DOUG,



As long as you're not a Kaiser, I'll try to answer: "it depends". My answers will be based on the following assumptions:

*         The conformal coat (CC) material is current in its designated shelf life

*         The CC has been stored properly

*         The CC has been mixed or measured to assure proper application

*         The environmental conditions are proper in the CC room

*         The CC process has been qualified and the current process control indicators are all in the acceptable range

*         Coupons are available to establish initial acceptance and thickness requirements

*         The printed board assembly (PBA) has been cleaned to meet the substrate cleanliness requirement

*         The PBA has been dried if it was an aqueous cleaning process of any kind

*         The PBA was stored properly if not immediately coated after the cleaning and drying process

*         This is a single pass process

*         The PBA design is robust enough that the application of CC is only to negate the need to de-rate the performance in harsh environments, whereas the presence of bubbles that would reduce the effectiveness of the dielectric barrier are not a concern

*         This is only dealing with Type AR and UR



1.  Although those two groups have struggled with the grasp of process indicators and given the above I would accept bubbles as long as they didn't blur any areas that needed some visual inspection (marking, solder joints). Many people have wanted to always state a number, size or percent when it comes to the acceptability of voids of any kind.



2.  Again, given the above a bubble per say would not need a disposition. A bubble that is a large void which demonstrates loss of adhesion would be an example. In some cases a bubble in which a small filament wire passes through unsupported could be problematic.



3.  Again, given the above I think I have answered this.



Dewey



-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Douglas Pauls
Sent: Thursday, March 21, 2013 8:19 AM
To: [log in to unmask]
Subject: [TN] Conformal Coat and Bubbles



OK, Minions, your next question in the quest to improve J-STD-001 and

A-610 relates to bubbles in the conformal coating.



I think we can all agree that the ideal conformal coating layer contains

no bubbles or voids and is "purdy".    BUT:



1.  Are there bubbles in coatings in areas where they will not impact reliability and their presence should be viewed as a "Process Indicator"?

If so, where and what limits would you use?



2.  What would you classify as a bubble requiring disposition, i.e.

Becomes an actionable defect?  If so, where and why?



3.  Would any of your answers change depending on what KIND of coating it is, i.e. Acrylic vs. silicone vs. Parylene?



Well, OK, that is three questions.  I'm on a roll.





Doug Pauls

Chairman, IPC Cleaning and Coating Committees Galactic Emporer







______________________________________________________________________

This email has been scanned by the Symantec Email Security.cloud service.

For more information please contact helpdesk at x2960 or [log in to unmask]<mailto:[log in to unmask]> ______________________________________________________________________

______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
For more information please contact helpdesk at x2960 or [log in to unmask] 
______________________________________________________________________