Hi Michael! Here is my best guess at what "might" work in terms of getting
a leaded component to have useable solderability after 30 years of storage
( I say "might" because the only data I have is in the 5-10 year range).
First and foremost, you need sufficient surface finish thickness such that
room temperature diffusion will not cause the base lead alloy (i.e. copper
or alloy 42) to diffuse thru the surface finish. If you can tackle that
issue then you just need to prevent surface finish oxidation. If you seal
the components in moisture proof package (aka MSL type packaging) using
argon as a backfill gas and then store the sealed bags in a
humidity/temperature controlled environment, you might have a chance. You
will be able to achieve at least 5-8 years of storage depending on the
specific component surface finish you are dealing with. This is not a
cheap procedure to use. Good Luck.
Dave Hillman
Rockwell Collins
[log in to unmask]
"Jeremias, Michael" <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>
03/26/2010 06:21 AM
Please respond to
TechNet E-Mail Forum <[log in to unmask]>; Please respond to
"Jeremias, Michael" <[log in to unmask]>
To
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cc
Subject
[TN] Long term Shelf life of electronic components
Hi partners,
for long term storage and extended shelf up to 30 Years of Plastic
BGAs J-STD-033 is very valuable.
We need long term shelf life 20....30 Years for Flash PROMS and Flash
Memories.
1. Do You know Humidity seal bag materials for longer shelf life than
12 months e.g 5 Years or more?
2. Do You know test procedures to be done before longterm storage of
the iece parts?
3. Do You know standrds for storge conditions and packing
materials?
Thanks in advance for Any helpful answer
Michael Jeremias
-----Ursprüngliche Nachricht-----
Von: TechNet [mailto:[log in to unmask]] Im Auftrag von Bev Christian
Gesendet: Freitag, 26. März 2010 11:21
An: [log in to unmask]
Betreff: Re: [TN] Need some opinions
Inge,
What is a schrecklich photo?
Bev
----- Original Message -----
From: Inge <[log in to unmask]>
To: Bev Christian; [log in to unmask] <[log in to unmask]>
Sent: Fri Mar 26 03:11:06 2010
Subject: Re: [TN] Need some opinions
Bev,
The purpose of lead finish, either it is tinned or gold plated or silver
plated, is not only to make the leads solderable, but also to protect the
bulk material from corrosion. A Kovar leg that is not 100% covered will
be attacked and can corrode to the degree that the whole component falls
off.
If the leads are bent after tinning, there is still more risk of problems.
So, of course negative wetting is something that the quality responsible
must consider as a high priority case. If you are interested, and if I
can find, I can send some schrecklich photos to you.
Inge
--------------------------------------------------
From: "Bev Christian" <[log in to unmask]>
Sent: den 25 March 2010 18:58
To: <[log in to unmask]>
Subject: Re: [TN] Need some opinions
> Steve,
> Gull wings.
>
> Yes, cheap, cheap cheap!
>
> Bev
>
> ----- Original Message -----
> From: TechNet <[log in to unmask]>
> To: [log in to unmask] <[log in to unmask]>
> Sent: Thu Mar 25 21:49:18 2010
> Subject: Re: [TN] Need some opinions
>
> Hi Bev,
>
> Don't leave us hanging, what components are you seeing that with? I'd
like
> to have a "heads-up".
>
> This begs the question, why do you think they are doing that? Are things
> getting so tight that they're trying to pinch a penny by reducing
plating
> coverage? Hmmmm...
>
> Steve
>
> ----- Original Message -----
> From: "Bev Christian" <[log in to unmask]>
> To: <[log in to unmask]>
> Sent: Thursday, March 25, 2010 9:08 PM
> Subject: [TN] Need some opinions
>
>
>> Technetters,
>> It seems that more and more component suppliers are not plating their
>> leads
>> all the way up to the component body. In fact some are getting
downright
>> skimpy and only plating to the bottom bend, never mind the upper one.
If
>> you
>> put down a lot of solder paste you end up with a bulbous joint, a
>> negative
>> wetting angle and a stress concentration point. If you put down less
>> paste
>> and have a co-planarity issue, then you have the potential for opens.
>> The
>> other option of course is getting the supplier to plate higher up the
>> leads.
>>
>> Question: would you consider the condition of the formation of the
>> negative
>> wetting angles a failure during process qualification?
>>
>> Bev
>> RIM
>>
>>
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