Alistair

The presence of Nickel oxide on suspect pads shows up the problem. There
is a lot of material on the NET/ archives and lots of gurus out there
who advise higher gold in ENIG to cure this problem. The problem occurs
due to low Gold in ENIG. U can ask for 0.1microns minimum.

Best wishes
Anil




-----Original Message-----
From: Alistair Murray [mailto:[log in to unmask]]
Sent: Wednesday, August 11, 2004 1:29 PM
Subject: Solder skipping on ENIG finish

Hi to all. This is my first visit to this forum and I apologise if this
subject has been aired and exhausted in previous correspondence.

My customer has an issue with a simple double sided PTH board (no
surface
mount pads) with ENIG finish all over. After standard wave soldering, he
is
experience random skipping of test pads on the solder side. Normally,
this
would not be a problem but some of these test pads do not provide a good
electrical contact when subjected to electronic testing. Again, this
phenomenon is quite random.
The wave soldering parameters have been modified but with little success
as
the skipping persists in a random fashion.
We have carried out SEM analysis on good and suspect pads and have
concluded
that (1) there are no unexpected elements present thereby eliminating
contamination such as solder resist (2) evidence of nickel oxide is
present
on the suspect pads (3) there is a physical difference in the material
structure of the good and suspect pads - the good test pad has an
homogenous
structure with no discontinuities whilst the suspect pad is not
homogenous
and has a series of parallel lines which are boundaries in the material
deposition (4) SEM analysis on the test pin found no insulating
material.

Can anyone explain how such skipping can occur and how it can be
prevented?
The random failure to make electrical contact on non soldered pads is
puzzling. We are convinced that there are no insulating elements
present.
Could the different structures be a clue? Could the deposition rate
differ
from pad to pad? Could the process control parameters of the nickel and
gold
solutions be a factor here?

Thank you for your anticipated help.

Alistair F Murray
Technical  Manager
Artetch Circuits Limited
Tel: 01903 725365
Voice Mail Ext. 1260
e-mail: [log in to unmask]
www.artetch.co.uk

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