Jack -
Your question got me to thinking, so I did a little research. Way, way
back in time when the Mil specs were king we used MIL-STD-275E as the
guide for design. In it was a much simpler table for the spacing of
conductors with only 8 possible classes. This table was for edge to edge
spacing only, z-axis spacing was fixed to 3.5mil [89um] minimum. This
language was carried in to the IPC-D-275 specification, however with the
advent of IPC-2221 it changed to include z-axis spacing - I for one
missed this change until now. I have always used the dielectric
withstanding numbers from the slash sheet/material data sheet de-rated
by 1/3-2/3 to determine z axis spacing and have only once in twenty
years experienced a z-axis punch through short. This short, by the way,
was as a result of exceeding the rated voltage output by an order of
magnitude not as a result of the design.
Have I been doing it wrong for so many years?
Jeffrey McGlaughlin, CID
Engineering Designer
Battelle
505 King Avenue
Columbus Ohio 43201-2693
(614)424-7582 Phone
(614)458-7582 Fax
-----Original Message-----
From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of Jack
Olson
Sent: Tuesday, November 27, 2007 6:19 PM
To: [log in to unmask]
Subject: Re: [DC] How to Read a Slash Sheet
Well, no one ventured a guess on how to read line 5 of a slash
sheet, so maybe I will try to ask the question a different way....
What good is it to list a certain amount of dielectric strength on a
slash sheet, if paragraph 6.3 of IPC-2221A specifies that we use
Table 6-1 for determining z-axis clearance?
For example, if I need to design for 260V, and Table 6-1 specifies
an 8mil (.2mm) laminate thickness, that's what I need to use,
right? So the fact that someone says a material strength is xx
kilovolts is a moot point once I have been constrained to 8mils
for 260V.
In my memory no one has ever discussed this subject on any IPC
listserver, which makes me wonder if I'm asking a valid question.
Am I mixing terms here?
Jack
On 11/14/07, Jack Olson <[log in to unmask]> wrote:
>
> Can someone please help me interpret slash sheets of IPC-4101?
>
> We are having some board problems, so I went to look up the voltage
> breakdown (line 5 in the laminate section)
> It lists 40kV for laminates over .5mm, thick, but nothing is listed in
the
> column for laminates less than .5mm
> (Our design has .1mm laminate)
>
> What does that 40kV mean, and why is it only given for thicker
laminates?
>
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