David,
That stuff looks like tar that goes on roofs!!!!
David A. Douthit
Manager
LoCan LLC
David D. Hillman wrote:
>Hi Ken! Now those are interesting photos! The "typical black pad" defect
>associated with ENIG surface finishes is more subtle than what is
>illustrated in your photos. My guess is that you are dealing with a severe
>breakdown of the plating process on those affected pads - the amount/type
>of disturbance of the pad finish is extreme. It almost appears that you had
>some organic contamination of those pads which is reacting with the
>solderpaste deposit. Let us know what the microsections reveal.
>
>Dave Hillman
>Rockwell Collins
>[log in to unmask]
>
>
>
>
> Ken Patel
> <[log in to unmask]
> OM> To
> Sent by: TechNet [log in to unmask]
> <[log in to unmask]> cc
>
> Subject
> 11/04/2004 12:29 Re: [TN] Solderability issue...
> PM
>
>
> Please respond to
> TechNet E-Mail
> Forum
> <[log in to unmask]>
> ; Please respond
> to
> Ken Patel
> <[log in to unmask]
> OM>
>
>
>
>
>
>
>Steve and all,
>Our CM is using no clean AIM solder paste and we think that there is no
>problem from that angle. When I personally went and looked the board, the
>quality person told me that she is seeing black color on the pad. I laughed
>at saying that can't happen on my boards after problem was fixed in the
>industry 5-7 years ago and what you are seeing must be reflection (optical
>illusion) of black molded QFP or similar components on a very shinny solder
>joint. And also ALL fab house knows the black pad phenomenon and they
>control the phosphorous content in nickel bath to prevent this from
>happening!
>
>I looked board from different angles, took to different microscopes and
>also
>used couple of regular magnifying glasses to clear any doubts about the
>blackish looking pads. And indeed it turned out black/dark gray. We found
>some locations were you can see thru naked eye. What surprised me was only
>passives were affected, mostly on one side of the board. Also one pad was
>affected 1/2 making solder joint half as there was de-wetting on the black
>part portion.
>
>Few equations for TechNet experts:
> (1) Why only one side was affected more than other?
> (2) Why only few locations are affected and not the entire board?
> (3) Why problem persists more near the edge of the board then the
>center of the board?
> (4) Why name black pad was given - is it due to black color looking
>pads?
> (4) Can this be reworked?
>
>We have given board for cross section to confirm the problem. I will update
>you with the finding.
>
>Re,
>Ken Patel
>
>
>Hi Ken and TechNetters!
>
>Ken sent me some pictures of some solder problems he's seeing on some
>assemblies and wanted me to post them on my page. I got the pictures up. Go
>look at:
>
>http://www.stevezeva.homestead.com/files/solderability_1.jpg
>
>http://www.stevezeva.homestead.com/files/solderability_2.jpg
>
>http://www.stevezeva.homestead.com/files/solderability_3.jpg
>
>I have a few questions; are you seeing this quite a bit, or just very
>random? What kind of solder paste is it?
>
>I had some strange looking joints one time in the past when I was out in
>California building memory modules. We were using water soluble paste at
>the
>time. One of the inspectors called me said that she was seeing cold solder.
>I went and looked at the assembly, and saw what really did look like cold
>solder. But the strange thing was that it was occuring on a couple of leads
>on a part, and all the rest of the leads were fine...including the ones
>right next to the leads that looked cold.
>
>I was thinking;"Something doesn't add up, convection heat doesn't work like
>this...how can one lead have cold solder, then the one right next to it is
>fine?"
>
>I started looking a little more, and took a pair of tweezers and gently
>probed the cold solder joint. To my suprize, there was a solid fillet of
>solder that was wetted to the lead and pad beneath a layer of what looked
>like cold solder. Things were getting really strange now.
>
>To make a long story short, what it turned out to be was that the screen
>print operator was using a wet rag to clean the underside of the stencil
>periodically. It was an old MPM SP2400 that didn't have an automatic
>cleaning system. The operators heart was in the right place, but the rag he
>was using was overly wet. When he wiped the bottom of the stencil, some of
>the water was trapped in the apertures. So on the next print, the was
>enough
>water to alter the chemistry of the past that gave us these random cold
>looking solder joints.
>
>After I took his wet rag away, gave him some decent wipes and alcohol, the
>problem went away.
>
>The point of this story is that maybe whatever they're using to clean the
>stencil with might becoming trapped in some of the apertures, and the
>screwing the paste up on the next couple of prints.
>
>Just a WAG...
>
>-Steve Gregory-
>
>---------------------------------------------------
>Technet Mail List provided as a service by IPC using LISTSERV 1.8e
>To unsubscribe, send a message to [log in to unmask] with following text in
>the BODY (NOT the subject field): SIGNOFF Technet
>To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL)
>To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
>Search the archives of previous posts at: http://listserv.ipc.org/archives
>Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
>-----------------------------------------------------
>
>
>
>
---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 1.8e
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL)
To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
Search the archives of previous posts at: http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
-----------------------------------------------------
|
