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44 The PCB Design Magazine • May 2016 and how they are used. Finally we finished up with an explanation of how vias are created and managed in hybrids. Now, let's talk about com- ponents. The selection of components in a hybrid design is influenced by the operating temper- ature of the working design. Higher operating temperatures will require components that can withstand those extremes while at the same time necessitating a different amalgamation of soldering elements for manufacturing. Passive components will use packaged parts while active components will use bare dies (no packaging). This is something different for the PCB designer who would rarely see a bare die used on a board design. Packaged active com- ponents can be used on a hybrid, but this is dependent upon the operating temperature of the design. And by using bare dies, a hybrid de- sign realizes the benefits of shorter circuit paths, smaller size, and better thermal conditions for the device as it is glued directly to the substrate making for a better heat sink. There is also another benefit to using bare dies over packaged devices: wire bonding. The connectivity points on a bare die are on the top of the die and in order to connect to the con- nectivity points of the substrate circuitry, little gold or aluminum wires are bonded between the connection points during the manufactur- ing process. Although this is a labor-intensive operation, it does have its advantages. Since the connectivity points on the substrate circuitry can be moved, the hybrid designer can organize the design in order to optimize the connection path. Imagine on a PCB if you could move the pins of an IC to wherever you wanted to in or- der to improve the routing channels. Well, on a hybrid design you can do just that with the wirebonds. Hybrid design CAD applications have built into them the ability to move the wirebond land patterns (connectivity points) on the sub- strate. The designer also has the ability to ro- tate the land pattern (which is usually an ob- long shape) in order to match the angle of the wirebond. Wirebonds are routed between the connection points in the same way that a regu- lar conductor is routed. Also, the wirebond is routed from a net guide just as you would see on a PCB when routing a trace. Once routed, the wirebond itself will show up in the CAD application as a differently colored wire that is displayed on a different CAD layer in the ap- plication. The wirebond is an intelligent net object just as a conductor (trace) is, so that net rules and connectivity lengths can all be analyzed and accounted for within the CAD applica- tion. And in addition to that, wirebonds can be assigned their own unique reference desig- nators as well as height properties to assist in the manufacturing process. They can also have DRCs run on them to check for spacing viola- tions. Additionally, wirebonds can be used as a regular conductor (wire) connection on the substrate if needed. This gives the designer the ability to connect a net that there isn't room for on a regular layer in the substrate. In this way the designer may be able to prevent the print- ing of an additional conductive layer for just a few extra connections. There is yet another type of component that is unique to a hybrid design, and that is the ink resistor. An ink resistor has some distinct ad- vantages to it over using a standard SMT com- ponent resistor. Ink resistors can reduce cost by eliminating the need to maintain a stock of similar packaged parts. They also can be laser trimmed for a precision tolerance which makes them more cost effective than finding and us- ing component mounted resistors having the same tolerances. The creation of an ink resistor starts in the schematic where the required resistance value is designated. This information is forward an- notated into the layout of the hybrid where THE BASICS OF HYBRID DESIGN, PART 3 " Passive components will use packaged parts while active components will use bare dies (no packaging). "

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