Hi Mary:

Your problem really revolves around residues left on the board 
and not the materials used to produce the board.  Some 
polyethylene glycols are difficult to remove from the board and 
others are not.  Some solder masks will pass cleanliness 
requirements and others will not.  It is my opinion that what you need
is to call out a cleanliness requirement with regard to Surface 
Insulation Resistance (SIR).  This gives you an indication of the harmful 
residues left on the bare board surface whether they are ionic or not.  You may 
also wish to call out an ionic residue requirement but I believe that 2 
micrograms/sq.in. NaCl equivalent may be too tight to control without special 
cleaning.  If you wish to discuss this further, I can be reached at (972) 
519-3916.  

Harry O'Halloran


______________________________ Reply Separator _________________________________
Subject: No Clean Bare Board Controls
Author:  [log in to unmask] at smtplink
Date:    3/3/97 3:02 PM


I would appreciate some guidance on a subject that could be of interest
to others in the same dilemma.

We are specifying controls for unpopulated PWB's to be used in low
residue/no clean process.  We plan to restrict bare board bulk ionic
levels to no more than 2 micrograms/sq.in. NaCl equivalent.   Also, it
has been suggested that we require that 'polyethylene glycol substances,
as well as certain dry film and even some liquid photoimageable masks be
avoided'.  The bulk ionic requirement is easy to communicate but I am
struggling with the verbiage and test methods that describe restrictions
on polyethylene glycol substances and other potentially harmful
materials. 

Any help in this matter will be greatly appreciated.

Mary Davis
Sr. Material & Process Engineer
Hughes Aircraft
Naval & Maritime Systems
206-356-3311
[log in to unmask]


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