In PCB design we must pay attention to vibration. We must plan for vibration fatigue. If we do not, a PCB will not last long. Many boards sit still and do not move much. Other boards work in places with large motion. These devices can be anything from small toys to complex spacecraft. Some boards do not move, but they still face stresses from manufacturing, thermal change, or hard shocks from users. To deal with this, PCB designers need to know the basics of vibration fatigue in their designs and how to reduce its effects. Here are some ideas that help.
Environmental stress and vibration fatigue
Up to 20% of PCB failures are caused by vibration and shock. These numbers were first cited by the Air Force, but many other industries report similar rates. This shows how important it is to design PCBs to resist random vibration fatigue stress. This is more important for boards used in vibration-prone environments, such as aerospace.
Core board materials (for example FR-4) handle vibration and shock fairly well. But electronic components soldered to the board do not. Vibration makes the board bend. Component leads can break from bending and stretch. Solder is also vulnerable to vibration stress. It can crack and break the electrical link between a lead and the board. Even small vibration over long time can fatigue component leads and solder joints. Without good PCB design practice, solder joints can crack from vibration fatigue.
Manufacturing stress can cause vibration fatigue
Another factor that leads to vibration fatigue failure is stress from the Fabricación de PCB process. Component leads and solder joints are vulnerable to thermal shock. Good DFM (design for manufacture) practices are critical to handle these effects. One example is designing pads on the PCB so component leads can be soldered correctly.
Poorly designed pads can stop solder from filling surface-mount leads correctly. Solder can wick away from a through-hole pad. These problems can make a poor solder connection. For example, on a large thermal pad, wicking away of solder from an uncovered via can stop a device ground pin from getting a good solder connection. That part may pass manufacture and test. But vibration can wear a thin solder joint until it fails intermittently or fully in the field.
What can you do to prevent vibration fatigue?
The first step is design for reliability (DFR). DFR is the design stage work that ensures PCB reliability before you build the board. Part of this work is to include good DFM practices in the design. Your PCB maker can help you pick the correct pad and package sizes for parts. They can give you design rules so you can follow the right IPC class for your PCB. Another DFR step is to use simulation tools to predict where failures might happen in the design. Then you can change the design before manufacture.
New tools and methods arrive every day to handle vibration fatigue and to run random vibration analysis. Still, it is common to test new designs with physical vibration and shock tests. You force failures fast by applying higher vibration and shock than the product sees in normal use. This highly accelerated life test (HALT) is an important part of new product development. It finds potential vibration-related failures. It helps make sure the board structure will run reliably.
