ESDA Threshold March/April 2015
Q1) In the scope, 200 volts CDM & 35 volts on isolated conductors are added. What is the intention to add them? Why are both of them determined on the value of 200 volts and 35 volts,respectively?
Q2) As defined in clause 8.3.1,“If the field measured on the process required insulator is greater than 125volts/inch and the process required insulator is less than 2.5 cm (1 inch) from the ESDS item, steps shall be taken toeither A)… or B)...”, is there any relation between 125 volts/inch in here and 200VCDM in scope? If there is ESDS items whose sensitivity level is lower than CDM200 volts (e.g., 100 volts) to be handled,which additional control elements or adjusted limits should be required?
Answer: Yes, there is a relationship to the 125 volts/inch and 200V CDM. The CDM testing itself uses a large charging plane to determine the CDM withstand of the device. If there was a large infinite insulator and a device was placed on it and there was a ground connection made,in theory with a 125 volts/inch limit a device with a 125 withstand CDM voltage would still be safe. If there was a device that was less than 200V CDM then the process would need to be evaluated to see what specific steps the device would be at risk at and there may be a need to adjust the field requirements in this case.It really depends on the process and if there are any insulators that may cause a problem.
Q3) For 8.3.2 Isolated Conductors, which should be considered as isolated conductors in practical electronic manufacturing processes; could you provide more examples? Is an electrical screwdriver a typical isolated conductor while the tip cannot be grounded stably in 10 ohm the same as a soldering iron?
Answer: It is more than just isolated conductors.It is an isolated conductor that comes into contact with an ESDS device.So while a screwdriver may be isolated it may not come into contact with an ESDS device. Typical isolated conductors that come into contact would be the contact pins in an in circuit tester, a probe that cannot be grounded, or tweezers with insulated handles. In reality, there should not be too many isolated conductors that come into contact with ESDS. Also, when the new checklist comes out, this will only result in an observation for a while as it may require new equipment or a survey of the process. This is also a qualification issue, not something that would be part of compliance verification.
Q4) For production qualification of shielding bag, the test method defined in ANSI/ESD STM11.31-2012 as well as test equipment and criteria (<50 nj) is seldom used in current practice. Is there alternative method as well as criteria?
Answer: There is no alternative method at this time. This is the only way to measure the effectiveness of the buried metal layer of a bag. There are many manufacturers that provide this information as part of the product data sheet.
Q5) For the walking test, is it accepted to put the hand on the metal panel of the CPM instead of a Hand Held Electrode in test?
Answer: Putting a hand on a CPM would be acceptable.