I believe you are correct and a solution is to use dissipative corrugated.

You may not be correct that the cardboard and wood would measure in the
insulative range, but that would only be due to them being hygroscopic and
they would measure high when environment became dryer.  It is not an
acceptable ESD protected product.  The cardboard is the worksurface which
per ANSI/ESD S20.20-2007 Table 3 has a "required limit" less than 1 x 10E9
ohms.

Per ANSI/ESD S20.20-2007 " ESD damage can occur when:
i. A charged object comes into contact with an ESDS device, or
ii. An ESDS device is grounded while exposed to an electrostatic field."
[ANSI/ESDS20.20 section Foreword]  So if the cardboard has a charge, your
product can receive a discharge when the grounded operator handles the
product.

Gene Felder
[log in to unmask] 


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of - bogert
Sent: 2007-07-20 6:51 AM
To: [log in to unmask]
Subject: [TN] ESD Question Regarding ANSI/ESD S20.20 and use of cardboard or
wood

July 20, 2007

We have an OEM that has an ESD control program in place per the subject 
specification invoked via J-STD-001.  However, my position is that he does 
not comply with the requirements since during his conformal coating hand 
spray process, he places the PWAs ontop of cardboard then sprays them with 
coating (no ionizer machine is used in the coating area).  Additionally, 
sometimes ESD sensitive assemblies are placed on top of cardboard or wooden 
blocks during the assembly or inspection process.  In all cases when wood or

cardboard is used, the wood and cardboard rests ontop of a properly grounded

ESD mat, and the operator is grounded via a properly connected wrist strap.

I maintain that this practice violates the subject specification since wood 
and cardboard are insulating materials which are not to be used at the 
workstations, and if one took a surface insulation resistance measurement 
across the wood or cardboard surface, one would obviously not meet the value

specified for a properly grounded mat.

I would appreciate any comment on the above, and whether other folks use 
wood or cardboard upon which ESD assemblies rest.  How do other folks 
support assemblies during conformal coating or assembly/inspection if wood 
or cardboard is not used?

If the operator is properly grounded via a wrist strap, would any static 
charge that may exist on the cardboard or wood surface dissipate through the

wrist strap without damage to the product?  I suspect not otherwise there 
would be no need to require that the grounded mats be used.

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