Hi Paul,
Plywood...good point. Layers of unidirectional fibers laid at 90 degrees to
each other, and almost always odd layer count. However, if we model the
center ply as two layers in the same direction at 1/2 the thickness, we now
have a even layer count.
Copper in the boards needs to be called out and would be modeled as an
individual layer with isotropic properties. What we call a 4 layer card
would need to be modeled as 7 layers using the same trick described for the
plywood (splitting the center dielectric and modeled as 8 layers).
Cross-ply laminate (assuming same Fiber count in both directions) would have
equivalent properties in two directions (0 and 90 degrees)not in all
directions like copper. The properties of the cross-ply, say at 30 degrees
would be considerably different than along the fiber axis at 0 and 90
degrees.
Isn't modeling composites fun!
Scott
-----Original Message-----
From: Paul Klasek [mailto:[log in to unmask]]
Sent: Monday, August 30, 1999 6:18 PM
To: [log in to unmask]
Subject: Re: [TN] In Circuit Test
lclclcl ; lclclclcl ;
Got the plywood dilemma Scott ; we should be actually calling the layers of
glass ; not of copper hey ?
Been just curious if it ever happened ; funny enough it did .
The cross ply should in theory be neutral ; practice seems different .
paul
-----Original Message-----
From: Severson, Scott M. [mailto:[log in to unmask]]
Sent: Monday, 30 August 1999 22:37
To: 'TechNet E-Mail Forum.'; 'Paul Klasek'
Subject: RE: [TN] In Circuit Test
Paul,
Charles Barker hit the nail on the head. Laminate Theory tells us that a
"balanced" lay-up (as described by Charles) is the most desirable to provide
even stresses in the laminate and thus prevent warp. In composite
structures (non PCB) it can be even more critical because uni-directional
laminate (vs cross-ply used in boards)is often used at various angle to get
pre-defined properties in a given direction.
Scott
-----Original Message-----
From: Paul Klasek [mailto:[log in to unmask]]
Sent: Friday, August 27, 1999 6:26 PM
To: [log in to unmask]
Subject: Re: [TN] In Circuit Test
interesting , how thick is 52 ? (just curious) .
Earl we have the layers cost dilemma here :
What would be ratios of yields and costs from simple double sided FR4 ;
to 4 layers, 6, 8, >>> etc. ?
And why even's only ; no odd layers ever ?
thanks paul
-----Original Message-----
From: Enter your name here [mailto:[log in to unmask]]
Sent: Saturday, 28 August 1999 8:22
To: [log in to unmask]
Subject: Re: [TN] In Circuit Test
Your 2 cents noted. No biggy, but we build bare boards up to 52 layers and
loaded cost over too many thousands. Even our cheap stuff ain't cheap. DFM
and T is critical. It just can't happen without concurrent engineering
including all responsible "experts" from design through test.
Earl Moon
----- Original Message -----
From: Darrel Therriault <[log in to unmask]>
To: <[log in to unmask]>
Sent: Friday, August 27, 1999 11:35 AM
Subject: Re: [TN] In Circuit Test
> TechNet....
>
> I'd like to put in my $.02 for DFT......
>
> We specify 100% netlist coverage for ICT unless there is a compelling
design
> reason why a net can not be accessed. It's part of our Mfg DFT
requirements.
>
> The rationale.....our boards are expensive and complex. Having to scrap
> out or spend
> a lot of debug time at Functional costs a lot more in time and resources
> then adding
> some test points or taking up a little more real estate or adding a
> layer. I think if you
> look at the cost implication of production and service/customers it works
> out to a
> much bigger advantage to have ICT at the highest level possible.
>
> DT
>
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