The same phenomenon occurs with horizontal HASL. Its normally only
associated with mask defined features or tight pad to mask clearances. Re
designing the test point and/or mask aperture to provide a high energy point
to wet from should solve the problem. We solved the equipment problem by
using high velocity solder jets to displace the flux, I am sure a chip wave
would work..
-----Original Message-----
From: Wenger, George M. [mailto:[log in to unmask]]
Sent: Wednesday, August 11, 2004 12:02 PM
To: [log in to unmask]
Subject: Re: [TN] Solder skipping on ENIG finish
Alistair,
Are your test pads circular lands or are they vias? What is the thickness
of your solder mask? Solder skips in wave soldering on test pads that don't
have an opening to the top of the board are not uncommon. Since flux is
applied to the board prior to hitting the solder wave, the flux in the well
made by the solder mask can prevent the solder from touching the pad. My
guess is that the reason you don't find anything wrong with the ENIG pads is
because there is nothing wrong with them I assume that you've tried to add
solder to the pads after wave soldering and they accept solder so telling
you that there isn't a solderability issue. If this is the case than what
you are experiencing is a physical soldering issue caused by flux entrapment
in a "well".
Regards,
George
George M. Wenger, Andrew Corporation
Reliablity / FMA Engineer
Base Station & Subsystems Group
40 Technology Drive, Warren, NJ 07059
(908) 546-4531 [log in to unmask]
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Alistair Murray
Sent: Wednesday, August 11, 2004 3:59 AM
To: [log in to unmask]
Subject: [TN] 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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