Quality assurance is therefore of paramount importance and is an integral part of industrially implemented Total Quality Management, Zero Defect or Six Sigma strategies, which demand constant quality improvement. The key to highest productivity at highest yield and lowest cost is 100% in-line inspection during production, to gain intimate knowledge about interdependencies between process steps and process parameters. This paves the way to what is called smart production, where ample measured information concerning key parameters at each process step during production is available in real time to allow 100% individual traceability and immediate feedback in the framework of a big data correlation scheme.

True novelty in failure detection

INLINETEST targets the design, realization, deployment and test of two novel in-line inspection systems for micro/nano-electronic components. Thereby, the fast, contactless and non-destructive full-field thermometric methods of Pulse-Infrared Thermography (PIRT) and Thermoreflectance (TR) are exploited for the first time to enable 100% in-line production monitoring. This will be done by adapting and upgrading existing lab prototypes for both methods to the challenges of real-life in-line testing, enhanced by hard- and software innovations. For validation under real-life conditions, both failure analytical method’s hard- and software will be customized and integrated into two production lines and demonstrated on two encapsulated power multi-chip module (MCM) components and one in-line production tool at the project partners. Three global players in micro/nano-electronics in Europe accompany this endeavor on the board of industrial advisors.

Micro/nano-electronic components fail under field and test conditions due to thermal and mechanical overload or over time (fatigue failures), both of which are governed by the structural integrity of the component. This structural integrity, however, is determined during production by e.g. tolerances in material or processing parameters. This can lead to weak points in the component as e.g. voids, material gradients or inhomogeneity, cracks, delamination, dewetting, or geometric tolerances, impairing robustness and reliability:

1. High power transients can damage the semiconductor by overheating due to local thermal hot spots or decisively reduce its lifetime due to the set-in of unwanted diffusion processes.
2. Weak spots can lead to thermo-mechanical reliability issues like cracking or delamination.

For that reason, the consortium has decided to demonstrate the envisaged in-line inspection system on two power components from relevant European market segments with also silver sintered die attach material in application, designed also for use in harsh environment:

1. A GaN RF HEMT HPA power MCM encapsulated component for avionics and telecom applications, using eutectic solder as die attach material and epoxy molding compound (EMC) encapsulant.
2. A Si-based power MCM for automotive applications, using sintered silver as die attach material and an EMC encapsulant.

From Lab-Scale to In-Line Process

It is, however, important to note that the employed failure analytical techniques can also be in-line-applied to non-power components as e.g. advanced packages during ramp-up of consumer products.

The principle of the failure analytical methods on which the in-line inspection systems are based are highlighted in Figure 2. After transient energetic excitation, propagating thermal waves probe the heat path in the component which is determined by the material properties, i.e. also the structural integrity. Aberrations or anomalies can thus be made visible by recording the thermal signature of the component as response to that excitation. This thermal signature (surface temperature over time) is recorded either by PIRT or TR. As one can see, the methods are complementary in the sense that PIRT is sensitive for non-reflective surfaces (e.g. encapsulated components) whereas the other, TR, is sensitive to reflective surfaces. So many stages in the production process can be monitored. One major advantage is that the equipment probes exactly those flaws which are responsible for a later failure by the same physical effect of high temperature. So the thermal contrast detected by the two methods is physically very motivated and justified and better suited than time-honoured methods which, if at all in-line capable, monitor derived qualities as acoustic reflection or absorption of radiation. Further, cooling down time (tens of seconds) after processing can ideally be used for thermographic methods as it is not used otherwise.

So, new information on production process quality can be obtained which has so far been inaccessible, allowing countermeasures and control to potential aberrations in the process flow. This new information renders the production smarter and will thus enable higher yield, narrower tolerances, better reliability, less maintenance cost and thus result in a higher productivity, less waste and higher profits. Limitations of today’s in-line testing

For manufacturing of micro and nanoelectronic components in-line-capable failure analytical techniques must feature capability (detect/measure the defect in question), precision (how good the defect can be detected and differentiated from others without fault) and efficiency (measurements per unit time) by preferably non-contact methods.

The absence of insight: why INLINETEST is necessary

Whereas fast automated in-line equipment is available on the market, the bottlenecks are the respective measurement systems and the real-time data processing. Many methods are too slow to keep track of the production. Thermography is used today already for in-line measurements as it is a fast optical method, but only for approximate thermal resistance determination (e.g. LED). Electrical hot probing is an alternative, but not all samples allow to be electrically contacted at relevant production stages due to their complexity or sensitivity. So, whereas this is done and possible for LEDs on different complexity levels, it is much more complex for RF-circuits, and electrical response signals do not reveal a spatially resolved map of structural deviations from the standard. But a temperature contrast detected on reflective surfaces could. X-raying of samples, often a method of choice, is not sensitive to most surface or small scale defects, especially for low-Z elements (e.g. encapsulants, etc.)

The result is, that often indirect methods are applied, i.e. offline analysis by random sampling tests for process control followed by statistical schemes like six sigma to minimize the risk of failures in the field. Therefore, specifications of the components are chosen that typically reduce the production yield significantly which is of course not desirable.

Testing costs is another limitation which translates into test time and equipment cost. However, for newly designed, advanced high quality products, as targeted here, testing in production is required, and to widen the scope incorporating also thermo-mechanical parameters is highly desirable. The absence of defects is a figure of merit for the operation conditions that can be applied to the device. Thus, the determination of the structural integrity with a significant accuracy enables a unique selling point: performance will be improved according to the true capabilities of the device to sustain the applied thermal and mechanical load. In sum, today’s hard- and software solutions for in-line testing cannot reach out to the opportunities represented by thermography as established method for industrial application (high TRL) to the point that smart production can be leveraged up to a new level.