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August 2006

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Subject:
From:
"Kane, Amol (349)" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Kane, Amol (349)
Date:
Fri, 18 Aug 2006 09:39:10 -0400
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No Problem! Thank you for the clarification Richard

Amol Kane
M.S (Industrial Eng.)
Process Engineer
Harvard Custom Manufacturing, Inc. 
941 Route 38  Owego, NY 13827
Phone: (607) 687-7669 x349
[log in to unmask]
www.harvardgrp.com

 -----Original Message-----
From:   TechNet [mailto:[log in to unmask]]  On Behalf Of Stadem, Richard D.
Sent:   Friday, August 18, 2006 8:23 AM
To:     [log in to unmask]
Subject:        Re: [TN] LEADFREE BGA ISSUE

Amol,
Sorry about any confusion I caused, what I meant was that
Klein-Wassink's charts describe the rate of dissolution of nickel into
molten pure tin, not a tin alloy. 

-----Original Message-----
From: Kane, Amol (349) [mailto:[log in to unmask]] 
Sent: Friday, August 18, 2006 6:50 AM
To: TechNet E-Mail Forum; Stadem, Richard D.
Subject: RE: [TN] LEADFREE BGA ISSUE

Hi Richard,
Not to split hair, but I am a little confused with your statement "the
information on the dissolution rate of nickel into a tin alloy from
Klein-Wassink's charts are based on pure tin, not a tin/lead alloy",
but how can tin be pure if it is in a alloy form with some other metal??
Am I missing something here?

Regards,
Amol Kane
M.S (Industrial Eng.)
Process Engineer
Harvard Custom Manufacturing, Inc. 
941 Route 38  Owego, NY 13827
Phone: (607) 687-7669 x349
[log in to unmask]
www.harvardgrp.com

 -----Original Message-----
From:   TechNet [mailto:[log in to unmask]]  On Behalf Of Stadem, Richard
D.
Sent:   Thursday, August 17, 2006 1:56 PM
To:     [log in to unmask]
Subject:        Re: [TN] LEADFREE BGA ISSUE

Don't always assume that just because the finish was ENIG, that it was
the root cause. It may have contributed to it, but usually there is no
one root cause when this happens.
Secondly, even when good wetting does take place on ENIG-finished pads,
upon removal the pads often appear dull. This is just the nature of the
nickel finish. It does not always indicate a solderability problem with
the finish.

The problem may have been a reflow profile that was not hot enough, with
TALT being insufficient to form a good IMF to the nickel base. It is
slightly more difficult to achieve this with standard 63/37 solder on
nickel than on copper, and appears to be even more difficult with SAC
alloy on nickel than on copper. While the temperature is significantly
hotter, the SAC alloy does not seem to form a good IMF with nickel as
readily as the 63/37 solder does.
Werner, the information on the dissolution rate of nickel into a tin
alloy from Klein-Wassink's charts are based on pure tin, not a tin/lead
alloy. What is the effect on nickel's dissolution rate when the amount
of lead in the solder alloy is varied, say from 37% to 0%?

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Colin McVean
Sent: Thursday, August 17, 2006 9:34 AM
To: [log in to unmask]
Subject: Re: [TN] LEADFREE BGA ISSUE

<Certain pads were very dull and when solder is applied on it, it seened
there was dewetting issue>

Sounds like an issue with the solderability of the ENIG rather than the
substrate. Check with your PCB fab supplier for their comments.

<By the way, such kind of issue happened only to one customer...>

It only takes one instance of poor process control on ENIG to see faults
occurring. Looks like this is what has happened in this case.

Rgds
Colin

Colin McVean M.Inst.C.T.
Production Manager
Artetch Circuits Limited
Main: 01903 725365
DD:    01903 712926
Email: [log in to unmask]
www.artetch.co.uk
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Poh Kong Hui
Sent: 17 August 2006 15:24
To: [log in to unmask]
Subject: Re: [TN] LEADFREE BGA ISSUE

Hi Technetters,
Could someone advise me the reasons to following issue.

1.      There are total 25 boards for the evaluation purpose.
2.      Round 1, we assemble d11 units SAC BGA onto board of ENIG. The
result
was 10 passed functioonal, 1 piece was not working. There was no signal
& power to the BGA unit.

3.      Round 2,  4 boards were being assembled, 3 passed, 1 was not
working

4.      Round 3, 10 boards were biring assembled, 1 was working, 9 not
working.

The above-stated boards undergo the same temperature profile.

At the beginning, we were suspecting the board of ENIG. When 1 BGA was
being removed from the failed board, and intend to perform the
reballing, we realise the not all BGA substrate pads were able to
solder. Certain pads were very dull and when solder is applied on it, it
seened there was dewetting issue.

My question is, if the failure of the BGA that was due to BGA's
substrate or otherwise.

By the way, such kind of issue happened only to one customer...
Thanks

KH Poh

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