How to Design for Reliability When Building Semiconductor PCBAs

For electronic systems users, the two most important factors are performance and reliability. Performance simply means that the device or product meets its functionality requirements. Reliability, on the other hand, denotes the device’s ability to not only perform but to do so consistently over its expected operational lifetime. Since semiconductor repair is often impossible, meeting this requirement is critical.

Semiconductor reliability begins with a manufacturing process that stresses QC. However, ensuring reliability does not end with manufacturing. To ensure that your PCBAs that contain semiconductors achieve expectations, there are design for reliability considerations that must be understood and applied during development.

Understanding Semiconductor Design for Reliability

The importance of semiconductors for modern industry cannot be overstated. This is especially true for critical applications, such as automotive systems, aerospace and medical devices, where even common board failure modes can lead to catastrophes and sometimes fatalities. Therefore, semiconductor PCBAs must be designed to perform reliably over the entire expected operational lifetime.

Ensuring the reliability of semiconductors once deployed requires the optimization of several processes. These processes include the design and manufacturing of the semiconductor and the board on which the semiconductor is a component. Key factors that promote and support good semiconductor component and board design for reliability are often quite similar, as discussed below.

Semiconductor Component Design for Reliability

Semiconductor devices include diodes, transistors and ICs, which typically have specialized functionality. A common type of specialized semiconductors is known as application-specific ICs or ASICs. This group includes processors, floating-point gate arrays (FPGAs) and analog front ends (AFEs). When designing these devices, accuracy, spacing, power dissipation and grounding are primary considerations that can affect device performance. Another important consideration is packaging, as contamination and moisture can lead to premature degradation.

Semiconductor PCBA Design for Reliability

Overwhelmingly, contemporary circuit board design includes at least one, if not several, semiconductors. For boards that contain semiconductors, trace routing is typically a primary consideration, as these devices are often small with fine pin pitches that may limit solder masking or require webbing. Many semiconductors are SMDs that require the routing of vias and may utilize BGAs. And, similar to semiconductor component design, package size that accurately matches the component footprint, spacing, and protection against contamination are also critical considerations that support reliable operation.

Applying Semiconductor Design for Reliability to PCBA Development

Many semiconductor components are—at least initially—designed for non-production and intended as the central component on evaluation and/or development boards. However, regardless of the board type, PCBA design for reliability practices, as listed below, should be applied.

Guidelines for Semiconductor PCBA Design for Reliability

• Optimize your component selection process

Instituting practices to ensure that your supply chain is secure may seem fundamental, and it is. However, failing to optimize your component selection process can reduce reliability for semiconductor boards.

• Ensure components are not moisture sensitive

Components that are moisture sensitive are more susceptible to premature failure, which may be due to poor handling, storage or other issues. The best option is to avoid using semiconductors that are moisture sensitive on your board.

• Apply good thermal dissipation techniques

Both thermal dissipation and distribution are important for semiconductor boards. However, as many of these components generate high heat, applying adequate thermal dissipation techniques is critically important.

• Utilize board protection

Contamination is a major cause of board failure and degradation. Therefore, PCBA techniques and actions to avoid contaminants, with emphasis on moisture protection, should be instituted.

• Apply an appropriate risk management strategy

To minimize the probability of board failure, a comprehensive risk management plan that includes effective controls should be created and implemented.