Dear ESD experts
in a screen production line, does the station where the film paper is removed from the panel and then be wiped using a special glass panel wipe cloth to remove dust particles requires neutralization via ionizers.
Awaiting your advice
Meriem,
The need for ionization would depend on the electric field strength on the panel after the film is removed and wipe is done and how far the panel is from the ESDS items. Per ANSI/ESD S20.20:
• 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.
• 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.
Generally the process of removing the film and wiping the panel will generate thousands of volts and the only effective way to remove this charge in a timely way is ionization. Keep in mind that ionization itself will take some time to reduce the charge to an acceptable level. The amount of time any ionizer needs to remove the charge effectively should be measured as this can vary from ionizer to ionizer
Meriem,
Andy is correct in the requirements of S20.20. You must consider the work you are completing on the particular item and its proximity to other parts. If there are no ESD sensitive items within 12" of this operation than chances are there is no need for ionization. However, without know all of your and your customers standards you are required to meet this cannot be stated for sure.
Regards
Chris
Dear Mr. Andy,
Please teach me further on this.
During the apprearance of an over-limit charged insulator close to ESDS, if we don’t have any “grounding” activity to the ESDS (especialy metal contact to ESDS), I understand that we don’t need ionizer there.
Is that right?
Best regards,
LuanDD
Luan,
You are correct. If the ESDS item cannot be grounded, the presence of an electric field from a charged insulator will not cause a discharge directly. Thus ionization at that point may not be needed. You do need to be careful that this point of no “grounding activity to the ESDS” item is in fact true and you would want to ensure that the ESDS item is moved far enough away from the charged insulator’s electric field before contacting it. You should consider ionization at the next point the ESDS item is handled or grounded.
For a screen production line, would we need to use ionizers at the station where the film paper is removed and the panel is wiped down to remove dust?
As with anything, you need to collect the data to see if this proces casuse a threat to your ESD sensitive item. I would measure the field at the ESD sensitive item while the paper is removed to see if the field at the ESDS item exceeds 125v/in or 5000/meter. If the field is exceeded than ionization may be required. If this process is far enough away from the ESDS item, it may not need ionization.
Thank you a lot, Mr. AndyN.