Hello Bev,

You had a very complete set of options for Sven-Erik but there is another
option that is also making its way in as an alternative, the µBGA® CSP. It
offers a compliant structure that mitigates the stresses resulting from the
CTE mismatch between the silicon and FR-4 that Werner Englemaier has been so
long warning us all about. In addition, it has a coarser lead pitch, a
smaller proilfe and a can be placed using a chip shooter at rates up to
20,000 uph at near 100% yields. While presently aimed primarily at packaging
flash memory, it is being targeted to replace the existing TSOP packages by
a number of IC manufacturers around the world based on the demands of their
users.   

Cheers!
J. Fjelstad

>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
Tessera ...System Building Blocks for the Next Generation of Electronics
 3099 Orchard Drive
 San Jose, CA 95134
 Phone 408 894-0700
 Fax   408 894-0768

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