Component Reliability Considerations with Circuit Simulation
When I first learned how to fly, I had a friend who really wanted me to take him up for a ride. The problem was that we are both big guys (6’3 & 6’5), and I was flying a very small airplane. Eventually I calculated our combined weights and told him that our weight budget allowed us to go flying, we just didn’t have enough room left over to put any fuel in the plane. I am often reminded of that moment when something goes wrong with a design that I am working on. You can be completely prepared with detailed schematics, circuit simulations, and a perfect layout, but one unexpected problem can upend all of your intentions.
One of those problems that can sneak in and ruin your day is a component failure. All of your simulation will show that the design should work, and you can’t find any obvious issues with how the board is laid out, but still there is a problem somewhere. Component failures can be complete failures or worse, intermittent problems that can cost you time and money to find and correct. To avoid this headache you should consider the reliability of the components that you want to use before you take the time to simulate the circuit. Here’s a little more about what we are talking.
Component Reliability Problems in PCB Design
If there are any component failures during assembly, they are usually discovered through the manufacturer's quality assurance processes. These processes include visual inspection, automated optical inspection (AOI), in circuit test (ICT), or functional test. Your manufacturer will usually rework the boards to correct the problem, or at worse, scrap the board and start over.
The bigger problems are those component failures that occur after manufacturing. These can be caused by different factors:
Sub-Standard Parts: Some components may not be manufactured as well as their counterparts from other vendors. Here is where the services of a good contract manufacturer (CM) can help by recommending high quality part vendors and suppliers.
Component Failures: Parts can have different tolerances and operating limitations, and may fail in the environment that you are using them for. Careful selection of the parts that will work best for you specific application is critical.
Incorrect Parts: Although rare, parts are sometimes incorrectly labeled or loaded into the wrong locations in the assembly pick and place machines. Working with a high quality contract manufacturer (CM) with a well defined manufacturing process is the key to avoiding this problem.
Bad PCB Pad and Footprints: If the pad or footprint is incorrectly designed on the board, the parts will have a difficult time soldering correctly. This can lead to solder joints breaking over time and intermittent board failures.
Manufacturing Problems: There can even be problems directly related to manufacturing. Here again, partnering with a high quality CM is the best answer.
Component failures can cause you a lot of headaches trying to find the source of the problem, and they will definitely cost you a lot in time and money. The best thing is to reduce or eliminate these problems with careful component selection ahead of time.
Component reliability problems can be difficult to find on a manufactured board
Work Ahead to Get the Components that You Need
You don’t want to have to change the components in your design after you’ve spent a lot of time simulating your circuitry and drawing the schematics. The best thing is to consider all of the parameters through component reliability calculations before you go through circuit simulation and schematic capture. Here are some of those parameters to consider:
Component Values and Tolerances: This may seem very basic, but make sure that you choose the correct part for the circuit that you are designing. Your simulation should reveal these kinds of problems, but double check your work.
Temperature Sensitivity Level: Different devices and different manufacturers will have different temperature limits on their components. Make sure tochoose components that will operate in the specific environment that you are designing for.
Moisture Sensitivity Level: Components can absorb moisture during handling which will in turn cause problems with solder reflow as the trapped moisture expands with heat. Use a CM that has good quality control practices to make sure that your components are handled correctly.
Electrostatic Discharge Classification: In the same way that moisture can be absorbed due to miss-handling during manufacturing, sensitive ESD parts can be contaminated in the same way. Again, use a CM with good quality control practices to guard against this.
Manufacturability (Design for Assembly): Make sure that the printed circuit board is designed correctly for manufacturing. DFA rules that are ignored can lead to reliability problems with solder shorts and other issues.
WIth all of this in mind, you can build up a list of reliable hardware and good design practices before you spend time simulating your circuitry.
Make sure to simulate your design with reliable component selections
Simulate the Design that You Are Going to Build
Armed with the proper information, you can work from a list of acceptable components for your design. Once you are ready, you can then create your schematics and simulate your design knowing that the components that you are using will be reliable throughout the life cycle of the design. Good design for reliability engineering like this will save you the problems of having to redesign and resimulate your circuits in order to correct component reliability problems that arise after the boards have been built.
Now that you are ready for schematic capture and design simulation, you need PCB design tools that will give you the best design advantages over the rest. The simulation software from the Cadence line of high performance PCB design tools has been the go-to choice of designers the world over for a long time. PSpice is fully integrated into the Cadence schematic capture tools and is feature rich with its functionality and capabilities.
If you’re looking to learn more about how Cadence has the solution for you, talk to us and our team of experts.