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August 2005

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Subject:
From:
John Burke <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, John Burke <[log in to unmask]>
Date:
Tue, 9 Aug 2005 13:33:57 -0700
Content-Type:
text/plain
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text/plain (143 lines)
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
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-----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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