May want to check the trace side-walls for coverage -- some shops use a
nickel/gold electro-plate as etch-resist...this may behave differently
than true ENIG...Ian
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D.
Sent: Thursday, June 14, 2007 8:58 AM
To: [log in to unmask]
Subject: Re: [TN] ENIG Solderability
If the surface finish is in fact ENIG (real ENIG as specified in per the
IPC standard) then the storage conditions should not cause any loss of
solderability. However, I still recommend all circuit boards be
dry-packed as if they were an MSD, because they are. Moisture saturation
in PWBs prior to reflow will lead to other issues not related to
solderability.
But real ENIG with a gold coverage of 2-5 uinches will not readily
oxidize or lose solderability, at least not within a year in an
environment free of harsh chemicals, especially chlorides.
I suspect that the boards that are the subject of this discussion were
not properly plated, and that the resulting level of phosphorus between
the gold and the nickel is higher than it should be, if they are in fact
ENIG. This does lead to a nickel oxide barrier forming over the nickel
underneath the gold. It is not always "Black Pad" per se, but a barrier
to soldering nonetheless.
This barrier can continue to grow long after the boards have been
soldered, and its growth is accelerated by heat. So it often manifests
itself as a "through-hole" problem, but this is usually because after
having gone through two reflow cycles and washes and dry-bakes, etc.,
the problem becomes so bad that hand-soldering becomes difficult. The
description of the problems they are having follows the classic pattern
of this type of issue.
But there are other issues that can lead to this, and they are similar
in nature. Nickel skips or nickel that is too thin, or gold that is too
thin to prevent the nickel underneath from oxidizing (flash gold
improperly deposited) are some other causes that come to mind.
But those are not really ENIG as defined per the specification.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Jim Ma
Sent: Thursday, June 14, 2007 1:55 AM
To: [log in to unmask]
Subject: Re: [TN] ENIG Solderability
Hi Nancy:
I think the shelf life is very importment for the solderability,
please make sure that the PCB w/ the vacuum package before opening, and
make sure that the time between the PCB opening to pre-reflow.
From:Jim Ma
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