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May 2010

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Subject:
From:
Werner Engelmaier <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Werner Engelmaier <[log in to unmask]>
Date:
Fri, 21 May 2010 14:10:02 -0400
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 Hi Bob,
Have yet to see any QFN reliability data according to IPC-9701----I'm waiting like you.
Werner

 


 

 

-----Original Message-----
From: Robert Kondner <[log in to unmask]>
To: 'TechNet E-Mail Forum' <[log in to unmask]>; 'Werner Engelmaier' <[log in to unmask]>
Sent: Fri, May 21, 2010 9:02 am
Subject: RE: [TN] Solder joint height


Werner,

 The other day I saw the reference to any solder joint of less than 50um
being composed mostly of intermetallics I almost fell from my chair. I guess
I should have thought that one out but this realization made me wonder about
QFN and leadless package reliability.

 Can you point me to any data on reliability of leadless packages compared
to Gull Wing?

Thanks,
Bob Kondner

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Werner Engelmaier
Sent: Thursday, May 20, 2010 6:30 PM
To: [log in to unmask]
Subject: Re: [TN] Solder joint height

 Hy Wayne,
Well, those QFNs and LCCs are deja vu all over again.  With LLCCCs we had an
obvious huge CTE-mismatch between ceramic and FR-4, with QFNs it is not so
obvious since the CTE-mismatch comes from the die--so die size and die
attach are a big part of the equation.
So it depends on the stresses developed by the thermal expansion mismatch
from the product of DNPxDCTExDT whether the thin SJs will survive long
enough for reliability.
Werner

 


 

 

-----Original Message-----
From: Thayer, Wayne - IIW <[log in to unmask]>
To: [log in to unmask]
Sent: Thu, May 20, 2010 4:17 pm
Subject: [TN] Solder joint height


Should there be a spec for minimum solder joint height for leadless
components?  
An old paper from Werner (mid 90's, I believe) popped up on the Internet
when I 
queried this, and Werner has a statement in it that joints less than about
50 
microns thick are basically all intermetallics, but that is not necessarily
a 
bad thing since the intermetallics are stronger than the solder (but more 
brittle).

I figured since we often try to get additional height for BGA joints to
improve 
reliability, we should be concerned about QFNs and LCCs.

I grabbed a 1.5mil (37 micron) tungsten rod out of our cleanroom (used for 
clearing clogged wirebond capillaries)and started seeing if I could get that

under my leadless components.  Couldn't get it under any of them, likewise
with 
the QFNs.

Checked Technet archives and didn't see an obvious thread, but maybe I
didn't 
have the correct search parameters--if you just enter "height" you get a
couple 
of thousand hits.

Wayne Thayer

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