Randy Johnson (Loveland) wrote:
>
> Our company is a manufacturer of industrial turbine and reciprocating
> engine control systems, used a variety of environments. We are in the
> process of converting from home grown (Mil driven) printed wiring board
> design and inspection standards to IPC standards. In particular, we are
> utilizing IPC-D-275, IPC D-279, IPC-A-600 and IPC-A- 610.
>
> We in engineering are told by purchasing there is a premium of around
> 15% to be paid for non standard specifications, which we are told, means
> deviation from IPC Class 2. We have noted several exceptions where we
> feel Class 3 or better is necessary, primarily in the specifications
> affecting circuit spacings. Specifications affecting inner layer and
> outer layer spacings at Class 2 will require substantially increasing
> spacings by design to allow for spacings reductions in manufacturing
> allowed by Class 2 . For example IPC -A-600 2.1.10.2 allows a 20%
> reduction in spacings in isolated areas. We design to minimum spacings
> required by UL and IEC standards reflecting dielectric strength,
> impulse, and EMC surge test requirements. Spacings violated by spikes,
> rough edges, conductive islands and inclusions will result in a
> failure to meet these requirements. Therefore, to allow even a Class 3
> reduction in spacings requires compensation of the designed spacings in
> the event some of the allowed violations do occur. We can't afford the
> real estate, especially for higher voltages where spacings are required
> to be over 3mm.
>
> If you have industrial market experience as a board supplier or user,
> please comment.
> Do you use IPC standards as controlling documents ?
> Do you find there is a substantial cost adder for exceeding Class 2
> requirements on some specifications?
> Do you accept the added cost ?
> Do you inspect for spacings violations on purchased Class2 bare boards?
>
> Thank you very much.
>
> Randy Johnson
> Reliability & Safety Compliance Engineer
> Woodward Governor Company
> Loveland Colorado
> [log in to unmask]
>
Hi Randy, this response will help you out in the use of IPC documents, I
don't have current information on additional costs as it is too
dependant on how far the requirements deviate from the IPC's default
specification requirements.
First the major IPC documents you'll need are as follows:
IPC-D-275 -- the rigid printed board design document you mentioned
(it's in the process of being replaced with the IPC-2221
and IPC-2222, respectively the Generic Standard and Sectional
Design standards for Rigid Printed Boards
IPC-D-279 -- you listed is the reliability design guideline for rigid
printed boards
IPC-6011 & 6012 -- the Generic and Sectional Performance (manufacturing)
Standard for Rigid Printed Bords
IPC-A-600 -- the acceptance standard for rigid, flex, rigid/flex, and
metal-core printed boards
ANSI/J-STD-001, Electrical/Electronic Assembly Soldering Specification
IPC-A-610 -- Acceptance Standard fo Electronic Assemblies
These are most of the overall specs/stds you'll need.
The IPC-A-600 should never be used as a manufacturing standard,
it is a "visual" acceptance standard for printed boards. The IPC-601x
series of documents are what's called the "Performance Specifications"
for the manufacture of printed boards.
Almost all of the IPC's documents have an "Unless Otherwise Specified"
series of default characteristics.
The one you mentioned, the acceptable allowable reduction of up to 20%
of the conductor spacing for a Class 2 product is the "unless otherwise
specified" default, unless otherwise specified in the technical
procurement documents (should be the master drawing).
The key is to using IPC documents is to either design to use the
defaults (unless otherwise specified's), or to specify the exceptions
to the default the requirements in the technical documnents.
Randy, in a previous life (employer), I converted there printed board
manufacturing, soldering and electronic assembly documents from
a family of "in-house" specifications to IPC industry documents. In
particular, the number of notes on a printed board master drawing went
from (an average) of less than six to about 18-24. This was necessary
in order to maintain both forward and backward compatibility of
materials,
manufacturing tolerances and other requirements.
Hope this partially helps you.
Ralph
Ralph Hersey & Associates
e-mail: [log in to unmask]
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