squeegee blade design

The SEMA listing [ http://www.smema.org/smema5.pdf ] says: * D CUT SQUEEGEE: A single diamond edge squeegee which is shaped like an upside down house and made of polyurethane. * FOUR-SIDED DIAMOND EDGE SQUEEGEE: A polyurethane 3/8 x 3/8 four sided, four edged squeegee. The diamond corners are used as the printing edges. * TRAILING EDGE SQUEEGEE: Any squeegee mounted at an angle such that the printing edge of the squeegee trails behind the print head and the face of the squeegee slopes forward.

Alden Johnson at Cookson Electronics says, �Typically, in a standard PWB paste-printing application, a metal squeegee blade is used. Tests have shown that when printing a standard, fine-pitch application with device pitch down to as low as 0.3048mm and aperture sizes of 0.2032mm, a metal squeegee blade is perfect.

However, when printing wafers, with the pitch of the device as low as 150�m and aperture sizes as small as 80�m, a polypropylene 90 durometer, trailing edge squeegee blade is used. With such a fine mesh, there is potential to damage the stencil with a metal squeegee. There is no measurable scavenging or scooping of the apertures when using a polypropylene blade. This type of squeegee yields the best results in this application when optimized.�

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