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July 2008

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Subject:
From:
"David D. Hillman" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, [log in to unmask]
Date:
Thu, 31 Jul 2008 06:55:43 -0500
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Hi Greg - I recommend you conduct a literature search for published papers 
on the following project:

Electronic Miniaturization for Missile Applications (EMMA)
Time frame: October 2001
Funding Agency: American Competitiveness Institute

A QFN style device was included in the EMMA study which conducted both IPC 
Class 3 thermal cycle and vibration testing as part of their assessment 
program of SMT components. The data you are looking for is included in the 
EMMA reports. Good Luck.

Dave Hillman
Rockwell Collins
[log in to unmask]




"Temkin, Gregg" <[log in to unmask]> 
Sent by: TechNet <[log in to unmask]>
07/30/2008 04:26 PM
Please respond to
TechNet E-Mail Forum <[log in to unmask]>; Please respond to
"Temkin, Gregg" <[log in to unmask]>


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Subject
[TN] Use of QFN devices in high reliability applications






Our team is working on several new electronic devices whose application is 
primary, flight critical hardware for commercial aircraft.

Our initial component selection includes many QFN packaged devices 
(leadless, bottom side termination only) which will be mounted on .063" 
FR4 boards using SN63.  The devices range from 20 to 44 terminations.

From studies that are available on the web, a picture has emerged that QFN 
packages have reduced long term solder joint reliability when compared 
with leaded or some of ball grid array devices.  Board thickness, flexing 
and whether the device has a central solderable heat sink seem to have a 
significant affect on reliability.  Problem is there are no absolute 
numbers, so for critical applications it seems that thorough testing is 
required.  We'd rather not wait until the end of a lengthy test regimen to 
find we've gone down the wrong path.  Is there newer information 
abbailable?   Two of the studies stated that further testing was being 
performed to support the reliability requirements for aerospace and other 
high-rel applications however I cannot find any updated information on the 
web.

We have decided to replace several of the QFN's with leaded devices, 
however there are no direct crosses for 3 of the devices. One of them will 
require a number of components to create the same function; possibly an 
additional circuit card.

Is anyone aware of information or recommendations that would be useful for 
our assessment?  Is there any specific information that would drive us to 
use or not use them?

Thanks for your help

Gregg






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