ESD (Electro-Static Discharge)
These charges are generated during the friction of two different materials. At the time of separation of these two elements they abruptly discharge in contact with a material of different potential. The discharges can be violent until the spark, it is a well-known situation when leaving a chair or when leaving a vehicle, in this case the tension of the shock is of 3KV minimum.
Many active components do not support those discharges especially in CMS technology, some special components like RF front-end (very sensitive) do not support ESD> 50V!
Environmental conditions impact the generation of ESD, such as materials and humidity level. The lower is the humidity level, more loads are generated, so it is important to reinforce the ESD protections in dry areas (exit of the oven, dry cupboard, drying ovens , …).
Examples of daily tensions generated:
– Walk on a carpet: 1.5 to 35 KV.
– Walk on untreated vinyl flooring: 1 to 12 KV.
– Work on a workbench: 1 to 6 KV.
– Handle a document in a plastic pouch: 1 to 7 KV.
– Handle a plastic bag: 1.5 to 20 KV.
ESD discharges can cause weaknesses in some components, causing breakdowns in time that are difficult to diagnose.
For all those reasons it is important to hedge against electrostatic charges when handling electronic boards. It is also essential to protect the electrical inputs and outputs of your card with which the end user of your product may be in contact. There are specific components that are dedicated to this function (TVS, ESD protection, …).
EPA (Electrostatic Protected Area) zone
In order to guard against all ESD problems, we have set up an EPA zone within the EMSPROTO factory.
All tools, bins, containers, packaging coming into contact with the boards are conductive (metal or plastic loaded).
People are connected to the ground to ensure the flow of loads. There are several methods like the bracelet which is the simplest method. In our factory we have a conductive ground and heels or ESD shoes. The staff is also equipped with an ESD (conductive mesh) blouse closed in order not to have contact with acrylic clothes loaded with ESD.
All machines, shelves, work tables are connected to the ground and only have plastics or paints loaded also connected to the ground. The work tables are covered with an ESD carpet (conductive and capacitive).
All equipment are tested every year at EMSPROTO in accordance with IEC 61340 norm with a calibrated megohmmeter and specific probes. The staff control is done several times a day (ESD controller) to guarantee a full ESD protection.
ESD is scary and we often do not notice the effects, but it can happen sooner or later, and cause a breakdown difficult to diagnose. More and more components have inputs / outputs already protected against ESDs, such as microcontrollers, but this is still limited and some components are still ESD sensitive.
We advise to adopt minimal equipment and good practices.
You can equip your work table with an ESD carpet (about 20 € H.T. / m at ATOO Electronics) connected directly to the ground. Get in the habit of having your hands and forearms in direct contact with the carpet. If you are working on ESD-sensitive boards, add a grounded ESD strap via a specific jack with a 1MΩ resistor and wear an ESD blouse if possible or at least cotton.
Be careful not to have plastic on your worktable.
Be sure to remove the card from its ESD packaging only on your equipped table, then repack it in an ESD bag (metallic grey) to be able to move and handle it safely.
By following these advise the ESD risk is close to 0!
Zoom: pouches and ESD protection
There are several qualities of protection, be careful because some materials are conductive such as the black or pink bags and unshielded as metallic grey. These protect your card the others distribute the charges and can transmit ESD to your card! These protections are to be used in EPA zone or inside a shielded bag.