After hearing that the issue is with corrosion prevention, would conformal
coating be an option for these boards? Even if the board was gold plated,
what corrosion resistance is being offered to the solder joints and leads?
----------
From: Phil Bavaro [SMTP:[log in to unmask]]
Sent: Thursday, June 08, 2000 1:44 PM
To: [log in to unmask]
Subject: Re: [TN] still confused
You will no doubt get a lot of responses to this one.
The reason why the immersion gold usually specified on pwb drawings
as the
finish is to protect the delicate nickel beneath it from oxidizing
to the
point that wetting is hindered when trying to assemble the boards
using a
solder process.
If the boards are built already, and functioning, it would be a
shame on
all involved if they were not dispositioned as "use as is".
As was already stated, as soon as molten solder comes into contact
with the
immersion gold, the gold is gone which takes away the leg your
customer was
using as the reason (especially if these are SMOBC boards).
We've built RF CCAs for many years and have never seen the circuitry
yet
that required the nickel gold for the skin effect property
differences
between HASL and NiAu. Corrosion resistance is not a justification
for
reworking loaded functioning boards.
We use the copper nickel gold because of the inherent problems with
immersing thin non soldermasked PTFE boards with very fine line
filter
circuitry into a molten bath of solder.
Your customer still does not have a clue but I hope you are not
confused
anymore. If you still find that you have to apply gold to your
loaded
assemblies, respond accordingly and we can point you in the right
(??)
direction.
At 09:55 AM 6/8/00 -0700, Ralph Richart wrote:
>We have answers....
>
>So I had a long talk with my customer this morning to provide input
>based on the invaluable advice from you all.
>
>I said - "is there a specific reason for choosing 3-8u" of
immersion
>gold over tin/lead solder?"
>He said - "absolutely, the gold provides corrosion resistance, the
gold
>does not"
>I said - "even such a thin amount - only 3-8u"?"
>He said - "definitely, all we need is the coverage, the thickness
is
>irrelevant"
>
>Is this true?
>
>Needless to say, we are rebuilding the parts as we speak. Rework
sounds
>difficult to say the least, although I may try to come up with some
>scheme for fun as they have a bunch of boards that are no good
right
>now.
>
>thanks for all the help.....
>
>ralph
>
>PS - more on the larrylobster story later; it's more silly than
anything
>else. Paul's poem may soon become our own, however. Very funny!
>
>Off to build some boards....
>
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