Doug, thanks for the information

Answer to your questions
The Chlorine spikes were relatively small, what is a better test to
ascertain chlorine contamination

Your last comment about the corrosion problem when mixed with moisture was
like you looked into crystal ball and know the problem that we are having!!!

How much moisture is required?

Have you ever seen a glass diode that loses the "normal" orange color and
turns a pale color, it seems that the copper oxide layer between the diode
slug and glass is being etched and then causing the diode to become leaky,
the diode is surrounded by polyurethane but there is a chance that moisture
could have a path onto the pcb. Also the negative side of the diode
discolors first.

Jason Larson

-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Douglas Pauls
Sent: Tuesday, June 27, 2000 12:07 PM
To: [log in to unmask]
Subject: Re: [TN] Axial lead preparation


In a message dated 06/27/2000 1:32:57 PM US Eastern Standard Time, CSLPAT
writes:

>
>  Hi Technet, I have a question for those that are involved with component
>  manufacturing.

Well, we don't manufacture components, but we analyze a bunch.

>
>  What type of flux is used for preparing leads for tinning?

You would get as many answers to this one as you have component
manufacturers.  Most use a fairly active flux, say a type M or type H flux.
Several use sulfuric acid or methane sulfonic acid a oxide strippers.  The
more aggressive material allows them to process at a faster speed.

>  Also is there anywhere that chlorine is used in this process? Where would
chlorine come
>  from if not from the manufacture?

It depends on the materials chosen.  Some component manufacturers use
hydrochloric acid as the etchant.  I think that you will find chlorine on
components about as common as nitrogen in air.  The stuff is everywhere.

>
>  We analyzed some of our raw goods with a SEM and noticed that there was
>  chlorine present in the junction of diodes and also on the leads by the
>  glass / slug interface

A SEM tends to be more qualitative than quantitative.  It is not surprising
that a SEM shot picks up chlorine.  How strong a peak was it in relation to
the other peaks?

We have seen a few cases where the seal material is not glass, but an epoxy
material.  Depending on the construction techniques, you may have the
aggressive material absorbed or trapped in the interface material, which
then
causes lots of corrosion problems when mixed with moisture.

Doug Pauls
CSL

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