I work with flex and adhesive materials and this type of etch is
characteristic with plasma, sometimes called a "dogleg".  There seems to be
an interaction between the temperature in plasma and the copper traces or
planes on layer 2, such that resin in contact with the copper can etch at a
higher rate.  We also see "sidedness" to the etch, as you see in this
cross-section, where the base material etches more on one side of the via
than the other.

I wonder if a plasma cycle was added after via generation for cleaning
purposes?

Jana Carraway
MSEI - Advanced Technology Group
6024 S.W. Jean Road
Lake Oswego, OR  97035
503.697.5291, ext 1180
email: [log in to unmask]

-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Dennis Fritz
Sent: Monday, September 12, 2005 7:16 AM
To: [log in to unmask]
Subject: Re: [TN] Microvia Puzzle


The microvia you have sectioned will be an enormous problem to  electroplate
- as you have found out.

It appears that very significant etchback of the resin/glass  under the
copper foil has occured. The "shelf" left by the copper surface foil  is
requiring
the copper to plate back under itself.  This type of "desmear"  was common
when plasma was used to remove resin only dielectric some years  ago.  The
way
the overhang problem was solved was to agressively  microetch the surface
foil
to remove all the overhang.  I suggest the same  thing here.

How was the original copper foil removed for this  microvia?  You say CO2,
but it appears to me that too much copper is  present for the CO2 to cut
through
it.  Either, this was a combined UV/CO2  microvia drill where the UV cut the
initial foil and the CO2 removed the epoxy  and glass fibers, or the
original
hole in the foil was chemically etched.   Notice how the microvia drill
stopped nicely at the level two copper foil - the  way CO2 drills do.

I think your microvia will be easier to plate with more of a  "V" shape, and
certainly no copper foil overhang.

Denny Fritz
MacDermid, Inc.

---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 1.8e
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt or (re-start) delivery of Technet send e-mail to
[log in to unmask]: SET Technet NOMAIL or (MAIL)
To receive ONE mailing per day of all the posts: send e-mail to
[log in to unmask]: SET Technet Digest
Search the archives of previous posts at: http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16
for additional information, or contact Keach Sasamori at [log in to unmask] or
847-615-7100 ext.2815
-----------------------------------------------------

---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 1.8e
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL)
To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
Search the archives of previous posts at: http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
-----------------------------------------------------