Stencil Printing Application Guide for Thermal Interface Materials

Stencil Printing Application Guide for Thermal Interface Materials

Table of Contents Stencil printing hardware Stencil specifications Squeegee applicators Manual stencil holder mechanism o Setting up o Spacing and leveling o Surface contact Stencil printing mechanism o Squeegee suggestions Applying Thermal Interface Materials (TIMs) to the stencil Stencil printing TIMs Final considerations 2

Stencil Printing Hardware Stencil holder for manual stencil printing Stencil holder with typical stencil attached Stencil holder, stencil, and squeegee applicator 3

Stencil Specifications Stencils are commonly a stainless steel film supported by a polyester mesh mounted to a frame. Stencil thickness determines printed pad thickness. o 3 to 7 mils stencil thickness common Any style of pad design can be made. Variety of frame sizes available. 4

Squeegee Applicators for Printing TIMs Squeegees can be custom made for specific stencil and print pattern sizes. o Aluminum handles o Rubber squeegee blade Rubber squeegee blade can range in hardness. o 60 to 80 durometer range is good for most TIMs o 70 durometer common o 80 durometer good for higher viscosity TIMs 5

Stencil Holder Mechanism Place the stencil frame into the stencil holder/hinge. Clamp the stencil frame using the screen locking nuts. Use hinge adjustment screws to change stencil height. Use hinge locking nuts to fix the hinge position. 4 3 1 2 1 1 4 3 Typical stencil holder (manual printing): Stencil locking nuts Counter weight Hinge adjustment screw Hinge locking nut 6

Stencil Printer Set-up Depending on the specific stencil holder design, a spacer may be required to hold the stencil frame when the stencil is placed down. Use a heat sink of similar height 7

Stencil Printer Set-up Leveling Use the hinge adjustment screws to level the stencil frame. The stencil must be in contact with and parallel to the printing surface. o Unlike screen printing where a gap setting is required, stencil printing requires that the stencil be in direct contact with the printing surface. 8

Stencil Printer Set-up Surface Contact The stencil should be in contact with the surface. o Contact must be even (parallel and flat) o Printed pad thickness is dependent on stencil thickness 9

Stencil Printing Mechanism The TIM is deposited onto the heat sink surface as the squeegee travels over the stencil openings. 10

Stencil Printing Suggestions Maintain constant pressure, angle, and speed when drawing squeegee across stencil. Printing direction Too steep Suggested start angle ~45 o High viscosity grease 11

Applying TIM to the Stencil Apply a small amount of TIM to the upper part of the stencil, in front of the opening. 12

Stencil Printing TIM Place the squeegee down on the stencil behind the TIM and tilt it down to ~45 o angle. Draw the squeegee across the stencil opening toward the opposite end. o Make sure to maintain constant applied pressure and speed. 13

Stencil Printing Completed Once complete, you will have a nice, clean print. 14

TIMs can be applied to many different styles 15

Final Considerations Manual stencil printing hardware, stencil holders, stencils, and squeegees are relatively inexpensive. o Dow Corning can provide vendor contacts in your area The optimum conditions will be different for each application and may require fine tuning. o In some cases screen printing may be more appropriate Custom stencils can be designed for challenging printing applications. Proficiency in stencil printing can be developed rapidly with minor training and practice. o Also refer to Dow Corning Screen Printing Guide for more information Contact your local Dow Corning representative with questions. 16

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