High Temperature High Reliability Electronics

High-temperature capability and high reliability describe different requirements.

High-temperature capability concerns whether an electronic device or assembly can operate within its specified performance limits at an elevated temperature. Reliability concerns the probability that it will continue to perform its required function for a specified duration under defined conditions.

An assembly can therefore function successfully during a short high-temperature test without having demonstrated the reliability required for years of operation. Equally, equipment with a strong service record in a moderate environment cannot automatically be assumed suitable for a hotter installation.

For critical electronic systems, these requirements must be considered together. The assessment needs to establish the operating environment, required function, acceptable degradation and intended life, then examine whether the design and supporting evidence are adequate.

“High reliability” is consequently more useful as a measurable requirement than as a product description. The required reliability depends on the application, the consequences of failure and the level of confidence needed in the supporting evidence.

There is no single temperature boundary that usefully defines high-temperature electronics across all technologies. Semiconductor processes, packaging systems, passive components and attachment materials have different operating limits.

The duration and type of exposure also matter. A brief manufacturing excursion, unpowered storage and continuous powered operation place different demands on an assembly.

Temperature must also be associated with a physical location:

• Ambient temperature describes the surrounding environment.
• Case temperature describes a specified location on the package.
• Junction temperature concerns the active semiconductor region.
• Local material or interface temperature may govern degradation elsewhere in the assembly.

Self-heating can make a powered device hotter than its surroundings. In a multi-chip module, individual devices and interfaces may experience different temperatures and gradients.

A chamber setpoint therefore cannot automatically represent every temperature relevant to reliability. The assessment must identify where the important stresses occur and whether those temperatures have been measured or estimated with sufficient confidence.

A useful mission profile also captures operating states, dwell times, start-up and shutdown events, power changes and relevant mechanical or environmental loads. Peak temperature alone is insufficient to describe the exposure.

The semiconductor die is only one part of an electronic assembly. Electrical connections, mechanical attachments, insulation and heat-flow paths must also remain functional throughout the mission.

Packaging brings together materials with different thermal expansion, stiffness, conductivity and chemical behaviour. Their interaction creates reliability questions that cannot be answered by checking the semiconductor’s temperature rating alone.

An adhesive may provide attachment, electrical conduction, thermal conduction or several functions at once. Its suitability depends on which properties must be retained in the finished assembly.

Glass-transition temperature, Tg, is relevant because stiffness and thermal expansion can change through the transition. However, Tg is not a universal continuous-use temperature rating or an independent measure of service life.

Cure state, filler content, bond geometry, moisture exposure and mechanical loading can all influence behaviour. A material that performs adequately in one configuration may behave differently when its bond thickness, substrate or processing conditions change.

Chemical compatibility also matters. In a sealed package, substances released from internal materials may remain within the enclosure. Hermetic sealing limits exchange with the external environment, but it does not establish that internal adhesives, residues, metallisation and other materials are compatible over the required exposure.

A credible materials assessment therefore considers both the properties listed on a supplier’s data sheet and the conditions under which those properties were measured. The relevant question is whether the material retains its required function in the intended assembly throughout the mission.

Sustained exposure to elevated temperature can promote time-dependent physical and chemical changes. Thermal cycling introduces repeated deformation as neighbouring materials expand and contract by different amounts.

Power cycling creates another loading condition. Internal heat generation can change local temperatures and gradients even when the surrounding environment remains relatively stable.

These differences affect which failure mechanisms are relevant and which tests provide useful evidence.

Consider two assemblies with the same maximum operating temperature. One remains hot for long periods with few shutdowns. The other repeatedly starts, heats and cools. Their peak temperatures match, but their exposure histories and dominant degradation mechanisms may differ substantially.

This is why a high-temperature storage result should not be treated as complete evidence of powered-operation reliability or thermal-fatigue resistance. Each test answers a particular question, and its relevance must be connected to the mission.

The appropriate programme may need several complementary activities rather than one severe test intended to represent every aspect of service.

Accelerated life testing can shorten the time needed to observe degradation. Its value depends on whether the applied stress accelerates a relevant mechanism and whether the relationship between test and service conditions can be justified.

For suitable temperature-dependent mechanisms, an Arrhenius model can relate degradation rates at different temperatures. The activation-energy parameter must be appropriate to the mechanism and technology being assessed.[3]

Two limitations are particularly important for high-temperature electronics.

First, increasing temperature can change the behaviour being investigated. A test may cross a material transition, alter an interface reaction or introduce damage that does not dominate during intended operation. Failures may occur sooner while becoming less useful for the proposed life prediction.

Second, an application already operating near its justified temperature limit may offer little thermal headroom for acceleration. A modest difference between operating and test temperatures can make a long-life demonstration difficult to complete within the programme schedule.

Neither problem is resolved by selecting a larger acceleration factor. The factor is a model output whose validity depends on the underlying assumptions and evidence.

The Arrhenius acceleration factor calculator can help explore the numerical effect of assumed inputs. It cannot establish that those inputs describe the hardware’s actual degradation mechanism.

Where thermal acceleration is limited, useful evidence may come from longer-duration testing, representative prior data, targeted interface studies or validated modelling. Design changes may also be necessary. Additional stresses should be introduced only when their relationship to the intended service damage is understood.

Qualification establishes whether specified hardware meets defined requirements under an agreed evaluation programme. A service-life assessment addresses what the available evidence supports about performance over a particular duration and operating history.

These activities overlap, but a qualification pass does not automatically establish every proposed lifetime claim.

The relevance of a result depends on the tested construction, manufacturing process, sample selection, stress conditions, monitoring and acceptance criteria. This is central to component and system qualification planning.

For high-reliability electronics, unacceptable performance should also be defined carefully. Failure may include electrical drift beyond an allowable limit, intermittent behaviour or loss of a required function, as well as an obvious open or short circuit.

A test with no observed failures is useful evidence, but its strength depends on sample size, exposure and the statistical assumptions used. It does not demonstrate that failures are impossible.[3]

A defensible assessment should establish:

• Which production configuration and population the evidence represents.
• Whether the applied conditions address the expected service mechanisms.
• Which performance limits and failure criteria were used.
• Whether monitoring could detect relevant degradation.
• How test results were translated into any service-life claim.
• Which uncertainties remain and how they affect the decision.

The objective is a traceable argument connecting the requirement, the hardware, the potential failure mechanisms and the evidence.

Research demonstrates that specialised electronics can achieve demanding temperature capability when the device and packaging technologies are developed together.

Neudeck and colleagues reported yearlong operation at 500°C in air for particular NASA-developed SiC JFET integrated circuits. That result provides evidence for the investigated technology under the reported conditions.

Chen and colleagues also described an alumina-based packaging approach for testing low-power SiC integrated circuits at 500°C, including the associated metallisation, die attachment and wire bonding.

These results are valuable because they demonstrate an integrated approach to extreme-temperature electronics. They should not be treated as evidence that an unrelated commercial device, conventional circuit board or encapsulated module has comparable capability.

A temperature demonstration must be interpreted alongside its duration, electrical loading, atmosphere, package construction and performance criteria. Transferring the conclusion to another design requires evidence that the relevant conditions and mechanisms remain applicable.

A credible high-temperature reliability programme starts with the intended mission and a clear definition of required performance. It then examines the complete assembly, identifies plausible failure mechanisms and determines which existing evidence is relevant.

The next step is to resolve the uncertainties that matter to the engineering decision. This may require additional measurements, materials characterisation, targeted tests, failure analysis or changes to the design.

For example, an assembly may pass an unpowered storage test while leaving powered electrical drift or local thermal gradients unresolved. Simply increasing the storage temperature might introduce additional material damage without answering those questions.

The assessment therefore needs to connect each activity to a specific concern. General guidance can identify what deserves attention; product-specific evidence determines whether a particular design is suitable.

SPACEREL provides high temperature high reliability electronics services to support this process, from mission-profile and materials reviews to service-life assessment and qualification planning.

Need to substantiate a temperature rating, operating life or qualification approach? Describe your application, expected exposure and current engineering concern through our technical enquiry form.

These technical books and research publications provide further insight into high-temperature electronics, packaging reliability, material behaviour and service-life assessment. Interpret their findings in the context of your hardware, operating conditions and programme requirements.

• McCluskey, Grzybowski and Podlesak — High Temperature Electronics. Semiconductor technologies, packaging materials and interconnections for elevated-temperature operation.
• Licari and Swanson — Adhesives Technology for Electronic Applications. Adhesive selection, processing, thermal behaviour and reliability in electronic assemblies.
• O’Connor and Kleyner — Practical Reliability Engineering. Reliability assessment, test planning, statistical analysis and accelerated-life models.
• Shi et al. — Improved Electrical Isolation and Reliability in SiO₂-insulated Flip-Chip Packaging of SiC Chips. Research into insulation and interconnection performance in high-temperature packaging.
• Neudeck et al. — Yearlong 500°C Operational Demonstration of SiC Integrated Circuits. Reported long-duration operation of specialised circuits under defined high-temperature conditions.
• Chen et al. — An Alumina-Based Packaging System for 500°C Testing of SiC Integrated Circuits. Packaging materials and assembly approaches supporting high-temperature circuit testing.