Graham
I have seen hundreds of assembly drawings that included keepout areas
for the conformal coatings. I have seen them at Honeywell, General
Dynamics, ADC, Goodrich, and many, many other companies while I was
employed at those places.
Having also worked for three contract manufacturers, including the one I
own, I have had to review the assembly notes for developing the process
flow of literally hundreds of customers, and using the assembly drawing
to designate keepout areas for conformal coating is a very common
everyday method of controlling which components need masking to prevent
cc flow.
Most of these companies are well aware of the potential problems of
allowing cc to flow under BGAs. Just as underfill properties are (should
be) very carefully matched to the size and type of the BGA and the
substrate type to prevent voiding and CTE mismatch issues, these very
issues are why cc should not be applied under BGAs. Conformal coating is
kept out from under certain sockets and connectors to prevent it from
seeping inside the connector contacts, it is kept out from under certain
SMA coax connectors so as to prevent unintentional insulating of the
ground connection on the outside, it is kept out from many areas for
many different reasons. And the only acceptable place to note these
keepout areas is on the assembly drawing. It is not just "assumed
knowledge". Most conformal coating have a capillary action greater than
water, if it is not masked properly it will get into literally every
space where it is possible for any liquid to flow, including some areas
it should not be in.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Graham Collins
Sent: Thursday, November 23, 2006 2:28 PM
To: [log in to unmask]
Subject: Re: [TN] BGA and conformal coating
Hi Bogert
Happy turkey day!
I have to ask, do you apply conformal coating? If so, how do you apply
it under things like pin grid array parts? Quad flatpacks? Vertical
plug connectors where you don't have access to the top side solder
joints? DC/DC converter blocks? SMT Chip resistors?
Sorry, but I've got to disagree with you. I've never seen a drawing
that specified "no coating required" under shadowed parts, and I have
never talked with a quality engineer or process engineer who thought
that meant coating under the parts (maybe you are the first, what is
your job???).
regards,
Graham Collins
Process Engineer,
L-3 Communications Electronic Systems Inc.
Halifax
(902) 873-2000 ext 6215
>>> [log in to unmask] 11/23/06 03:27PM >>>
November 23, 2006
Dave, happy turkey day. My response did not mean I agree that conformal
coating should in fact be applied under a component. What I indicated
was that if the drawing specifically mandated that the assembly be
conformal coated, then the expectation is that coating must be applied
under, over, and everywhere else on the assembly unless the assembly
drawing specifically requires masking free of certain areas from
conformal coating.. If conformal coating should not be applied under a
part, then the drawing needs to say so.
----- Original Message -----
From: David D. Hillman<mailto:[log in to unmask]>
To: [log in to unmask]<mailto:[log in to unmask]>
Sent: Monday, November 20, 2006 6:27 PM
Subject: Re: [TN] BGA and conformal coating
Hi Bogert! Sorry but I respectfully disagree. If the contract requires
the
assembly to be conformal coating and provides no other process
guidance
then I would process the assembly in accordance with best industry
practice/accepted material process practice for the particular
conformal
coating material specified. As other TechNettees have documented,
intentionally forcing AR or UR conformal coating under a component is
not
standard conformal coating practice as the such an action results in
degraded component/product integrity due to CTE mismatch for many use
environments. However, if I was using a paralyene conformal coating,
standard material process practice is quite the opposite - paralyene
conformal coating is design to coat all pwa surfaces. The application
process for each conformal coating material dictates how/where it
should be
applied unless there are specific instruction that deviate from
standard
practice (such as a specific exclusion area for RF, etc.).
Dave
- Bogert
<[log in to unmask]<mailto:[log in to unmask]>>
Sent by: TechNet
To
<[log in to unmask]<mailto:[log in to unmask]>>
[log in to unmask]<mailto:[log in to unmask]>
cc
11/20/2006 03:52
Subject
PM Re: [TN] BGA and conformal
coating
Please respond to
TechNet E-Mail
Forum
<[log in to unmask]<mailto:[log in to unmask]>>
; Please respond
to
- Bogert
<[log in to unmask]<mailto:[log in to unmask]>>
If the contract assembly drawing requires the assembly to be conformal
coated, unless it also allows the area under the BGA to be free of
coating,
then you are in violation of the contract drawing regardless of what
610
says or does not say.
----- Original Message -----
From: David D.
Hillman<mailto:[log in to unmask]<mailto:ddhillma@ROCKWELLCOLL
INS.COM>>
To:
[log in to unmask]<mailto:[log in to unmask]<mailto:[log in to unmask]<mailto:Tec
[log in to unmask]>>
Sent: Monday, November 20, 2006 2:20 PM
Subject: Re: [TN] BGA and conformal coating
Hi Joe - Your statement......." type AR or type UR does not coat the
BGA
solder balls/solder connections located under the BGA so you are
violating
the acceptability requirements in IPC-A-610" has me some confused.
What
IPC-A-610 requirement is violated?
Dave Hillman
Rockwell Collins
[log in to unmask]<mailto:[log in to unmask]<mailto:
[log in to unmask]<mailto:[log in to unmask]>>
"Macko, Joe @
IEC"
<joe.macko@L-3COM<mailto:joe.macko@L-3COM<mailto:joe.macko@L-3COM<mailto
:joe.macko@L-3COM>>
To
.COM>
[log in to unmask]<mailto:[log in to unmask]><
mailto:[log in to unmask]<mailto:[log in to unmask]>>
Sent by: TechNet
cc
<[log in to unmask]<mailto:[log in to unmask]<mailto:[log in to unmask]<mailto:Te
[log in to unmask]>>>
Subject
Re: [TN] BGA and conformal
coating
11/20/2006 12:47
PM
Please respond to
TechNet E-Mail
Forum
<[log in to unmask]<mailto:[log in to unmask]<mailto:[log in to unmask]<mailto:Te
[log in to unmask]>>>
; Please respond
to
"Macko, Joe @
IEC"
<joe.macko@L-3COM<mailto:joe.macko@L-3COM<mailto:joe.macko@L-3COM<mailto
:joe.macko@L-3COM>>
.COM>
Vered,
I would start with IPC-A-610 and J-STD-001 documents. One item that
is
over
looked is that spraying a board with for example type AR or type UR
does
not
coat the BGA solder balls/solder connections located under the BGA
so you
are violating the acceptability requirements in IPC-A-610!
Good luck,
- Joe
-----Original Message-----
From: Vered BS [mailto:[log in to unmask]]
Sent: Monday, November 20, 2006 8:40 AM
To:
[log in to unmask]<mailto:[log in to unmask]<mailto:[log in to unmask]<mailto:Tec
[log in to unmask]>>
Subject: [TN] BGA and conformal coating
looking for reviews/articles or case studies regarding conformal
coating
on
BGA
for military/aerospace environment
Appreciate any comment or sharing your experiance
Thanks
Vered
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