The continuing move to high volume, high density printed circuit boards for handheld electronic equipment such as mobile phones has increased packing density on the PCBs. One way this has been accomplished has been the use of multiple layer boards with blind via interconnects. A “via” is a hole through a material which, when filled with a conductive material such as copper or silver-conductive ink, creates an electrical connection between at least two conductive layers. The simplest form involves two conductive layers separated by an insulating substrate, commonly either polyamide (PI), polyester (PET), or epoxy resin. Vias can be “through” that is from all layers of the laminant structure or “blind” type, a connection hole where the board is multilayered and the hole is attached to the surface and only goes partway.

Vias are routinely drilled by mechanical methods with diameters from 0.50 mm (0.020”) down to 0.12mm (0.005”). However, as the diameter decreases, the vias become more difficult and costly to produce using mechanical methods. An advantage that laser via drilling (or microvia drilling) offers is that lasers can readily drill small diameter vias from 0.20mm (0.008”) down to 0.25mm (0.001”).

For copper coated PCBs a visible or UV laser is used to remove the copper coating in the correct location for the via. This aperture then acts as a conformal mask for the removal of the PCB substrate material using a laser. By careful control of laser pulse energy and number of pulses used the blind vias can be cleaned out to the required depth. BEST can work with you on accomplishing your goal of drilling microvias in FR4, flex or other materials.