WO2000048845A9 - Improved stencil - Google Patents

Improved stencil

Info

Publication number
WO2000048845A9
WO2000048845A9 PCT/US2000/004300 US0004300W WO0048845A9 WO 2000048845 A9 WO2000048845 A9 WO 2000048845A9 US 0004300 W US0004300 W US 0004300W WO 0048845 A9 WO0048845 A9 WO 0048845A9
Authority
WO
WIPO (PCT)
Prior art keywords
stencil
apertures
flux
substrate
paste
Prior art date
Application number
PCT/US2000/004300
Other languages
French (fr)
Other versions
WO2000048845A1 (en
Inventor
John W Blazek
Original Assignee
Fry Metals Inc
John W Blazek
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Fry Metals Inc, John W Blazek filed Critical Fry Metals Inc
Priority to AU40032/00A priority Critical patent/AU4003200A/en
Publication of WO2000048845A1 publication Critical patent/WO2000048845A1/en
Publication of WO2000048845A9 publication Critical patent/WO2000048845A9/en

Links

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
    • B41C1/145—Forme preparation for stencil-printing or silk-screen printing by perforation using an energetic radiation beam, e.g. a laser
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41N—PRINTING PLATES OR FOILS; MATERIALS FOR SURFACES USED IN PRINTING MACHINES FOR PRINTING, INKING, DAMPING, OR THE LIKE; PREPARING SUCH SURFACES FOR USE AND CONSERVING THEM
    • B41N1/00—Printing plates or foils; Materials therefor
    • B41N1/24—Stencils; Stencil materials; Carriers therefor
    • 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 relates to a method and apparatus of depositing materials on a substrate. More specifically, embodiments of the present invention are directed to a stencil for printing solder paste and flux on surface mount substrates, such as circuit boards, flip chips and the like. Background of the Invention
  • Prior art methods of depositing solder paste or flux on substrates include techniques such as stencil printing, screen printing, pin transfer and automated dispensing.
  • Stencil printing generally involves forcing solder paste or flux through apertures of a stencil onto substrates when the stencil and substrate are in intimate contact. Solder paste or flux is applied to the top surface of a stencil and forced through the apertures by movement of a squeegee applicator horizontally across the stencil surface. Solder paste or flux flows through the apertures by compression of the squeegee applicator and deposited on a substrate in a particular image or pattern as dictated by the stencil.
  • Printing as described above is a simple and effective technique for application of solder paste and flux onto solder pads or contacts on the surfaces of circuit boards and flip chips to which electronic components are ultimately mounted. Depositing a precise and consistent amount of paste or flux on solder pads is desirable to create strong, and reliable permanent solder connections between electronic components and surface mount substrates. Precise and consistent application of paste and flux results in printing an accurate and repeatable stencil pattern which is desirable for high volume production of printed substrates. The quality of paste and flux patterns is, however, affected in large part by the viscosity of materials being deposited and the construction and design of the stencil used for paste or flux application.
  • Prior art stencils have the potential of depositing materials inaccurately and inconsistently on solder pads of surface mount substrates. Inaccurate and inconsistent depositing is caused by an uncontrolled flow and release of materials through stencil apertures. This is especially true when depositing materials with low viscosity, such as flux, onto surface mount substrates. Uncontrolled flow of solder paste or flux results in excessive deposits on solder pads which causes weeping and bridging of solder or flux and produces poor surface mount component connections.
  • Prior art stencils typically comprise through-hole type apertures which do not provide control of the flow and release of paste or flux. The amount of paste or flux deposited is often dependent upon the consistency of compression applied by the squeegee applicator and the consistency of the depth of the layer of paste or flux being spread across the surface of the stencil.
  • Prior art stencils often comprise apertures without uniform geometry which affects the volume of paste or flux each aperture is capable of holding and depositing on solder pads.
  • Such prior art stencils include mesh emulsion type stencils which include stainless steel mesh that is bonded to a frame with a stencil pattern created by a photographic emulsion.
  • Mesh emulsion screens have a disadvantage in that by their design and construction mesh apertures do not have uniform geometry and, therefore, deposit inconsistent volumes of paste or flux on solder pads. For example, the area of an aperture may not be fully open due to inconsistent emulsion coating of mesh strands forming the perimeter of the opening of the aperture, resulting in segments of the perimeter with more or less emulsion coating.
  • apertures are similarly affected by inconsistent emulsion coating whereby aperture walls do not have smooth surfaces and are irregular. Similarly, the surface surrounding the aperture may not be smooth due to inconsistent coating of mesh strands.
  • Emulsion coating of mesh stencils creates apertures with coarse and irregular surfaces, producing inconsistent aperture geometry which does not permit consistent deposits of paste or flux nor repeatable stencil printing.
  • the present invention provides a stencil and method of solder and flux application which prints stencil patterns with greater precision, consistency and repeatability than prior art stencils.
  • the present invention also provides a more efficient transfer of stencil patterns to surface mount substrates.
  • Fig. 1 represents a side sectional view of the stencil of the present invention
  • Fig. 2 represents a top view of the stencil of the present invention.
  • Figs. 1 and 2 show a diagrammatic sectional view and a top view respectively, of one embodiment of the present invention which includes a stencil 112 made of a sheet with a plurality of apertures 106 etched in the upper surface of the stencil 108 in a desired image or pattern for printing paste or flux to a surface mount substrate.
  • the stencil is constructed in a plurality of thickness 100 and preferably between about 2 and 42 mil.
  • the apertures 106 are laser or chemically etched and stepped down to precise dimensions in a particular geometry and preferably between about 2 and 40 mil in depth 100 and preferably between about 2 and 60 mil in diameter 101.
  • An aperture 106 is etched in the upper surface of the stencil 108 as a stepped down hemisphere to a depth of preferably between about 2 and 40 mil 102.
  • the bottom curve of the hemisphere 103 includes a plurality of laser cut through-holes 107 which pass through the stencil 112 opening to the bottom surface of the stencil 110. While four through-holes 107 are shown in Fig. 2, it is understood that any number of through-holes may be used as selected by the stencil designer in accordance with factors as hole size, viscosity of material being deposited, etc.
  • the stencil also includes in the bottom surface 110 laser or chemically etched impressions or notches 109 stepped up to accommodate carrier wafers used to support and maintain flip chips and other surface mount substrates during stencil printing.
  • Solder paste or flux is applied at an end of the stencil 112 and moved across the upper surface of the stencil 108 by a squeegee applicator (not shown, but well know in the art) moving horizontally, in a well known manner, across the stencil 108.
  • the squeegee applicator moves the paste or flux across the upper surface of the stencil 108 with minimal compression forces paste or flux into the aperture 106.
  • Paste or flux flows into the aperture 106 by the compression created by the squeegee applicator and flows to the bottom hemispherical curve 103 and retained in the aperture 106 by capillary action.
  • the through-holes 107 act as capillary tubes and controUably release paste or flux from the bottom surface of the stencil 110 and deposit a controlled, precise amount of paste or flux onto solder pads. Altering the geometry of the apertures 106 and the number and diameter of through-holes 107, precise control and consistent deposition of materials, such as paste or flux, onto surface mount substrates is achieved.
  • Another embodiment of the present invention as shown in Figs. 1 and 2 includes a stencil constructed of stainless steel.
  • Stainless steel construction permits laser and chemical etching of the surface of the stencil to produce apertures with openings and side walls free of irregularities and roughness. Apertures are etched to uniform geometry throughout a stainless steel stencil. Uniform aperture geometry enables consistent volumes of paste or flux to be deposited onto solder pads, creating accuracy and consistency in printing the stencil pattern. The durability of stainless steel construction also minimizes wear of the stencil and allows the stencil to be repeatedly used without diminishing the accuracy, consistency and repeatability of the stencil pattern achieved.
  • Stainless steel permits easy cleaning of the stencil and is resistant to chemical cleaners which prevents damage to the structure of the apertures and preserves the quality of the stencil pattern.
  • Stainless steel stencils also provide a smooth surface upon which paste or flux is applied which reduces wear of the squeegee applicator blades and allows the squeegee applicator to operate with minimal compression and at high speeds. High squeegee speed provides a more efficient stenciling operation, whereby a high volume of printed substrates is produced.
  • Other metallic materials, such as alloy 42, and non-metallic materials, such as plastics, may be substituted for the stainless steel as desired.
  • the present invention provides a stencil for printing solder paste and flux onto solder pads or contacts of surface mount substrates, such as circuit boards and flip chips, which achieves more accurate, consistent and repeatable printing than prior art stencils.
  • One embodiment of the present invention relates to apertures of uniform geometry laser or chemically etched in the surface of the stencil. Uniform aperture geometry permits a precise and consistent volume of paste or flux to be held in each aperture and deposited onto solder pads.
  • the stencil comprises a plurality of apertures in the upper surface of the stencil with each aperture laser or chemically etched down to a precise dimension with a plurality of through-holes connecting to the bottom surface of the stencil.

Landscapes

  • Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • Physics & Mathematics (AREA)
  • Health & Medical Sciences (AREA)
  • General Health & Medical Sciences (AREA)
  • Optics & Photonics (AREA)
  • Toxicology (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Electric Connection Of Electric Components To Printed Circuits (AREA)

Abstract

A stencil is disclosed in which the area of each aperture in the upper surface is greater than the area of the apertures in the lower surface which comes into contact with a substrate upon which materials are deposited. The differential areas in the upper surface and in the lower surface serve to control the amount of material which is deposited through the stencil and onto the substrate.

Description

IMPROVED STENCIL
Field of the Invention
The present invention relates to a method and apparatus of depositing materials on a substrate. More specifically, embodiments of the present invention are directed to a stencil for printing solder paste and flux on surface mount substrates, such as circuit boards, flip chips and the like. Background of the Invention
Prior art methods of depositing solder paste or flux on substrates include techniques such as stencil printing, screen printing, pin transfer and automated dispensing. Stencil printing generally involves forcing solder paste or flux through apertures of a stencil onto substrates when the stencil and substrate are in intimate contact. Solder paste or flux is applied to the top surface of a stencil and forced through the apertures by movement of a squeegee applicator horizontally across the stencil surface. Solder paste or flux flows through the apertures by compression of the squeegee applicator and deposited on a substrate in a particular image or pattern as dictated by the stencil.
Printing as described above is a simple and effective technique for application of solder paste and flux onto solder pads or contacts on the surfaces of circuit boards and flip chips to which electronic components are ultimately mounted. Depositing a precise and consistent amount of paste or flux on solder pads is desirable to create strong, and reliable permanent solder connections between electronic components and surface mount substrates. Precise and consistent application of paste and flux results in printing an accurate and repeatable stencil pattern which is desirable for high volume production of printed substrates. The quality of paste and flux patterns is, however, affected in large part by the viscosity of materials being deposited and the construction and design of the stencil used for paste or flux application.
Prior art stencils have the potential of depositing materials inaccurately and inconsistently on solder pads of surface mount substrates. Inaccurate and inconsistent depositing is caused by an uncontrolled flow and release of materials through stencil apertures. This is especially true when depositing materials with low viscosity, such as flux, onto surface mount substrates. Uncontrolled flow of solder paste or flux results in excessive deposits on solder pads which causes weeping and bridging of solder or flux and produces poor surface mount component connections. Prior art stencils typically comprise through-hole type apertures which do not provide control of the flow and release of paste or flux. The amount of paste or flux deposited is often dependent upon the consistency of compression applied by the squeegee applicator and the consistency of the depth of the layer of paste or flux being spread across the surface of the stencil.
Other prior art stencils often comprise apertures without uniform geometry which affects the volume of paste or flux each aperture is capable of holding and depositing on solder pads. Such prior art stencils include mesh emulsion type stencils which include stainless steel mesh that is bonded to a frame with a stencil pattern created by a photographic emulsion. Mesh emulsion screens have a disadvantage in that by their design and construction mesh apertures do not have uniform geometry and, therefore, deposit inconsistent volumes of paste or flux on solder pads. For example, the area of an aperture may not be fully open due to inconsistent emulsion coating of mesh strands forming the perimeter of the opening of the aperture, resulting in segments of the perimeter with more or less emulsion coating. The walls of apertures are similarly affected by inconsistent emulsion coating whereby aperture walls do not have smooth surfaces and are irregular. Similarly, the surface surrounding the aperture may not be smooth due to inconsistent coating of mesh strands. Emulsion coating of mesh stencils creates apertures with coarse and irregular surfaces, producing inconsistent aperture geometry which does not permit consistent deposits of paste or flux nor repeatable stencil printing.
Summary of the Invention The present invention provides a stencil and method of solder and flux application which prints stencil patterns with greater precision, consistency and repeatability than prior art stencils. The present invention also provides a more efficient transfer of stencil patterns to surface mount substrates.
Brief Description of the Drawings To better understand the present invention, reference is made to the drawings which are incorporated by reference, in which:
Fig. 1 represents a side sectional view of the stencil of the present invention; and Fig. 2 represents a top view of the stencil of the present invention.
Detailed Drawings Embodiments of the present invention will now be described with reference to Figs. 1 and 2. Figs. 1 and 2 show a diagrammatic sectional view and a top view respectively, of one embodiment of the present invention which includes a stencil 112 made of a sheet with a plurality of apertures 106 etched in the upper surface of the stencil 108 in a desired image or pattern for printing paste or flux to a surface mount substrate. The stencil is constructed in a plurality of thickness 100 and preferably between about 2 and 42 mil. The apertures 106 are laser or chemically etched and stepped down to precise dimensions in a particular geometry and preferably between about 2 and 40 mil in depth 100 and preferably between about 2 and 60 mil in diameter 101. An aperture 106 is etched in the upper surface of the stencil 108 as a stepped down hemisphere to a depth of preferably between about 2 and 40 mil 102.
As shown in Figs. 1 and 2, the bottom curve of the hemisphere 103 includes a plurality of laser cut through-holes 107 which pass through the stencil 112 opening to the bottom surface of the stencil 110. While four through-holes 107 are shown in Fig. 2, it is understood that any number of through-holes may be used as selected by the stencil designer in accordance with factors as hole size, viscosity of material being deposited, etc.
The stencil also includes in the bottom surface 110 laser or chemically etched impressions or notches 109 stepped up to accommodate carrier wafers used to support and maintain flip chips and other surface mount substrates during stencil printing.
Solder paste or flux is applied at an end of the stencil 112 and moved across the upper surface of the stencil 108 by a squeegee applicator (not shown, but well know in the art) moving horizontally, in a well known manner, across the stencil 108. The squeegee applicator moves the paste or flux across the upper surface of the stencil 108 with minimal compression forces paste or flux into the aperture 106. Paste or flux flows into the aperture 106 by the compression created by the squeegee applicator and flows to the bottom hemispherical curve 103 and retained in the aperture 106 by capillary action. With a second subsequent movement of the squeegee applicator horizontally across the surface of the stencil 108, paste or flux flows into the through- holes 107. The through-holes 107 act as capillary tubes and controUably release paste or flux from the bottom surface of the stencil 110 and deposit a controlled, precise amount of paste or flux onto solder pads. Altering the geometry of the apertures 106 and the number and diameter of through-holes 107, precise control and consistent deposition of materials, such as paste or flux, onto surface mount substrates is achieved. Another embodiment of the present invention as shown in Figs. 1 and 2 includes a stencil constructed of stainless steel. Stainless steel construction permits laser and chemical etching of the surface of the stencil to produce apertures with openings and side walls free of irregularities and roughness. Apertures are etched to uniform geometry throughout a stainless steel stencil. Uniform aperture geometry enables consistent volumes of paste or flux to be deposited onto solder pads, creating accuracy and consistency in printing the stencil pattern. The durability of stainless steel construction also minimizes wear of the stencil and allows the stencil to be repeatedly used without diminishing the accuracy, consistency and repeatability of the stencil pattern achieved.
Stainless steel permits easy cleaning of the stencil and is resistant to chemical cleaners which prevents damage to the structure of the apertures and preserves the quality of the stencil pattern. Stainless steel stencils also provide a smooth surface upon which paste or flux is applied which reduces wear of the squeegee applicator blades and allows the squeegee applicator to operate with minimal compression and at high speeds. High squeegee speed provides a more efficient stenciling operation, whereby a high volume of printed substrates is produced. Other metallic materials, such as alloy 42, and non-metallic materials, such as plastics, may be substituted for the stainless steel as desired.
The present invention provides a stencil for printing solder paste and flux onto solder pads or contacts of surface mount substrates, such as circuit boards and flip chips, which achieves more accurate, consistent and repeatable printing than prior art stencils. One embodiment of the present invention relates to apertures of uniform geometry laser or chemically etched in the surface of the stencil. Uniform aperture geometry permits a precise and consistent volume of paste or flux to be held in each aperture and deposited onto solder pads. The stencil comprises a plurality of apertures in the upper surface of the stencil with each aperture laser or chemically etched down to a precise dimension with a plurality of through-holes connecting to the bottom surface of the stencil. By means of capillary action, a precise volume of paste or flux is held in the apertures and subsequently controUably released onto solder pads or contacts of surface mount substrates. The number and dimension of apertures and through-holes is determined by the viscosity of materials and the level of control desired.
Having thus described at least one illustrative embodiment of the invention, various alterations, modifications and improvements will readily occur to those skilled in the art. Such alterations, modifications and improvements are intended to be within the scope and spirit of the invention. Accordingly, the foregoing description is by way of example only and is not intended as limiting.
What is claimed is:

Claims

1. A device for printing materials onto surface contacts on a substrate comprising: a stencil having an upper planar surface and a lower planar surface and wherein one or more apertures are formed through the stencil thickness from the upper planar surface to the lower planar surface; and wherein the one or more apertures formed in the top surface of the stencil are larger in surface area compared to the one or more apertures formed in the lower planar surface of the stencil.
2. The device of claim 1 in which the one or more apertures in the upper surface are generally hemispherical and penetrate to about one-half the distance of the thickness of the stencil.
3. The stencil of claim 2 in which the one or more apertures on the bottom surface of the stencil comprises a plurality of shafts extending from the lower surface and into the stencil thickness and intersect with the hemispherical opening formed through the upper planar surface of the stencil.
4. The device of claim 3 in which the one or more apertures in the lower surface are generally cylindrical so as to control the amount of material which is deposited on the substrate.
5. A method of depositing material onto the surface of a substrate which comprises: forming a stencil as recited in claim 4; placing the stencil in contact with the substrate such that the lower surface of the stencil is in contact with an upper surface of the substrate; and passing a squeegee applicator across the upper surface of the stencil with a material to be deposited, the squeegee pressing material through the upper hemispherical surface of the stencil through the stencil and out the apertures in the lower surface of the stencil onto the substrate.
PCT/US2000/004300 1999-02-19 2000-02-18 Improved stencil WO2000048845A1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU40032/00A AU4003200A (en) 1999-02-19 2000-02-18 Improved stencil

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US12085299P 1999-02-19 1999-02-19
US60/120,852 1999-02-19

Publications (2)

Publication Number Publication Date
WO2000048845A1 WO2000048845A1 (en) 2000-08-24
WO2000048845A9 true WO2000048845A9 (en) 2001-08-30

Family

ID=22392914

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/US2000/004300 WO2000048845A1 (en) 1999-02-19 2000-02-18 Improved stencil

Country Status (2)

Country Link
AU (1) AU4003200A (en)
WO (1) WO2000048845A1 (en)

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE202008004821U1 (en) * 2008-04-07 2008-06-12 Heil, Roland screen printing forme
US20100139561A1 (en) * 2008-12-10 2010-06-10 Bloom Terry R Counter sunk screen
GB2556102A (en) * 2016-11-21 2018-05-23 Wilkinson Alan Improved method of abrading or slicing off a high point of a surface

Family Cites Families (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE1960723A1 (en) * 1969-12-03 1971-06-09 Siemens Ag Printed circuit screen printing template
JPH0313393A (en) * 1989-06-12 1991-01-22 Sony Corp Mask screen for cream solder printing and preparation thereof
GB2307446A (en) * 1995-11-25 1997-05-28 Ibm Solder paste deposition
CN1198247A (en) * 1996-06-11 1998-11-04 菲利浦电子有限公司 Provision of color elements on substrates by means of screen-printing or stencil-printing method
DE19651462A1 (en) * 1996-12-11 1998-06-18 Udo Dr Lehmann Gravure printing

Also Published As

Publication number Publication date
WO2000048845A1 (en) 2000-08-24
AU4003200A (en) 2000-09-04

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