Six Important Tips for how to choose PCB components

- Feb 08, 2017-

PCB Design Best Practices: Six things to consider when making PCB component choices based on part footprints. All the examples in this article are developed using the NI Multisim design environment, however the same concepts apply when using different EDA tools.

PCB design best practices, according to parts placeholder area for PCB components six things to consider when the choice. All the examples in this article is to use NI Multisim design environment development, but use different EDA tools, also apply these concepts.

1. Consider the component footprint
In the schematic drawing phase, please consider to occupying space in the layout phase and land pattern decision.Placeholder area for component based on components should consider when the choice, please refer to the following Suggestions.
Remember, encapsulation including welding plate connection and device machinery (X, Y, and Z) size.This includes the body of the parts contour and the pin is connected to the PCB.Choosing component, please consider the top and bottom of the final PCB any shells or packaging.(such as polarization capacitor) can have some parts need to be regarded as the height of the component part of the selection process clearance limit.Start in the original design, please consider the drawing basic plate of contour shape, and placed some of the larger or critical placed components such as connectors, in order to plan to use.In this way, can make the board's rapid virtual rendering (no routing) visualization, with the relative positioning plate and parts and components of highly relatively accurate said.This will help to ensure that after the PCB assembly, parts will be suitable for packaging (plastic, chassis, frame, etc.).Call 3-d preview mode from the tools menu to view your plate.
Welding plate design display welding parts precisely the PCB solder or hole shape.The copper on the PCB design can also include some basic shape information.Welding plate design needs to be properly determine size to ensure that the correct welding and ensure that the appropriate mechanical and thermal of joint integrity.When designing PCB layout, consider how to make a circuit board or if the hand welding, how to access the welding plate. 
Re-flow soldering (molten solder paste) in the control of furnace can handle a variety of surface mount devices (SMD).Wave soldering is typically used for welding plate with fixed hole on the back of parts, but can deal with some of the SMD components placed on the back.Often use this technique, any downside SMD will must be oriented in a particular direction, and can be modified with welding plate to weld in this way.

Component selection can be changed throughout the design process.Early in the design process to choose which parts should be plated through hole (PTH) or surface mount technology (SMT) can help PCB planning as a whole.Consider the parts cost, availability, parts area density and power, etc.From a manufacturing perspective, SMD components are usually cheaper than the through hole components, and are usually more likely to win.Prototype for small and medium-sized project, larger SMD or through-hole components may be preferred, in order to facilitate the manual welding, and to promote better bonding pad and signal access, for troubleshooting and debugging steps.
If no footprint available in the database, usually from the tool to create custom footprint.

2. Use good grounding method
Make sure there is enough in the design of the bypass capacitors and the ground plane.When using IC, ensure that in the near the power of the grounding position (ground plane) using the appropriate decoupling capacitor.Depends on the application of appropriate size of the capacitor, the capacitor technology and frequency.When the jumper power and ground pins placed bypass capacitors and located close to the corresponding IC pins, will optimize the electromagnetic compatibility of the circuit and magnetic permanency.

3. Assign a virtual component footprints
Run material list (BOM) to check the virtual parts.Virtual parts no footprint associated with it, and not transferred to the layout.Generate the BOM and view all of the virtual components in a design.The only entry should be the power and ground signals, because these are considered to be virtual part, and special processing in principle diagram environment instead of layout.Virtual part, unless for simulation purpose only shows parts application has a footprint of parts replaced.

4. Make sure you have the complete bill of material data
Check whether there is enough data in the BOM report.After running BOM report, please check it, and try to fill any incomplete part of all of these components, supplier or manufacturer information.

5. Ordering reference indicator
In order to help categorize BOM and review, please make sure that the reference indicator are numbered consecutively.

6. Check the door
Usually, all spare gate should be connected to the input signal, in order to prevent the input.Ensure the door, see any spare or have forgotten to full connection disconnected when needed can be input.In some cases, if the input hung up, the whole system might not work properly.Consider, for example, used in the design of dual operational amplifier.If in a part of the IC components, using only a single operational amplifier is recommended in the unused part in IC design single parts, will be placed in the input, and the appropriate units (or other) placed feedback network and amplifier gain, in order to ensure the proper function of the parts.

In some cases, the floating pin of the IC may not be able to work properly within the specifications.In general, the operation of the IC specification only within the same component parts or other door does not work in the input or output near or in parts of the saturated state of the power supply rail.Simulation model simulation usually don't capture this kind of circumstance, because usually do not connect the IC parts used in the modeling of the effects of floating connection together.

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