Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.

screen blade length

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screen blade length | 2 September, 2009

I have always gone with blade length equal to board width plus 2 inches - 1 inch either side. Is there any technical reason that I could not use a longer blade, say 2.5 inches on either side?

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screen blade length | 3 September, 2009

Yes, it is important to ensure blade pressure over stencil is uniformly distributed across the entire length of blade. Such is possible only if the stencil is firmly supported from below, which during printing is done by the presence of the PCB itself. Beyond PCB dimension there exists no support. Hence using a longer blade will cause uneven pressure distribution, and in turn affect the process quality.

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screen blade length | 3 September, 2009

When you increase the blade length you have to use much solder paste. As a result, we will dry-out extra quantity of solder paste. If it's not a problem then you can use longer blades, just change/adjust the process parameters.

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screen blade length | 8 September, 2009

Important mainly for consistency of pressure across the entire board length... But also quite abusive of stencils to use longer blades.

Especially since (most people) when using the longer blades will bump the pressure up even higher to minimise the pressure consistency effect.

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