We are currently evaluating the impact of changing the cutting sequence on a DISCO sawing machine from Sequence 1 to Sequence 2. The primary difference between these two sequences is that cutting will start from Line 2 instead of Line 1.
As part of our assessment, we have conducted ESD measurements to determine any potential ESD-related changes due to this modification. Our evaluation included verifying machine groundings, ionizers, and RTG, all of which were found to be within specification. Additionally, we measured ESD events during the cutting process using a dummy panel. In both sequences, we observed the presence of ESD events, with recorded values reaching up to 510V.
We would like to seek your guidance on the following questions:
Is this method of evaluation valid for determining ESD differences between the two sequences?
Does the use of a dummy panel impact the validity of the assessment?
Are there any additional measurement techniques or best practices that we should consider to ensure there are no ESD risks or concerns associated with changing the cutting sequence?
First, it does sound like you have a good evaluation technique, however It seems as it is focused on resistance type measurements and decay time of your ionizer. I would suggest making some fieldmeter measurements on your board and cutting machine to see if there are charges being generated during handling of the board and operation of the saw.
Remember, you cannot ground and insulator or insulative materials. If resistances are good then what’s left is the charge source… eliminate that and your events should go down or be eliminated.
Also, check the positioning of your ionizers and your sequencing of when you have them turned on. Make sure the ionizers are in operation prior to you placing the board on the cutter and make sure you have a clear path for the ion flow.
During the sawing process, our devices are mounted on ESD tape before cutting begins. However, based on my measurements, the tape does not consistently maintain a charge below 100V, particularly on the adhesive side. I suspect this may be a contributing factor to the ESD events observed during the process.
Since the sawing process is fully automated, it is not feasible to use a field meter to measure static charge directly during cutting. As a result, I can only measure static charge before and after cutting, which may not be sufficient to fully assess ESD risks. Additionally, DI water with a resistance of 0.22 MΩ is used during the cutting process.
Given these constraints, do you have any recommendations on alternative measurement methods or additional controls for better evaluations?
I am not altogether familiar with this process so with that I do have a couple of comments.
The ESD tape you mentioned, is it a type of conductive tape? if so, if it is not grounded by some means then any charges will not be effectively removed.
What type of safety enclosure do you have around the saw mechanism? If it is a plastic, then you should using a field meter measure the amount of charge coming off of the face of the plastic. You could be having a field induced charge on your board and with the saw blade (which is presumably grounded through the drive motor) contacting the board having discharges.
How did you detect the ESD events of 510V that you mentioned earlier? If you check and mitigate the 2 items i mentioned above and then re-test again, you might find a difference.
Also, I would like to refer you a document that ESDA has available ANSI/ESD 17.1 Process Assessment Techniques as it will give you pretty much step by step instructions on how to assess this automated process, and provides a pretty good list of measurement equipment you can use.
The ESD tape mentioned is dissipative material type of tapes uses to mount our device before cutting.
Yes I’ve tried to to run the saw blade without contact with panel ( motor dry run ) and found no ESD Event ( 0V consistently ). So I deduced that the events are from the saw blade having contact with our device. As for the blade, it is properly grounded from spindle to motor to machine body. As of now I’m Still doing investigation and improvements to reduce the ESD events in the process.
Thank you for your input Matt. It gives me idea on how to conduct my findings on this process.