Why is ESD important
ESD protection - what does it mean?
In some professions it is ESD protection very important or even vital. But what does ESD protection actually mean and which ESD protective measures can be taken? This article aims to clarify this.
What does ESD mean and what is it?
The term ESD comes from English and is the abbreviation for "Electrostatic Discharge". Translated it means electrostatic discharge. Requirement for an electrostatic EntFirst of all, the charge is an electrostatic one Oncharge of the body. An easily audible crackling sound is typical for this.
You have probably experienced this particular crackle quite often in your everyday life. It occurs, for example, when you take off a wool sweater over your head. Most of the time it starts to crackle when you "brush your hair". You are statically charged. If you then touch a metal part, you discharge yourself on the part again. This can be uncomfortable to painful, but completely harmless Be experience. For sensitive electronic components This discharging can also do that without any ESD protection end mean. The sensitive conductor tracks inside the components are suddenly damaged by the electrostatic discharge destroyed.
In the above case, electronic components should be protected by ESD protection. However, there are also activities that can be caused by a spark Flammable liquids or Gases in sensitive environments ignite and Explosions cause. You don't want to be around then ...
For this reason, ESD is protection for people in such professional fields vital.
Professions with the necessary ESD protection
Below are some professions and professions in which a more comprehensive ESD protection must be ensured.
- Manufacture of microchips
- Television technician
- Solder / assembler (handling of sensitive electronic components)
- Laboratory technician
- Medical staff
- Chemist (handling flammable liquids and gases)
What exactly is electrostatic discharge?
It is enough if you know that the term "electrostatic discharge" describes the equalization of two electrical charges. Before you can discharge yourself, you have to recharge yourself first. The charging is on two Because of possible.
1. Touching and separation of substances
this is the most common Case. When contact is established between two substances, both substances exchange their charges. At least one contact partner must be a insulator be. When these two substances are then separated again, high tensions occur when they are torn apart. This effect is also under the name "Static electricity" known.
This is by far the most rarer ones Case. Here, the charge separation takes place within an uncharged conductor when it is in an electric field and becomes charged as a result.
In both cases there is a not movable Charge imbalance on the surface of the insulator. So the charges cannot simply flow away. Hence this condition is called "Static electricity". The term also finds "Electrostatics" Application.
In our case, the second substance is worn by a person in the form of Dress. This charged state is transferred to an uncharged medium (for example a microchip) when it is touched.
You can read more about electrostatic discharge and ESD protection under this Wikipedia article or in this PDF
How high are the voltages that occur in various ESD cases?
So that you get an impression of how much you can charge yourself with certain activities and thus of course also more or less painfully discharge, the following table.
The amount of charge is heavily dependent of the humidity in the room.
|event||10% to 20% humidity||65% to 90% humidity|
|walk on carpet||35,000 volts||1,500 volts|
|walk on plastic floor||12,000 volts||250 volts|
|work at the desk||6,000 volts||100 volts|
|Remove paper from plastic sleeves||7,000 volts||600 volts|
|Pick up the plastic bag from the work table||20,000 volts||1,200 volts|
|slide around on foam cushions||18,000 volts||1,500 volts|
It should be noted here that a person only feels a discharge voltage of around 2000 volts, which is irreparable Damage but already through on sensitive components much lower Tensions can occur. In a zone protected by ESD protective measures, a limit value of 100 volts should not be exceeded.
Sparks can occur from a charge of approx. 10,000 volts and in sensitive areas without ESD protection Explosions cause. This is particularly dangerous in areas with flammable liquids or gases. But extremely dry materials such as scraps of paper or sawdust also pose a risk. ESD protection is therefore not just important in the electronics processing industry. This must always be kept in mind.
Why are electronic components destroyed by ESD?
ESD can cause an electrical overload in the conductor tracks of sensitive electronic components. This leads to preliminary damage to the components. This usually results in failures or a shorter service life of the component. When there is a sudden discharge into a component, the energy of small voltages behaves somewhat like a lightning strike into a tree, considering the low mass of the component. Similar to how a fly feels a "hurricane" when you blow on it.
The danger of ESD, however, is that the resulting damage to the component mostly occurs invisible are, and you don't noticed, that one has just finished a component through ESD destroyed Has. This can have expensive and far-reaching consequences, especially if the components are installed in medical devices or in safety technology.
Therefore, one strives with ESD protection to control charges and discharges in such a way that they no Cause damage.
Electronic assemblies are usually sensitive to ESD. Therefore, the data sheets always include the ESD sensitivity called. The classification system is different four Levels, each marked with a letter. These levels are printed with the ESD symbol on the item or packaging.
L = low charging (low charging): Materials and packaging that ensure that the chargeability is minimized
C = conductive (electrostatically conductive): Materials and packaging with a surface resistance of 100 ohms to 100 kilo ohms
D = dissipative (electrostatically conductive): Materials and packaging with a surface resistance of 100 kiloohms to 100 gigaohm
S = shielding (electrostatically dissipative): Shielding against electrostatic discharge
However, for an electrical discharge not always a Contact necessary. The air a discharge can take place from the statically charged object to the statically uncharged element.
ESD protection - which standard applies?
The standard for ESD protection is DIN EN 61340-5-1: Protection of electronic components against electrostatic phenomena - general requirements
ESD protective measures
In the following, various measures are described in the context of ESD protection, which are specified in detail in the standard mentioned above. The ESD protective measures are always carried out in two different ways.
1. Try to avoid charging or to keep it as low as possible by earthing
2. Allow possible charges to drain off slowly and in a controlled manner.
Control of employees and the workplace
- Training of employees
- Determination of the necessary ESD protective measures
- Checking the effectiveness of the ESD protection (e.g. avoiding lock bypassing)
Clear identification of areas with ESD protection
A clear identification of ESD-protected areas within a company in electronics production is important. Internationally one speaks of one EPA (electrostatic protected area) which means as much as "Electrostatically protected area" means. Signs and dashed yellow lines on the floor indicate such special work zones down. In most cases, these zones are also sealed off from the other areas by locks or doors. Before entering such rooms, ESD protective measures must be taken, for example, put on ESD shoes.
However, it can also be the case that work has to be carried out at the customer's site. In many cases, then it is no Marking of areas in which ESD protection is necessary is available. To be on the safe side, you should wear ESD clothing here as a precaution.
As I said, it has climate one in a room big influence on the Strength of charge of the people in this room. Therefore you should have a suitable temperature in an EPA (electostatic protected area) according to ESD protection guidelines moderate humidity produce. The relative humidity should be about here 50% are located. If the air is also ionized by an ionizer, electrostatic charges can dissipate more quickly. Such devices should Not be used as a substitute for insufficient efforts in ESD protection.
ESD protection through ESD shoes
In many fields of activity, such as the assembly of printed circuit boards, or in microfabrication imperative ESD shoes required. They keep the contact resistance to the ground as small as possible so that a charge cannot arise in the first place. Further details on ESD shoes can be found in the Special shoes section in the article ESD shoes.
ESD protection - Special ESD clothing is also important
You will surely guess it, just wearing ESD shoes alone is not enough in ESD protection areas. In order to rule out any risk, you also have to wear special ESD clothing when working in such an area. This requires the ESD protection guideline. ESD clothing belongs to
- ESD work coats
- ESD t-shirts
- ESD shirts
- ESD sweatshirts
- ESD gloves
- ESD wristbands for earthing (this is also part of ESD clothing)
You have probably heard of ESD wristbands for earthing the working person. But did you also know that ESD clothing is special ESD T-shirts for the ESD protection? 😉
Resources for daily work
It's hard to believe, even mundane things like Trolleys must be approved for EPA areas as part of ESD protection. For this reason, there are special protective measures required by ESD
- ESD table trolleys
- ESD push bar trolleys
- ESD shelf trolleys
ESD protection through workplace design
Likewise, as part of ESD protection, the workplace must be ESD capable and as free as possible from ESD-active materials. The following ESD protective measures therefore apply to the workplace
- Antistatic or dissipative work surfaces
- ESD suitable chairs
- Avoidance of unnecessary isolators in ESD-protected areas (e.g. adhesive tapes, styrofoam, coffee cups, transparent covers)
- Use of air ionizers for the targeted reduction of static charges during the production process (e.g. when peeling off plastic films)
- ESD mats
- Use of ESD packaging instead of normal packaging
Prohibited objects at a workplace with ESD protection
As a basic rule, only those items should be brought into an EPA that are absolutely needed there. Because what is not there cannot charge itself.
In any case, the workplace must be free of any materials that contain:
- Unsuitable ESD protective covers or folders
ESD protection through work guidelines
In order to avoid static discharge on sensitive components, an ESD protection is required Work table With Earth connection necessary. The working person is then connected to this via an earthing bracelet. In addition, the work table should be equipped with dissipative resp. antistatic work surfaces be equipped. In order to protect employees in the event of a malfunction, the connection to the earthing network should be implemented via resistors. This is also necessary so that a possible charge of the person can drain off slowly and in a controlled manner and arcing can be avoided. This compliance with the guidelines is also an important part of the ESD protective measures.
The following table shows the permissible resistances with the permissible discharge times for the person to the earthing network. This guarantees electrostatically safe work.
|Type of derivation of the person||Max. Permissible resistance||Max. Permissible discharge time|
|Floor mat for grounding||1,000 MΩ||less than 1 second|
|Table mat for earthing||1,000 MΩ||less than 1 second|
|Grounding bracelet||100 MΩ||less than 0.1 second|
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