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April 2007

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Subject:
From:
Joel Alexander <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, [log in to unmask]
Date:
Mon, 30 Apr 2007 08:49:48 -0400
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Please humor my question regarding coating thickness.


Besides adding weight to the end product, what is the significance of 
listing a maximum thickness to conformal coating?   Why would 0.010 be 
less reliable then the maximum thickness of 0.005?





Joel Alexander
Quality Assurance Manager
TT APSCO, INC. 




Edward Mines <[log in to unmask]> 
04/29/2007 12:54 PM


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Re: [TN] bubbles in conformal coating






Joel-
 
The thickness you are using is far greater rthan the maximum coating 
thickness called out by MIL-I-46058 & IPC-CC-830. Some customers would 
reject the coating for that reason alone. 
 
Contact Dymax.
 
Ed

[log in to unmask] wrote:

We are using Dynamax Multi-Cure 984LVUF and it is about 10 mils thick on 
the flat section. I know this sounds thick but the machine drop dispenses 
so the coating will not run into keep our areas. 



Joel Alexander
Quality Assurance Manager
TT APSCO, INC.  



Edward Mines <[log in to unmask]> 
04/27/2007 10:17 AM 

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Re: [TN] bubbles in conformal coating








Joel- 
You're right. 830 (the son of MIL -I-46058) is used by manufacturers to 
qualify the material. As a former employee of a manufacturer I know this 
document very well. 
 
I am less familiar with IPC-A-610. 
 
46058 used to be on the internet. The versions of IPC-CC-830 that I am 
familiar with (there may be a newer one) followed the same format as 
46058. 
 
Near the very beginning in MIL-I-......it states something like "the 
coating must be free from etc." Our interpretation was that this applied 
to the users too.That MIL SPEC is vague on many other things like 
thickness. Our interpretation was that the thickness the SPEC called out 
was on flat area of the board. 
 
I think foam is mentioned in the statement "the coating must be free 
from....." I know of many instances where coaters did things that weren't 
specifically prohibited that would adversely effect coating performance. 
 
Which coating are you using? Is the thickness on flat sections within the 
1-3 mil range? 
Some HumiSeal polyurethane coatings do not cure properly if they are too 
thick. To the best of my knowledge no document says you have to follow the 
manufacturers instructions but if the don't the coating may not provide 
the protection for which the coating was designed. 
 
Ed

[log in to unmask] wrote: 

IPC-CC-830 is a standard used by the manufacturer of the conformal coating 
to qualify their material. Can these also be applied to the application by 
the end user. IPC-A-610 states that bubbles are acceptable as long as they 
do not bridge adjacent conductors. 

Also is there a specific reference that states anything about the 
appearance of foam? 



Joel Alexander
Quality Assurance Manager
TT APSCO, INC.  


Edward Mines <[log in to unmask]> 
Sent by: TechNet <[log in to unmask]> 
04/25/2007 10:26 AM 

Please respond to
TechNet E-Mail Forum <[log in to unmask]>; Please respond to
Edward Mines <[log in to unmask]>


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Subject
[TN] bubbles in conformal coating










MIL-I-46058 & now IPC-CC-830 say conformal coatings should be "bubble 
free". Some have interpreted this as meaning that a few small bubbles away 
from components are acceptable.
Foam is not acceptable.
 
Some polyurethane conformal coatings generate gas as they cure. They 
should not be coated on very humid days. 
 
Bubbles are also apt to form in conformal coatings when the coating is too 
thick. I've seen this happen in between closely spaced tall components 
even when the coating on most of the board is within customary limits and 
has no bubbles. The solution was to change the application technique.
 
Get the coating and equipment manufacturers involved. They want your 
future business.
 
Ed Mines

     
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