FROM: I. MEMIS, DEPT GGMG/BLDG 257-4, AISLE A, ENDICOTT
ENDICOTT ELECTRONIC PACKAGING
SUBJECT: CTE Values for PWB
The previous postings are atttached.
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The problem mentioned requires accurate local CTE values. For a PWB,
CTE changes after each process such as drilling through holes, filling
the holes with solder, copper plating etc. The PWB CTE also changes
with it's geometry. The entire PWB area of interest must be measured
to accurately assess CTE impacts in the area of components and other
features such as heat sinks.
Advanced computational mechanics tools such as the
Finite Element Method (FEM) are tempting for CTE
determination. A numerical prediction of CTE, however,
requires accurate assessment of material properties such as
Youngs modulus, Poissons ratio, CTE etc. and the linear or
nonlinear constitutive relationship of each material used in the
component. The in-situ material data, especially temperature-
dependent material properties and nonlinear constitutive
relationships, are not readily available in the literature, which
makes prediction uncertain.
Recently, moire interferometry was proposed as a tool for CTE
measurement of electronic packaging components. The abstract
of the paper can be found below.
ABSTRACT
Moire interferometry
is a whole-field displacement measurement technique with a
sub-micron sensitivity, which can produce the global CTE and
the local CTE across the entire component with high accuracy.
The large dynamic range of the method makes it compatible
with CTE evaluation of a broad range of components. Two
experimental procedures were suggested for (1) CTE over a fixed
temperature range and (2) CTE as a function of temperature.
The procedures are implemented for various thin small outline
packages, a plastic ball grid array package and a stacked
memory cube. The results emphasize the importance of a
whole-field measurement technique. A supplementary TMA
test on an aluminum alloy is conducted and the results are
compared with a moire measurement to discuss the accuracy of
the proposed measurement procedure.
{1} B. Han and Y. Guo, "Determination of Effective Coefficient
of Thermal Expansion of Electronic Packaging Components: A
Whole-field Approach, IEEE Transactions on Components,
Packaging and Manufacturing Technology-Part A, (submitted
for publication), 1995.
KEY CONTACTS FOR MORE INFORMATION:
Bongtae Han, IBM ENDICOTT, 607-757-1077
INTERNET ID - [log in to unmask]
C.K. Lim , IBM ENDICOTT, 607-757-1138
INTERNET ID - [log in to unmask]
Previous Postings
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We found that using TMA can be misleading, especially in an
"unbalanced" design (e.g. amount of copper NOT symetric around the
center (thickness) of the board. We found strain gageing both sides
of a PWB the only reliable way to get CTE data.
Jim Maguire
Principal Engineer, E/E M&P
(206)657-9063
Boeing Defense & Space Group
[log in to unmask]
Reza,
Might we be able to measure the CTE of this gentleman's boards using TMA? He
may have coupons available... It seems he is looking for an analytical means
to
predict CTE differentials. Just a thought.
Phillip
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Subject: CTE Values of Printed Circuit Board and Heatsink combination
From: [log in to unmask] at Internet
Date: 10/31/95 11:15 AM
Help!
The Engelmaier equations used to estimate cycles to
failure for leadless SMT components has, obviously, as
one of it's terms the CTE of the printed wiring board. I
have been unable to obtain information on CTE of printed
circuit boards, at least with any confidence, and
measuring the CTE after build is too late in the product
development cycle. This is cirtical to our applications
due to the long thermal cycling requirements of some of
our programs (7-15 years).
The CTE of the board is effected by:
Base Material (Kevlar, Polyimide, G10)
Resin
Materal Lot
Layer count
Amount of copper (planes)
Heatsink bonding
Heatsink bonding material (epoxy, acrylic, thermabond)
Heatsink material (aluminum, copper)
1. Has anyone done any testing on CTE of boards as a
function of the above?
2. Are there any equations which can be used to predict
the CTE of the board and/or heatsink combination?
3. Is there any data on the CTE of boards besides the
ranges I have seen in the text books.
I am considering running an experiment to determine the
effects of these parameters. Would anyone be interested
in the data and of course help support the effort with
boards, heatsink and bonding?
Jim Faris
AlliedSignal Aerospace
Guidance & Control Systems
(201) 393-3779
USERID: MEMISIRV, NODEID: ENDVM5, TEL: 855-6022 FAX: 857-1126
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