AN1110| Application Note
Maxim > App Notes > GENERAL ENGINEERING TOPICS Keywords: PCB, circuit board, prototype
PROTOTYPING AND PC BOARD LAYOUT
Jun 14, 2002
APPLICATION NOTE 1110
Prototyping with Surface Mount Devices
Abstract: Surface mount devices can often be prototyped without etched PCBs by using plain copperclad and simple cutting tools. As surface-mount technology (SMT) has become more prevalent (and many devices are only available in surfacemount), prototyping techniques have changed. Many engineers and technicians are comfortable with through-hole devices, perforated fiberglass boards, IC sockets, and wire-wrap or point-to-point wiring. Prototyping with surface-mount devices requires different materials and tools. In some ways, these techniques are easier, once the proper skills have been developed. This application note presents prototyping methods for surface-mount ICs. This technique is readily used for ICs with a lead pitch down to 0.05 inches (1.27 mm), and with practice can be used down to 0.025 inches (0.64 mm), so it works for well SOICs and virtually all passive SMT components. The basic idea is to cut narrow slots in a copper-clad board, creating rectangular pads, and place the components across the slo
ts. Each rectangular pad is a node in the circuit. It requires copper-clad board and a rotary hand held grinding tool, plus a few other basic tools. To illustrate this technique the circuit of Figure 1, a 5 Watt DC-DC step-down voltage converter, is constructed.
Figure 1. This DC-DC converter circuit is used to illustrate SMT prototyping technique. Start with a fully annotated schematic and gather the parts so you have a good idea of their relative sizes. It is also helpful to have the pin configuration drawings for any ICs in the circuit. Use blank paper, and two pencils of different colors to make a rough drawing of the physical circuit layout. An eraser is essential, and quite often a few iterations are required. Make the drawing larger than life, but stay more-or-less true to scale. You don't need to be very picky with size, but placement matters. Use the lighter color to draw the component outlines, placing parts that share a node close together where practical. Once all the part outlines are drawn, use the darker color to draw lines separating the different nodes of the
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