Yes
We have tested low gold. After 2 months to 3 months storage give the
PCBs a bake for 120/ 140 degC for 30 mins and then check solderability.
It will be worse than earlier and will get worse with every reflow/
solder cycle.
Anil
-----Original Message-----
From: Wenger, George M. [mailto:[log in to unmask]]
Sent: Friday, August 13, 2004 6:38 PM
Subject: Re: Solder skipping on ENIG finish
Peter,
The short answer is yes a thin gold could cause sodlering problems on
the sencond side reflow. Along with the analysis of contamination I
would suggest measuring the gold thickness. This can be done
non-destructively uing XRF.
Regards,
George
George M. Wenger (908)-546-4531
Reliability / FMA Engineer
Base Station and Subsystems Group
Andrew Corporation, 40 Technology Drive, Warren, NJ 07059
[log in to unmask]
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Peter Barton
Sent: Friday, August 13, 2004 8:48 AM
To: [log in to unmask]
Subject: Re: [TN] Solder skipping on ENIG finish
I have a supplementary question relating to this answer. Could a low
amount
of gold in ENIG also be attributed with poor solderability of assemblies
at
second side reflow?
We have an assembly that is ENIG finished, and solders perfectly well on
side 1. When turned over to second side, placed and reflowed, a lot the
joints are not wetted to the pads. There is sufficient solder, and the
components themselves have wetted. If the process is reversed i.e. side
2
reflowed first, followed by side 1 then there is non wetting on that
side.
Could it be that if the immersion Au is particularly thin that the first
side heating process could promote oxidation of the underlying Ni and
this
oxidation migrate through the thin Au?
I have had the PCB analysed and no contamination can be found.
Regards,
Peter Barton
===== Original Message from [log in to unmask] (TechNet E-Mail Forum) at
12/08/04 09:15
>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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Peter Barton
Senior Process Eng
ACW Technology Ltd
Dinas Isaf West
Tonypandy
Mid Glamorgan. CF40 1XX Wales
Tel: 01443 425200
Fax: 023 8048 4882
International Tel : +44 1443 425200
International Fax : +44 23 8048 4882
Website/URL: www.acw.co.uk
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