Advanced Metrology Suite for Linking Residual
Stress to Fundamental Properties of Thermoset
Packaging Materials
Polette Centellas
National Intitute of Standards
and Technology
Gaithersburg, MD, USA
polette.centellas@nist.gov
ORCID: 0000-0003-3248-3409
Stian Romberg
National Intitute of Standards
and Technology
Gaithersburg, MD, USA
stian.romberg@nist.gov
ORCID: 0000-0003-1026-2023
Ran Tao
National Intitute of Standards
and Technology
Gaithersburg, MD, USA
ran.tao@nist.gov
ORCID: 0000-0002-5208-7895
Alexander K. Landauer
National Intitute of Standards
and Technology
Gaithersburg, MD, USA
alexander.landauer@nist.gov
ORCID: 0000-0003-2863-039X
Karl F. Schoch, Jr.
Materials and Processes,
Northrop Grumman
Baltimore, MD, USA
k.eric.schoch@ngc.com
Huong Giang Nguyen
National Intitute of Standards
and Technology
Gaithersburg, MD, USA
huong.nguyen@nist.gov
ORCID: 0000-0002-1052-7565
Gale Holmes
National Intitute of Standards
and Technology
Gaithersburg, MD, USA
gale.holmes@nist.gov
ORCID: 0000-0002-5639-4112
Gery Stafford
National Intitute of Standards
and Technology
Gaithersburg, MD, USA
gery.stafford@nist.gov
ORCID: 0000-0003-3445-9402
Abstract—Residual stresses inevitably develop in
thermosetting materials used for semiconductor packaging during
the curing process and in service. Understanding the development
of these deleterious stresses is necessary for improving predictive
models and engineering design. Here, we present a suite of
metrologies and methodologies, including advanced thermal
analysis, rheological characterization, shrinkage, and evolved
stress measurements, to link residual stress development with
fundamental material properties in a commercial liquid
encapsulant.
Keywords—liquid encapsulant, cure kinetics, rheology, cure
shrinkage, residual stress
I. INTRODUCTION
Semiconductor packaging materials are typically
thermosetting polymer formulations with multiple components.
In these materials, residual stresses develop during the curing
process and are closely linked with the reaction kinetics, liquid-
to-solid transition, and cure-induced shrinkage [1]. Residual
stresses continue to evolve in the cured material in response to
hygrothermal conditions during service [2]. Characterizing these
behaviors is often challenging due to the complex formulations
used in the semiconductor industry. However, understanding the
development of residual stresses is necessary to inform
predictive models and thus improve the engineering design and
manufacturing productivity of semiconductor assemblies.
Here, we present a suite of advanced metrologies and
methodologies to measure and analyze the fundamental material
properties of a commercial liquid encapsulant. Thermal analysis
is used to measure and accurately model the cure kinetics for
complex mechanisms. Rheological measurements supplement
the cure kinetics study and are used to identify the liquid-to-solid
transition during curing. Thin film curvature measurements
demonstrate that this transition accurately predicts the
development of residual stress caused by the observed cure-
induced shrinkage. Stress measurements on the post-cured
material further reveal the effect of hygrothermal conditions on
the mechanical response. Taken together, this metrology suite
ties fundamental to part-scale measurements for a holistic
understanding of the evolution of residual stresses during curing
and in service, an essential step for improving predictive models.
II. E
XPERIMENTAL
A. Chemical Composition
All experiments are performed on a commercial liquid
encapsulant designed for semiconductor devices. As shown in
Table I, the formulation comprises multiple epoxy resins with
varying concentrations. It also includes a reactive diluent to
reduce the resin viscosity while still participating in the curing
process [3], an adhesion promoter to couple organic and
inorganic components [4], and inorganic silica fillers to match
the coefficient of thermal expansion of the encapsulant with
other device components [5]. The latent curing agents inhibit
the curing of epoxy resin to prolong the processing time of the
Christopher Soles
National Intitute of Standards
and Technology
Gaithersburg, MD, USA
christopher.soles@nist.gov
ORCID: 0000-0002-1963-6039
Official contribution of the National Institute of Standards and Technology;
not subject to copyright in the United States.
National Institute of Standards and Technology Award # 70NANB24H283.
432
2025 IEEE 75th Electronic Components and Technology Conference (ECTC)
2377-5726/25/$31.00 ©2025 IEEE
DOI 10.1109/ECTC51687.2025.00078
2025 IEEE 75th Electronic Components and Technology Conference (ECTC) | 979-8-3315-3932-0/25/$31.00 ©2025 IEEE | DOI: 10.1109/ECTC51687.2025.00078
Authorized licensed use limited to: NIST Virtual Library (NVL). Downloaded on July 02,2025 at 16:56:07 UTC from IEEE Xplore. Restrictions apply.
