Quality assurance of printed circuit boards with optical 3D measurement

Microvias: optical 3D measurement of diameter and depth

Optiprint’s quality assurance puts great emphasis on providing printed circuit boards that are well-suited to further processing by customers. In order to ensure proper electrical bonding (interconnecting) of multi-layered circuit boards, it is vital that the so-called microvias have been drilled according to pre-defined depth and diameter parameters. Bruker Alicona's measurement systems allow Optiprint to verify diameter and height step of the microvias to confirm that the correct layers have been bonded.

Roughness measurement ensures functionality

Another type of measurement of laser-dilled microvias is checking for traces of powder. Traces of powder form at the outer edge of drill holes when molten material lumps together. With optimized laser parameters for the different materials these bulges are minimized. To identify bulges, the planarity at the transition of the surface to the microvia is carried out with roughness measurements by Bruker Alicona systems.Apart from the above-mentioned measurements of depth, diameter, and planarity, microvia bottoms also need to be examined during quality assurance. The most critical fault to check for here is residual insulating material, as this can impede the electrical conductivity of the entire circuit board. It is therefore essential to verify that this area of the microvia is clean before further processing. Optiprint accomplishes this with Bruker Alicona's high-resolution true-color 3D visualization systems. 

Chip pockets: Area based measurement of shape and flatness

As the next step of the production process, so-called milled pockets, also referred to as chip pockets, are milled into the circuit board to make room for the chips the end customer will later attach to the circuit board. Attaching the chips to the milled pockets is also called Chip-on-Board technology. In order for the silicone chips to remain in place securely, the milled pockets must have the correct shape and be flat. Thanks to Bruker Alicona’s roughness measurement system, Optiprint has managed to gain a better understanding of the interaction between surface properties and assembly process. This in turn has resulted in a much more efficient manufacturing process. In order to ensure proper surface quality and, consequently, flawless attaching, Optiprint measures the height steps as well as shape and flatness of the chip pockets. "Only when we started using areal roughness measurement was it that we mastered the process for milled pockets," says Simon Hütter.

3D profile form measurement of bondpads

Another step in the manufacturing process is the electrical bonding (interconnecting) of the Chips on Board. The electrical interconnecting of chips with the circuit board with using the so-called bond wires is also called wire bonding. Bondpads must be free of faults such as roughness and dirt, as these weaken the bond interconnection. Bruker Alicona's 3D profile measurement system enables Optiprint to verify the form and co-planarity of contact pads on the printed circuit board and ensure perfect conditions for wire bonding. 

The following parameters of multi-layer circuit boards can be measured and documented precisely with 3D measurement systems by Bruker Alicona:

• Depth and diameter of microvias
• Areal roughness at the transition of surface to drill hole
• Areal roughness and flatness at the bottom of microvias
• Areal topography and roughness of milled pockets (chip pockets)
• 3D profile form of bondpads
• Analysis and rating of quality characteristics