I'm just wondering if there are other factors here if the parts are good then bad afterwards. 

A possibility is stress factors in handling, use of board racks versus ESD trays, depaneling, press, wash or test. 

In this situation the parts fail when put into service. 

-  I've seen a problem with parts to close to the edge of a board where the FNK depaneler, some call the pizza cutter, set up a vibration that damaged the parts that were too close to the board edge. 

-  You can also have the problem if the break-away tabs are too close to the edge and the boards are manually separated versus having access to a board router. We changed the panelization and resolved the issue 

- I had a situation many years ago where the flux trapped in the epoxy under the caps and resistors changed the value. 


----- Original Message ----- 
From: "Wayne Thayer" <[log in to unmask]> 
To: [log in to unmask] 
Sent: Wednesday, April 15, 2009 2:54:15 PM GMT -05:00 US/Canada Eastern 
Subject: [TN] Bad resistors 

I had a bad 0201 part once--resist material mis-alignment with endwrap metallization.  That was years ago and 0201 parts were brand new at the time, so I wrote it off. 

I just had an identical situation with an 0402 part from a large production order.  The part only failed when put into service.  How do I protect myself from this situation? 

Wayne Thayer 



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