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| Date: | Sat, 4 Jul 2009 20:48:31 +0200 |
| Content-Type: | text/plain |
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Gaby,
solder joints are often expected to be perfect and according to the school
book, but in the real world they are more or less imperfekt.
Plus:
good geomtry
good wetting
good surface formation
no big dendrites
no big voids
good nickel barrier
good grain structure
Minus
flux inclusions wich have not have time enough to withdraw to the surface.
I think you have got a too dry paste. I've seen similar solder joints and
we had no problems. If we had, some boards ought to show up after years
of operation.
I can't see any reason to panic, your solder joints are rather normal. Do
this: take the polished
crossection samples and put then in a jar with a flux remover. Place the jar
in a water filled ultrasonic tank and let go for a minute. If the 'dark'
streaks disappear, it's certainly flux.
It's good for all to know how strong and longlasting solder joints can be
despite numerous 'anomalies' as brother Creswick call them.I've tested
solder joints with up to 50% voids...and they have been nearly as good as
normal ones. Because the metallurgical properties have been good.
Finally, judging solder joints from light microscope images demands a very
experienced eye. If I were you , i.e. young and sweet and uncertain , I'd
fine polish the samples, etch in a weak solution for a minute and have them
placed in a SEM. Does not take many minutes to get a safer platform for
determination.
Inge
----- Original Message -----
From: "Gabriela" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Saturday, July 04, 2009 9:54 AM
Subject: [TN] Weird solder joints
> Dear all,
> By cross sectioning BGA solder joints on a failed assembly, I found that
> the
> suspected joints are not uniform and that they contain unusual separation
> areas.
>
> I suspect mixed assembly and/or bad reflow profile.
>
> Steve was so kind and enabled me to send the links.
> Please may I have your opinion?
> http://stevezeva.homestead.com/files/small.jpg
>
>
>
> <http://stevezeva.homestead.com/files/small1.jpg>
> http://stevezeva.homestead.com/files/small1.jpg
>
>
>
> <http://stevezeva.homestead.com/files/small2.jpg>
> http://stevezeva.homestead.com/files/small2.jpg
>
> http://stevezeva.homestead.com/files/small3.jpg
>
> <http://stevezeva.homestead.com/files/small4.jpg>
> http://stevezeva.homestead.com/files/small4.jpg
>
>
>
>
> Gaby
>
>
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