Substrates - Autostat is a range of heat stabilised polyesters that have low residual shrinkage at elevated temperatures. To help you select the best Autostat film for your application visit macdermid.com/autotype and enter Autostat into the search field.
Frames - It is critical that the mesh releases from the ink film immediately after the squeegee passes, so high tension mesh stretching (> 25 N/cm) onto a rigid metal frame is required. CPS Screen Adhesive MF will hold the high mesh tensions that are required and will not slip when exposed to CPS ink cleanning solvents.
Mesh - Always choose the highest quality polyester or stainless steel mesh for printing conductive or dielectric inks. The required ink film thickness will ultimately dictate which mesh count to select, however, the table below gives some guidelines on where to start:
|Mesh||Mesh Angle||Dry ink film|
|Silver conductive||68.64 to 110.34/cm polyester or 230.36 to 325.28 stainless steel||22.5°||8 to 12µm|
|Carbon||61.64 to 90.40/cm polyester||22.5°||6 to 10µm|
|UV Dielectric||77.55/cm polyester||0°||10 to 15µm|
Stencil selection for conductive inks – Controlled profile capillary stencil films are always recommended over emulsion stencils. CPS Ultra Cap HD has been specifically formulated to give a low EOM and low Rz stencil for optimum print reproduction and control with conductive inks. There is a lot more information on the benefits that Controlled profile capillary films offer functional printing on our website.
Top tip:- controlling the EOM (stencil profile) is critical for control, as even a 1µ difference in EOM can give up to a 1µ difference in wet ink film thickness.
For best edge quality and surface levelling, a slow print speed is advisable for both Silver and Carbon conductive inks as this helps to optimise the flow. Even small print defects that reduce the cross sectional area of the conductive track can have a large impact on their resistance. Good track edge definition also helps to reduce the potential propagation points for Silver migration.
Drying conductive inks
It is imperative that all the solvents are removed from the conductive inks during drying to give the lowest resistance possible, efficient drying is also critical for interlayer adhesion and flex life. Autostat is heat stabilised in our factory to give minimum shrinkage at the high temperatures required to dry conductive inks. Consult the Autostat Technical Data Sheet for more details, this is downloadable from macdermid.com/autotype
Dielectric inks – printing a complete, uninterrupted film for the Dielectric layer is critical. As these layers are typically large negative images, the final ink film thickness will be controlled primarily by the mesh. It is best to avoid high EOM stencils as these can lead to thick edges on the image. If the print speed is too fast this can generate air bubbles in the dielectric layer which will lead to pinholes. Often a double print pass is used for the Dielectric layer to mask any pinholes and provide the desired thickness and performance requirements.
Curing Dielectric inks
Complete curing of the Dielectric is critical for good interlayer adhesion and flex life. Follow the ink manufacturer’s guidelines for their curing recommendations.
How to minimise dust contamination
Dust is impossible to remove from the dried print, therefore prevention is always better than contamination!- Remove any contamination from the dry screen prior to printing with a low tack roller
Ink cleaning On Press: If the screen needs to be cleaned during printing use CPS Screen Opener 511 or CPS Screen Cleaner K3x and allow the mesh to dry out completely before recommencing printing.
Ink cleaning Archiving: If the screen is to be archived for reuse, it can be cleaned with CPS Screen Opener 511 (Flash point 44°C), CPS Screen Cleaner K3x (Flash point 43°C) or CPS Screen Cleaner Vx (Flash point 63°C), paying particular attention not to damage the stencil.
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Name: William Shorter
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