Thanks to Ernie, Bev, Alain, Jon for comments. I did talk with a couple of Kester people about the rise in Cu content. We have HASL on all boards for a good 8 months or so. OSP may have appeared, rarely, before that, likewise for white tin. I have a better picture of where the copper is or may be coming from. I think we are getting it from trimmed leads on through hole parts. Production has increased enormously over the past 2-3 months.
What I'm thinking of doing is making a regression SPC chart to allow for a rise in Cu content with time, rather than have the familiar chart with a constant center line. Since data are a bit limited (13 points), I will try using Q statistics to make the chart.
Regarding Ernie's experience with tin, I can say that our tin chart (a standard Shewart one) showed an out of control condition a few months ago. When I looked into it, I learned why tin is depleted and that we had not been adding it to the pot. A few bars fixed the short term problem. I'll change the preventive maintenance procedure to call for adding smaller amounts at more frequent intervals. And I wonder about the tool by which these constituents and contaminants in solder are measured. How much of the 1% drop is due to gage variability? And how much gage variability is in the copper measurements I've seen? Lou Hart
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From: Ernie Crump[SMTP:[log in to unmask]]
Sent: Wednesday, December 06, 2000 3:57 PM
To: [log in to unmask]
Subject: Re: [TN] Copper contamination is wave solder
Lou; We don't run a large quantity of cca's through our machine, but with pwb's
solder masked over tin/lead, we don't see much movement in the copper reading.
Always around .075%
I find it wise every so often to do several tests at an independant lab on the
solder from the bath, and in several cases on the bar stock received, which is
to the QQ-P spec.
One phenon. I find strange is the need to add tin fairly regularly, we can drop
1% in a short time, with very little soldering being processed. Less than 100
6x8 " boards.
Your case may have to do with the use of bare copper runs, even with smobc.
Ernie Crump
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