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July 2008

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Subject:
From:
Paul Reid <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Paul Reid <[log in to unmask]>
Date:
Thu, 31 Jul 2008 09:28:18 -0400
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Hi Gregg,

My sense is that 30% of the reliability failures, in a tin-lead
application, are due to PCB failures.

There are two papers on PCB reliability and field life testing that
might be interesting to you.

Advanced Testing Using Real Life Evaluation and Statistical Data
Analysis: by Jason Furlong, PWB Interconnect Solutions, and Michael
Freda, Sun Microsystems, Inc.

Application of Reliability/Survivability Statistical Analyze
Interconnect Stress Test Data to Make Like Predictions on Complex,
Lead-free Printed Circuit Board Assemblies: by Michael Freda, Sun
Microsystems, Inc., and Jason Furlong, PWB Interconnect Solutions.

Although these articles refer to lead-free the methods outlined work in
both lead-free and tin-lead applications. These methods are limited to
testing the PCB reliability however. They do not embrace solder joints
or component reliability. 

I can forward both articles if you are interested.

Sincerely,

Paul Reid

Program Coordinator

PWB Interconnect Solutions Inc.
235 Stafford Rd., West, Unit 103
Nepean, Ontario
Canada, K2H 9C1

613 596 4244 ext. 229
Skype paul_reid_pwb
[log in to unmask] <mailto:[log in to unmask]>
 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Temkin, Gregg
Sent: Wednesday, July 30, 2008 5:27 PM
To: [log in to unmask]
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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