Posted on 12 Sep, 2019 by Neil Sharp
Electrostatic discharge (known as ESD) is a major contributor of device failure within electronics manufacturing facilities - with industry experts estimating that the average product losses due to static discharge could range anywhere from 8% to 33%.
ESD occurs whenever the electrons on the surface of one object pass onto the surface of another object and cause it to become positively charged.
When those additional electrons come into contact with a differently charged object that allows the passing of electricity, then the result is what is termed an 'ESD event'.
ESD events are occurring around us all the time.
Whether it's the static sensation we get when removing laundry from a tumble dryer, the sharp shock of touching a metal door knob after having walked over carpet, or the spectacle of a lightning storm in full force.
In an electronics manufacturing context however, ESD is a less obvious but far more serious threat - and the level of charge is often so low that manufacturers won't even realise there is a problem until it is too late.
Without proper static control safeguards, these silent electrostatic impulses have the power to zap digital equipment, fry networks and make short work of circuit boards and microprocessors.
Counting the cost of ESD
Damage from ESD can affect electronic components in a variety of ways. Sometimes the damage will be instantaneous and catastrophic - such as in the case of an oxide failure or a metal melt - and meaning that the device will stop functioning completely.
In other cases though, the effects of ESD can be less obvious - or what's termed a 'latent defect'.
When this type of damage occurs, the harm has already been done, but the fault may not be flagged as a problem during a general inspection. But the device is now destined to malfunction, or to fail completely, at some point over its lifespan.
The cost of damage to devices can be anything from a few pennies for a simple diode to hundreds or even thousands of pounds in the case of a more complex electronic circuit.
And when you also take into account the associated costs of repair and rework, labour, overheads and shipping, it's clear to see why it's so important to have static control programmes in place to mitigate the effects of ESD.
Combating ESD in electronics manufacturing
According to the ESD Association there are six principles to bear in mind when developing an ESD control programme:
1. 'Designing in' protection by making your products and assemblies as robust as possible in resisting the effects of ESD.
2. Identifying the level of control that your environment needs - according to the different classes of sensitivity for the Human Body Model (HBM) and the Charged Device Model (CDM).
3. Defining the electrostatic protected areas (EPAs) where you're most likely to be handling ESD-sensitive parts - typical areas include receiving, inspection, assembly, warehouses, R&D, packing, repairs, laboratories and cleanrooms.
4. Reducing electrostatic charge generation by eliminating or reducing the processes that generate static - and by providing suitable ground paths to reduce the generation and accumulation of static charge.
5. Implementing grounding, ionisation and conductive/dissipative static control materials - from the provision of ESD wrist and heel straps for staff, to investing in anti-static mats and flooring, tooling and ESD-resistant packaging solutions.
6. Protecting electronic products from ESD through the use of proper grounding, shunting, and static control material handling products.
ESD is a constant but invisible force within electronics manufacturing that can have a powerfully detrimental impact on production yield, product quality, product reliability and company profitability.
And as the circuitry within electronic devices continues to get faster, smaller and more sophisticated, their sensitivity to the effects of ESD is only likely to increase.
For electronics manufacturers, the solution lies in the continual development of targeted ESD control programmes to identify, define and mitigate the most sensitive areas - and the most vulnerable processes - within their facilities.
Topics: electronics manufacturing
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