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RF Electronics Chapter 11: Circuit Manufacture Page 364 2022, C. J. Kikkert, James Cook University, ISBN 978-0-6486803-9-0. Chapter 11 Circuit Manufacture Introduction Once the design of the electronic circuit is complete, the circuit has to be produced. The fabrication method used will depend on: 1) The frequency at which the circuit operates, 2) Whether it is a prototype or a full production design and 3) The type of market the circuit is designed for. Low cost consumer circuits require very different manufacturing techniques compared with military or space electronics, to achieve the required electrical, mechanical, thermal and reliability performance. The most common technique for manufacturing a circuit is to use a printed circuit board (PCB). A PCB consists of an insulating material forming the PCB substrate onto which conductive tracks are placed. Components forming the circuit are connected to those tracks. There are two basic ways of producing PCBs: Subtractive Process: Conductive Layer Removal A conductive layer, like copper, covers one or both side of the PCB substrate and the conductive layer is removed where there are to be no tracks. The metal can be removed using chemical etching, milling or laser ablation. Chemical etching of copper clad printed circuit boards is the most common PCB manufacturing technique. In that process, the whole PCB is covered with a thin layer of photo resist material, which hardens when exposed to UV light. For commercial PCB manufacture, a Laser plotter shines UV light on areas where tracks need to be. For non- commercial applications, a photographic transparency, with dark areas where the conductor is to be removed and clear areas where the track is to be, is produced. That is then placed on the PCB and exposed to UV light. The unexposed areas of photoresist are then washed away. The resulting exposed board is then etched to remove the unwanted copper as shown in figure 11.1. Note that there will be some undercutting of the copper tacks. These chemical techniques are used for producing most commercial PCBs. Figure 11.1. PCB Etching process Including transport, it typically takes one week to produce an etched FR4 board and it takes slightly longer for an RF PCB. For prototypes, a faster turn-around time may be required. With in-house PCB milling or Laser ablation equipment, described later in this chapter, turnaround times of less than one hour are possible for FR4 or RF PCBs. Additive Process: Depositing Tracks and Vias In this method, the conductive tracks are deposited onto the substrate. For thick and LTCC circuits, the conductive or dielectric tracks are printed on a bare substrate material and then fired to make them permanent. Such tracks have a higher resistance than the copper on etched PBCs. RF Electronics: Design and Simulation 364 www.cadence.com/go/awr

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