Bringing reliability to the forefront
What comes to mind when you think of reliability? Maybe you consider reliability in connection with experiences defined by high-quality, satisfaction, trust or achievement. Or perhaps you measure reliability relative to realized expectations. Whatever your criteria for assessing reliability, you need a clear understanding of its attributes before you can ever recognize it. And this is certainly true when it comes to PCB reliability.
PCB reliability is attained when a board operates as intended for its projected operational lifecycle in the intended end-use environment. To do so, reliability must be prioritized during board development. Prioritizing reliability during development, though, does not necessarily ensure its attainment. The only way to irrefutably verify board reliability is through post-deployment monitoring.
However, the achievement of reliability objectives can be predicted by instituting a PCB reliability analysis.
What Is a PCB Reliability Analysis?
Evaluating board reliability before deployment and installation offers important practical benefits. Such benefits include the satisfaction of customer expectations, which can translate into more and larger contracts. Before devising a reliability analysis plan, though, we first need to adequately define PCB reliability analysis.
A PCB reliability analysis can be defined as a set of steps or actions performed prior to a circuit board being put into operation. The analysis is intended to evaluate the likelihood that the board will meet or exceed its functionality and durability expectations.
The above is a general definition as the specific steps or actions for analyzing board reliability may vary. However, any reliability test will likely include physical testing processes such as Highly Accelerated Life Testing (HALT) and Highly Accelerated Stress Screening (HASS).
HALT and HASS
It is well-known that flex and rigid-flex boards possess well-defined stress or bendability requirements as provided in IPC-6013D. Rigid boards, however, are not routinely tested for stress. HALT, commonly used for critical system PCBAs such as aerospace electronics, can be utilized for these cases. A typical HALT consists of the following five stages.
- High-temperature test
- Low-temperature test
- Vibration test
- Rapid thermal cycling test
- Combined environment test
The above test stages are performed to the point of board breakdown; therefore, HALT is destructive testing.
HASS is similar to HALT because it utilizes some of the same test regimens. However, HALT is intended to find the point of failure, and HASS is implemented to find material, manufacturing or process flaws that could cause premature failure in the field. This can be seen by examining the figure below.
PCB reliability analysis testing limits1
In the figure above, the UDL and LDL are limits that would be defined by a process such as HALT. These, in turn, inform the HASS upper and lower range of limits. Although HALT or HASS may be a major aspect of PCB reliability testing, there are additional considerations.
1Image from TT Electronics
How Best To Analyze Your Boards for Reliability
From an end user’s perspective, reliability means more than your board’s durability. Reliable functionality is equally important. Therefore, functionality testing that checks for the accuracy of performance metrics is also essential. These tests may be performed in-house, by your CM (depending upon their services and capabilities), or by a third party. Even CMs that perform these tests will likely be required to institute design for testing or DFT to facilitate the process by providing additional information such as test points. To ensure your boards meet regulatory requirements and end-user, be sure to follow a set of guidelines.
Guidelines for Implementing PCB Reliability Analysis
- Know and adhere to the reliability standards for the environment where your board will be deployed
- Incorporate Design for Reliability (DFR) into your process
- Choose a CM that can perform reliability testing or aid you in having the necessary testing performed
By following the guidelines above and opting to work with a CM that is committed to aiding you in producing the best boards that meet your objectives, you should be able to satisfy your reliability requirements.
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Tempo Automation leads the industry in building custom PCBAs that meet or exceed the most stringent quality standards. And we do this while providing the best turnaround time. Additionally, we will work with you throughout the development process and perform in-house board testing to ensure that your boards meet your requirements. If necessary, we will help you transition to a third-party facility for testing or high-volume production.
And to help you get started on the best path, we furnish information for your DFM checks and enable you to easily view and download DRC files. If you’re an Altium Designer or Cadence Allegro user, you can simply add these files to your PCB design software. For Mentor Pads or other design packages, we furnish DRC information in other CAD formats and Excel.