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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