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July 2009

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Subject:
From:
Steven Creswick <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Steven Creswick <[log in to unmask]>
Date:
Sun, 5 Jul 2009 11:47:18 -0400
Content-Type:
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Vladimir, Gaby, Inge, Mike - People!!!  This is Sunday!!  Are we trying to
start the work week a day earlier??  

It is really close for Ingemar already!


Maybe this is the weekend troubleshooting crew!  Kind of like the weekend TV
anchor team...

   I can just imagine how Dewey's response to 'grains' might be related to
beverages.


Gaby - At least it appears that you have gotten a fair amount of information
already this weekend - making your Monday a bit more efficient.

I enjoyed the calm winds and 68-70°F temps to go flying this morning.  From
the micro to the macro.  A pleasant change in perspective

Enjoy the remainder of your Sunday

Steve C

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Vladimir Igoshev
Sent: Sunday, July 05, 2009 10:20 AM
To: [log in to unmask]
Subject: Re: [TN] Weird solder joints

Thank you inge,

Even though I believe I know a few things, a person can not know everything
:-). That is why I asked the question.

Honestly, I'm still almost confused every time I hear someone referring to
the grain structure in solder joints. I know  it's pain in the neck to
reveal the real grain structure in solders (and even more so in Pb-free
world, than in the eutectic one), meaning it's not a practical thing to do.

Therefore  I always ask the same question: "what do you mean by "grain
structure" and almost always it turns out to be the phase (not grain)
structure, which makes much more sense to me. 

Honestly, I'm not even sure whether the grain structure (which would mainly
their size inside the individual phase) plays a role in reliability of
solder joints.

In fact, a few years ago we deliberately tried to grow Sn grains in one of
the SAC alloys and ended up with nothing - the original grain size (a few
microns) never changed. I thought it was very interesting.

Regards,

Vladimir
SENTEC
SENTEC
11 Canadian Road, Unit 7.
Scarborough, ON M1R 5G1
Tel: (416) 899-1882
Fax: (905) 882-8812
www.sentec.ca


-----Original Message-----
From: Inge <[log in to unmask]>

Date:         Sun, 5 Jul 2009 10:42:49 
To: <[log in to unmask]>
Subject: Re: [TN] Weird solder joints


Vlad,

1. the alloy members have solidified evenly all through the ball
2. the distribution of phases are even
3. the grains are fine

you'd know it well, being a guru yaself

Inge


----- Original Message ----- 
From: <[log in to unmask]>
To: "TechNet E-Mail Forum" <[log in to unmask]>; "Inge" 
<[log in to unmask]>
Sent: Saturday, July 04, 2009 11:06 PM
Subject: Re: [TN] Weird solder joints


> Inge,
>
> Could you elaborate on what you mean by "good grain structure"?
>
> Thanks,
>
> Vladimir
> SENTEC
> SENTEC
> 11 Canadian Road, Unit 7.
> Scarborough, ON M1R 5G1
> Tel: (416) 899-1882
> Fax: (905) 882-8812
> www.sentec.ca
>
>
> -----Original Message-----
> From: Inge <[log in to unmask]>
>
> Date:         Sat, 4 Jul 2009 20:48:31
> 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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