ESD and static control flooring in Semi-Conductor manufacturing.
Semi-Conductor manufacturing and services industries needs
Special notes on high precision ESD flooring issues which is in high reliability zone. Although it is common knowledge that ESD Floorings or static controlled floorings are a must in manufacturing setting we in the semiconductor industry see high risk of product and device failure. That is why in terms of preventing component or product failure special note has to be put forward in what we choose for ESD flooring. Also we must look into the features of the electronic or semiconductor manufacturing units for that.
How to determine High Reliability process or manufacturing environment?
In the terms of safety what we see in a High Reliability process or manufacturing setting is that there is no report of human or component damage from static charge or accidents. In this setting we see elements like awareness of potential failure, no tolerance for deviation from Standard Operating Procedures, very close attention to the success of operations and that of the final product, and a dedicated resilience to the customer and constant improvement of expertise. These principles play out in many complex industries which include aerospace, defense, nuclear power, air traffic control, automotive controls, and health care in which we see major failures which may be catastrophic and or life threatening. Karl Weich and Kathleen Sutcliffe have looked at some of these industries and how they put into practice the tenets of high reliability.
Let's see how this plays out in the Static Control of the Manufacturing Environment?
That include the manufacturing, processing, assembly, installation, packaging, labeling, service, testing, inspection, transport, or other handling of electrical or electronic components, assemblies and equipment which are at risk of damage by electrostatic discharges of 100 volts HBM, 200 volts CDM, and 35 volts on isolated conductors.
In every case at Chem Co we see to it that ESD Flooring is used which mainly is for grounding personnel and mobile equipment. We have extensive experience in proper ESD Flooring grounding.
To maintain personnel voltages at below 100 volts and thus see to it that discharges from a person to a sensitive device are below the 100 Volt HBM limit. Chem Coats has that expertise).
To that end ANSI/ESD S20.20 has put forth these standards for ESD flooring which:.
The full system must have a resistance (point to point and to ground) of less than 1.0 x 109 ohms as determined by ANSI/ESD STM7.1.
The complete system of person to floor to footwear must have a resistance to ground of less than 1.0 x 109 ohms as tested per ANSI/ESD STM97.1 and.
The total system of person to floor to footwear must be out at less than 100 volts as determined by ANSI/ESD STM97.2.
So according to ANSI/ESD S20.20 which Chem Coats has assumed to be at 100 volts HBM is what the standard is based on. But in the case that the devices which we handle are more sensitive that is to say have a lower with stand threshold? For those situations the standard just states:.
Activities which include items of lower withstand voltage may require additional control elements or changed limits. Also what if we want to limit HBM to below 100 volts which in turn increases the error prevention margin which in turn prevents failure? What if we want to raise the bar for static control program reliability beyond what an ANSI/ESD S20.20 program offers? Only that which does that will give high reliability.
How does ESDA ANSI S 20.20 define high reliability?
In the issue of high reliability has become such a large issue in the ESD community that the Electrostatic Discharge Association formed a Working Group. That group reports now we see a need for conductive flooring.
In the case of static control flooring the electronics manufacturing industry has used what we may term as 2 categories of flooring, conductive and dissipative. These terms are defined in ANSI/ESD STM7.1 that which also present:.
Conductive flooring that has a resistance to ground of less than 1.0 x 106 ohms.
Dissipative floor systems which have a resistance to ground of over 1.0 x 106 ohms but less than 1.0 x 109 ohms.
But in the semiconductor industry which is slowly outpacing the general electronics industry we see different approaches in the classification of ESD flooring by grade. As we noted above ANSI/ESD S20.20 does require that flooring have a resistance of <1.0 x 109 ohms, so either of these “grades” will meet the requirement as long as they also pass the walking voltage test in conjunction with the to be worn footwear in the area. While the ESD flooring footwear combination is very much a factor in body voltage generation, all else being equal the lower the resistance of the flooring the lower the body voltage.
So we have to see that ESD Flooring which also includes Static Control is not a stand alone product but a system which all components must work as a whole.
For in any ESD control program which flooring system is used it is important to note the type of system, the components which make it up, and how those components work together. For instance a conductive vinyl flooring system which is glued in place has the conductive vinyl tile, the glue, the substrate it is put to and the grounding mechanism. Also many of the epoxy or resin based coating systems have a primer layer, a very conductive ground layer, and a dissipative finish coat. (Chem Coats also included).
In many cases one component in the system has developed a resistance which is higher than we would like which in turn causes the entire system to go out of compliance. In a high reliability setting which is what we are dealing with when we choose a floor system it is prudent to know all of the components and the risks of failure which may cause a future non compliance issue.
(Chem Coats handles it.)
ESD TR53 provides procedures for compliance verification as a part of the ongoing verification that control items of an ANSI/ESD S20.20 control program are in use. When dealing with flooring, the following aspects can be considered as the basis of ongoing compliance verification:
- Testing periodicity: Neither ANSI/ESD S20.20 nor TR53 nor the periodicity of testing is mentioned. The periodicity of testing should be sufficiently regular to overcome non-compliance, which should be defined by:
- Use and maintenance: A floor that is heavily trafficked and dirty may be checked less regularly than one that is not. The frequency and scope of floor cleaning will determine how often the floor should be checked for this reason.
- Life of electrical properties: Certain flooring systems have the necessary lifetime electrical properties, while others, for example, only last for a few months such as applied finishes.
- Any changes: Changes in the use and maintenance practices and materials should result in the floor being checked. The performance of the floor can even be impacted by such small changes as these.
- Past results: Getting a sense of if or how the floor is changing over time and being able to make adjustments to the periodicity as appropriate by monitoring results over time.
- Incorporating regular walking body voltage tests: The method of ESD TR53 for verifying flooring is a very simple resistance to ground check. Body voltage generation is the most important measure of the effectiveness of the flooring-footwear system, as has been already noted. In fact, the method of ANSI/ESD STM97.2 should be used for taking body voltage measurements during walking together with the periodicity. By doing this, one can become quite certain that a static control system both in the form of a flooring system and the combination of flooring and footwear is still functioning effectively.
Each one of these is a high-reliability solution (Chem Coats is the one that does the precision) for ESD flooring, electronic and semiconductor manufacturing industry which is a High Reliability Environment that has to be maintained.
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