Printed circuit board assemblies (PCBAs) or PWB (Printed Wiring Boards) or CCAs (Circuit Card Assemblies) may vary in use, from remote controls to hospital equipment, extending even to airplanes. But the cost of a PCB failure is easy to predict: Loss of money and/or applications, as well as valuable time. It is important for quality engineering to be paired with good PCB layout design practices to create and deliver a robust and functional PCB assembly.
Quality Versus Reliability
When a PCB assembly is manufactured, the quality of the board is easily measured and can be tested according to a checklist of requirements related to technology and performance. The manufacturer has a variety of responsibilities related to quality and workmanship once the customer accepts the boards, and the customer expects the boards to perform and function properly.
There is no simple answer for determining reliability. Measured over the lifespan of the board, reliability is much more difficult to quantify than quality. Failure can occur after one year, five years, or ten. Below are design tips to help improve PCB reliability.
Maintaining Connectivity
If a board is highly reliable (as in IPC Class 3), all connections will remain intact for the lifespan of the device. Connections can be copper, silicon, gold, or other materials, and maybe fused by means of soldering, vias, or bonding wires. Quality design and workmanship will increase the probability of constant connectivity and improve the reliability of the board.
Matching Coefficient of Thermal Expansion
A PC Board has parts made of a range of materials. When the board or its components increase in temperature, each will expand at a different rate due to its composition. The rate of expansion for each material is known as the Coefficient of Thermal Expansion, or CTE. Designers are advised to use materials with matching CTEs to prevent uneven expansion. If components with differing CTEs are used, cracking or delamination may occur, rendering the PCB unusable and leading to potential failure.
Thermal Profile
Boards may be built using reflow soldering or wave soldering. For either type, it is important to calculate the best temperature at which the board will be processed. PCB components must be able to withstand the high temperatures required for lead-free soldering. While lead-free solder requires temperatures that are higher, the time will be shorter. Adjusting the reflow oven to the correct thermal profile will allow all parts to be effectively soldered.
Printed circuit board assemblies are crucial in important electronic devices, the failure of which can be catastrophic. Through implementing these best practices, designers can increase not only the quality of PCBs but also their reliability, improving the long-term value of the boards and, more importantly, allowing devices to function as expected. BESTProto uses advanced software for creating reliable PCB layouts. We will work with your organization to ensure all design rules are met and that high quality, the reliable layout is produced.