Precision measurements in micro-drilled holes

In co-operation with: Schmoll Maschinen GmbH / Impex Leiterplatten GmbH

Test objects:

Micro-drilled holes (microvias) in multi-layer circuit boards

Relevant parameters:

Copper layer position, hole depth and surface quality (roughness)

Metrological challenge:

very small hole diameters (≥ 0.6 mm) that cannot be accessed using conventional measuring devices due to their size and thus cannot be inspected; Goal: non-destructive, 100-percent inspection during production


FDM-2 precision fiber-optic measuring system with miniature probe (Ø 125 µm)

A precise plated through hole is critical to the quality and functionality of multi-layer printed circuit boards (PCBs). As such, the ability to precisely determine the depth of each copper layer during production is important in order to avoid contact dislocation and faults.

A non-destructive inspection of the layer position is difficult with PCBs with micro-drilled holes, as the diameter of these microvias is in the micrometer or low millimeter range. Conventional measuring devices are unable to enter the micro-manufactured spaces due to their size. Because of this, quality control has been thus far performed using techniques such as micrographic inspection.

In order to perform a non-destructive, production line 100% inspection of the micro-drilled holes, fionec further developed its FDM-2 fiber-optic distance measuring system to accept miniaturized probes. The micro-probes have a diameter of just 125 µm and can contactlessly scan the individual layers at measuring speeds of up to 20 kHz and accuracies in the sub-micrometer range.

In addition to precisely determining the layer position, the FDM sensors can also record parameters such as surface roughness or hole depth.