Builds of multilayer boards is a ripe subject for standardization, as
one way to keep US shops competitive. However, the flip side is it also
provides an easier pathway to export the job off-shore.
Historically the US marketplace (laminate and Pcb shops) have
accommodated the tendency of designers to create unique builds by making
available just about any dielectric thickness and twinking of dielectric
properties. The philosophy has been to allow the designer max freedom
in dielectrics and conductors -- so lots of boards have been designed
with special layer thickness of 3.5, 4.0, 4.5, 6.2, 6.5, 7.0, 7.5, 16,
19, etc. We've had to accommodate designs that require 1.0 and 1.25 mil
copper foil, amongst other oddballs.
And you can get an 8 mil core with 4-5 different glass/resin
constructions (would you like the high resin%/low Dk special with 3
plies of 1080, or the asymmetric 1080/7628 to balance out that nasty
single ground plane you dropped into layer 2, or the el-cheapo 1-7628,
or the standard 2-2116 ???)
The laminate suppliers are striving for greater standardization to
improve raw material availability and efficiencies. They are passing
these imperatives on to the board shops. Any of them can supply
information on board stack-ups of 4, 6, 8, etc layers and with overall's
of 062, 080, 093, 110, etc.
Also see IPC-4121 for recommendations on standard laminate constructions
(this is pretty dated, however but it does show the diversity that
exists.)
Jim Paulus
at Itron: 507-837-4326
at office: 608-787-0817
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Tempea, Ioan
Sent: Tuesday, July 13, 2004 9:32 AM
To: [log in to unmask]
Subject: Re: [TN] Board Stack geometry
Jeffrey,
could you write down for us an example of good stackup specification?
Something that gives enough freedom to the fab, so that they do a
competitive quote, but also keeps a rigorous functional spec, that is
portable when the board supplier changes.
Thanks,
Ioan
> -----Original Message-----
> From: Jeffrey Bush [SMTP:[log in to unmask]]
> Sent: Tuesday, July 13, 2004 10:15 AM
> To: [log in to unmask]
> Subject: Re: [TN] Board Stack geometry
>
> If needed for performance, the stackup on the drawing should only
> specify the required dielectric thickness and finished copper weights.
> The PCB can be constructed in many several methods to obtain the
desired
> end thickness. If, for example, you spec out some plies of 2116 glass
> in an opening, and supplier B only uses 2165, this becomes an issue.
If
> signal/performance integrity is not an issue in the design, leave it
up
> to the PCB fab house and the compliance testing to your drawing
> requirement to ensure thermal and mechanical integrity is there.
>
>
>
> Jeffrey Bush
> Director, Quality Assurance and Technical Support
>
> 76 Technology Drive - POB 1890
> Brattleboro, Vermont 05302-1890
> Tel. 802.257.4571.21 Fax. 802.257.0011
> [log in to unmask]
> http://www.vtcircuits.com
>
>
>
> -----Original Message-----
> From: Roger Stoops [mailto:[log in to unmask]]
> Sent: Tuesday, July 13, 2004 9:05 AM
> To: [log in to unmask]
> Subject: [TN] Board Stack geometry
>
>
> This brings up a question I have had bumping around in my head for a
> while, for example:
>
> A pcb has been designed, assembled, tested, and now goes through FCC
and
> CE emissions and susceptibility testing. The board stack was
determined
> by the pcb vendor. The assembly passes first time. Purchasing or the
> EMS finds a less expensive yet reliable board house and buys
production
> boards from this new house. The new house changes the board stack to
> their preferred lay-up.
>
> Would not this board need re-testing for FCC/CE
> emissions/susceptibility? For boards requiring this type of testing,
> would not a board stack specified on the print be required?
>
> TIA and much appreciated,
>
> Roger Stoops
>
>
> -----Original Message-----
> From: Jeffrey Bush [mailto:[log in to unmask]]
> Sent: Monday, July 12, 2004 8:40 AM
> Subject: Re: 7628 prepreg?
>
>
> Common type, stable, low resin content and likely predicable thickness
> is this is important. Otherwise PCB house should be left to determine
> the optimal stack for the board geometry and end use.
>
>
>
> Jeffrey Bush
> Director, Quality Assurance and Technical Support
>
> 76 Technology Drive - POB 1890
> Brattleboro, Vermont 05302-1890
> Tel. 802.257.4571.21 Fax. 802.257.0011
> [log in to unmask]
> http://www.vtcircuits.com
>
>
>
> -----Original Message-----
> From: Brooks,Bill [mailto:[log in to unmask]]
> Sent: Friday, July 09, 2004 5:08 PM
> To: [log in to unmask]
> Subject: [TN] 7628 prepreg?
>
>
> Bill Brooks
> PCB Design Engineer , C.I.D., C.I.I.
> Tel: (760)597-1500 Ext 3772 Fax: (760)597-1510 http://pcbwizards.com
>
> Why would a designer specify 7628 prepreg in the construction of a
> board? What characteristics are unique to it? Bill Brooks, CID
>
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