Might I suggest that you check the quality of your supplied solder as well?
We once changed a process and had difficulty in maintaining our copper level
in the HASL pot - we normally take a fixed square footage through the bath,
then drop 20% of the solder, and top up with fresh. We found all of a sudden
that we had to drop the number of square feet processed before a dilution
to a ridiculously low level. We blamed this on the change to the copper
surface from a previous operation. It turned out that we had also changed
solder to a more "commercial" grade alloy, which basically was not pure
enough to maintain our normal throughput. We changed back to our original
supply, and within a very short time we were back to where we had been!
Dougal Stewart
Exacta Circuits
Scotland
Date: Tue, 6 Aug 1996 14:14:06 +0400 (EDT)
From: <[log in to unmask]>
Subject: Re: FAB: HASL drossing
To: joef <[log in to unmask]>, [log in to unmask]
Sorry I forgot to mention this in my previous
submission. The operator takes 2 slugs, not 1, twice per month. One
before cleaning and one after. We have SPC charts for both. The
"before" and "after" slugs are not that much different. I can provide
data for anyone interested. Lou
.
On Mon, 5 Aug 1996 [log in to unmask] wrote:
> Joe, here are my comments about your HASL.
>
> OUr guys clean the pot once per day. The machine is only used on second
> shift.
>
> When we got a new Quicksilver machine about 2 years ago, it looks like Cu
> contamination went down, according to our SPC chart. The operators say
> it is easier to clean the new machine than the old one.
>
> We have an SPC chart to monitor Cu in the pot. On the 5th and the 20th
> of each month, the operator pulls a sample slug to be sent out for analysis.
>
> Lou Hart
>
>
> .
>
> On Mon, 5 Aug 1996, joef wrote:
>
> > Hello Technet,
> > We are having difficulty maintaining our HASL pot below 0.25% Cu, even
> > with 2x daily drossing. The machine is an old vertical Electrovert
> > with less than easy access.
> > - Is this 0.25% more critical at assembly than at fab?
> > - What is the practical USL for copper in HASL?
> > - How often should metal contaminants be measured?
> > - Should drossing be done at a constant frequency, or based on panel
> > loading?
> > - Are there any studies out there correlating HASL quality with Cu
> > contamination level?
> > - Any special recommended procedures or tools?
> >
> > As always, we appreciate any input.
> > Joe Felts
> > PC World, Toronto
> >
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