Poor component selection can lead to many problems within our electronic design, PCB layout, schedule, etc. Luckily, there are many ways to choose parts that will deliver projects on time and produce functional boards, leaving both you and your clients happy.
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The most important step in part selection is design requirements. The real problem we&#;re solving isn&#;t which parts to choose, but which parameters and functions we need to satisfy the project needs&#;parts just help achieve those needs.
How to select electronic components
The following guidelines will help to find and select the ideal electronic components/devices for any project.
A picture is worth a thousand words; a functional block diagram is worth ten thousand. An accurate depiction of the system is essential to understand the problems we are solving and is achieved with the functional block diagram. Nothing describes an electrical problem better than a system block diagram. System block diagrams allow us to see how things are connected as well as what functions, features, and objects affect one another and why. Once we meet the needs of those function blocks, we meet the needs of the system.
Now that we have a functional block diagram and function blocks, we dig deeper. We must create the circuit topologies that perform the functions in those function blocks.
For instance, let&#;s say we need a function block to change a 12 V input to a 24 V output. With our engineering knowledge and expertise, we know a boost converter is needed to perform that function.
Sometimes additional resources can be used to aid in the creation of these circuit topologies. I recommend reading application notes and reference designs for projects similar to yours. They can act as cheat sheets to find the types of circuits you need to meet a system block&#;s required functionality.
We need to find parts that meet our circuit requirements (topology, operating voltage, and current). Electronic devices are rated for specific parameters, such as voltage, current, bandwidth, temperature, etc. These part selection requirements come from the circuit topology. Once we know the types of components that will meet our topological, voltage and current needs, we need to go shopping for those components.
Time to market is very important for many hardware designers, so we need our parts to show up on time to meet project deadlines. To achieve this, we work with reliable part vendors. It&#;s even better when those vendors help us boost our efficiency in selecting and ordering those parts through a good online bill of materials tool, great customer service, and good shipping practices. Some of the best examples in the USA are Digi-Key, Mouser (in Texas), Newark, Element 14, just to name a few.
Now that we have determined design requirements and part vendor, we need to find components. When searching, enter the electrical and physical criteria we need to get a specific function/task handle.
For example, if we need something that multiplies input voltage to give a certain output voltage, search for a boost converter. A driving factor in the part selection is voltage and current specifications. Filter the search findings on the vendor&#;s website for the design requirements. While this narrows down the options, there are still other criteria to consider.
Lead times and unavailable parts are currently at an all-time high. Before deciding on a part, make sure it is currently available or the lead time fits within the design schedule.
I have two clients in alone who had to slow down their schedules for a couple weeks because they were waiting on parts.
Whenever I work with pre-existing designs, there is at least one part that has a superior version of itself or has become obsolete. Unless a specific version of a part is needed, it's important to take advantage of newer parts that can act as direct substitutes for the older device. The newer parts tend to be more reliable, cost the same or less, are easier to find, and in stock.
Designs are typically spec&#;d out to work in certain temperatures, environments, and so on. Luckily, we don&#;t have to guess at this. PCB&#;s are categorized by specific classes and categories. Based on IPC standards IPC-B, IPC-CM-770E, and IPC-D-330, specific class ratings are given to circuit boards depending on their performance and materials.
To meet the environmental and performance requirements of your product, it is essential to choose parts to match the class of the board (operational temperature, medical grade, etc.).
The first major limiting factor in earning money is time. How long will the product take to make? The second, more important, factor is money. How much will it cost to make it? Cost is extremely important in business because it cannot survive if mass producing a product always loses money.
The cost of an electronic part goes up the harder it is to manufacture; therefore, traits such as precision of value or measurement will greatly affect part price.
In the end, consider the price and cost of every component in your circuit and go with the lowest priced parts that also adhere to design requirements.
We don&#;t want to be purchasing 15,000 components when only 1-15 are needed. Specific component packaging (bulk, tape and reel, etc.) will have minimum order quantities associated with them. Many suppliers have different vendor part numbers based on the packaging as well. Over time, I learned that while ordering in bulk could drop part prices to fractions of a penny, most individual projects or one-off products need a minimum one-off quantity of 1, not 15,000.
Pro tip: Price per part usually decreases as you order parts in multiples of 10. Sometimes it&#;s more cost-effective to order 10 capacitors instead of 8. Weird, I know.
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Methodology is Key
The company, client, or customer only benefits from a working product. Having a strong methodology to properly select parts is key, as one small mistake can cause a product to not work, resulting in missed product release deadlines, extended delivery schedules, more money, and frustrated customers. Selecting electronic components can be confusing and intimidating if you have never selected them on your own before. Every single component we choose will either make or break the product. Even if you choose the right components, things like budget and schedules are greatly affected by whether those parts are cost-effective and available when we need them, affecting the bottom line.
The electronic component selection guidelines above are not fully exhaustive, but will help keep your budgets and product delivery on schedule, build products that work, and satisfy your customers and clients. Then, be sure to capture your schematic properly to convey the original intent of the block diagram.
You need to be able to source electronic components for your new product that reach your cost, quality, and reliability expectations. In fact, the success of your product is riding on the components that it&#;s made up of being perfect for the job. It&#;s not as simple as just going online and choosing something that works, either. In order to find perfect components, we follow this process&#;
What follows is a summary of the electronic component selection steps, but I discussed it in far more detail on our group&#;s podcast here.
The electronic component selection process is more complex than many people think. Proper electronic component selection is not actually as simple as going to Radio Shack, buying a part, and just using it as long as it works. Today&#;s manufacturers need to make sure that their components to be used in mass production meet certain criteria and there are many elements to consider during the sourcing process. We&#;ve broken the process down into 18 steps&#;
1. Define your Requirements
To define your requirements you&#;ll consider what your product does, its users, the environment it will be in, and how this particular component needs to function in order to help it achieve its goals among others. Each part&#;s cost, specifications, etc, must be noted now, too.
2. Select the Key Components
Key components are those that the product relies upon to function correctly. For electronics, it might be a display, type of chip, enclosure, etc. Without these, you are in trouble so they must be noted and considered with care.
3. Analyze the Operating Environment/s
Note your product&#;s intended operating environments. Components that can handle the environment without failing are crucial, otherwise, the product will be unreliable.
4. Identify Critical Parameters per component
Your requirements will demand that components that work in a specific range must be sourced, therefore you need to work on the range of parameters you need for each part. This might be voltage, tolerances, etc. If you select parts without the right parameters you may find that they fail if the environment alters slightly, such as a power surge, or those that are too highly rated just cost you too much.
5. Source the Components
Sourcing components directly from component manufacturers is usually the best option in terms of cost and reliability of supply. You should always obtain the datasheets and check the specifications against your requirements.
6. Consider the Supply Chain
It will reduce risks of disruption if you choose to source from well-established and professional manufacturers. At the same time, find a second-source supplier, especially for key components, so they can step in and supply you if there is ever a problem with your main pick.
7. Check for Obsolescence
Design engineers should be wary of each part&#;s lifecycle and confirm with the manufacturer that they plan to produce it for the long term. This will reduce the risks of you incorporating a part into your new product that is then suddenly unavailable.
8. Analyze costs
Purchasing components at the right cost impacts the sale price of the product. If you buy in large quantities prices will be far lower, so it&#;s better to find a supplier who can supply your required quantity at a reasonable price.
9. Selecting Components at the right level of Reliability and Quality
To guarantee better reliability you should try to select parts that have a margin of reliability, for example, they can handle temperatures outside of the usual operating environment of the product. To do this, you need to perform reliability testing on samples of the parts.
10. Purchase Second-Source Components
If you have found second-source suppliers for your critical components at least, be sure to purchase some and then if there is an emergency you will already have a supplier who can step in and won&#;t have to do the sourcing process from scratch causing delays.
11. Component Database
Implement a component database and keep it updated with new versions of datasheets, version numbers, etc. Be sure to remove obsolete information so your team only sees up-to-date information about the components.
12. Design for Excellence, especially DFM
Use DfX to design your product with design goals in mind that will reduce risks later on, for example, Design for Manufacturing, or DFM , is a popular principle to embrace because it emphasizes designing the product to be easier and more straightforward to manufacture and at a lower cost.
13. Compliance and Standards
Check each component&#;s datasheet to confirm that it complies with the safety standards and regulations of wherever you intend to sell it. If you unwittingly miss a compliance requirement it&#;s very unlikely you can sell the product which will be a disaster if they&#;re all waiting on the docks in a container.
14. Simulating and Prototyping the Product
Now you can make tangible samples or prototypes. You will use the components to make rough prototypes at first and then, as you iterate the prototypes, they will get closer and closer to production standard. This helps you to qualify and validate the functions, performance, looks, etc, of the product.
15. Documentation and Record-Keeping
The many changes that design engineers make to the product during the development process need to be documented so progress can be tracked and team members know when changes were made. Fixes to problems may be collected in a lessons-learnt database, along with dates, who made a change or fix, etc.
16. Design Reviews
Not long before production starts you will have done a lot of testing on components and prototypes and will be close to satisfied that it looks and works correctly, reaching your goals and expectations. But, before signing off, a design review meeting should be called where all engineers and management examine each part of the product being in mind if it reaches its requirements. The purpose is to validate and verify that the product reaches its requirements for performance, reliability, quality, etc, and functions as expected.
17. Lock the Bill of Materials (BOM)
Before manufacturing the BOM is locked which means that there are no more changes to parts used or designs. Component suppliers are contacted to confirm costs and availability and place orders. Everyone works together to make sure that all of the parts will arrive on time for production to start on a specific date. Then attention turns to setting up the manufacturing assembly line/s, writing SOPs, hiring staff, etc.
18. Pilot Run
Before starting mass production it&#;s the last chance to check that the components you have selected can be used to manufacture the products at scale. For this, use the components that you have, by now, tested and validated in a short pilot run using the same line, staff, equipment, processes, etc, as will be used in mass production. If there are any production issues, packaging problems, etc, you will encounter them now and can fix them before things go any further and you have produced thousands of units of your product.
Agilian has a supply chain management team that can assist you in sourcing the ideal components for your needs. Here&#;s how we manage supply chains for you.
If you have any questions about bringing your new product to market, please don&#;t hesitate to get in touch with us&#;we&#;re happy to offer some friendly advice and let you know if and how can help you.
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