What is your reflow oven? Convection with x zone? 
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----- Original Message -----
From: TechNet <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Sent: Tue Sep 08 08:45:13 2009
Subject: [TN] Non Wetting Problem

Technetters,

We have a problem with non wetting on a very specific component. Only 
this part exhibits the problem. These are double stacked FLASH TSOP 
components that are stacked from the vendor.

http://stevezeva.homestead.com/files/test6.jpg shows the same pin as in 
test7 but enlarged.

http://stevezeva.homestead.com/files/test7.jpg shows the most extreme 
case with no heal fillet.

http://stevezeva.homestead.com/files/test8.jpg hows another example with 
a heal and toe fillet, but there is a crease on both sides of the pin

The process is lead free. Our peak is about 245 for these components. We 
hold peak for 20-30 sec. TAL is about 70.  I can not run much hotter 
since there are large (676 pin) BGAs that reach 260. We have been all 
over the spectrum with respect to profile. My revision log shows I have 
done about 25 different ones. We have tried long soak, medium soak and 
short hot ramp to spike. We have also experimented with different solder 
types. The winner so far is a Water Soluble SAC305. The best results 
(least defects) do come with a shorter RTS profile. The FLASH vendor 
recommends we peak and hold at 255 -260 for ~30 sec. I am not able to do 
that since then the 672 pin BGAs (3 of them) reach well above the 
recommended temp of 250. With the current profile they are already at 
260. As you have already guessed, there is a 10 - 15 degree delta on 
this board that is very heavily populated with these TSOPs. This board 
has in other words a large mass. This condition does result in loose 
pins. It is not the same pins every time either, so it does not appear 
to be related to the ground planes. This is a 14 layer .062 board.

The questions:
1. Any obvious remedies to eliminate the problem?
2  Anyone with similar experience?
3. How do you like my pictures?. I am trying out a new tool. This pics 
are at 45X.


-- 
Leif Erik Laerum

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