I agree with you. Mostly in the wave soldering conditions, the TSOP in the topside will be double reflowed and cause the failure. The fracutre very smooth. You can find this failure mode in QFP and SOP packages. 
Sometimes, you can find the failure joints are local at one corner of the package, not the random distribution.

How about Change the surface finish? and run a compare test.

Another one maybe is NiSnCu failure mechanism, because the immersion Silver is too thin, and the Copper can immigration to lead side. The solder joint will failure when they meet the high stress or high strain rate conditons.




******************************************************************************************
 This email and its attachments contain confidential information from HUAWEI, which is intended only for the person or entity whose address is listed above. Any use of the information contained herein in any way (including, but not limited to, total or partial disclosure, reproduction, or dissemination) by persons other than the intended recipient(s) is prohibited. If you receive this e-mail in error, please notify the sender by phone or em
ail immediately and delete it!
 *****************************************************************************************

----- 原邮件 -----
发件人: "Wenger, George M." <[log in to unmask]>
日期: 星期四, 五月 24日, 2007 下午10:27
主题: Re: [TN] Silver Embrittlement?

> My guess is that the TSOP packages do have Alloy 42 lead
> Steve,
> 
> My guess is that the TSOP packages do have Alloy 42 leads and that you
> may be seeing a failure that has gotten the name "Double Reflow"  
> I hate
> that name almost as much as I hate the name "Black pad".  What do the
> solder fillets look like on your TSOP packages?  If they look good but
> your testing is indicating an intermittent and you can pass test by
> pushing down on a TSOP lead I think you most likely have a brittle
> interface solder joint fracture.  It will look like a perfect surface
> mount solder joint with nice feathered solder fillets like it is wet
> well to the PCB pad, and it probably was when it was formed.  However,
> then the temperature is elevated and there is any mechanical 
> stress the
> solder joint can facture at the IMC bulk solder interface.  You 
> won't be
> able to see the fracture unless you view it at a low angle under high
> magnification.  The "Double Reflow" name was coined by IBM Austin back
> in 1979 presentation at NEPCON.  They called it "Double Reflow" 
> becausetheir surface mount solder joints look great after surface 
> mount reflow
> soldering but failed (fractured) after the boards were wave soldered
> (i.e., failed at the second reflow).  I've attached their NEPCON paper
> as well as one we did describing a solder joint fracture we had using
> QFPs with Alloy 42 leads.  We also saw similar failures on another
> product on corner leads after the initial surface mount reflow.  Those
> failures occurred during the first reflow and had nothing to do with
> double reflow.  The solder joint fractures occurred on corner leads
> during the surface mount reflow cooling process.
> 
> Regards, 
> George 
> George M. Wenger 
> Senior Principle FMA / Reliability Engineer 
> Wireless network Solutions 
> Andrew Corporation, 40 Technology Drive, Warren, NJ 07059 (908) 
> 546-4531
> [log in to unmask] 
> 
> 
> -----Original Message-----
> From: TechNet [[log in to unmask]] On Behalf Of Steve Gregory
> Sent: Thursday, May 24, 2007 8:45 AM
> To: [log in to unmask]
> Subject: [TN] Silver Embrittlement?
> 
> Mornin' all!
> 
> I know this subject has been talked about before, but my memory is
> getting rusty. I was wondering if it was possible to get solder joint
> embrittlement on a board that has immersion silver finish and 
> componentsthat have a flash gold finish? As you might have 
> guessed, it's those
> pesky Samtec SMT connectors...
> 
> We're experiencing another issue on that board as well. We're seeing
> solder joint problems with some TSOP-66 DDR SDRAM that are on the
> topside of the board. They're arranged close around two XILINX 
> 1152-ball
> BGA's that get very hot when the assembly is under power. Both BGA's
> have large finned heatsinks mounted to the top of them. The BGA's 
> get so
> hot that if you power the board up without the heatsinks, and 
> touch one
> of the BGA's, you will burn your finger. There have been some 
> cases that
> during testing the board will fail and the failure points to one 
> of the
> SDRAM TSOP's. If you take something like the end of a wooden Q-Tip and
> press on a suspect lead, the board passes test. The solder joint looks
> fine upon initial inspection, but there's obviously an open 
> connection.I remember at one time TSOP leadframe material used to 
> be made of
> Alloy-42, is that still the case? These are parts from Micron
> (MT46V16M16TG-6T), and I haven't yet found what the leadframes are 
> madeof. I'm wondering if the stiffness of the leads may be 
> contributing to
> the solder joint failures that we're seeing. My theory is that because
> the BGA's run so hot, they heat the PCB and cause board to expand 
> in the
> area around them (where the SDRAM are mounted).
> If the leads on the SDRAM are stiff and non-compliant, the solder 
> jointsmight fracture.
> 
> Crazy theory I know, but I'm trying to figure what's going on with 
> theseboards...
> 
> Steve Gregory 
> 	
> 
> ---------------------------------------------------
> Technet Mail List provided as a service by IPC using LISTSERV 15.0 To
> unsubscribe, send a message to [log in to unmask] with following 
> text in
> the BODY (NOT the subject field): SIGNOFF Technet To temporarily 
> halt or
> (re-start) delivery of Technet send e-mail to [log in to unmask]: SET
> Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the
> posts: send e-mail to [log in to unmask]: SET Technet Digest Search the
> archives of previous posts at: http://listserv.ipc.org/archives Please
> visit IPC web site 
> http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for
> additional information, or contact Keach Sasamori at 
> [log in to unmask] or
> 847-615-7100 ext.2815
> -----------------------------------------------------
> 
> -------------------------------------------------------------------
> -----------------------------
> This message is for the designated recipient only and may
> contain privileged, proprietary, or otherwise private information. 
> 
> If you have received it in error, please notify the sender
> immediately and delete the original.  Any unauthorized use of
> this email is prohibited.
> -------------------------------------------------------------------
> -----------------------------
> [mf2]
> 
> 
> ---------------------------------------------------
> Technet Mail List provided as a service by IPC using LISTSERV 15.0
> To unsubscribe, send a message to [log in to unmask] with following 
> text in
> the BODY (NOT the subject field): SIGNOFF Technet
> To temporarily halt or (re-start) delivery of Technet send e-mail 
> to [log in to unmask]: SET Technet NOMAIL or (MAIL)
> To receive ONE mailing per day of all the posts: send e-mail to 
> [log in to unmask]: SET Technet Digest
> Search the archives of previous posts at: 
> http://listserv.ipc.org/archivesPlease visit IPC web site 
> http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional 
> information, or contact Keach Sasamori at [log in to unmask] or 847-
> 615-7100 ext.2815
> -----------------------------------------------------
> 

---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 15.0
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL)
To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
Search the archives of previous posts at: http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
-----------------------------------------------------