The first thing I would do is an XRF meas


Leif Erik,





The first thing I would do is an XRF measurement on the leads of the

flash TSOP components to determine what the surface finish is.  From

your comment about non-wetting and the best so far was with "water

soluble" seems to suggest that the flash TSOP have exposed IMC that has

oxidized and when that happens the oxidized IMC isn't solderable with

the typical fluxes used for electronic assembly.  If that is the case

you might have to pre-tin the TSOP leads with an extremely aggressive

flux and then wash off the aggressive flux residue before soldering them

to your PCBA



Regards,

George

George M. Wenger

Andrew Solutions

Senior Principal FMA/Reliability Engineer

40 Technology Drive, Warren, NJ 07059

(908) 546-4531 (Office) (732) 309-8964 (cell)

[log in to unmask]

-----Original Message-----

From: TechNet [mailto:[log in to unmask]] On Behalf Of Leif Erik Laerum

Sent: Tuesday, September 08, 2009 8:45 AM

To: [log in to unmask]

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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