How effective is a desiccant shrink wrapped together with the boards? If the
boards are not completely dry before they are shrink wrapped, would the
desiccant shrink wrapped with the boards remove the humidity?
In case of Immersion Silver plated boards, is their a concern that the
desiccant may contaminate the surface (even if placed at the side (edge) of
the stack of boards and not on the surface)?
Sherif Refaat,
----- Original Message -----
From: "Franklin Asbell" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Wednesday, August 10, 2005 9:00 AM
Subject: Re: [TN] PCB Storage
> Yes, it can last over a year if packaged correctly, again, shrink wrapped
> with dessicant, the 'oxide' (or other contaminates) on the surface have
> more
> to do with initial processing, if the bath is not precise shelf life will
> suffer greatly regardless of the packaging.
>
> And if the immersion tin supplier say's they can 'refresh' the tin after
> long term storage...hmmmm...well let's just say pass on that as it is not
> a
> good thing!
>
> The supplier needs to put more than 40 microinches tin to ensure it will
> last that long, in my opinion.
>
> Franklin
>
>
> -----Original Message-----
> From: TDK [mailto:[log in to unmask]]
> Sent: Wednesday, August 10, 2005 7:32 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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