At 08:41 AM 7/9/01 -0700, Brad Velander wrote:
>Michael,
>         while I can generally agree with your advice you leave one aspect
>wide open. If you do not specify your layer thickness, you could get a board
>that works fine from manufacturer A, switch to manufacturer B and have a
>board that doesn't work fine.


I want to underscore this.

If one is comfortable with a particular fabricator, there is no harm asking 
that fabricator what thicknesses they would recommend based on what is 
easily available, and then writing that into the board stackup 
specification. Work with the fabricator.

The down side of this would be that a less than scrupulous fabricator might 
suggest a thickness that they happen to have a lot of and need to dump. But 
that is not very likely.

IPC-2222 does have a table of laminates.

If you join the IPC Designer's Council, $50, you get -- last time I looked 
-- a $50 credit toward publications, *and* you get the publications at the 
member prices.

The sizes of FR-4 material marked in the chart as low cost are, in mm.:

0.07
0.11
0.13
0.18
0.26
0.32
0.37
0.43
0.53
0.61
0.64
0.74
1.52 is not given the lowest cost value, but it is very available.


Abd ul-Rahman Lomax
LOMAX DESIGN ASSOCIATES
PCB design, consulting, and training
Protel EDA license resales
Sonoma, California, USA
(707) 939-7021, efax (419) 730-4777
[EMAIL PROTECTED]
[EMAIL PROTECTED]


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