Sven-Eric,
TSOPs on FR-4 with a high daily temperature swing are not reliable.
There are many papers out in the open literature that substantiate this.
 Recently Jean Paul Clech (hope I spleed that right) had a little
article in the SMT newsletter saying as much, also.  I am also sure that
Werner Englemaier, another reliability expert, would also agree.

You have several options
1) ignore the problem and hope that your product becomes obsolete or
breaks for another reason
2) go to Thermount (aramid) or Ceracom (ceramic) boards
3) lower the temperature swings of your product (eg don't sell you
portable phone in Minneapolis)
4) use a different part type (eg SSOP)
5) embed the leads in a underfill material (so far not reworkable,
although rumors have it that we should see something in this area in
1998)
6) get TSOPs with the longest, thinnest leads possible
7) wait for the new TSOPs with copper lead frames which are going to
replace the Alloy-42 currently used in most of them today.

Good luck!

Bev Christian
Nortel
>----------
>From:  SVEBA[SMTP:[log in to unmask]]
>Sent:  Thursday, November 27, 1997 9:38 AM
>To:    [log in to unmask]
>Subject:       [TN] TSOP, TQFP reliability
>
>Hello Technetters,
>I have understood from different sources that use of thin plastic packages
>like TSOP and TQFP is not rekommended in more severe environments. Does
>anyone know the reason for that?
>Are there tests done that show bad reliability over time or is the problem
>that they cannot withstand the soldering process?
>
>Regards
>Sven-Eric Bäckström
>
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