IEC 62435-7-2020 Electronic components – Long-term storage of electronic semiconductor devices – Part 7: Micro-electromechanical devices

IEC 62435-7-2020 Electronic components – Long-term storage of electronic semiconductor devices – Part 7: Micro-electromechanical devices. 4 Storage considerations 4.1 Overview of MEMS applications MEMS (Micro-electromechanical Systems) are miniaturized mechanical or electromechanical elements that typically vary in size from 1 micron to 1 000 microns that are used to mechanically measure or manipulate matter, light or create electric signals from environmental inputs. Storage of MEMS devices should consider different sensitivities and risks compared to other semiconductor devices due to the mechanical nature of the devices. MEMS may be subject to additional mechanical related performance and failure mechanisms in addition traditional semiconductor performance mechanisms. The storage program should consider the end use and failure mechanisms related to the function of the MEMS device. Typical uses are listed for initial consideration and risk assessment. – Actuator mechanical movement related to electrostatics, thermal changes or piezoelectric effects. – Physical sensors related to acceleration, vibration, field/flux, force, magnetic field, electro- static, optical stimulus or radiation effects, pressure, temperature. – Chemisensors related to gas or liquid induced mechanical response changes (may also have requirements for moisture or solvent which also have shelf life). – Biosensors liquid, mechanical or fluidic induced mechanical response changes (may also have requirements for moisture or solvent which also have shelf life). 4.2 Failure mechanisms 4.2.1 Occurrence of failure and driving force Failures during long-term storage may be mitigated by control of the stimuli driving given failure modes of interest as defined by risk assessment tools, for example, failure modes and effects analysis (FMEA). Storage related failures are often detected as modes of non-operation, visual quality, reduced life time or other non-conformance. The modes of failure during storage are typically related to a failure mechanism that is driven by a physical stimuli or condition. Example failure stimuli are given in Table 1 . Additional examples of deterioration mechanisms are found in IEC 62435-2. Successful long-term storage is accomplished by mitigating failures through control of the stimuli or driving force. 4.2.2 Storage environment and mitigation for stimuli to prevent failure Mitigation of failures during and after long-term storage occurs by directly controlling or limiting the stimulus for failure by a number of means. Common requirements for sustained long-term storage are given in Table 2. Knowledge and control of the storage environment is of primary importance to identify the risk of failure occurrence and to control or eliminate failure stimuli during storage. Examples...