In this area you will find frequently asked questions. If you have a new question, please send it to the following email address: FAQ@stat-x.com. Depending on the frequency of the question, we will either answer it individually or post it online anonymously.
Why should I not ground my trolley with a loop chain?
Do metal racks cause ESD failures?
Why can’t I just ground my insulating surfaces with a cable ?
Why should I not ground my trolley with a loop chain?
Answer: Loop chains are unreliable discharge paths. Depending on the weight of the chain, the roller speed and the evenness of the ground, insufficient traction is made with the ground. The heavier the chain, the more dirt accumulates in the course of the day and the contact with the ground deteriorates. If a lighter chain is used, it will only rarely lie flat on the surface on the floor during transport. This behaviour can be well documented with a walking test. Experience shows that these chains have no or only moderate success after a few days.
Solution: At least ESD two roles together with static dissipative coatings are the cheaper, more durable and “audit-proof” option.
Do metal racks cause ESD failures?
A galvanized metal rack is connected to the potential equalization by a ground cable with a 1 MOhm safety resistor. Why do I still suffer from ESD failures?
Answer: Due to the large electric capacity of the rack floors. When an electronic module is placed in a charged metal rack, the rack capacity is significantly larger than that of the module. The first point of contact between the two leads to a potential equalization between the module and the shelf.
Solution: The surface on which the assembly is placed must have a static dissipative resistance. For example, synthetic rubber coverings are suitable for this. If the metal rack is already grounded, the coverings must not be grounded again by cable.
Why can’t I just ground my insulating surfaces with a cable ?
Answer: First, we would like to point out a common linguistic misunderstanding: The word “insulating” is used differently in different sectors; what is often meant is an excessive electrical resistance. For electricians, materials in the megohm resistance range are insulating. In the ESD world insulating materials are understood to start at 100 giga ohm, and plastics engineers go even further. Depending on the electrical resistivity of the material, the charge decay duration via a grounding line varies. Conductive materials need about 0.2 seconds for a charge dissipation from 1000 V to 100 V, dissipative materials, depending on the ambient conditions, up to 2 seconds. In ESD insulating materials, the charge decay is so slow that it is not acceptable from an ESD point of view. This results in the possibility of a permanent electrostatic charge.
Solution: Replace the affected surfaces with ESD material or use ionisation.