Hello Mumtaz 

1. Looking at the pictures I see that it appears the damage was caught not in SMT inspection but after wave solder and the cleaning process. I don't see any No-Clean residue so it looks like water soluble flux was used. 

 - I just realized these are customer returns. I don't know how thick the board is. The test operators could be causing the stress if connnecting to the coax connector and the board is not secured in a chassis. The only other step after final inspection if packing in the shippping area if the boards are shipped individually and not in chassis and not secured to a mother board. They may not realize how careful they have to be in handling them. The other end is the customer's receivers. You may have to audit the customer when the board arrives and they are unpacking and how they storing them.  



2. Looking at the direction of the cracks towards the coax connector side of the board I wonder if they are using those slotted board racks rather than placing the boards down flat on a tray lined with an ESD mat. It would be important to check the QFN after reflow and again if the boards are cleaned after SMT to get the flux off within the time limit or to provide clean boards to pre-wave assembly. If the QFN are good to this point then the problem is in the following process steps I've included below.   



3. Another possibility is if there is some stress in the area of the QFN when the coax connectors are inserted due to hole size or extra solder on the leads or holes. With the added weight of the coax connectors slotted board racks should not be used. 

  

4. Another stress issue may be if spring loaded clamps are used to hold the coax connectors flush to the PCB. If the clamps are swung over and allowed to snap down, then stress could cause the problem. Trainig will correct the problem at wave solder. 



5. Another stress point is in the handling of the boards and the orientation of the boards when they go in the cleaner. The heavy side must be toward the leading edge when put on the cleaner's conveyor belt. If the light end is leading then the board will be bouncing all the way through the cleaner and when the hot air knives dry the board. If the board is directly on the cleaning belt and not on specially designed nitril/carbon cleaning mats then many of the SMT parts will be stressed and the bottom ones knocked off when operators slide them out the exit end of the wire conveyor belt. 

 See attachment. The attachment may help you if not with this issue, then with some other process improvements. 

John Goulet 

MFG Engineer 


----- Original Message ----- 
From: "Mumtaz Bora" <[log in to unmask]> 
To: [log in to unmask] 
Sent: Sunday, December 5, 2010 2:00:27 AM 
Subject: [TN] QFN package crack post Reflow 

  
Hello Technetters, 
  
Received a customer return showing QFN package cracking after double 
sided reflow on a board with coax connectors near the package.  Board 
shows a lot of thermal mass on one side. Do not have the details of 
solder material and reflow  profile. I have posted a .PDF file of images 
on the following link. Please go to the file tab , not photos. Your 
comments/feedback will be appreciated. 
  
  
http://ipc-technet.groupsite.com/main/summary 
<http://ipc-technet.groupsite.com/main/summary> 
  
  
  
Thank-you, Mumtaz 
  

Mumtaz Bora 

Senior Packaging Engineer 

Peregrine Semiconductor 

9380 Carroll Park Drive 

San Diego, CA 92121 

858-795-0112-direct 

858-731-9499 -fax 

[log in to unmask] 

  

  

______________________________________________________________________ 
This email has been scanned by the MessageLabs Email Security System. 
For more information please contact helpdesk at x2960 or [log in to unmask] 
______________________________________________________________________ 

--------------------------------------------------- 
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 email has been scanned by the MessageLabs Email Security System.
For more information please contact helpdesk at x2960 or [log in to unmask] 
______________________________________________________________________

---------------------------------------------------
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
-----------------------------------------------------