Positive etchback was a general requirement for Aerospace and in
developing the IPC standard performance sheets for this a concession was
made. However, the commercial standard for post connection did allow
negative etchback and this was determined not allowable for flight
systems and the no-negative etchback was added in this sheet. This is a
good rule for any design in my opinion for hi-rel products.
Same applies for the vias where a plugged via may have issues that
affect the reliability of the barrel - expansion, chemistry entrapment,
and I also think the ability to inspect the holes. This in
counter-intuitive as a via that is filled with the correct
materials/process will improve the reliability of the via.
Jeffrey Bush
Director, Quality Assurance and Technical Support
VERMONT CIRCUITS INCORPORATED
76 Technology Drive - POB 1890
Brattleboro, Vermont 05302
Voice: 802.257.4571.21 Fax: 802.257.0011
http://www.vtcircuits.com
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of schaefer, dave
Sent: Friday, August 26, 2005 11:30 AM
To: [log in to unmask]
Subject: [TN] IPC-6012B Class 3A Questions
I have a few questions regarding the requirements of IPC-6012B
classification "3A" (ref. "IPC-6012B Performance Specification Sheet for
Space and Military Avionics"):
- Why does the Performance Sheet define NEGATIVE ETCHBACK (3.6.2.8) as
being
unacceptable?
- The description of "Through Via Plugging" requires clarification - is
the
Performance Sheet indicating that Vias and Through Holes cannot be
plugged?
If so, why?
Thanks,
Dave Schaefer
Bristol Aerospace
(204)775-8331 ext 3186
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