December 3, 2021

CHICAGO PIXELS

SEMICONDUCTOR RESEARCH CENTER

Proper Selection of Electronic Components for Your Design

There are many factors involved when choosing the components for your board assembly.   Whether it is a consumer, aerospace, down-hole drilling,  industrial, or test boards – At KES, we help our customers by selecting the parts for their Bill Of Materials (BOM) based on their criteria and the application. Here are a few guidelines for anyone designing an electronic product that will help them be successful.

ENVIRONMENT

The environment the design is going to be used in has a major effect on the selection of components.  Some critical areas to be considered are:

Temperature

Will it be used at very hot or cold temperatures? Be sure to look at the datasheets for passive components such as resistors. A give resistor that will dissipate 100% of it’s rated value from -55C to 70C may fall off drastically above 70C. Check the component datasheet and it’s derating curve to determine if it will work in your applications. It may be necessary to choose a higher wattage component to function reliably. Keep in mind, higher wattage components are often larger and can affect the density of your circuit and placement of components.  Ther are specialized high-temperature devices made, but their availability may be limited.
Sample derating curve for a resistor showing the power dissipation falling off above 70C
An example of a derating curve

Case size

Many designers choose to use the smallest case size possible in order to make their end product the most compact it can be. This can present challenges in manufacturing the boards. Some assembly manufacturers cannot place components smaller than 0402 case size. And, with components that are 0402 or smaller, there is a risk of the device ‘tombstoning’ if not laid out correctly on the board.
Tombstoning refers to one end of the component being soldered to the board and the other lifting up off the board and not being properly soldered. This can usually be avoided by placing these smaller parts perpendicular to the solder flow so that the part does not lift up.
A component on a circuit board that has the tombstone defect
Example of a component that has ‘tombstoned’

Availability

Component availability should always be checked before using it in your design. There is no sense choosing a component that is not in stock anywhere, and for which the lead time might be 22 weeks or more – provided there is an available alternate solution.
Component suppliers such as Digi-Key are an excellent resource to find stock and pricing. Another good resource is FindChips which searches stock availability across multiple suppliers around the world.

Price

Many board manufacturers such as KES purchase such large quantities of components that they have arranged preferred, discounted pricing with many suppliers and manufacturers of components. This can help you in several ways.
  • Obviously, controlling costs should be important — as long as it does not sacrifice the final quality of your design. An experienced board manufacturer like KES can help by helping you craft your BOM in a way that is both lower in cost and has better availability, all without compromising on quality.
  • Your order may not have enough components to meet the supplier’s Minimum Order Quantity (MOQ). Your board manufacturer may already have these components in stock or may be able to arrange a smaller MOQ with the distributor to fill your order.
  • Logistics – managing the logistics of receiving all the components in your BOM can be a challenge. Your board manufacturer is in a better position to handle this for you. Plus, they are likely to have the tools available to perform a vital incoming inspection of the parts as well as properly kitting them for the assembly.

Performance

All of the above will not be helpful if the components do not fit the performance characteristics needed for your design. As the designer, you have the role of defining those parameters. Active devices such as D/A converters, processors, memory,etc., are best determined by you, the designer of the circuit. Other components such as LDOs, crystals, inductors, and other passive and active components can be left to a quality board manufacturer like KES. They have the experience and skillset to take this one, provided you communicate your needs clearly in the specification and schematic.
Choosing components is one of the most important parts of creating your design. By following the above guidelines and working closely with a trusted board manufacturer, you can minimize the potential pitfalls and maximize the success of your project.
KES Engineers have a proven process for selecting components and handing the logistics of large Bills of Material.  For help with your design, schematic, layout, or component challenges, please contact us. We’d be glad to help.
KES Systems – Dallas Support Center
1601 N Glenville Dr
#105
Richardson Texas75081

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