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Date: | Sat, 13 Jul 96 03:00:17 UT |
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APeder01,
One source of information that you might want to check out is the July 1996
issue of PC FAB magazine. This issue has many articles related to different
surface finishes currently being used.
Here are answers to your other questions:
1. Is "electroless gold" the same as "immersion gold?"
The answer is both yes and no depending on who you are addressing. Specific
terminology for electroless plating are sometimes not the same from person to
person and region to region. It is best to clarify the term with the person
before starting a discussion to prevent any misunderstanding.
Example: Immersion Gold is also called
Self Limiting Gold
Metal Replacement Gold
Electroless Gold
Flash Gold
2. How thick can we expect the gold to deposit?
Most Immersion gold will stop plating at approximately 8 microinches. You
will find some people say that the thickness is closer to 10 and maybe 15
microinches but I believe along with many others that 8 microinches is more
accurate.
There are some modified Immersion Gold baths that claim to be able to plate
up to 20 micro inches but these "juiced" up bathes tend to have spotty plating
thickness, and are not
reliable.
There are Autocatalytic Gold (electroless process) baths which will plate
thicker gold deposits. In theory the process will plate forever as long as
the bath is in balance. But for most wire bonding applications 15 to 30
microinches for aluminum wire and 50 to 70 microinches for gold wire are
typical.
3. Is the gold deposition process a self limiting one?
Yes. The Immersion Gold solution replaces the Electroless Nickel with gold
until all the Nickel sites are sealed, at which point the reaction stops.
4. How much gold is required to adequately keep the nickel solderable?
Typically the gold is plated to the maximum of approximately 8 microinches.
This to insure that the electroless Nickel is completely sealed to protect
from it from passivating.
Lately I have evaluated some Simm Chip Modules from off shore that have as
little of 1 to 2 microinches of gold over the nickel. Some modules were
successfully assembled in the 1st pass, while other required various degrees
of rework.
I hope this helps you with your evaluation and if you have other questions,
call me at (714) 842-1987 or (714) 842-4853.
Cheers
Frank Kurisu
Aurelon, Inc.
Huntington Beach, CA
----------
From: APeder01
Sent: Friday, July 12, 1996 6:55 AM
To: [log in to unmask]
Cc: APeder01; MCHAN
Subject: FAB: Electroless Nickel - Immersion Gold
My company is in the process of evaluating the use of Electroless
Nickel - Immersion Gold as a finish, for both SMT and mixed technology
PWBs. Is this a good plating system to evaluate?? Is there any
"conventional wisdom" that we're missing?
Secondly, some questions about the gold deposition.
1. Is "electroless gold" the same as "immersion gold?"
2. How thick can we expect the gold to deposit?
3. Is the gold deposition process a self limiting one?
4. How much gold is required to adequately keep the nickel solderable?
Any other comments regarding this topic is appreciated.
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