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December 1997

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Subject:
From:
Bev Christian <[log in to unmask]>
Reply To:
TechNet Mail Forum.
Date:
Mon, 1 Dec 1997 10:01:49 -0500
Content-Type:
text/plain
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text/plain (82 lines)
Guenter,
Do you really believe that TSOPs can be used in an application where the
daily temperature swing is 40 C   ?

Bev Christian
Nortel

>----------
>From:  Guenter Grossmann[SMTP:[log in to unmask]]
>Sent:  Monday, December 01, 1997 2:57 AM
>To:    [log in to unmask]
>Subject:       Re: [TN] TSOP, TQFP reliability
>
>Hi Sven-Eric
>
>It is a matter of fact that the solder joints of TSOP's are less reliable
>than the ones of packages with high standoff since it is the length of the
>leads which absorbs most of the deformation due to the CTE mismatch of
>component and PCB. Long leads deform easier than short leads. Additionally
>if the leadframes of TSOP's are made of Alloy 42 than the leads are stiff
>compared to copper leads. Using copper leads instead of Alloy 42 eases the
>problem to a certain extend.
>
>However, I believe it is important to consider the environment the product
>is used in. Namely the temperature swing, the temperature extremes the
>temperature gradient and the reliability goal of the solder joints ( As
>Werner already mentioned, there is nothing wrong with TSOP's per se ). In
>my opinion the reliability of these solder joints has to be estimated for
>the application their used in, since even a material combination that is
>potentially harmful might lead to a reliability of the solder joints that
>is well within the requirements for a given stress.
>Let's say one uses TSOP's on FR 4 in an office environment 20- 30deg. C and
>the equippment sees a temperature swing of 40deg.C with a ramp of 1 deg.
>C/min. When switched on and off once a day. I don't see a point why not
>using TSOP's unless the thing has to live 100 years.
>
>Reliability testing does not always mean to find the evil part in an
>assembly corrupting the reliability of the whole equippment but also to
>find out whether a technology that is absolutely disastrous for some
>applications but has advantages ( price, space ) may be used in an
>application with moderate stress. Therefore I think it doesn't make sense
>to use data from tests with extreme testconditions to estimate the
>reliability for a much less severe application without checking whether the
>testconditions are applicable to the real stress.
>
>Besides that's the work Werner and I are living of so it's got to be
>important.
>
>
>Best regards
>
>Guenter Grossmann
>Swiss Federal Institute of Technology
>Reliability Laboratory
>
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