Bill,

Your problem is like something I encountered on several occasions 
in the 90's. It was a solderability issue at the PTH knee caused by 
some unusual processing. It can also be caused by a HASL or 
tin-lead reflow process out of control.

Your problem solder joints are appearing on 2-pin dips, 
CKR22,23,24, which are likely tied to power and ground planes. 
These are the worst case pads on your boards for the problem I 
encountered. I have also seen this on the bottom side of the board, 
depending on how the boards were processed.

The three problem designs I had were multilayer RF boards that were 
part of a military GPS receiver. Because these particular designs 
had some unusual feature I now fail to recall, the boards were not 
processed as standard SMOBC.

The solder on the pads was being abused by the vendor's alternate 
process, and the solder was so thin at the PTH knee, that it 
disappeared, and only intermetallic was present. Because of the 
heavy power and ground planes in these controlled impedence boards, 
the power and ground connections retained more heat longer, causing 
them to have the worst of the solderability issues. Worst case 
boards were easily identifiable by looking at them prior to 
assembly, as they had a "reddish-brown ring-around-the-collar" 
syndrome very visible on one side at the PTH knee.

Marginal boards can escape visual inspection, which led us to 
return the these lots.

The problem later returned, because the el-cheapo program manager 
allowed the vendor to return these boards after we proved that 
vendor reprocessed boards failed worse than "fresh bad boards". The 
PM held the boards until the end of the lot when no other boards 
were available (yeah.. he held the purchase reqs for the 
replacements) and we needed something to build for units. We were 
profitable enough that he didn't care about the rework nightmare. 
He went home at five and played golf on weekends.

I would examine your boards for a unique lot date code, or 
consecutive lot date codes (2-4 week period). I would also discuss 
with the supplier the exact process used, and if any process issues 
or changes occurred during that time. I can't tell you what a new 
operator or supervisor can do!

good luck
steve mikell
[log in to unmask]


----- Original Message -----
From: "Bill Kasprzak" <[log in to unmask]>
To: [log in to unmask]
Subject: [TN] Plating problem at the "Knee"
Date:         Fri, 20 May 2005 10:25:00 -0400

>
> Morning Technetters,
>
> I thought I would try to get this in before the Friday Follies (NTC)
> begins.
>
> I have a board that we have wave soldered and I have a number of joints
> where the solder reaches the top side pad then stops as if though there
> was a barrier. Upon closer examination, I noticed that there is something
> not quite right near the edge of the  hole on the top side. I remember
> reading about "Knee" problems on PTH's on this forum and searched the IPC
> archives for more information. I couldn't find anything.
>
> So I'm asking the community at large to comment about this condition at
> the "knee" and the causes for it. We are certainly able to do touch up on
> these joints but I'd like to try and see this before we process the board.
> There are a couple of pictures that Steve G has graciously placed on his
> "Picturepallooza" site.
>
> Go to: http://www.stevezeva.homestead.com
>
> The picture names are, "Topside Fillet and Topside Fillet 2".
>
> Let me know what you think. Thanks.
>
> Bill Kasprzak
> Moog Inc


-- 
___________________________________________________________
Sign-up for Ads Free at Mail.com
http://promo.mail.com/adsfreejump.htm

---------------------------------------------------
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
-----------------------------------------------------