Guarding chips against “electric floods”

Composed of minute charged particles, electrical current naturally flows from the higher voltage to lower: like a river flowing from the mountains to the sea. The integrated circuit technology exploits upon this spontaneous flow like a dam, producing what seems like a wonder to the uninformed observer. Indeed, this flow plays as fundamental a role to the chip as river plays to the civilization. The analogy, however, does not end here. Just like the city needs its own emergency arrangements to tackle with natural disasters like floods, the modern chip needs to guard itself against "electric floods". -- Dushyant Juneja, Analog Devices, Inc. (India)

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While the engineer can implant limited ESD guard devices in the chip, care must be taken at the assembly and consumer level to keep away from these failures. An ESD sensitive device would generally come with a warning on the label, manual or datasheet. An example is as shown in the figure below. Generally, such a device would come in an ESD protective package like conductive foam, an antistatic tube or a static dissipative bag. ESD warnings may be visible at the package to warn the end user over careful handling. Similar care is taken during chip testing at the industry end, where specialized anti-static suits and specialized test-benches may be employed. It is best to inspect the required devices at grounded workstations and minimize manual handling. Any sub-assemblies made out of the device should also be handled with proper ESD cautions. Dedicated devices such as LVDS transceivers and TVS may be used for ESD protection on a system level. Care should be taken at consumer level in handling the boards or the devices. For instance, it is advisable to not touch such sensitive equipment with bare hands as to avoid unintentional damage. Generally, one would use an anti-static suit and grounded gloves to assemble or operate on such equipment. A further precaution is to not expose them to direct or sudden high voltages, unless they classify to such an operation. Generally, placing a chip or a board in an already active supply would render a serious ESD spark, often called as “hot-plugging”. Only specially designed devices can sustain a long term stress of this intensity, and often the general devices will easily fail in first operation itself. A better option is in fact to gradually ramp up the supplies through the system using linear supplies or other equipment. If the board or system intends to an end user application, such equipment would be deemed mandatory for a reliable operation. Another concern in this direction rises with using multiple interconnected devices on the board, not all of which may be operable at the same time. Care must be taken in such a scenario that parts that are active do not communicate with the unpowered parts, as to avoid unintentional electric current through them. Generally, one would need to use some kind of isolators in such a scenario. This can otherwise short circuit multiple devices, leading to significant inconvenience and losses.

For the end consumer, it is always better to not operate on an apparently not working equipment of this kind, and leave it to the specialized engineers to service the part. This way, additional damages due to touching the device can be avoided. Additional external spike guards like varactor based plugs also act efficiently to improve the long term reliability and avoid ESD damage. If the equipment is known to be sensitive to such spikes, it is often a better choice to use an external stabilizer before connecting to the supplies.

Figure 4 Example ESD Caution Note in a datasheet



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