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NOVEMBER 2019 I DESIGN007 MAGAZINE 103 Physical Failure Analysis Results from Failed Type2-LED We performed cross-section and scanning- electron-microscope (SEM) analysis on a failed Type2-LED. It showed that the failure mode is a fracture in the conductive adhesive used for surface mounting the component to the elec - tronic film, Figure 12. The failure mechanism is conductive adhesive creep caused by thermo- mechanical stresses during thermal cycling. Conclusions We have demonstrated structural electronics designs with 70% weight and 90% thickness reduction when compared with conventional multi-part assemblies. Structural electronics is also a reliable technology. The tested certifi- cation platforms and demonstrator products endured thermo-mechanical stresses and el- evated temperature-humidity. Injection mold- ing resin strengthens the structures and also protects electronics from environmental condi- tions, such as moisture, dust, and mechanical impacts. Part 2: Standardization for Advanced Technologies Many PCBA Standards Are Not Applicable for Structural Electronics Structural electronics technology differs sig- nificantly from conventional electronics. This means that many PCBA standards are not rel- evant to structural electronics. For example, the IPC-9704 Printed Circuit Assembly Strain Gage Test Guideline defines how to measure strain in rigid PCBs during the assembly pro- cess. Even if IPC-9704 defines only the mea- surement method, some OEM manufacturers have defined strain limits and require compli- ance from their suppliers. TactoTek substrates are thin and flexible plastic films. They inher- ently bend and cannot comply with the strain limits made for rigid PCBs. PCBs also tolerate higher temperatures than most plastic films. The typical maximum op- erating temperature for FR-4 is around 130°C. Many elevated temperature and thermal cy- cling tests assume that the substrate materi- al is FR-4. Thus, they have a maximum tem- perature of 125°C or even 155°C. Usually, structural electronics substrate materials can- not tolerate those temperatures. Furthermore, temperatures, such as 125°C or 155°C, may not be relevant for the application environ- ment. Two Similar Technologies Have Standards Printed electronics and device-embedded substrate technologies bear a resemblance to structural electronics. Figure 13 shows their definitions. TactoTek follows printed electron- ics standardization developments in IEC and IPC. We have also acquired relevant IEC stan- dards for device-embedded substrates. Figure 12: SEM-images of the cross-section show a fracture in the conductive adhesive used for surface mounting.