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September 2013

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Subject:
From:
Steve Gregory <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Steve Gregory <[log in to unmask]>
Date:
Fri, 13 Sep 2013 08:13:38 -0600
Content-Type:
text/plain
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text/plain (193 lines)
Hi Dave!

Hi to you too Doug, got your picture. WOW. I had no idea that happens!

http://stevezeva.homestead.com/SquishedBalls.jpg

So when you coat a board that has BGA's, I take it that just a layer of
coating won't cause this, but if the coating wicks beneath the BGA you
can have problems?

Steve 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of David D. Hillman
Sent: Friday, September 13, 2013 6:17 AM
To: [log in to unmask]
Subject: Re: [TN] Gull wing solder joints and minimum electrical
clearance

Hi Victor - I don't have an example of what happens to a QFP as Ian 
detailed but  Doug and I have the same phenomenon for a BGA.   Hey Doug
- 
can ya send Steve one of the BGA pictures?


Dave Hillman
Rockwell Collins
[log in to unmask]



From:   Victor Hernandez <[log in to unmask]>
To:     <[log in to unmask]>
Date:   09/13/2013 05:50 AM
Subject:        Re: [TN] Gull wing solder joints and minimum electrical 
clearance
Sent by:        TechNet <[log in to unmask]>



Can you share this phenomenon photo?
Victor,

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Fox, Ian
Sent: Friday, September 13, 2013 2:39 AM
To: [log in to unmask]
Subject: Re: [TN] Gull wing solder joints and minimum electrical
clearance

Here's a phenomenon that can occur Richard. On fine pitch QFPs with a
generous volume of solder in the joint or a bulging joint, the presence
of a reasonable thickness of acrylic conformal coating (say 100um)
between the feet of the device, together with regular extended periods
of time below zero degC (say -10 degC) can result in the solder being
extruded out of the joint thus forming a short to the adjacent lead. The
modulus of the acrylic is greater than that of the SnPb at sub zero
temps so the solder is under compression and flows.

Been there and got that particular T-shirt

Regards
Ian

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D.
Sent: 11 September 2013 20:03
To: [log in to unmask]
Subject: Re: [TN] Gull wing solder joints and minimum electrical
clearance

Joyce, how would it affect reliability?

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Joyce Koo
Sent: Wednesday, September 11, 2013 1:18 PM
To: [log in to unmask]
Subject: Re: [TN] Gull wing solder joints and minimum electrical
clearance

More likely effect your reliability than electrical clearance.

Joyce Koo
Researcher
Materials Interconnect Lab
Office: (519) 888-7465 79945
BlackBerry: (226) 220-4760

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Peter Wong
Sent: Wednesday, September 11, 2013 2:06 PM
To: [log in to unmask]
Subject: [TN] Gull wing solder joints and minimum electrical clearance

We have assemblies where gull wing solder joints have so much solder
that along the side joint, the solder connection extends out to the
adjacent leads similar to Figure 5-1, Image C from IPC-A-610E.  "the
solder connection to a termination may exhibit a wetting angle exceeding
90 degrees when it is created by the solder contour extending over the
edge of the solderable termination area or solder resist" (We will be
modifying our stencils to reduce the amount printed on these parts in
the future).

There is no IPC-610 spec for this condition so we were thinking that if
the spacing between the solder joints does not violate Minimum
Electrical Clearance, they are acceptable.

Is this a correct acceptability criteria?

Thanks,
Peter

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