**4.3 Machine corrections**

To reduce errors during the manufacturing process, machinery side effects must be identified and characterized. In case of using a multipurpose UV Laser System such as a cutter/plotter laser, these lasers are slightly tilted [11]. So that substrates will be

*Manufacturing Methods Based on Planar Circuits DOI: http://dx.doi.org/10.5772/intechopen.109114*

**Figure 12.**

*Calibration kits. a) Microstrip calibration kit without removable connectors, (b) coplanar calibration kit with removable connectors, (c) coplanar calibration kit with soldered connectors.*

cut with certain angle, producing a small ramp instead of a 90° cut (see **Figure 14**), which can be measured with a microscope or a vision system to incorporate the proper correction during the design phase of the prototype. Thus, an over-cut equal to the measured deviation compensates the effect of non-perpendicular laser cutting.

As it is shown in **Figure 15**, this ramp can be divided in three points: 1 (upper point of the ramp), 2 (lower point of the ramp), and 3 (middle point or average point of the ramp). Without correction or overcut, points 2 and 3 are lightly smaller than they should be. Over-cutting enlarges this cut adding this laser error and moving the desired size to point 3, the middle point, instead of point 1. This shifting produces point 1 to be a bit larger and point 2 to be a bit smaller; however, on average this cut is just as it should be. By doing this, the frequency shift presented by selective devices, such as filters, is drastically reduced, with the measured parameters of the prototype being more similar to the simulated ones.

Some cuts have complex geometries or are very tiny. These machines may have problems doing them correctly, because of that, additional cutting phases with simple shapes in certain areas are interesting to solve these issues. The same can happen for difficult milling areas and the solution is similar; additional milling layers should be defined, but it must be done carefully to avoid substrate from burning or getting damaged.

**Figure 13.** *Die cut example.*

Although these machines work similar along the time, tools may need to be adjusted manually to seek for optimal performance every few months. This can be done easily using scraps of previous substrates.

If the prototype has holes used to pass through a wire or alignment pins, the overcut must be double to assure enough clearance in the whole hole to pass the wire or pin properly. In case there is a metallization, holes and cuts are reduced due to the presence of the additional metal and need to be taken into account to define the needed overcutting. Metallization can be either measured or calculated depending on the process, with the measured value being preferable when possible.

In case of using a mechanical cutter such as a drilling machine, the drill is really close to a perfect perpendicular cut. However, drilling tools are usually bigger or smaller to the theoretical size, due to fabrication tolerances. To avoid this, the size can be easily measured by doing a small cut in the substrate that we are using and measuring it, applying the proper correction in case it was needed.

#### **Figure 14.**

*Laser cut error. Lasers are slightly tilted, and this produces a small ramp instead of a 90° cut with some negative impact.*

#### **Figure 15.**

*Laser cut error, Figure extracted from [12].*

The absence of these corrections can produce frequency shiftings and misfunctions in the performance of the prototypes, among other effects.
