We see good results to 1 year+ with vac packing for both tin and silver.
The control of the immersion process is a factor in good shelf life and
durability.
Jeffrey Bush
Director, Quality Assurance and Technical Support
VERMONT CIRCUITS INCORPORATED
76 Technology Drive - POB 1890
Brattleboro, Vermont 05302
Voice: 802.257.4571.21 Fax: 802.257.0011
http://www.vtcircuits.com
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Wenger, George M.
Sent: Wednesday, August 10, 2005 8:50 AM
To: [log in to unmask]
Subject: Re: [TN] PCB Storage
TDK,
Don't believe everything you hear. My other comment is you need to know
about the environment of the shelf and packaging conditions before a
shelf life number in months has any real meaning.
We use immersion silver boards and do prototype assembly in new Jersey
and Virginia and production assembly in Canada, Italy and China and we
haven't experienced any soldering problems with immersion silver. Our
board vendors provide us boards shrink wrapped in plastic typically
10-12 boards per package. I don't have details about the storage
environment at each of our locations but I think it is typical for those
regions. Also, most of our boards are probably assembled within a 3-4
month time period but there have been occasions where boards were in
storage for over a year before assembly without any soldering issues.
Regards,
George
George M. Wenger
Reliability / FMA Engineer
Base Station and Subsystems Group
Andrew Corporation, 40 Technology Drive, Warren, NJ 07059 (908) 546-4531
[log in to unmask]
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of TDK
Sent: Wednesday, August 10, 2005 8:32 AM
To: [log in to unmask]
Subject: Re: [TN] PCB Storage
I heard that Immersion Silver has a shelf life of about 6-9 months as a
thin
oxide also forms on it, making soldering a potential problem.
Correct ???
Regards
TDK
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Dehoyos, Ramon
Sent: Wednesday, August 10, 2005 6:20 AM
To: [log in to unmask]
Subject: Re: [TN] PCB Storage
At absolute Zero there is no metallic migration, thus no
intermetalic forms. So the cooler the metals are the less migration,
less intermetalics.
I like HASL for the final plating instead of uplating. I agree
with the comments from others that HASL plating can last longer than 12
months and it is a more solderable finish than uplating with less
process problems such as slivers.
Ramon
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Franklin Asbell
Sent: Tuesday, August 09, 2005 4:41 PM
To: [log in to unmask]
Subject: Re: [TN] PCB Storage
Wow...the freezer? Now that's unique. Would never have suggested that
but it kind of makes sense.
Franklin
-----Original Message-----
From: John Burke [mailto:[log in to unmask]]
Sent: Tuesday, August 09, 2005 3:34 PM
To: [log in to unmask]
Subject: Re: [TN] PCB Storage
Intermetallic growth rate over time is constant with temperature. Once
the intermetallic reaches the surface of either the via or the pad lack
of wetting will be come apparent particularly on the areas of the pad
that were entering the air knife first since these can show very thin
tin lead thickness'.
To really answer this question you need to know how thick the tin lead
is and then you can give an indication of storage life at a certain
temperature.
The thinner the HASL the shorter the storage life at a given
temperature.
The lower the temperature the longer the storage life for a given
thickness of HASL.
"Pack 'em in dry nitrogen gas and throw them in the freezer" would
maximise the solderability in any event.
John
------------------------------------
Avanex
John Burke
Senior Manager RoHS Compliance
[log in to unmask]
40919 Encyclopedia Circle
Fremont
CA 94538
tel: 510 897 4250
fax: 510 979 0189
mobile: 510 676 6312
------------------------------------
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Dehoyos, Ramon
Sent: Tuesday, August 09, 2005 1:13 PM
To: [log in to unmask]
Subject: Re: [TN] PCB Storage
I have encounter resistance from a mentality type of folks
that strongly argue that HASL boards need to be etched and replated
after 12 months. These people recommend TIN/LEAD uplating instead of
HASL if the boards are not going to be used within a year. Their
argument is that the intermetalics in the barrels would render the
boards unsolderable. Any thoughts on this mater?
Ramon
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Franklin Asbell
Sent: Tuesday, August 09, 2005 4:01 PM
To: [log in to unmask]
Subject: Re: [TN] PCB Storage
While I certainly do not recommend this practice, I had some boards in
my desk for 5 years, under some papers, beneath a box...I had
'forgotten' they were there, just for kicks I soldered them without bake
and they looked good.
For storage in an office (or controlled)environment I would suggest
vacuum seal with dessicant for the environment you suggest. Time in
itself for that period should not be an issue, just keep them sealed and
they may last up to
7 years or more.
Franklin
-----Original Message-----
From: Black, Paul [mailto:[log in to unmask]]
Sent: Tuesday, August 09, 2005 2:32 PM
To: [log in to unmask]
Subject: [TN] PCB Storage
Hi All,
I have some bare PC boards that may be built up in the future, but not
in the near future. I would like to put them into storage until needed
(anywhere from 6 months to 2 years). The boards are .062" FR-4 HASL
boards.
What would you recommend for protection, assuming that the storage
conditions are typical of an office environment? Would I have to do
anything special to them when they are removed from storage? Any
suggestions would be greatly appreciated.
Thank you,
Paul Black
Manufacturing Engineer
Kronos
E-mail: [log in to unmask]
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