Date: Thu Aug 17 2000 - 14:14:46 PDT
On the contrary, there are several things "special" about the Zycon/Hadco
processes (note the plural, it does matter) that makes it not only work, but
work reliably. I'm drawing on my relationship (and my memory) with Zycon
that goes back to 1989-1993 for the following; therefore, don't shoot me if
there are some minor misstatements. FYI, I first met Istvan Novak in Hungary
in 1993 while presenting the merits of Zycon's ZBC2000 (buried capacitance)
product in reducing EMI in high-speed designs (as part of the Hewlett-Packard
High-Speed Design seminar series).
The original guideline (and a defacto requirement if you wanted to sell your
products in the commercial telecom market) was set by the Bellcore limits of
no less than 4 mils dielectric thickness. This level, based on thousands of
qualification tests on materials available back in the 1960s (and continuing
into the late 1980s), was also insisted upon by the US military and aerospace
Zycon developed special techniques for generating a smoother (i.e., a finer
granular) finish that would still reliably bond to the core material and NOT
experience electromigration while still withstanding 500 VDC stress (a key
requirement). This copper smoothing process is now sometimes referred to as
"double-treating." Superior bonding and laminating techniques also had to be
developed. It's my understanding that these processes are also patented.
They then ran a formal series of qualification tests to obtain approval from
Bellcore that was then included within the specifications as an allowable
exception for telecom products. To my knowledge, no other company has that
approval. Zycon holds multiple patents on the many processes, as well as the
formally qualified deviation from the 4-mil "minimum thickness." Is anyone
aware of any other company that produces a standard 2-mil core product? I
think not, for the cited quality (and probably legal) reasons.
I DO know that if you simply throw together a 2-mil sandwich with "normal"
commercial foils, you will (not withstanding possible patent infringement for
anything less than 4 mils) typically experience voltage breakdowns, local
delaminations (i.e., air pockets that could not be extracted with "normal"
processes), and further degradation with field use caused by thermal cycling.
My current legal knowledge on this subject may be outdated, but patents run
for >20 years.
Since it has taken a decade for buried capacitance to really take hold,
perhaps Charles Grasso can give us an update since the excellent presentation
of last fall at the BC confab (in Colorado, I think).
Michael L. Conn
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