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May 2010

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Subject:
From:
Paul Edwards <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Paul Edwards <[log in to unmask]>
Date:
Tue, 4 May 2010 14:24:00 -0700
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Werner,

I beg to differ...

When I did peel tests with TABed parts I found a +30% increase in peel strength when I had side fillets verses not having any...

Without side fillets you end up peeling through the lap joint surface interface...

With side fillets, your peel forces must propagate through bulk solder and not only just through the lap joint interface....

Paul 

Paul Edwards
Surface Art Engineering


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Werner Engelmaier
Sent: Tuesday, May 04, 2010 5:08 AM
To: [log in to unmask]
Subject: Re: [TN] Minimum Side Joint Length

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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