Dear Bob,
don't you need read a little about ESD basics? If you remove electrons from an insulator (plastic comb, acrylic clothings, cat etc) by rubbing it, the loss of electrons will make the insulator positive. Or you may get a charge in the insulator by means of outer electric fields, that can move electrons in the insulator in a way that you get a potential difference. Pulling a plastic comb through dry hair (if you get any)can charge your comb up to a thousand volts. Pulling off your acrylic pullover can generate 10,000 Volts! However, you are right in a way, the PE bag is not dangerous IF THE SURROUNDING ALWAYS GOT THE SAME POTENTIAL. But that is seldom the case. So, do this for me. Get a PE bag, wave it in the air (won't work if you have a high RH or ionizers)and keep it close to your ESD charge meter and see what happens. I'm afraid you will be bombarded with more about this topic.
Good Luck
Inge
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Robert Kondner
Sent: torsdag 14 maj 2009 22:58
To: [log in to unmask]
Subject: Re: [TN] Bare PCB Packaging Requirements
Richard,
Your wrote:
"Non-ESD polyethylene bags are notorious ESD generators. I wouldn't want them in my factory."
You will NEVER get a ESD event from polyethylene because it is an insulator, right?
However I see lots of ESD events with grounded metal objects. Since UL requires metal machines to be grounded I guess you don't want any metal machines in your factory?
What is going on here?
Bob Kondner
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D.
Sent: Thursday, May 14, 2009 3:12 PM
To: [log in to unmask]
Subject: Re: [TN] Bare PCB Packaging Requirements
1. The same moisture barrier bags that are ESD-safe Faraday bags also work well as moisture barrier bags for shipping and storing PWBs. These Faraday bags often work well for storage of the CCA during assembly. Why use two different types of bags if one fits the bill? Non-ESD polyethylene bags are notorious ESD generators. I wouldn't want them in my factory.
2. Many CEMs and OEMs have requirements for the PWBs to be shipped in MBBs, in order to prevent against surface finish oxidation in the case of IAg, ISn, HASL and FTL finishes. Some invoke a requirement such as IPC 4552 or 4553 in order to ensure the boards are dry and hermetically sealed.
3. All PWBs absorb moisture from the air. Having the boards sealed prevents excess moisture ingress, in some cases if the boards are shipped in sealed bags with desiccant, the user may not need to pre-bake if they are able to successfully perform Kanban pull from the fabricator within a short time frame. This, of course, requires qualification and validation of the process and procedures.
So, if a bag is required, use one from start to finish that meets multiple requirements.
I assume you understand why moisture within the PWB is not a desirable condition.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of John Parsons
Sent: Thursday, May 14, 2009 1:37 PM
To: [log in to unmask]
Subject: [TN] Bare PCB Packaging Requirements
Tell us, how many CEM's out there are demanding that bare PCB's be received in vacuum sealed moisture barrier anti-static bags. If so, what is your reasoning? Just to be clear my focus here is "anti-static" not the moisture barrier properties of the packaging.
Regards
John Parsons
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