Hi James,
I am sure that most, if not all of us aerospace engineers would agree that
today's SMT PWBs are composed of a blend of old materials, modified materials
and new materials, and the pros and cons related to the materials are vast, and
selecting materials for SMT PWBs is unlike selecting materials for standard
through-hole mounting type components.
Nevertheless, the material selection criteria associated with a PWB design
usually addresses a generic list of criteria to supplement the functional list
criteria in the selection process. In essence, how well a PWB performs during
its production fabrication is of equal value as its performance reliability
during exposure to environmental field applications.
Having said that, it's obvious that engineering design without due consideration
for economics is neither engineering nor design, but is, instead, a brute-force
contrivance. In other words, design economics is not only centered on the
materials used to build a PWB, or any product, but also must be rooted in
high-yield manufacturability considerations.
Design is the dominant determinate on how cost-efficiently a PWB, or any object
can be produced because 70 to 80 percent of the eventual production costs are
determined by the design and is set-in-place during the design development
phase. The bottom line is its imperative that a design focus its efforts on
creating manufacturable designs and eliminate as many aspects of the design that
may be counterproductive. Yields, within the manufacturing activity, are among
the major contributors to product costs. Consequently, an engineering team must
consider a significant number of guidelines in order too promote high-yield PWB
manufacturing employing SMT components.
Our company is also an aerospace company and manufactures military and
commercial electronics that require the usage of MLPWBs with LCCCs (Leadless
Ceramic Chip Carriers), PQFPs and other types of components.
Many of our designs that are presently in the production phase, and in the
design development phase utilize CIC/CMC materials. However, there is only one
military fighter program to my knowledge that is presently designed that has one
of its PWBs which is made with the "LANXIDE" core material.
Moreover, there were a few military design configurations originating back in
the early to mid 90's which utilized CIC in conjunction with the silicone
carbide matrix aluminum (LANXIDE) core materials in order to achieve effective
control of TCE mismatch between the assortment of materials used in the PWB
designs. However, because there were cost initiatives requested primarily by
our Customers during the passing of time it became necessary that these specific
materials (CIC & LANXIDE) be designed-out of the PWBs for two of our major
military fighter on-going production programs, and without adversely affecting
the performance reliability of the products as a result of removing these
materials. The "Cost Affordability Initiatives" for both of these military
programs were implemented and both the cost, and the reliability criteria were
successfully achieved, which resulted in enormous benefits.
Therefore, rather than going into a long dissertation that explains what does
all these alternatives and trade-offs add up to in benefits? Let it suffice to
say that there were significant dollar savings associated with the revised PWB
designs that have resulted in simpler PWBs construction, Customer specification
compliance, Customer acceptance, major producibility advantages, significant
weight reductions, reduced life cycle costs-of-ownership, significantly improved
procurement schedules, and finally, performance, maintainability and reliability
characteristics that are equal too, or better than the original design
configurations.
In essence, the primary "alternative" design features that were implemented that
resulted in the above benefits being realized was the simple attachment of
"leadwires" to the LCCCs style components in conjunction with the use of an
aluminum alloy core material, and a thermal/structural adhesive material to bond
the standard polyimide material MLPWBs to the core material.
I trust that the above information is of some help in your quest to find a more
cost effective way to do it!
best regards,
faz
SMITHS AEROSPACE ELECTRONICS SYSTEMS,
Clearwater, Florida.
727-532-6333
____________________Reply Separator____________________
Subject: Re: [TN] Cu-In-Cu boards
Author: "Marsico; James" <[log in to unmask]>
Date: 10/2/2001 7:08 AM
Well, we primarily build military electronics with LCCCs, thus the need for
a restrained board. (We're using silicon carbide/aluminum composite cores.)
I've been tasked to look at this design/technology and come up with
alternatives. I'm interested in alternate restraining core material, board
material, leaded SMT components, near-hermetic plastic components, etc.,
etc. What are you military guys/gals doing these days?
Jim Marsico
Senior Engineer
Production Engineering
EDO Electronics Systems Group
[log in to unmask] <mailto:[log in to unmask]>
631-595-5879
-----Original Message-----
From: Earl Moon [SMTP:[log in to unmask]]
Sent: Tuesday, October 02, 2001 4:19 AM
To: [log in to unmask]; Jim Marsico
Subject: Re: Cu-In-Cu boards
I don't do well at 0200. Maybe you meant thermal-mechamical
stability. If
so, CIC obviously applies as does Kevlar and Carbon fiber materials.
Diamond
types are best but anyone up for that?
I quit, thankfully to us all.
MoonMan
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