TECHNET Archives

October 2013

TechNet@IPC.ORG

Options: Use Monospaced Font
Show Text Part by Default
Show All Mail Headers

Message: [<< First] [< Prev] [Next >] [Last >>]
Topic: [<< First] [< Prev] [Next >] [Last >>]
Author: [<< First] [< Prev] [Next >] [Last >>]

Print Reply
Subject:
From:
Lee Hitchens <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Lee Hitchens <[log in to unmask]>
Date:
Mon, 28 Oct 2013 14:39:33 +0000
Content-Type:
text/plain
Parts/Attachments:
text/plain (114 lines)
HI Phil

Phil mentioned the cleanliness and this is one of the key factors when
coatings wet out. If you get bad wetting or too much fluid getting scavenged
around devices due to strange surface tension behaviour then you get extreme
build up of coating around leads and devices which leads to cracking. 

So, as Phil and Doug state get your coating on as laminar as possible and it
shouldn't be a problem. How are you intending to or are apply the coating?
This can be a critical factor in the whole process?

Best Regards

Lee Hitchens


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Phil Kinner
Sent: 28 October 2013 14:34
To: [log in to unmask]
Subject: Re: [TN] Exceeding Maximum thickness of urethane conformal coating

Hi Phil,

As Lee suggested, the main thing you should be looking for is coating
coverage.  At the higher end of the thickness range you mention, many of the
commonly used Urethane materials will be susceptible to cracking.  Multiple
thin coats will always give better and more uniform coverage than 1 thick
(or even 2 thickish) coat(s) and this is what you should be looking for.

When you factor in the possible extended curing times (especially oxidative
cure systems), potential reliability issues (mentioned by Doug) and the
additional cost of the materials, over and above what you really need, then
I would say that 3 mils should be your maximum nominal thickness, and work
hard on your process to get better coverage and uniformity at lower
thicknesses.

Lee referred to the work done by Per-Erik Tegerstrom at the IVF.  I think
from memory, that this would have been over Tin/Lead solder and scrupulously
cleaned... if this applies to you great.  Most of the work that I have seen
more recently have shown at best no-correlation and at worst, a significant
correlation between greater coating thickness and significantly reduced
thermal shock/cycling lifetimes.  If you are coating over no-clean then that
that is a whole new can of worms to consider, but the same basic premise,
work hard on the process to achieve better coverage and uniformity at
thinner coating builds.

Best Regards,

Phil.

Phil Kinner
Conformal Coating Consulting

Desk +44 1483 600293
Cell +44 7946 020614



-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Phil Bavaro
Sent: 25 October 2013 20:45
To: [log in to unmask]
Subject: [TN] Exceeding Maximum thickness of urethane conformal coating

I was reviewing a process specification regarding Type UR conformal coating
and it contained a sentence which struck a nerve.

This particular specification stated that the thickness shall be
.003"+/-.002" and .010" maximum if two coatings are applied.

I always thought there was a good reason why the coating should not exceed
.005" such as CTE mismatch which might cause cracking of the coating or
perhaps worse, component damage in thermal cycling.  But I haven't found any
papers to that effect yet.

Naturally, any comments/experiences from this forum will be appreciated,
especially if I am completely off based.

Phillip Bavaro
Senior Manufacturing Engineer, Manufacturing Engineering
L-3 Telemetry-West
9020 Balboa Ave. | San Diego, CA 92123
858-694-7874 | 858-740-8260 mobile
[log in to unmask]<mailto:[log in to unmask]> | L-3com.com/TW




________________________________
This message and any attachments are solely for the use of the addressee and
may contain L-3 proprietary information that may also be defined as USG
export controlled technical data. If you are not the intended recipient, any
disclosure, use or distribution of its content is prohibited. Please notify
the sender by reply e-mail and immediately delete this message and any
attachments.

______________________________________________________________________
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]
______________________________________________________________________


______________________________________________________________________
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] 
______________________________________________________________________


______________________________________________________________________
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] 
______________________________________________________________________

ATOM RSS1 RSS2