Peter,
>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?
>
Yes!
David A. Douthit
Manager
LoCan LLC
Peter Barton wrote:
>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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>>-----------------------------------------------------
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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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