Does ESD20:20 allow tailoring to the extent that you can completely remove requirements related to the distance requirements for charged insulators?
Kevin,
ANSI/ESD S20.20 Annex C says, “tailoring allows users of ANSI/ESD S20.20 to deviate from or exclude a requirement of the standard if the user can provide justification and technical rationale for the deviation or exclusion.”
I’m not sure what justification or technical rationale you could give to tailor out the insulator distance requirements. If you want to specify what kind of justification or technical rationale you are thinking of using, perhaps someone can better evaluate
On looking at the examples of tailoring - excluding distance requirements does not seem to fit here.
The rational appears to be that if you don’t have ionizers, and you don’t want to separate a charged insulator from a SSD, then you rely on the operator handling to ensure that no discharge event occurs. Basically removal both risk mitigations and relying operator handling.
If you have a specific example, then we might be able to help. In general, for insulators there are a few things to do. Insulators can be present as long as they don’t pose a threat. A threat can be determined from ANSI/ESD S20.20. If the insulator does not pose a threat, then there is nothing else to do, no tailoring is required. If it does pose a threat, you need to do something. Tailoring to delete this requirement would require data such as a very robust CDM withstand or by ensuring that a discharge cannot happen.
This is the key.
The plan is remove all distance requirements regardless of the technology.
So from wafer fabrication, to die separation, wire bonding, encapsulation, to mounting onto PCBs, PCAs, and assembly into instruments that have SSD ports that when subject to a discharge event breaks the inputs. The lot.
Basically the want to remove the risk mitigations of ioinizers and distance, for all charged insulators within an EPA. Therfore, relying on somehow manging to ensure a SSD never gets grounded when in the presence of a static electric field that never dissipates
Kevin,
As John mentioned, there are 2 ways you could tailor out of the insulator requirements. Neither are easy.
-
The first is to be able to show that there is no means to cause a discharge anywhere in the process. If the sensitive ports are either never contacted or are covered or shunted, this may be a possibility. If your process currently does not use any ionizers or insulator distance rules and you have had no ESD events that you know of, this may help the argument, but it won’t prove it.
-
The second is to show that the CDM withstand voltage is much higher than the 200 volts that the limits in ANSI/ESD S20.20 are based on. This could be difficult as you may only know the withstand voltage at the chip level. This could be much lower as it is assembled on the PCB depending on the on-board protections.
Since you are looking to get out of the insulator distance requirements for all processes from wafer fab to final assembly, perhaps you will find that there is no chance of a discharge in some of the processes. These processes could have the insulator distance requirements tailored out. The other processes would still need to mitigate this risk, but it may, at least, reduce the number of areas you need to provide a risk mitigation solution (i.e. ionization, move or shield insulators, or apply a topical anti-stat).
Okay. So what i think you are saying is.
- You just can’t do a blanket tailoring out.
- you need to look at each step in the process and evaluate based on experimental data to show that there is no risk of discharge event e.g. the techical justification.
The irony here is, all EPA users will be grounded either by shoes and/or wrist straps and the SSD will be typically in a grounded fixture or a dissipative box/traveller. So, at least from my perspective, introducing a charged insulator is a disaster waiting to happen in the majority of cases.
Kevin,
I wanted to make sure you understand the insulator requirements in ANSI/ESD S20.20. The first is that nonessential insulators be 300 mm (12 in) from ESDS material. Hopefully you can control this in your process. The second requirement has two methods of testing. The first method is “Measure the field at the location where the ESDS item is handled. The electrostatic field shall be less than 5000 volts/meter (125 volts/inch).” This requirement has no distance requirements to observe like the second method which is either “For any process essential insulators located less than or equal to 25 mm from an unprotected ESDS item, the voltage on the surface of the insulator shall be less than 125 volts when measured with a non-contact electrostatic voltmeter. When using an electrostatic field meter, the reading shall be less than 125 volts when measured at the meter’s stipulated measuring distance.” or “For any process essential insulators located more than 25 mm, but less than 300 mm from an unprotected ESDS item, the voltage on the surface of the insulator shall be less than 2000 volts when measured with a non-contact electrostatic voltmeter. When using an electrostatic field meter, the reading shall be less than 2000 volts when measured at the meter’s stipulated measuring distance.”
I recommend using the first method at each process step that an ungrounded ESDS product may come in contact with a grounded item. If all your product is in a grounded fixture or a dissipative box/traveller as you say, the field at the ESDS item is likely low due to the voltage suppression of the fixture/box/traveller.
You are correct that you cannot just have a blanket tailoring statement without data. As far as insulators being a disaster, there are many cases where insulators are needed. They might be in fixtures, they could be in test points, they could even be in connectors.
The point is you need to evaluate if an insulator is posing a threat. If there are no insulators in your process, then there is no threat and no need to worry about the distance rule.