—PRINTING, DUPLICATING, MARKING, OR COPYING PROCESSES; COLOUR PRINTING
  • B41M1/00—Inking and printing with a printer's forme
  • B41M1/12—Stencil printing; Silk-screen printing
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
  • H05K3/00—Apparatus or processes for manufacturing printed circuits
  • H05K3/10—Apparatus or processes for manufacturing printed circuits in which conductive material is applied to the insulating support in such a manner as to form the desired conductive pattern
  • H05K3/12—Apparatus or processes for manufacturing printed circuits in which conductive material is applied to the insulating support in such a manner as to form the desired conductive pattern using thick film techniques, e.g. printing techniques to apply the conductive material or similar techniques for applying conductive paste or ink patterns
  • H05K3/1216—Apparatus or processes for manufacturing printed circuits in which conductive material is applied to the insulating support in such a manner as to form the desired conductive pattern using thick film techniques, e.g. printing techniques to apply the conductive material or similar techniques for applying conductive paste or ink patterns by screen printing or stencil printing
  • H05K3/1225—Screens or stencils; Holders therefor

Definitions

• the present invention concerns an improved stencil for application of solder paste, adhesive or other printing medium and method of producing such.
• stencils from continuous sheets of metal or metal foil which are etched or laser cut or otherwise apertured to provide through passages for solder paste and such stencils are illustrated in, for example, GB 2264460 and PCT/GB96/01722 , and are more durable and enable a high degree of accuracy to be achieved.
• solder paste deposition in some areas, such as are known as the "quad pack"
• the paste is to be deposited in fine pitch and to stabilize the deposition it is sometimes necessary to reduce the height of paste in such area and this is achieved by “stepping down” or reducing the thickness of the stencil over the general area of the quad pack which is troublesome and costly.
• a stencil having one or more apertures therethrough for the deposition of a fluid material onto a lower surface which includes at least one first and normally lower aperture or recess which is in communication with the normally upper surface via a plurality of second apertures or recesses or passages of smaller diameter or width or cross sectional area than said first normally lower aperture.
• an improved stencil having one or a plurality of apertures therethrough for enabling a printing medium to be deposited on a receiving surface and including a first and normally lower surface which in use is to be proximate the receiving surface and a second and normally upper surface over which a squeegee or other printing medium applicator means is to pass, characterised by the feature that : -
• At least one larger diameter or width first aperture is formed in the first, normally lower surface, and at least one but preferably a plurality of smaller diameter or width second aperture of smaller diameter or width than said first aperture is formed in the second and normally upper surface and leads into said first aperture;
• At least one recess or aperture is provided in the normally upper surface and in the normally lower surface and a bridging portion is formed between the upper and lower surfaces having at least one but preferably a plurality of apertures therethrough of smaller diameter or width than that of those of the said recesses or apertures in the upper and lower surfaces .
• the first aperture is in effect partially closed in a normally upper region by a tie or bridging portion or portions of the stencil material preferably of mesh-like appearance extending across the normally upper end of said lower first aperture to resist any stretching or distorting effect when the stencil is subject to tensioning and, where necessary, acts to reduce the overall height of fluid material being deposited relative to other regions of the stencil with apertures without such smaller width apertures .
• a plurality of second smaller apertures are provided for each first larger aperture i.e. preferably the bridging portion is provided with a plurality of said smaller apertures forming a mesh- like appearance for the passage of the printing medium, such as solder paste or adhesive, to the normally lower, larger aperture and form a mesh-like or sieve-like appearance.
• the printing medium such as solder paste or adhesive
• the stencil is strengthened or reinforced in such region and the tendency for stretching - especially with long features or long track apertures - is minimised or avoided.
• the smaller apertures in the or each bridging portion forming the mesh may be of any desired shape such as circular or hexagonal .
• each first or lower larger diameter aperture determines the height of printing medium which is deposited .
• a method of producing a stencil having apertures for passage of printing medium comprises removing material from the normally lower first side of the stencil to form at least one first aperture extending part way through the stencil material, and removing material from the normally upper and opposite second side of the stencil to form at least one second aperture of smaller diameter or width than of said first aperture with said first and second apertures extending into each other.
• a first transparency with continuously opaque areas corresponding to the apertures to be provided in the normally lower surface is formed, and a second transparency is formed with at least one or more partially opaque areas generally corresponding in outline to that of said continuously opaque areas - said partially opaque areas being preferably made up from a plurality of smaller opaque areas or dots of circular or hexagonal or other outline - somewhat similar to the printing effect of tint-in or halftone as used in newspaper photograph printing.
• the transparencies are applied to opposite sides of a metal stencil to which a photo-sensitive resist has been applied and said resist is then hardened by exposure to UV light and the remaining soft resist under the opaque areas is washed away leaving bare metal which is then etched in known manner. Whilst half-etching is possible i.e. the first and second apertures in the opposite sides may be of equal length with 50% etching other ratio or possibilities are envisaged by adjusting the etching techniques.
• a preferably metal stencil is produced which has greater structural integrity and strength for resisting stretching and providing greater accuracy and permitting longer lower first printing apertures or cavities.
• a stencil according to the invention also enables the hitherto not possible formation of circular or other continuous circumference depositions which otherwise would not be possible because such previously would have created an "island" of stencil material which would fall out. Also, a stencil according to the invention enables the deposition of fluid material of a lesser height in selected areas relative to simple apertures elsewhere in the stencil without such different diameter apertures of the invention.
• the through apertures prefferably be tapered from the lower side decreasing in diameter to the upper side or for each through aperture to be formed from two opposing tapered portions each decreasing in diameter/cross section away from the surface it extends from.
• a plurality of said supporting projections are provided and will be formed by forming opaque areas on the normally lower surface of the stencil prior to etching. Whilst the shape/cross section of the supporting projections may be of any desired shape, such of circular cross section have proven satisfactory. Normally the supporting projections and the apertured stencil material from which they extend will be of a dimension equivalent to or approximating the overall thickness of the stencil since such are an original part thereof.
• Fig. 1 is a plan of transparency on reduced scale having opaque peripheral tensioning slots and a central region with an opaque configuration which is to mask a photo-sensitive resist layer on a stencil to be etched to produce apertures in the normally lower first side or surface of a sheet of metal to form the stencil;
• Fig. 2 is a transparency similar to that of Fig. l except instead of the stencilling configuration in the central region being formed of continuously opaque lines, the lines are made up of a plurality of dots each of any desired shape;
• Fig. 3 is an enlarged detail of the central region of Fig. 2;
• Fig. 4a is an enlarged fragmentary detail of the etching pattern of the normally upper surface of a stencil and Fig. 4b of the normally lower surface print or etching arrangement ;
• Fig. 5 is a schematic illustration of the etching process to produce the normally upper and lower apertures of a stencil.
• Fig. 6 is a fragmentary enlarged cross sectional view through an aperture and apertured bridging portion of a stencil according to the invention.
• Fig. 7 is an enlarged perspective detail of the normally lower surface of a stencil showing the first aperture and the lower ends of a plurality of second apertures ;
• Fig. 8 is an enlarged schematic cross section through a modified embodiment of the invention in which supporting projections extend from the lower surface of the mesh portion having smaller apertures;
• Fig. 9 is a schematic plan from below showing the mesh-like portions with hexagonal apertures of the modified embodiment .
• Figs. 1-3 correspond to an inverted plan and plan of a stencil produced therefrom and thus Figs. 1 to 3 will also be described in terms of a stencil produced therefrom since the apertures produced correspond to the dark portions.
• a stencil 1 of metal foil or sheet having a plurality of peripheral slots 2 for receiving tensioning teeth (not shown) , such as of the tensioning frames disclosed in PCT/GB96/01722.
• tensioning teeth such as of the tensioning frames disclosed in PCT/GB96/01722.
• a central apertured region 3 is illustrated in the normally lower surface/side wherein the apertures 3 ' extending part -way through the stencil are of circular and linear configuration.
• the normally upper surface or side 5 has a central apertured region 6 of corresponding outline to the apertures 3 of Fig. 1 except that the outline of Fig. 2 is not formed of continuous apertures or recesses as in Fig. l but made up of a plurality of much smaller apertures 6' extending part -way through the stencil Fig. 3 is an enlargement of the region 6 of Fig. 2 (and 4a) showing the plurality of smaller second apertures 6' which are preferably of hexagonal cross-section.
• Figs 4a and 4b are enlarged fragmentary plan of opaque regions of a transparency for use in the process and correspond to apertures produced in the upper and lower surfaces of the stencil. The black portions result in apertured regions in the stencil since no photo-resist layer results there.
• Fig. 5 is a schematic illustration of the formation of first and second apertures 3 ',6' in a stencil to which a photo resist layer 7 has been applied.
• the stencil according to the invention which will be formed from an integral sheet of continuous material which will normally be metal, may be for deposition of solder paste or adhesive or other printing stencil medium or material has in its normally lower surface continuous cavities of a depth requisite for the deposition of the necessary depth of printing medium and that the upper region of said cavities will be bridged or partially closed by a finely apertured portion of the stencil material in the upper region surface to provide for strength and structural integrity whilst enabling the printing medium to be supplied to said cavities for stencilling operations.
• each smaller second aperture may, for example, be equal or substantially equal to the thickness of the material of the stencil, for example, typically 0.15 mm.
• a stencil comprising a sheet of metal or other which is apertured or recessed to form the stencil image in which at least one recess is formed in the normally lower surface of a depth to determine the thickness of printing medium to be deposited and is partially closed by a finely apertured mesh-like portion forming part of the normally upper surface of the stencil which has fine apertures for the passage of a printing medium into said at least one lower recess and for deposition in the requisite area on a receiving surface.
• Fig. 8 is a fragmentary schematic cross section through a stencil 11 forming a modified embodiment according to the invention.
• the stencil 11 has a normally lower surface or side 14 and a normally upper surface or side 15 which has a central apertured region of corresponding outline to the apertures 3 of Fig. 1 except that the outline of Fig. 2 is not formed of continuous apertures or recesses as in Fig. 1 but made up of a plurality of much smaller apertures 16' extending part-way through the stencil and which are of hexagonal outline - as shown in Fig. 1.
• a larger diameter aperture 13 ' is formed by etching in the normally lower surface of the stencil and at the same time the smaller diameter hexagonal apertures 16' are formed in the upper surface 15 and extend into aperture 13' and form a mesh-like upper portion 17.
• the projections 19 are integral portions of the stencil material and of generally circular cross section and will have curved sides as a result of the etching process.
• the projection 19 extend downwardly and to or substantially to the plane of the lower surface 14 so as to rest on the supporting surface (not shown) during the application of fluid to be stencilled thereonto.
• the projections 19 are arranged at every alternate corner of the hexagonal so as to provide adequate support to prevent undesirable flexing of the mesh portion 17 whilst at the same time not providing too much interruption of the fluid material being deposited.
• a better fluid covering effect can be achieved using the stencil and a more even layer provided which in the use of glue increases the strength of the resultant bond.

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• Engineering & Computer Science (AREA)
• Manufacturing & Machinery (AREA)
• Microelectronics & Electronic Packaging (AREA)
• Printing Plates And Materials Therefor (AREA)

Priority Applications (4)

Applications Claiming Priority (6)

Publications (1)

Family

ID=27268640

Family Applications (1)

Country Status (6)

Cited By (1)

Families Citing this family (5)

Citations (6)

Family Cites Families (1)

• 1997
  • 1997-09-24 GB GB9720243A patent/GB2320462B/en not_active Expired - Fee Related
  • 1997-12-04 JP JP52742698A patent/JP2001506932A/ja active Pending
  • 1997-12-04 WO PCT/GB1997/003345 patent/WO1998027797A1/en not_active Application Discontinuation
  • 1997-12-04 EP EP97947775A patent/EP0947126A1/de not_active Withdrawn
  • 1997-12-04 CA CA002275275A patent/CA2275275A1/en not_active Abandoned
  • 1997-12-04 AU AU54020/98A patent/AU5402098A/en not_active Abandoned

Patent Citations (6)

Non-Patent Citations (5)

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