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February 2006

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From:
"Kane, Amol (349)" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Kane, Amol (349)
Date:
Fri, 17 Feb 2006 13:08:14 -0500
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Dear Technetters,
I have Immersion Ag and Immersion Sn LF boards that were waved using SAC305 alloy. I have a lot of tears/shrink voids in the waved connections. I am aware that SAC305 in wave has a propensity of shrink tears/voids due to the non eutectic property of SAC.

IPC 610 Rev D 5.2.11 says that as long as the bottom of the tear is visible, and the tear does not contact any lead land or barrel wall, it is acceptable. My issue is that clearly IPC did not put any thought in this statement. For starters, what magnification should I use for inspection of this tear? The physical appearance of these tears is such that it is impossible to be able to see the bottom (they branch out inside in a zigzag manner, and are seldom just straight down). The location of these tears may prove conductive to crack propagation during thermal cycling.

In view of this uncertainty, how do I pass these joints and ship the boards (Currently, I am in the process of x-sectioning the joints to determine the distribution and extent of these cracks in the solder to gather more info and pass/fail the boards based on it)

Any thoughts everybody???

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

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