FP-21T Precision enables resolution below 0.1 mm
The FP-21T Precision machine has an important role both in the teaching and research activities of our group. The machine enables rapid experimental verification of the design of microwave devices and, in particular, millimeter-wave devices.
The target substrate is in most cases a Teflon-based laminate, Rogers 4003 or a similar substrate. Some high-frequency circuits (e.g., filters) require very narrow gaps between microstrip traces.
Before purchasing the FP-21T Precision machine, our PCBs were produced by etching. The standard resolution of the available etching technology is 0.2 mm.
With particular care and manual processing, the resolution could be pushed down to nearly 0.1 mm, but with low yield.
However, the FP-21T Precision machine has enabled easy manufacturing with resolution below 0.1 mm.
We have successfully milled patterns with 0.05 mm resolution and we have been investigating possibilities even to push this limit further.
The new technology, which we have mastered owing to the FP-21T Precision machine, enabled production of filters with wider bandwidth than we could produce by etching and facilitated production of devices for the millimeter-wave range. Although we have been using the machine for only 3 months, we have already made several wideband coupled-resonator filters.
A significant step-up in PCB quality and fast turn-around time
Besides achieving a significant step-up in the quality of manufacturing of microwave printed-circuit boards, we have attained fast turn-around time, which is necessary for the development of laboratory prototypes. Instead of outsourcing the PCB manufacturing, we can now quickly get prototypes, even in the evening and on weekends, which is important in the research activities of both the faculty members and Ph.D. students.
Sharp edges obtained with suitable tools
The milling process should be carefully implemented. Microwave milling tools are of great help not only to obtain vertical metallization walls, but also to accurately control the width of conductors (strips, traces) and gaps.
Incremental milling helps to obtain clean conductor edges. Conical tools leave sloped conductors walls, with sharp and clean edges. However, good control of the tool depth is necessary to maintain the necessary precision of patterns.
Capable of designing microwave circuit with large copper leftover surfaces
Besides using the milling machine for efficient prototyping, the milling process has motivated us to undertake research activities aimed at obtaining accurate models of milled microwave circuits and also at speeding up the milling process by leaving large copper areas intact (rather than rubbing them out).
These large areas are coupled to the microwave circuit and they have a twofold influence. The first influence is modification of the characteristic impedances of traces in a broad frequency range. The second influence is caused by parasitic resonances of the copper areas. In our research, we have performed computer simulations, followed by experimental verification, which have given us sufficient information to be able to keep both influences under full control.
Hence, we are capable of designing microwave circuits with large copper leftover surfaces, keeping intact the circuit performance.
In conclusion, the FP-21T Precision milling machine has given us a significant technology boost which is of great help in our teaching, research, and design activities.
Professor Dr. Antonije Djordjevic
University of Belgrade
School of Electrical Engineering