Distance from neutral point (center of the component)
Bev
----- Original Message -----
From: TechNet <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Sent: Fri May 21 07:12:40 2010
Subject: Re: [TN] Solder joint height
Thanks for your reply, Werner.
DNP? I'm trying to figure that one out. Something to do with elastic modulii? Or is it number of cycles?
I got the 1.5mil number from the Amkor paper, BOARD LEVEL ASSEMBLY AND RELIABILITY CONSIDERATIONS
FOR QFN TYPE PACKAGES. Someone pointed that paper out on this forum a few months ago. That's why I decided to try the pin probe technique.
Wayne
________________________________
From: Werner Engelmaier [mailto:[log in to unmask]]
Sent: Thursday, May 20, 2010 6:30 PM
To: [log in to unmask]; Thayer, Wayne - IIW
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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