3D Stencils

A single thickness electroform stencil , with relief areas not to damage the protruded sections on the board or unit. Photo Stencil’s 3-D Electroform stencils are ideal for printing on substrate surfaces that have protrusions rising above the print surface. An example of this type protrusion might be a flip-chip device already mounted on the PCB prior to solder paste printing. A single thickness Electroform Stencil is formed with a raised relief pocket positioned over the protrusion. A squeegee blade with a 25micron slit is ideal for allowing the squeegee blade to raise up over the raised pocket but still be able to print in front of and behind the raised pocket. In some cases where there are no apertures in front of or behind the raised area a notched squeegee blade is the ideal solution.   Applications: 

• Ideal for printing on substrate surfaces that have protrusions or pre-assembled components rising above the print surface.

  Advantages:

• successful solder paste or flux printing
• Simplified process for multi level printing.
• Single stencil requirement – multi function design.
• Higher assembly yields from successful solder paste printing.

Squeegee Blade requirement: A squeegee blade with a 25micron slit (or appropriate to pocket height) to allow the squeegee blade to raise up over the raised pocket.

Reservoir Stencils

A special case of single thickness 3D electroform stencil used to print into a recessed pocket of the board. Stencil grown using the electroform process followed by – laser cutting of apertures (optional). Advantages:

• Typically used when depth of cavity is larger than can be accommodated by step stencils.

Applications:

• To print into cavities for LED assembly.
• Print into open cavities for die assembly in embedded packaging.

Please contact our expert staff for any questions or aggressive values of cavity depth.  

Step Stencils

A single stencil with varied thicknesses to print through

• Thin area for small devices
• Thick area for large devices and
• Providing relief for raised areas on board

Photo Stencil’s step stencils offer significant flexibility in achieving the proper solder paste height and solder paste volume for the overall paste printing process. Photo Stencil is pioneer in the field of Step Stencil technology with all processes contained in house for the most comprehensive service available in the industry. Available in all stencil technologies; Electroformed, Laser Cut and Chemical Milled. Applications:

1. Print for miniature components like 0201 metric and on large pads simultaneously using single stencil.
2. Relief-Step Board Side provides –

Barcode Relief: When the bar code is too close to PCB pads it can cause a gap between the stencil apertures and the pads. The relief pocket allows the stencil to cleanly gasket to the PCB. Raised via Pads: Raised via pads can prevent the stencil from gasketing to the PCB surface. A relief-step pocket around the vias prevents this situation. Relief for Paste (Two-Print Stencil): Used as 2nd stencil in two print process. This stencil has steps to provide relief on already printed material on board.

• Steps stencils are also used for multi-level printing

Step stencils can have steps on

1. Board side
2. Squeegee side
3. Both board and squeegee sides

Advantages

• Available as ‘step up’ and ‘step down’ squeegee side, ‘step up’ PCB side or on both sides.
• Ideal for providing bar code relief and thus maintaining the maximum gasket.
• Matched Slit squeegee blades allow for flexure over the raised pocket areas.
• Multi-thickness steps available.
• Match with Photo Stencils range of E-Blade™ squeegees for maximum life and performance.

AccuScreen

A high performance metal mask/screen fabricated using an additive process (Ni). Each large area is printed by mesh of apertures to control  print volume. Primarily used for printing on flexible electronics, to print varieties of pastes and inks. Technical Information:

• Various mesh sizes and wire thicknesses are available with the standard sizes such as
• Additional thickness and screen variation are also possible.

Applications:

• Accuscreens are designed to replace traditional stainless screens for printing thick film inks and other materials
• Accuscreens are printable on uneven surfaces and on flexible surfaces
• Accuscreens are used for controlled printing on large pad areas using a mesh pattern.

Advantages:

• Durable and chemical resistant than traditional screens.
• Perfectly flat squeegee-printing surface compared to the woven wire knuckles for woven screen mesh products.
• Tailor different mesh patterns can be used, as per paste/flux properties. Eg: hexagonal, oval, rectangles, squares, circles
• Mesh shape can be adjusted to material flow properties and viscosity
• Greater print deposit uniformity and higher printing yields
• Less pattern distortion since flat electroformed mesh does not stretch like screen wire mesh
• Longer life, up to 10 times longer than traditional screen
• Aggressive cleaning solvents can be used; there is no emulsion to
• wash-out

Two options available:

• Base Screen thickness (no pattern thickness built-up on contact side)
• Accuscreen + pattern build-up by nickel steps

Wafer Bump Stencils

Wafer bumping stencils are electroform stencils used to obtain bumps on wafer pads. The stencil usually has from 25,000 apertures up to 500,000 apertures. Photo Stencil produces two different sets of stencil to achieve this (a)Paste Print stencils: A print process where solder paste is printed on die pad on the wafer, the wafer is then reflowed, melting the solder paste to form truncated spheres (bumps)  on the wafer die Applications: Useful for bumping of wafers of various sizes and bump count and bump size (<200um).     Advantages: Typically used when pitch is at least more than 2 times the bump diameter. (b)  Flux print +Ball Drop Stencils: Set of two stencils.

Wafer Ball Drop Stencils

This is the second stencil from the set of Flux and ball-drop process used in wafer bumping. Flux is printed on to wafer pads using 1st stencil followed by using a wafer ball drop stencil to drop solder balls directly onto the connection pads of a wafer. Since flux is printed onto the wafer pads before the ball is dropped, it has optional relief or standoffs placed on contact side. Stand off on wafer Ball drop stencil can be obtained by:

1. Laminating a mask (photoresist)on the wafer side of the stencil to keep the stencil from contacting the flux.
2. E-form Nickel rib layer is grown on wafer side.

  Advantages:

• Used instead of wafer bumping using paste  printing

  Applications:

• Ball drop stencils are used for different wafer sizes, sphere size and pad pitch.
• Easy to use, regular solder paste printer can be used for manual ball drop.
• Ball drop process is also preferred when the wafer pad is larger or pitch is tighter to use paste printing application