Hi Goran,

In a message dated 02/03/0 9:12:26, [log in to unmask] writes:

>I have a question.  People say that plated through hole is the weak link
>in the printed circuit board.
Not necessarily, it depends on the design, material choices, PCB PTH/PTV
interconnect quality, the severity of the soldering operations, and the
severity of the use environment.
>What is the data, i.e., when does a PTH fail (at what temp cycling, at what
no.  of cycles)?
See IPC-TR-578 (September 1984), IPC-TR-579 (September 1988), and IPC-D-279,
Appendix B, (July 1996). If you need to know more details, you should attend
my workshop "Design for Reliability and Quality Manufacturing of
Plated-Through Holes and Vias" at NEPCON West, Fe. 29, 2000, or at IPC Expo,
April 2, 2000
>
>For microvias, PTH are often filled and planarized.  Is a filled PTH
>more reliable?  Any data on this? Has anyone looked whether a pure
>dielectric vs. filled dielectric vs. a Ag-filled paste make a
>difference?
Microvias, unlike PTHs/PTVs, are not loaded significantly during assembly and
service--so, unless there are quality problems no threat to reliability need
to be expected. Filled (solder better than organics) are more reliable than
unfilled PTHs/PTVs in terms of innerlayer separation (ILS), but are more
prone to barrel cracking if there are voids in the solder-fill (voids are
immaterial for organic fills).
A fill with a CTE closer to Cu is better as are fills with higher modulus of
elasticity--fillers typically tend to change the properties in these
directions.

Werner Engelmaier
Engelmaier Associates, L.C.
Electronic Packaging, Interconnection and Reliability Consulting
7 Jasmine Run
Ormond Beach, FL  32174  USA
Phone: 904-437-8747, Fax: 904-437-8737
E-mail: [log in to unmask], Website: www.engelmaier.com

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