Ingemar and Steve have provided good advice.
In
Gaby,
Ingemar and Steve have provided good advice.
Ingemar,
Your vast experience with solder assembly and material issues still
manages to amaze me. The only thing I would add is that Steve's idea of
an inclusion in the solder paste may also be the cause. I've looked at
the changing the brightness and contrast of the images and it does
appear that at least on the small2.jpg the dark area does look like a
fibrous inclusion that actually sticks out a short distance from the
solder ball into the cross section potting compound.
Regards,
George
George M. Wenger
Andrew Wireless Solutions
Senior Principal FMA / Reliability Engineer
40 Technology Drive, Warren, NJ 07059
(908) 546-4531 [Office] (732) 309-8964 [Mobile]
[log in to unmask]
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Inge
Sent: Saturday, July 04, 2009 2:49 PM
To: [log in to unmask]
Subject: Re: [TN] Weird solder joints
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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