Mary,
I would also caution you on expectations of 2 micrograms/sq in for a
production process. It has been my experience that board vendors
typically struggle to achieve 4 micrograms/sq in. The additional process
time, additional cleaning chemistry, and possibly equipment, would add
considerable cost to the bare board price.

Bob Metcalf
Morton Electronic Materials

>>> Fritz Byle <[log in to unmask]> 03/03/97 09:04pm >>>
At 12:04 PM 3/3/97 -0800, you wrote:
>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

Mary,
I cannot answer your question regarding wording for PEG's, etc., (Were
still
working on that one...) but I would like to caution you about relying
exclusively on bulk ionics.  We have had a similar specification for some
time, and have had boards which exhibit excessive electrical leakage at
elevated temperature and humidity while passing bulk ionics test.  I would
suggest that if the following conditions apply to your product, you should
use ion chromatography in conjunction with insulation resistance
measurements to characterize the acceptable levels of specific
contaminants
for your designs.

1.) Your products have circuits with impedances in excess of 100
Megohms
2.) Your requirements for product performance are stringent (higher than
50
C and/or 90% RH)

I'd be happy to provide more information off-line.

Regards,

Fritz Byle
Sr. Process Engineer
Rockwell Automation

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