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Photosensitive Polyimides as Enabling Materials for Advanced
Semiconductor Packaging
Chungen Hsu,* Chenlei Pang, Qinghua Lu, and Seongku Kim*
Cite This: https://doi.org/10.1021/acsami.6c09651
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ABSTRACT: Advanced packaging technologies have enabled electronic devices toward miniaturization,
higher integration densities, and scalable optoelectronic applications. Among the key materials for lowdielectric redistribution layers, photosensitive polyimides (PSPIs) have emerged as a suitable candidate,
owing to their combined capabilities in photo-patterning ability, mechanical strength, and low dielectric
loss. However, recent research challenges the conventional view of performance trade-offs, demonstrating
that molecular design and thermal management can be synergistically codesigned to enhance device performance. This review summarizes the latest advances in the molecular design of multifunctional PSPI
design and highlights their integration into wafer-level packaging architectures. We focus on their role
in promoting efficient heat dissipation from chip to external package and on reducing dielectric
losses to improve signal integrity. Finally, future directions for PSPI-based materials are proposed, offering
a forward-looking perspective for next-generation high-performance and flexible electronics.
KEYWORDS: photosensitive polyimide, advanced semiconductor packaging, low dielectric constant,
redistribution layers, thermal management, signal integrity
essential for high-performance computing,27 mobile devices,28
and optoelectronic applications.29 Their performances heavily
depend on high-density wiring substrates, thermal stability,30
and signal integrity.31 To mitigate power consumption,32,33 crosstalk noise,34 and resistance−capacitance (RC) delay,35 dielectric
interlayers in Fan-out wafer-level packaging must exhibit a low
dielectric constant (low-Dk). In these architectures, chips can be
connected face-to-face, face-to-back, or back-to-face. Currently,
organic dielectric materials such as epoxy molding compounds
(EMCs)36 and polyimides (PIs)37 have been widely used as interlayer dielectrics (ILDs)38 or redistribution layers (RDLs)39,40 in
advanced packaging.41 Among these, photosensitive polyimides
(PSPIs) serve as a promising candidate due to their extended
advantages by incorporating photoreactive groups into the PI precursor chain. This enables direct photolithographic patterning of
PSPI,42 eliminating separate photoresist coating and etching steps,
thereby simplifying manufacturing, minimizing film damage, and
interfacial contamination.43 The process supports fine linewidths
and spacings down to approximately 2−5 μm. Recent advances
have enabled the widespread adoption of PSPIs in microelectronic packaging44 as interlayer insulation,45 stress buffer layers,46
1. INTRODUCTION
The advancement of modern electronic products relies on the
development of high-performance integrated circuits (ICs).1,2
Artificial intelligence (AI) computing chips3,4 and highbandwidth communication5 and assisted driving technologies6
continue to push ICs toward greater system integration,7,8
reduced power consumption,9 and improved reliability.10 In the
post-Moore era, transistor channel scaling approaches its physical
limits,11 which leads to exponential rise in process complexity
and fabrication cost.12 To address these challenges, integrating
multiple chips onto a single substrate has emerged as a promising
strategy, creating new pathways for performance enhancement,
and driving the industry toward multifunctional system-onchips (SoCs).13 This shift places advanced packaging, particularly
through 2.5D (lateral chip-to-chip interconnects) and 3D (vertical stackings) architectures, at the forefront of innovation.14,15
These architectures facilitate the integration of high-bandwidth
memory (HBM) and graphics processing units (GPUs) through
fine-pitch interconnects,16,17 increase I/O density,18 reduce signal
transmission latency,19 and lower power consumption through
heterogeneous integration.20−22 Nevertheless, higher integration
densities come with new challenges. Interconnect lines narrow
and spacing shrinks, which inevitably leads to serious heat dissipation,23 transmission signal delay,24 and electromagnetic crosstalk
noises,25 particularly under high-frequency operation.26
Heterogeneous integration and advanced packaging are now
critical to extending semiconductor technology performance
beyond Moore’s law. Insulating dielectric materials, along with
wafer-level fan-in (Fan-in) and fan-out (Fan-out) packaging, are
© XXXX American Chemical Society
Received: May 12, 2026
Revised:
July 31, 2026
Accepted: July 31, 2026
A
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Figure 1. Photosensitive polyimide and their applications in advanced
packaging.
(a) Ester-type PSPIs: This class originated in 1976 with work by
Siemens, where a photosensitive alcohol was reacted with pyromellitic
dianhydride to form a diester diacid. This intermediate was then acylated with aromatic diamines to produce a stable polyamide ester
(PAE) precursor.75 This synthetic route remains representative of
commercial ester-type PSPIs today (Figure 3a). The key advancement
of PAE-based systems is the replacement of unstable carboxylic acid
groups (−COOH) in conventional poly(amic acid) (PAA) with stable ester groups (−COOR). This substitution significantly enhances
solution stability, reduces viscosity, and provides an excellent precursor for both solution processing and photolithography. Despite these
advantages, ester-type PSPIs are limited by high film shrinkage, moderate resolution (typically 5−10 μm), and relatively low photosensitivity, which have limited their adoption in high-end applications.
2. MOLECULAR DESIGN OF PSPI MATERIALS
PSPIs are polyimide derivatives that incorporate photoreactive functional groups directly into the polymer backbone. They are typically
synthesized through condensation polymerization of dianhydride
and diamine monomers, yielding precursors such as poly(amic acid)
(PAA) or polyamide ester (PAE), which are subsequently cyclized
to the final PI through thermal imidization.53 The development of
PSPIs can be traced back to 1970s; when researchers at DuPont company first introduced photosensitive groups into PI chains, they created the first negative-tone PSPI.54,55 Subsequent advancements
have incorporated various functional groups, such as sulfones,56 alicyclic,57 fluorinated,58,59 or cinnamyl moieties,60 as well as tailored additives61,62 to precisely modulate PSPI properties. These characteristics
make PSPIs highly suitable as RDLs,63,64 insulation interlayers,65 or
stress buffer layers66 in applications ranging from biomedical sensors67 and advanced semiconductor packaging to flexible organic
light-emitting diode (OLED) display (Figure 1).68,69
Compared with conventional photolithography, PSPI-based
patterning significantly reduces the number of processing steps
(Figure 2a−c).70,71 Depending on their response to optical exposure,
PSPIs are classified into positive-tone or negative-tone resists.
Positive-tone materials, typically derived from PAEs or ammonium
salts with crosslinking sites, exhibit increased solubility after exposure.72 In contrast, negative-tone PSPIs become insoluble upon irradiation with ultraviolet (UV) or X-rays.73 In both cases, exposure
induces photochemical transformations in the sensitive groups,
enabling direct pattern transfer through lithography (Figure 2d).59,74
Most commercial PSPIs are negative-tone types, owing to their relatively low thermal curing temperatures (<250 °C) and the retention
of the photocured pattern after development. These are commonly
synthesized by attaching different photo-crosslinking groups to the
amic acid moiety (Figure 2e). However, traditional negative-tone
PSPIs have been limited by photolithographic resolution (>10 μm)
and poor developability, thus driving ongoing molecular design efforts
to overcome these drawbacks while preserving essential PI properties.
Based on chemical design, negative-tone PSPIs are principally
divided into three categories: ester-type, ionic-type, and selfsensitizing PSPIs.
(b) Ionic-type PSPIs: Ionic-type PSPIs were developed to address the
poor hydrolytic stability of traditional PAA, whose carboxylic acid
groups tend to degrade, leading to changes in molecular weight, viscosity, and even gelation. These PSPIs attach photo-crosslinkable groups
(acrylate- or methacrylate-containing tertiary amine groups) to the
PAA backbone through ionic bonds (Figure 3b). This design confers
PSPIs with excellent thermal stability, good electrical insulation, and
favorable processability. However, a significant drawback is the lability
of the ionic linkage between the photosensitive moiety and the polymer chain. During exposure and subsequent thermal imidization, a
considerable portion of these groups dissociates, leading to higher curing temperatures, increased film loss, and reduced resolution.
(c) Self-sensitizing PSPI: These materials incorporate intrinsic photosensitivity within the PI structure, eliminating the necessity for separate
photosensitizers. Their crosslinking mechanism typically involves UVinduced excitation of ketone carbonyl groups, which abstract hydrogen
from adjacent alkyl groups to generate free radicals, thereby initiating
crosslinking (Figure 3c). Since no imidization step is required, processing is simplified and high-purity films can be obtained that align well
with the modern microelectronics miniaturization demands. The primary limitation remains the comparatively low photosensitivity, which
currently restricts broader practical application.
The molecular weight, Tg, and photolithographic performance of a
series of negative-tone PSPIs with varied chemical structures are summarized in Table 1.76−81 Apart from negative-tone systems, positive-tone
PSPIs have emerged as alternative candidates for chip manufacturing.
Over the past decade, they have achieved competitive performance, offering higher resolution, reduced particle sensitivity, and the practical advantage of development in alkaline solutions. In general, positive-tone PSPIs
are designed by incorporating photodegradable functional groups (such
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and radiation shielding layers.47 The excellent dielectric constant
(Dk = 1.5−3.2),48,49 high thermal stability (thermal decomposition temperatures Td,1% > 450 °C) and strong mechanical
strength (Eelastic = 3.0−5.0 GPa)50,51 of PIs are retained after patterning, making PSPIs a seamless evolution of conventional PI
technology. Moreover, as high-power optoelectronic applications
advance, thermal management within densely integrated packages
has aroused much attention.52 PSPIs offer distinct advantages,
owing to their properties that can be precisely tailored through
molecular design and compositional optimization to meet specific
electrical, thermal, and mechanical demands.
Here, we review the progress and prospects of PSPIs in
advanced packaging technologies. This review begins with molecular design approaches for tailoring key performance, including
their electrical, mechanical, and thermal properties. We then provide recent industry examples that illustrate thermal management
challenges in high-performance device integration, followed by a
discussion of heat transfer and signal integrity mechanisms in
advanced packaging architectures. We also investigate commercial
PSPI products to bridge academic research and industrial application. Finally, we propose future research directions to address
challenges such as performance trade-off and the need for
PFAS-free, self-healing, and bio-based PSPI materials, the development of multifunctional integrated dielectric systems, and novel
applications in flexible and integrated electronics.
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Figure 3. Negative-tone PSPI synthesized from (a) polyamide esters, (b) PAA salts, and (c) crosslinking through photoradical generation.
as o-diazo-naphthoquinone-based groups) into the polymer. Upon exposure, these groups undergo reactions that increase solubility of the irradiated regions in a developer, and enable pattern formation identical to the
photomask. For instance, Toray company has developed a positive-tone
PSPI with photolithographic resolution down to 5 μm by optimizing
the structure of photosensitive groups and polymerization processes.82
Based on photoactive chemistry, positive-tone PSPIs can be classified into
diazo-naphthoquinone sulfonate (DNQ),83,84o-nitrobenzyl ester,85 polyisoimide,86 and cyclobutene-based types. 87
(a) DNQ-type PSPI: This material incorporates diazonaphthoquinone sulfonate (DNQ), a widely used photoactive compound
(PAC), as an inhibitor into a soluble PI. The DNQ molecule forms
hydrogen-bonded complexes with polymer chains, effectively inhibiting solubility in alkaline developers (Figure 4a). Under UV exposure, DNQ undergoes a Wolff rearrangement reaction to generate
ketene intermediates, which hydrolyze to yield indene carboxylic
acid derivatives.88 This photoreaction allows exposed regions soluble in alkaline solutions, thereby producing positive-tone patterns.
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Figure 2. (a) Schematic of PSPI photopatterning and chemical changes after UV exposure. Reproduced with permission from ref 59. Copyright
2025 Wiley-VCH. (b) Comparison of photolithographic patterning processes using conventional photoresists and (c) PSPIs. Positive-tone patterns
form after development and photoresist removal, whereas negative-tone patterns form through removing unexposed areas. (d) Optical microscope
images of photomasks with complex, hole, and line patterns, alongside SEM images of crosslinked MK/PSPI structures, revealing microscale features.59,62 (e) Radar chart comparing the different performances of PSPIs. Reproduced with permission from ref 59. Copyright 2025 Wiley-VCH.
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Table 1. Molecular Weight, Glass Transition Temperature (Tg) and Photolithographic Performance of a Series of NegativeTone PSPIs
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a
Determined by DSC.
In contrast, unexposed regions undergo thermal decomposition of
DNQ-derived carbenes, which crosslink with the PI backbone to
form an insoluble network. Key advantages of this material include
compatibility with aqueous alkaline developers and high-resolution
patterning capability.89
(c) Cyclobutane-type PSPI: This resin is synthesized through
photochemical [2 + 2] cycloaddition of maleic anhydride derivatives to form a cyclobutene-based dimer. This dimer is then
reacted with appropriate monomers to yield PAA or polyphthalamic acid precursors, which are finally dehydrated into
cyclobutene-based PI. UV exposure induces ring-opening of the
cyclobutene units in the irradiated area, increasing solubility in
solvents such as dimethylacetamide (DMAC), thereby producing
positive-tone patterns.
(b) ortho-Nitrobenzyl ester-type PSPI: Polymer segments functionalized with ortho-nitrobenzyl carboxylate or phenoxide groups
undergo photochemical rearrangement and cleavage reaction
under UV irradiation90 and degrade them into soluble carboxylic
acid, phenol, or aldehyde groups (Figure 4b). As a result, exposed
areas become soluble in alkaline developers while unexposed
regions remain insoluble, enabling positive-tone patterning with
resolution down to approximately 1 μm.91
(d) Polyisoimide-type PSPI: This approach exploits the solubility
difference between polyisoimide (PII), which exhibits excellent
solubility, low k, and high stability, and its fully imidized counterpart. A representative synthesis, developed by Asahi Kasei
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Corporation, starts with an esterified dianhydride monomer polymerized with a diamine using N,N′-dicyclohexylcarbodiimide
(DCC) as a dehydrating agent. The reaction produces a precursor
that converts into PII under the strong dehydration conditions
afforded by DCC.92 The PII can be patterned through photolithography and then thermally cured at 180−250 °C to produce
the final PI film. The solubility contrast between PII and the fully
cured PI enables positive-tone pattern formation.
There are two approaches to reduce the PSPI dielectric constant by
reducing its overall polarizability. The first involves manipulating molar
polarization and dipole volume to restrict dipole alignment and chain
packing. This can be achieved by incorporating chemical groups with
low electron density or reduced electronegativity, which suppress
induced polarization and lower permittivity. Second, researchers introduce micropores (ϕ < 2.0 nm) or porous low-k fillers into the material.
Because air has a low permittivity of air (kair ≈ 1), vacant nanodomains
significantly reduce the dipole density within the films, offering a practical route to fabricate low-k PIs.106,107 The permittivity of PI depends on
the number density of molecular dipoles (N),102 polarization (P),
Boltzmann’s constant (kb), and temperature (T), as described by the
Debye equation in eq 1.
The molecular weight, Tg, and photolithographic performance of a
series of positive-tone PSPIs, with varying chemical structures, are summarized in Table 2.93−97 Apart from the development of highresolution negative- and positive-tone PSPIs, advanced PSPI packaging
materials are also required to meet high-performance demands, including low curing temperature,93 excellent heat resistance,98 good adhesion, low warpage,99 and high dimensional stability.100
k − 1 4π
μ2
=
N Pe + Pd +
k+2
3
3kb T
2.1. Molecular Structure Modulation for Low k
(1)
where Pe is the electron polarization, Pd is the distortion polarization,
and μ is the orientation polarization related to the dipole moment.
The dielectric constant is also frequency-dependent, with different polarizations associated with specific resonance regimes.108 A fundamental
understanding of these polarization mechanisms, particularly dipole
polarization and interfacial polarization, is significant for tailoring their
dielectric behavior to meet advanced electronic applications.
In polar PIs, dipole (orientation) polarization originates from
intrinsic reorientation of permanent dipoles and induced dipoles
due to asymmetric electron-cloud distortion relative to the nucleus.
The extent of polarization reflects a balance between the ordering
effect by an external electric field and disordering by thermal motion.
This competition directly influences the Dk and loss tangent, particularly near Tg where molecular mobility increases.
Interfacial polarization (Pint), also known as Maxwell–Wagner–Sillars
polarization,109,110 results from charge accumulation at heterogeneous
interfaces,111 creating dipole moments that contribute to macroscopic
polarization. In practical PI films, this can arise from structural
inhomogeneities, impurity phases, crystalline-amorphous boundaries, or
incomplete electrode contact. Strategies to raise Dk of polymers through
To meet the demands of miniaturization and higher performance in
microelectronics, scaling down the interconnect size in RDLs and
advanced packaging technologies has aroused much attention.101
Generally, materials in these structures exhibit low permittivity (K <
3.0) to prevent metal migration into the semiconductor and ensure
long-term stability. Conventional PI films typically show K = 3.0−3.4
across frequencies from 1 kHz to 1 MHz, which does not satisfy the
permittivity requirement (K < 2.5) for modern devices and advanced
packaging.102 Additionally, their high CTE values contrast with the
5−15 ppm/°C range of inorganic materials, leading to residual stress
and thermal deformation at interfaces under high temperatures. For
discussion on polarization mechanisms, the dielectric constant (Dk)
of polar PIs is fundamentally influenced by dipole alignment under
an electric field. At high-density interconnect densities and faster signal
speeds, a high-k material significantly increases parasitic capacitance,103
leading to detrimental effects such as signal delay (RC delay), power
dissipation, and crosstalk. To address these challenges, the use of
low-k PIs can offer several advantages, including minimized signal
delay104 and enhanced signal integrity.105
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Figure 4. Positive-tone PSPI synthesized from (a) diazonaphthoquinone (DNQ) derivative type, (b) ortho-nitrobenzyl ester type, and
(c) cyclobutene type.
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Table 2. Molecular weight, Tg, and Photolithographic Performance of a Series of Positive-Tone PSPIs
Determined by DSC.
high-permittivity fillers exploit interfacial polarization.112 While earlier
studies used microfillers in microelectronics, the incorporation of nanofillers and porous low-k materials is commonly employed to tailor the
microstructure and macroscopic interconnectivity of packaging materials.
The polarization response of molecular dipoles and interfaces
depends on temperature and electric field frequency, leading to corresponding variation in Dk. It is well-established that PIs exhibit significant changes in Dk near Tg, making high Tg polymers promising
candidates for high-temperature dielectric applications, owing to their
superior thermal stability and minimal dielectric property variation.
polarization and depolarization under alternating electric fields.112 At
high frequency (up to 1012 Hz), the polarization response may lag
behind rapid variations of the external electric field, leading to a hysteresis that contributes to relaxation loss. Therefore, the Dk of composites
with dipole polarization and interfacial polarization decreases with
increasing frequency. Electrical conduction loss arises from current leakage, which can be classified as volume-limited or electrode-limited conduction.113 At low frequencies, dielectric loss is dominated by
conduction loss due to insufficient charge trapping and ion migration.
Since molecular dipoles have sufficient time to respond, the loss remains
largely frequency-independent.114 As frequency increases, dipolar reorientation becomes constrained and leads to a rise in relaxation loss.
Thus, the overall dielectric loss in this range reflects both conduction
and relaxation mechanisms, resulting in a frequency-dependent
increase.115 Elevated temperatures intensify these losses, as higher charge
mobility and leakage current amplify conduction. Furthermore, high
ambient humidity facilitates ion transport and elevates internal conduction, further increasing dielectric loss.
2.2. Low Dielectric Loss for Advanced Packaging
The significance of dielectric loss has been heightened toward highfrequency operation and three-dimensional (3D) integration in advanced
packaging. When an electric field is applied, unreleased energy within the
dielectric is dissipated as heat (trapped electrical energy). For PIs, their
low dielectric loss characteristics involve relaxation losses during
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Several molecular design studies have been explored to lower the
curing temperature of PSPIs while maintaining their desirable
properties. One effective approach involves the introduction of alkaline
catalysts, such as photo-based generators (PBGs)81,134,135 and thermalbased generators,136 which efficiently reduce the energy barrier of the
reactions. Alternatively, the use of diamine monomers with heteroaromatic groups has been shown to facilitate the preparation of lowtemperature curable films.99 More recently, the utilized soluble PI as
the matrix for PSPIs has obviated the necessity for further intramolecular cyclization during the hardbake process.137
Despite these advances, low-temperature curable PSPIs still face
critical trade-offs. Reducing the curing temperature often results in
incomplete imidization, which can lead to elevated dielectric constant,
increased moisture uptake, and degraded mechanical properties such as
reduced Tg and increased CTE. Furthermore, the residual solvent and
unreacted precursor species trapped during low-temperature processing may outgas during subsequent packaging steps, compromising
interfacial adhesion and long-term reliability. Therefore, future research
should focus on developing integrated molecular design strategies that
simultaneously lower curing temperature while preserving or even
enhancing the comprehensive performance of PSPIs, including low
dielectric constant, high thermal stability, and robust mechanical
strength. This is particularly critical for emerging applications such as
panel level packaging and heterogeneous integration, where thermal
budget constraints are increasingly stringent.
2.3. Molecular Design for Enhanced Thermal Conductivity
(TC)
Thermally conducting polymers can directly dissipate heat from highpower chips through dielectric layers, thereby reducing junction temperatures and improving device reliability during the operation.121,122
This approach mitigates hotspot formation and minimizes dependence
on external cooling solutions. To begin with, the primary approach is
to enhance the intrinsic thermal conductivity of isotropic bulk polyimides.123 In PI, heat is carried mainly by phonons, whose mean free
path is limited by scattering at chain ends, defects, and disordered
regions. Designing PI backbones with rigid-rod or nonplanar conjugate
moieties strengthens interchain interactions and reduces phonon scattering that can make PSPIs suitable for thermal management.124,125 PI
contains polar C═O groups in the conjugated imide ring; the mobility
of electrons is greatly restricted, thus leading to excellent insulation
properties. In addition, hyperbranched or dendritic PIs can decrease
linear chain packing and entanglements, leading to higher free volume
and reduced phonon scattering sites. 126
Another approach is to develop composites incorporating highthermal-conductivity fillers, such as boron nitride,127 graphene,128,129
and carbon nanotubes.130 However, manipulating the rheology and
interface of polymer composites with a high percentage of fillers is
essential for achieving thermal improvement without degrading photosensitive or dielectric properties. Consequently, molecular engineering
of high-thermal-conductivity PIs is becoming a significant technology
to bridge electrical insulation and thermal management demands.131
Enhancing in-plane and through-plane thermal conductivity in PSPIs
remains a critical challenge. It requires a multifaceted approach that
balances other material properties, including high thermal stability,
low k, high breakdown voltage, and photoresponsive ability.
Furthermore, designing composites with anisotropic thermal conductivity is particularly desirable for electronics, where heat could be transported laterally from hotspots or conducted vertically through oriented
or crystalline polymer.132,133
3. THERMAL MANAGEMENT UNDER HIGH POWER
DENSITY
The pursuit of high performance in IC chips has driven transistor densities and operating frequencies to unprecedented levels.
This result may lead to localized power concentrations and voltage drops that exceed conventional thermal management capabilities. In high-power devices, such as those in hyperscale data
centers and RF power amplifiers, active regions become primary
joule heating sites. Inadequate heat dissipation elevates junction
temperatures and ultimately accelerates device aging,10 electromigration,138,139 and corrosion, thereby compromising device
reliability and lifespan. Advanced cooling technologies have
been developed to manage heat dissipation, which involves
transferring heat from the device junction to surrounding
areas.140 Key considerations in thermal design include
(Figure 5a) (1) optimizing heat dissipation pathways from the
chip backside or substrate; (2) enhancing heat transfer from
the package to heat sinks;141 (3) utilizing high-conductivity
materials and thermal vias; (4) mitigating stress from coefficient
thermal expansion (CTE) mismatch between the chip and substrate; (5) validating design objectives, modeling approaches,
and testing methodologies. Efficient thermal management relies
on the understanding of heat transfer mechanisms, thermal
expansion matching at interfaces, and controlling heat transfer
between physical or chemical reactions.
2.4. Low-Temperature Curable PSPIs
The drive toward advanced packaging with increasing integration densities has imposed stringent thermal budgets on dielectric materials.
Conventional PSPIs typically introduced fluorine-containing monomers to improve the optical transparency of PSPI films, but the issue
of the curing temperatures above 300 °C in the imidization process
remains unresolved.55 It is evident that such high-temperature processing poses detrimental impacts for advanced packaging architectures,
including thermally induced warpage, residual stress at heterogeneous
interfaces, and potential damage to temperature-sensitive components
such as organic substrates and embedded passive devices.
Consequently, there is an urgent need for low-temperature curable
PSPIs that can be fully processed at temperatures below 250 °C, without compromising dielectric performance, mechanical strength, or
photo-patterning resolution.
3.1. PSPI as a Thermal Bridge in RDLs and Stress Buffer
Layers
When deployed as RDLs and stress buffer layers, advanced
PSPIs can function as critical thermal management elements.
By engineering these layers with high thermal conductivity, they
can be transformed from mere electrical insulators and mechanical buffers into active thermal bridges. This enables a dual-path
thermal management strategy, namely, in-plane heat spreading
(through thermally conductive PSPI layers that dissipate heat
laterally from hotspots) and through-plane heat conduction
(via vertical extraction pathways such as TSVs and copper
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The polymer structures play an important role in dielectric and adhesive performance.116 However, the requirements for low k, minimal
dielectric loss, and strong adhesion often involve fundamental tradeoffs. For instance, strong adhesion to copper conductors typically requires
polar functional groups, such as amino,117 hydroxyl,95 or isocyanate moieties,118 within the polymer chains.119,120 These groups enhance interfacial forces through electrostatic interactions, improving durability and
reliability of circuit boards. However, orientation polarization of intrinsic
dipoles, along with additional dipole polarization induced by these polar
groups, can significantly increase dielectric loss. Consequently, optimizing
dielectric properties for low dielectric loss applications requires nonpolar
groups along the polymer backbone, and the spatial placement
of polar groups is also important. When attached as flexible side
chains, they can improve dielectric properties without compromising
overall performance.
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improving thermal stability and chemical inertness. In advanced
packaging, PSPI plays a critical role in wafer-level packaging
(WLP),146 typically applied by spin-coating on different substrates as a stress buffer layer.52 Meanwhile, slot-die coating is
another method used to deposit dielectric layers on large
panels. The CTE value should be preferably <40 ppm/k for
RDLs and smaller than 5 μm. High CTE values can cause significant mismatches with other interconnect components, leading
to reliability problems during thermal cycling. Therefore, the
polymer Tg should exceed the solder reflow temperature of
approximately 250 °C.39 In addition, the adhesion between
PSPI and copper is also important. By tuning the flexibility
and functional groups of polymer chains, thermomechanical
stress can be reduced and interconnect reliability between the
chip and substrate improved. The reason is that PSPI exhibits
intermolecular creep deformation at elevated temperatures.
Through molecular chain slippage mechanisms, strain energy
is dissipated and effectively relieves stress at the interface.
As an interlayer dielectric (ILD),59 PSPI enables microbump
pitch below 3 μm and supports higher-density integration.
Moreover, numerous breakthrough devices have been made
using PSPI in fan-out wafer-level packaging (FO-WLP).147
The standard integration sequence includes (i) PSPI coating
and soft bake, (ii) UV exposure through a photomask, (iii)
development to open vias, and (iv) metallization (Cu electroplating) to form interconnects, followed by a final curing step
(Figure 5d). As chiplet integration densities increase, dielectric
interlayers become major components for package reliability.
Through optimization of dielectric materials, coating processes,
and curing conditions, dielectric layers with a thickness uniformity < ±3% can be prepared and meet the high-precision
demands of high-density advanced packaging (Figure 5e).144
pillars, which channel the heat out of the package). First, inplane heat spreading is achieved through highly thermally conductive PSPIs within RDLs. These layers act as efficient lateral
heat spreaders, absorbing and dissipating thermal energy
directly from localized hotspots at the chip surface and redistributing intense thermal flux over a larger area. Subsequently,
through-plane heat conduction channels transfer laterally dissipated heat out of the package. The PSPI layer serves as a thermal conduit, bridging the heat source to primary vertical
extraction pathways, such as through-silicon vias (TSVs) and
copper pillars. These structures provide low-thermal-resistance
channels to the heat sink or package substrate.142 This integrated approach, combining lateral spreading with vertical conduction, establishes an efficient thermal management network
within the chip interconnect architecture. It reduces the overall
thermal resistance from the junction to the ambient environment. The PSPI material in interlayer dielectrics and RDLs
within a typical packaging architectures are illustrated in
Figure 5b,c, respectively.143
3.2. Fabrication and Integration of PSPIs in Advanced
Packaging
Within photoresist technology, PSPI has become a critical
enabler for advanced semiconductor manufacturing. For
instance, in TSMC’s 7 nm process, PSPI-based photoresists
are employed in gate patterning, achieving linewidth resolutions
limited to 10 nm.145 As a dielectric, PSPI also facilitates interconnection of RDLs and addresses issues of additional photolithography steps, such as high cost and limited resolution.
Compared with conventional photoresists, PSPI-derived polyimide can serve as an insulating dielectric layer after hightemperature curing, thereby reducing process complexity while
H
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Figure 5. Key material properties and integration process of PSPIs for advanced packaging. (a) Advanced package structure with RDLs for I/O density enhancement. (b) Schematic of the PSPI/electroplated (EP) Cu/Cu seed Ti thin-film multilayer structure sandwiched between Si wafers for the
four-point bending test. Reproduced with permission from ref 143. Copyright 2026 Springer Nature. (c) Selection of dianhydride or diamine with
different rigidities. (d) Schematic of RDL fabrication using PSPI in advanced packaging. (e) Cross-sectional C-mode scanning acoustic microscopy
(CSAM) image of the bridge die, the two surface die connected by the bridge, and the organic substrate in which the bride is embedded. Reproduced
with permission from ref 144. Copyright 2019 Willey-VCH. Reproduced with permission from ref 143. Copyright 2026 Springer Nature. Reproduced
with permission from ref 144. Copyright 2019 Willey-VCH.
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grain boundaries, which suppresses abnormal grain growth
and reduces interfacial void formation at elevated temperatures.155 These results help maintain a stable interface and
improve mechanical strength compared with nonpassivated
Cu−Cu bonding. The stacking of active chiplets has emerged
as a leading alternative design to monolithic dies in postMoore microelectronics.156
In traditional WLP and 2.5D/3D stacked packages, PSPI
offers high thermal stability, stress dissipation, and tunable
CTE. The growing demand for computing and automotive electronics has accelerated the adoption of chiplet integration,
mainly through 2.5D/3D interposers or embedded multidie
interconnect bridges (EMIB). These interposers interconnect
disparate chiplets, but CTE mismatches between upper and
lower substrates can induce warpage, cracking, and misalignment in fine-line patterning. Recent designs address these issues
through gradient-modulus architectures and improved thermalpath engineering.148
With the advent of transparent circuits and high-frequency
communications, developing PSPIs with excellent insulation,
low Dk, and high reliability has become imperative to minimize
signal transmission loss and distortion. The low dielectric loss
of PSPI also helps reduce interlayer parasitic capacitance. For
instance, PSPI-based RDL structures have enabled thinner,
more integrated devices by supporting fine-line patterning and
high thermal performance.39 In wafer-level packaging architectures, PSPI can be used both as a passivation layer and the
dielectric within RDLs for signal routing. In advanced
FO-WLP, PSPI dielectric interlayers incorporating nanosilica
(SiO2) fillers have achieved a Dk of 2.8 and a breakdown field
>150 kV/mm at room temperature.149 Current FO-WLP packages employ numerous dielectric layers and copper RDLs to
redistribute chip I/O ports. Advanced packages may use up to
four dielectric layers or dual-side RDLs for 3D package-onpackage (POP) stacking. This increases I/O density and accelerates communication between different chiplets.150
3.4. PSPI-Based Thermal Interface Materials (TIMs)
3.3. Evolution of Heat Transfer Technologies
Advanced packaging is a powerful technology for transmitting
electrical signals from ICs to external components. Early packaging, exemplified by plastic dual in-line packages (DIP) relied
primarily on natural convection and conduction, with heat flux
density below 10 W/cm2 (Figure 6a).151,152 The advent of surface mount technology (SMT) and ball grid array (BGA) packaging introduced more complex designs, making thermal
conduction the dominant heat transfer mechanism.153
Meanwhile, in ceramic BGAs, thermal conductivity mismatch
between metallization layers and ceramic substrate often creates
uneven thermal resistance and localized hotspots. The thermal
interface between the interposer, chip, and substrate becomes
a key bottleneck in 2.5D packaging (Figure 6b). A well-known
technology is TSMC’s integrated fan-out package. Their chipon-wafer-on-substrate technology (CoWoS) technology
improves performance, reduces power consumption and size,
and achieves efficient heat dissipation through optimized packaging architectures and material selection. CoWoS integrates
multiple high-conductivity layers that provide parallel heatspreading paths, effectively channeling heat from the chip to
the external system. Its architecture allows sophisticated thermal management schemes that mitigate heat accumulation
and enhance overall cooling efficiency. With the rise of 3D
stacking packaging and multichip module (MCM) technologies
in the 21st century,154 heat transfer mechanisms have grown
more diversified. Vertical stacking in 3D integration introduces
dual thermal transfer pathways, lateral heat spreading within
interlayers, and vertical heat extraction through the stack
(Figure 6c). For instance, Chen et al. introduced a 3 nm Ag passivation layer within Cu−Cu bonding. Through TEM and 4DSTEM strain mapping, they show that Ag diffuses along Cu
4. LOW DIELECTRIC LOSS AND SIGNAL INTEGRITY
4.1. High-Frequency Signal Integrity Challenges for PSPI
As optical communication systems advance into millimeter-wave
regimes, signal integrity demands on integrated photonic–
electronic platforms have aroused much attention.165 However,
as frequencies extend above 100 GHz, fundamental material limitations dominate transmission behavior, where transmission signal delay,166 interchannel crosstalk, and power consumption
remain as critical bottlenecks. High-frequency performance of
PSPI depends on dielectric properties, specifically frequencydependent Dk and dissipation factor (Df ).167,168 Conventional
PSPI formulations often exhibit significant dielectric dispersion
at elevated frequencies, degrading signal integrity through group
velocity delay and elevated insertion loss. These effects are exacerbated by interfacial polarization at polymer–conductor
boundaries169,170 and inhomogeneous curing-induced morphology,171 which collectively degrade impedance matching and
promote electromagnetic leakage.172 Nam et al. fabricated an
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Modern heterogeneous packaging often integrates hundreds of
passive and active components within a system. TSV and RDL
technologies enable high-density interconnects between chips
by vertically drilling holes and filling them with conductive
materials in silicon. As operational temperatures increase, the
selection of suitable packaging materials becomes limited.
Most polymers and composites transit into elastic states above
Tg and increase their susceptibility to thermal stress at interfaces. Thermal expansion mismatch can lead to interface cracking and void formation. In thermal management, materials are
classified as thermal interface materials (TIMs) or bulk heat
spreaders. TIMs provide a low thermal resistance path between
chips and the bulk substrate, while bulk materials distribute heat
over a larger area toward the heat sink. Early packaging heavily
relied on epoxy-based composites, which typically offered thermal conductivities of 0.2−0.5 W (m−1 K−1).122 Meanwhile, PIs
have been widely employed in ICs as buffer layer substrates,
passivation films,157 planarization layers for multilayer interconnects, and interlayer dielectrics,158 owing to their excellent
thermal stability,159 mechanical properties, and dielectric performance. Recent breakthroughs in high-thermal-conductivity
filler technology, such as graphene/boron nitride composite
fillers, have elevated thermal conductivity of epoxy resins to
2−7 W (m−1 K−1).160−162 Polymer-filler systems balancing
thermal performance with mechanical robustness, chemical
resistance, and electrical insulation are now commonplace in
electronic packaging.163 However, high filler loadings often
decrease mechanical properties and limit processing flexibility.
In structural design, TIMs can improve heat transfer across
rough or uneven surfaces, while TSVs integrate microfluidic
channels that can distribute the heat pathway and lower junction temperatures across the die.164
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electromagnetic interference (EMI) shielding film based on silver
ink and low-k PI. The film demonstrated high-performance characteristics, including an average shielding effectiveness of
−99.7 dB (6−18 GHz), a high in-plane thermal conductivity of
34.614 W (m−1 K−1), a significant reduction in crosstalk (up to
77.8%), and excellent mechanical durability, showing its potential
for advanced packaging applications.173 Recent advances in
molecular design have alleviated these limitations. The introduction of hyperbranched structures,174−176 fluorinated moieties,177
alicyclic segments,178 or controlled free-volume structures179,180
restricts dipole rotation and lowers energy dissipation at high frequencies. Such modifications have yielded PSPI variants with
excellent dielectric stability, maintaining Dk ≤ 2.8 and Df <
0.009 up to 10 GHz.181 Backbone rigidity and reduced volumetric dipole moment further suppress dielectric loss. These changes
also limit moisture uptake and polar-group density, thereby minimizing interfacial charge accumulation and capacitive coupling
between adjacent transmission lines.182,183 Moreover, integrating
photoactive chromophores with low polarizability and enhanced
alignment enables fabrication of dense, void-free
dielectric structures with tapered sidewalls. This morphology
significantly reduces conductor surface roughness scattering and
suppresses modal conversion at waveguide discontinuities.
Combined with gradient-refractive-index designs, tailored PSPIs
can facilitate impedance-matched transitions between silicon
photonic components and electronic interconnects, mitigating
power-ground noise. Synergistic optimization of the PSPI
molecular structure and photonic routing topology represents
a critical pathway toward terahertz-capable integrated
systems.184 Coupled with electromagnetic codesign methodologies, these innovations will enable next-generation communication infrastructure,185 high-performance computing chips,186
and millimeter-wave sensors.187
4.2. Evolution of Dielectric Properties under Multifield
Conditions and Long-Term Reliability
The long-term reliability of devices requires understanding the
relationship between dielectric properties (permittivity, k, and
loss tangent, tan δ) under combined frequency, temperature,
and humidity variations.188 The dielectric response of PSPIs is
intrinsically linked to molecular polarizability and charge transport mechanisms. With increasing frequency, molecular dipoles
exhibit reduced reorientation ability, leading to decreased Dk
and often a tan δ peak at specific relaxation frequencies, typically associated with Tg and local chain motions.189 Elevated
temperatures accelerate molecular and ionic motion in PSPIs,
shifting relaxation peaks and sharply increasing permittivity
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Figure 6. Technology evolution, progression and breakthrough, and advanced packaging examples. (a) Evolution of 2.5D/3D packaging technology
highlighting key milestones achieved from 1970 to 2025. (b) Evolution of the chiplet ecosystem, substrate, and thermal management technology,
highlighting key milestones toward 2030. (c) Advanced 2.5D/3D packaging examples. HBM: high-bandwidth memory, SoC: system-on-chip, LSI:
large-scale integration, and IPD: integrated passive device.
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4.4. Prospects for Next-Generation PSPIs
4.3. Commercial PSPI Products
Fluorinated polyimides (FPIs) are valued for their low k, inherent hydrophobicity, and high-temperature stability against
oxidation. However, impending regulatory restrictions on perand polyfluoroalkyl substances (PFAS) in regions such as the
European Union are encouraging the search for highperformance, nonfluorinated alternatives. PSPIs offer a
promising pathway, providing comparable performance without
fluorinated chemistry. A key limitation of conventional PSPIs is
long-term stability above approximately 450 °C, where thermal
decomposition of the imide ring can compromise mechanical
integrity. Recent research addresses this challenge. For instance,
PIs functionalized with pyrazine groups have shown higher heat
resistance with a Tg of 388 °C and a Td5% of 527 °C194 and nearzero CTE. This improvement is attributed to the orientation of
rigid-rod moieties along the polymer backbone, which
strengthens intermolecular packing and interactions.195
However, broader adoption of PSPIs has been restricted by relatively high manufacturing and processing costs. PSPI
technology encounters issues like line-edge roughness (LER) and
standing-wave effects during submicrometer patterning. Likewise,
common approaches to enhance thermal conductivity involve
incorporating inorganic fillers, but this may simultaneously increase
dielectric loss, which is detrimental for high-frequency applications.
In response, researchers have incorporated more robust molecular
architectures. The integration of ladder-type segments (biphenylbased) improves thermal stability, while spirocyclic structures can
effectively lower the Dk.196
Apart from materials science, the evolution of the industrial ecosystem is critical. Collaboration between material suppliers and
packaging manufacturers has become a key trend. A notable example is the partnership between Samsung Electronics and Sumitomo
Chemical that integrated PSPIs into 3D-IC packaging, thereby
advancing their adoption in high-end applications.197 Market
demand is driven by the development of 5G infrastructure, where
requirements for high-frequency operation and miniaturization in
base-station and terminal chips have accelerated PSPIs in antenna
packaging and radio frequency front-end modules (RFFEM). By
Beyond the academic development of PSPI materials, several
mature commercial products have been established by major manufacturers. Understanding the current industrial landscape is
essential for contextualizing the research gaps and future directions discussed in Section 4.4. Table 3 summarizes the key product
families, their tone types, curing temperature, and primary characteristics from the leading PSPI suppliers. The data presented in
Table 3 are compiled from the official product documentation
and websites of the corresponding manufacturers.
Toray Industries offers the PHOTONEECE series, a comprehensive lineup of liquid-type photodefinable polyimides.190
The product lineup includes the PW-Series (high-temperature
curable positive-tone), UR-Series (high-temperature curable
negative-tone), LT-Series (low-temperature curable positivetone, ≥200 °C), and PN-Series (low-temperature curable negative-tone). The LT-Series achieves resolution down to 5 μm
with a Tg ≥ 270 °C and CTE ≤ 50 ppm/°C. Toray has also
developed fluorine-free, NMP-free variants (GN-K, LT-K, and
PW-K Series) in response to environmental concerns.
Additionally, Toray’s FALDA polyimide low-dielectric adhesive
film achieves a dielectric constant of 2.41 and a dielectric loss
tangent of 0.003 at 20 GHz, demonstrating the feasibility of
low-loss PSPI materials for high-frequency applications.
HD MicroSystems provides both positive-tone and negativetone photodefinable polyimides and PBO precursors. The HD8820 is an alkaline-developable positive-tone polyimide designed
for stress buffer and packaging applications.191 It features low
moisture uptake and excellent dielectric properties. The HD4100 Series offers negative-tone options, while the HD-8930 is
an NMP-free alkaline-developable positive-tone PBO precursor.
It can be cured at low temperatures (200−250 °C) and used as
an RDL (3 μm) in advanced packaging materials.
Asahi Kasei commercialized PIMEL photosensitive polyimide in 1988, establishing it as one of the earliest PSPI products
in the market. PIMEL is applied worldwide for buffer coatings,
passivation layers, and dielectric layers for redistribution
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bumping.192 The product line includes various grades, with
the TL-series specifically designed for low CTE applications.
Recently, Asahi Kasei has developed a novel PSPI film that
combines PIMEL liquid PSPI technology with SUNFORT
dry film photoresist expertise, targeting from wafer-level to
panel-level packaging (PLP) applications. This film format supports lamination processes on large square panels and enables
fine circuit patterns down to 1.0 μm when combined with
appropriate lithography. The company plans to double
PIMEL production capacity by 2030 in response to rising
demand from AI and high-performance computing applications.
Fujifilm offers the Durimide family of solvent-developable,
negative-tone photosensitive polyimides.193 The LTC 9300
Series features low-temperature cure polyimides suited for
redistribution layer applications in advanced packaging, with
ultrafast curing capability. The Durimide 8300 Series comprises
high-temperature cure polyimides for buffer coat applications in
high-reliability packages. More recently, Fujifilm launched the
ZEMATES brand of photosensitive insulating materials,
encompassing both liquid-type polyimide for RDLs and protective films, as well as film-type polyimide for panel-level packaging. Notably, all ZEMATES polyimide products are PFAS-free,
aligning with emerging environmental regulations.
and loss at lower frequencies, threatening high-temperature
operational stability.
Humidity often poses the potential risk to PSPI reliability.
Even with inherent water resistance, these materials can absorb
environmental moisture and initiate degradation with two primary consequences. First, water can act as a plasticizer to lower
Tg and increase chain mobility, which raises permittivity and loss
at low frequency. Second, absorbed water facilitates ion migration, which drastically increases conductive loss. Under an
applied electric field, ion flow can induce electrolytic corrosion
and create conductive filaments, eventually leading to electrical
failure. Long-term reliability is further threatened by synergistic
degradation under combined thermal-humidity-bias stress.
Increased dielectric loss generates Joule heating, which accelerates hydrolysis and material degradation. Ultimately, the process
can cause insulation failure, short circuits, and severe duction in
operational lifetime. A fundamental understanding of the interplay between molecular dynamics, moisture introduction, and
electrical field distribution under multifield conditions is essential. Future material development should focus on enhancing
hydrophobicity, improving crosslink density to restrict chain
mobility, and developing novel monomers resistant to hydrolytic
attack. Such advances will be significant for the reliability of nextgeneration electronics in harsh environments.
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Table 3. Representative Commercial PSPIs and Their Key Characteristics
Manufacturer
PHOTONEECE series
Toray
Photodefinable PI
LT
PW
STF-1000
Negative tone
i-line (365 nm)
≥300
≥150
≥40
≥3
≤50
≥300
≥30
HD4100
Negative tone
i-line (365 nm)
350−390
200
45
3.5
Positive tone
i-line (365 nm)
≥200
≥130
≥50
≥2
≤50
≥270
≥5
HD7110
Negative tone
i-line (365 nm)
200−300
160−190
40
2.8−3.3
Positive tone
i-line (365 nm)
≥300
≥150
≥50
≥3
≤40
≥300
≥5
HD8820
Positive tone
i-line (365 nm)
280−350
170
100
2.2−2.7
Negative tone
h-line (405 nm)
≥200
90−100
6.0−8.0
2.0−2.5
70−75
200−250
≥10
HD8930
Positive tone
i-line (365 nm)
200−250
170
80
1.7−1.9
Negative tone
h-line (405 nm)
≥200
30−40
1.5−2.5
2.0−2.5
70−75
200−250
≥10
HD7204
Negative tone
i-line (365 nm)
200−300
180−210
50
2.5−2.9
320
5
PIMEL BL-301/401
Negative tone
200
150
60
3.4
50−60
200
LTC 9300-E07
Negative tone
i-line (365 nm)
200−250
181
83
2.5
55
229
230
5
LV-105
Negative tone
200
150
60
3.4
50−60
200
LTC 9300-E19
Negative tone
i-line (365 nm)
200−250
178
74
2.6
54
229
300
4
BM-302H
Negative tone
200
170
55
4.5
50
220
LTC 9300-E76B
Negative tone
i-line (365 nm)
180−230
175
65
2.9
50
231
230
3
MA-1001
Positive tone
220
135
65
3.6
35
240
Durimide 7020
200−230
6
AM-271
Positive tone
320
130
35
2.7
55
300
Durimide 7500
Positive tone
i/g/h-line
350−420
215
85
2.5
55
285
g-line/h-line (436/405 nm)
350−420
170
73
2.9
27
>350
STF-2000
conductivity, and low-temperature curable materials, while
future progress hinges on PFAS-free and resilient functionalities. In this review, we have discussed the evolution of advanced
packaging architectures, as well as roles and potential of PSPIs
in heterogeneous integration. While vertical chiplet stacking
and copackaged photonics represent prominent architectural
directions, recent studies highlight the enabling performance
of PSPIs. Their low-k, stress buffer capability, and planarization
properties can improve signal integrity and system reliability.
This functionality extends beyond a passive supporting role;
through tailored molecular design and processing development,
PSPIs are transitioning from conventional encapsulation auxiliaries into high-performance materials. Their excellent properties make them indispensable for constructing multifunctional
interconnects and passive structures in 2.5D and 3D packaging.
Such advancement expands the magnificent possibility in
advanced packaging materials, from mere mechanical protection
toward functional enablement.
The development of PSPIs requires synergistic breakthroughs across multiple areas. First, controllable regulation of
2026, 5G-related applications are projected to account over 40% of
the global PSPI market. Simultaneously, the AI and highperformance computing (HPC) sectors are experiencing rapid
growth in PSPI materials, which is expected to more than triple
in the next five years with data-center infrastructure expansion.
The proliferation of wearable electronics is expanding PSPI
applications into flexible packaging. Flexible electronics impose
stringent demands on material flexibility and cyclic durability.
Recent developments in PSPI films incorporating flexible chain
segments and plasticizers have demonstrated survivability beyond
100,000 bending cycles, making them suitable for flexible printed
circuit boards, display panels, electronic skin, and related applications.69,198 Moreover, the biocompatibility and thermal stability of
tailored PSPIs support innovation in medical devices,199 enabling
advanced circuit designs for wearable devices and biosensors.
5. SUMMARY AND OUTLOOK
The future development of PSPIs for advanced packaging relies
on the molecular design of low-dielectric, high-thermal
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Type
Exposure wavelength (nm)
Curing temperature (°C)
Tensile strength (MPa)
Elongation (%)
Modulus (GPa)
CTE (ppm/°C)
Tg (°C)
Resolution (μm)
HD MicroSystems
Type
Exposure wavelength (nm)
Curing temperature (°C)
Tensile strength (MPa)
Elongation (%)
Modulus (GPa)
CTE (ppm/°C)
Tg (°C)
Resolution (μm)
Asahi Kasei
Type
Curing temperature (°C)
Tensile strength (MPa)
Elongation (%)
Modulus (GPa)
CTE (ppm/°C)
Tg (°C)
Fujifilm
Type
Exposure wavelength (nm)
Curing temperature (°C)
Tensile strength (MPa)
Elongation (%)
Modulus (GPa)
CTE (ppm/°C)
Tg (°C)
GN
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material properties is crucial. Former studies demonstrated that
Dk, CTE, and other parameters can be precisely regulated
through molecular structure and composite design; these
approaches must shift from single-property optimization to
system-oriented codesign. For instance, balancing low-k properties with high mechanical strength can be achieved through
nanocomposites or porous structures. Second, process compatibility for high-density integration remains a challenge. Current
PSPIs still face bottlenecks in ultrathinning, high aspect ratio
through filling, and interface stability with heterogeneous materials. Particularly in 3D stacking environments, novel curing and
interface control technologies compatible with semiconductor
processes need to be developed.
From an application perspective, the integration of PSPI formulations with novel thermal management solutions will
address the challenges of power delivery and thermal management in high-power-density systems. For instance, embedding
thermal management functions within PSPI dielectric layers or
developing packaging structures with graded thermal conductivity can enable the co-optimization of multiple physical fields
such as electrical, thermal, and mechanical. Moreover, it may
be possible to integrate composite functions such as signal
transmission, power distribution, thermal diffusion, and electromagnetic shielding within a single material layer.
Looking further ahead, two emerging directions, bio-based
PSPIs and self-healing PSPIs, deserve particular attention for
sustainable and reliable electronics. Bio-based PSPIs, derived
from renewable monomers such as isosorbide, vanillyl alcohol,
lignin or furan-based diamines, offer a pathway to reduce the
carbon footprint and dependency on petrochemical resources,
while maintaining competitive thermal and dielectric properties.
Although their current performance often lags behind that of
petroleum-based counterparts, advances in monomer synthesis
and polymerization chemistry are rapidly closing this gap.
Self-healing PSPIs, on the other hand, address the critical issue
of microcrack formation and delamination during thermal
cycling and mechanical stress. Incorporating dynamic covalent
bonds (e.g., Diels−Alder adducts, disulfide linkages, or thiolene-based) or supramolecular interactions into the PSPI backbone can enable autonomic repair of damage, thereby extending
the service lifetime of packaging structures. These functionalities are particularly valuable for flexible, wearable, and harshenvironment applications where maintenance is difficult.
Future research should therefore explore the integration of
bio-based feedstocks with self-healing capability, as well as their
compatibility with existing photo-patterning and curing processes, to realize truly sustainable and durable PSPI materials.
The advancement of PSPI technology may open up new
pathways for electronic integration. Future exploration of the
connections between dielectric properties of PSPI and other
emerging fields (e.g., flexible electronics) might drive microelectronic systems toward higher integration density and lower
energy consumption.
Engineering, Eastern Institute of Technology, Ningbo, Zhejiang
315200, China; Email: kimsk@ylab.ac.cn
Review
Authors
Chenlei Pang – College of Chemical Engineering, Zhejiang
University of Technology, Hangzhou, Zhejiang 310014, China
Qinghua Lu – School of Chemistry and Chemical Engineering,
Shanghai Jiao Tong University, Shanghai 200240, China;
orcid.org/0000-0003-1522-1458
Complete contact information is available at:
https://pubs.acs.org/doi/10.1021/acsami.6c09651
The manuscript was written through contributions of all
authors. All authors have given approval to the final version of
the manuscript.
Notes
The authors declare no competing financial interest.
■ ACKNOWLEDGMENTS
We gratefully acknowledge funding support from the Yongjiang
Laboratory, Ningbo, China (Y-Lab Project P2, B400TASD02).
The authors also extend their appreciation to the technical staff
and collaborators at the Specialty Polymer Research Center for
their valuable insights and contributions throughout the preparation of this manuscript.
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■ AUTHOR INFORMATION
Corresponding Authors
Chungen Hsu – Specialty Polymers Research Center, Yongjiang
Laboratory, Ningbo, Zhejiang 315201, China; orcid.org/
0009-0003-4386-4212; Email: chungen.hsu@gmail.com
Seongku Kim – Specialty Polymers Research Center, Yongjiang
Laboratory, Ningbo, Zhejiang 315201, China; College of
M
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