ASSOCIATION CONNECTING ELECTRONICS INDUSTRIES …

1 IPC-7525 Stencil Design GuidelinesASSOCIATION CONNECTINGELECTRONICS INDUSTRIES2215 Sanders Road, Northbrook, IL 60062-6135 Tel. Fax 2000A standard developed by IPCT able of and 12 APPLICABLE .. Industry Standard .. 23 STENCIL Data .. Format .. List .. Paste Layer .. Stencils .. Orientation/Rotation .. Location .. Design .. Size .. Size Versus Board Pad Aperture Chip Technology Surface-Mount/Through-Hole (Intrusive Reflow).. Paste Volume .. Technology Surface-Mount/Flip Chip .. Stencil for Surface-Mount/Flip Chip .. Stencil Stencil .. Stencil .. Stencil for Contained PasteTransfer Heads .. Stencil .. Fiducials .. 84 STENCIL.

2 Border .. Fabrication .. Apertures .. 85 STENCIL of Image on .. Design Guidelines .. 96 STENCIL 97 USER STENCIL 98 STENCIL 99 END OF 9 APPENDIX A:EXAMPLE ORDER 10 FiguresFigure 1 Cross Sectional View of A Stencil 3 Figure 2 Home Plate Aperture Design .. 4 Figure 3 Bow Tie Aperture Design .. 4 Figure 4 Oblong Aperture Design .. 5 Figure 5 Aperture Design for MELF Components .. 5 Figure 6 Glue Stencil Aperture Design .. 5 Figure 7 Through-Hole Solder Paste Volume .. 6 Figure 8 Overprint without Step .. 6 Figure 9 Overprint with Step (Squeegee Side).. 6 Figure 10 Overprint with Step (Contact/Board Side) .. 6 Figure 11 Two-Print Through-Hole 7 Figure 12 Two-Print Stencil for Mixed Technology.

3 7 Figure 13 Trapezoidal 9 TablesTable 1 General Aperture Design Guidelines forSurface-Mount Devices .. 4 Table 2 Process Window for Intrusive Soldering .. 5 May 2000 IPC-7525iiiStencil Design Guidelines1 PURPOSEThis document provides guides for the design and fabrica-tion of stencils for solder paste and surface-mount adhe-sive. It is intended as a guideline Terms and DefinitionsAll terms and definitionsused throughout this handbook are in compliance with IPC-T-50. Definitions denoted with an asterisk (*) below arereprints from IPC-T-50. Other specific terms and defini-tions, essential for the discussion of the subject, are pro-vided ApertureAn opening in the stencil Aspect Ratio and Area RatioAspect Ratio = Width of Aperture / Thickness of StencilFoilArea Ratio = Area of Aperture Opening /Area of BorderPeripheral tensioned mesh, either polyesteror stainless steel, which keeps the stencil foil flat and border connects the foil to the Contained Paste Transfer HeadA stencil printerhead that holds, in a single replaceable component.

4 Thesqueegee blades and a pressurized chamber filled with sol-der Etch FactorEtch Factor = Etched Depth / LateralEtch in a chemical etching FiducialsReference marks on the stencil foil (andother board layers) for aligning the board and the stencilwhen using a vision system in a Fine-Pitch BGA/Chip Scale Package (CSP)Ballgrid array with less than 1 mm [39 mil] pitch. This is alsoknown as Chip Scale Package (CSP) when the packagesize is no more than the area of the original die Fine-Pitch Technology (FPT)*A surface-mountassembly technology with component terminations on cen-ters less than or equal to mm [ mil]. FoilThe sheet used to create the FrameA device onto which the foil is may be tubular or cast aluminum with the border per-manently mounted using an adhesive.

5 Some foils can bemounted into a tensioning master case and do not require aborder or a permanent fixturing of the foil to the Intrusive SolderingIntrusive soldering may alsobe known as paste-in-hole, pin-in-hole, or pin-in-paste sol-dering. This is a process in which the solder paste for thethrough-hole components is applied using the stencil, thethrough-hole components are inserted and reflow-solderedtogether with the surface-mount ModificationThe process of changing an aperturein size or OverprintingThe use of stencils with apertureslarger than the pads or annular rings on the PadMetallized shape on the circuit board towhich the terminal of a surface mount component is elec-trically or mechanically SqueegeeA metal or rubber blade used to wipeacross the stencil to force solder paste into openings in thestencil.

6 Normally, squeegee is mounted at an angle suchthat the printing edge of the squeegee trails behind the printhead and the face of the squeegee slopes Standard BGABall grid array with 1 mm [39mil] pitch or StencilA tool which may consist of a frame, bor-der, and foil containing apertures through which solderpaste, adhesive, or other media is Step StencilA stencil with more than one foilthickness Surface-Mount Technology (SMT)*The electri-cal connection of components to the surface of a conduc-tive pattern that does not utilize component Through-Hole Technology (THT)*The electricalconnection of components to a conductive pattern by theuse of component Ultra-Fine Pitch TechnologyA surface-mountassembly technology with component terminations on cen-ters less than or equal to mm [ mil]May 2000 IPC-75251