Hi Mordechai,
I would not worry too much about side fillets--the heel fillets are much more important.
 What should be your real concern about the reliability of your TSOPs SJs is whether your TSOP leadframe is made of Alloy 42 instead of copper. That is where your reliability concern needs to be because of the large CTE-mismatch with FR-4.
Werner


 

 

-----Original Message-----
From: Mordechai Kirshenbaum <[log in to unmask]>
To: [log in to unmask]
Sent: Tue, May 4, 2010 7:43 am
Subject: [TN] Minimum Side Joint Length


We have to assemble TSOP packages on SSOP foot print PCB. (The  TSOP 
package width is 40 mils  shorter than the SSOP package width).

We found that the theoretical ( calculated) side joint length (D) will be in 
some 
instances  less than the minimum acceptable side joint (as by IPC-A-610, 
#8.2.5.4). (The available pad length on the PCB under the component lead is 
less than the foot length). 
It may be even worse if we have a slight solder defect, or if the component is 
placed  several mils off side.
What is the reliability impact?
Do you know about accelerated reliability tests or field  data that show the 
correlation between the failure rate and the side joint length?

Thankfully,
Mordechai Kirshenbaum
QA Team Manager

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