VIA-fill stencil for LTCC substrates

Highest precision – our VIA-fill stencils

LTCC (Low Temperature Cofired Ceramic) technology is used in hybrid technology when multiple connection layers need to be implemented. The connections between the layers are made using very fine “through-plating,” known as microvias. A microvia is defined by a hole diameter of < 300 μm. Special requirements are placed on the fill level of the connection holes (vias). The stencil has a certain funnel function that guides the silver conductive paste into the vias. The positioning of the stencil relative to the hybrid and the tolerance chain of the maximum possible deviations require the relevant tolerance limits to be minimized in each process involved.

Typical sizes for laser-cut stencils:

• Thickness: t = 50–70 μm
• Aperture size of stencil: 100–300 μm
• Via opening: z.B. 60–250 μm
• Number of apertures: 15 000–60 000

Printing the vias:
The silver conductive paste is printed into the stencil openings using a steel squeegee. The stencil is positioned precisely in the center of the via.

• High positioning accuracy
• High accuracy of drilling diameters
• Precision of aperture size ± 3

All laser-cut templates from LaserJob are then brushed. A CNC-controlled brushing process removes the cutting burr on the laser exit side. The brush head moves in a meandering pattern in all four directions across the surface.

Benefits of this post-processing

• no enlargement of the apertures
• minimum material removal < 2 μm
• uniform sheet thickness